Vehicle Battery Fires: Why They Happen and How They Happen 0768081432, 9780768081435

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Vehicle Battery Fires Why They Happen and How They Happen

Gregory Barnett

Warrendale, Pennsylvania, USA

Vehicle Battery Fires: Why They Happen and How They Happen Front Matter Print ISBN: 978-0-7680-8143-5 eISBN: 978-0-7680-8361-3 DOI: 10.4271/R-443

Vehicle Battery Fires Why They Happen and How They Happen

Other SAE books of interest: Simulation, Modeling, and Analysis of Batteries By John Turner (Product Code: PT-176) Automotive 48-volt Technology By Johneric Leach (Product Code: JP-ABOUT-001) Lithium-Ion Batteries in Electric Drive Vehicles By Ahmad A. Pesaran (Product Code: PT-175)

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Acknowledgments The author would like to thank Mr. Mike Eskra for his valuable assistance and expertise during the development of this publication. Mr. Eskra contributed greatly to the accuracy of the text, and particularly to the battery chemistry material, with his extensive experience in battery manufacturing. His insightful review of the manuscript is greatly appreciated. Much appreciation, as well, to the following organizations for their technical advice, assistance, and permission to reprint material and text used within the publication: Robert Bosch (America), Battery University, Manmac Corporation, General Motors Corporation, Chrysler, and Ford Motor Company. Finally, thanks are extended to Dr. Richard Kaner (UCLA of California) and his team for the contribution of microscopic photographs of graphene and a molecule being inserted into the graphene matrix. Without Dr. Kaner's assistance, these images would not be included in this publication.

Introduction The vehicle of today is as much electrical and electronic as it is mechanical. The “backyard mechanic” has been replaced with highly trained dealership technicians. Engineering demands are in a constant state of change. The wiring harness on the average vehicle has become a large maze of wires routing throughout the vehicle. The rise in the use of electrical and electronic systems has come with a cost: The simple truth is that electrical fire is the most common type of fire occurring in automobiles. Reporting of fires to the National Highway Traffic and Safety Administration must occur within days of the auto manufacturer learning of the event or the manufacturer will risk incurring fines that can run into the millions of dollars. The first rule in fire analysis of automobiles and related products is that there are no absolutes. Electrical system failure modes vary widely and depend on many factors. Generally, for an electrical failure to cause a large fire, some type of fuel must be in the immediate vicinity of the failure. Still, if no fuel is available to help fire propagation, the electrical failure can still be catastrophic. The vehicle may well be destroyed by smoke damage. However, with a nearby source of available fuel, the damage path will be far greater. Any investigating engineer or technician who has been assigned to troubleshoot the cause and origin of a fire can only respond according to their individual level of training and experience. Troubleshooting is not a skill that can be taught in the classroom. It is a skill honed by many years of hands-on experience. Care should be exercised so that the investigation does not bend the facts to fit a given fire theory. Rather, the “big picture” should be examined in context with the evidence discovered. Because the topic of electrical fire is not a widely taught subject, the purpose of this book is to assist in the analysis with some understanding of the issues faced in electrical system design, battery construction, fault modes, etc. The investigating engineer should apply both deductive and inductive reasoning to the analysis. The scientific method should not be discarded in an attempt to make a pet fire theory work. However, some fires have consumed the evidence to the point where a determination cannot be made with any degree of certainty. In this instance, evidence will be quite limited. Therefore, the analysis will have its limitations, and this fact should be included in the discussion. In some cases, a “cause undetermined” report is all that the evidence will support. The following is a brief history of the battery from the earliest cell discovered in antiquity to

the modern lead-acid battery. Many more developments have occurred between inception and use in the modern automobile. Only the more notable developments are covered. A historical timeline is included to credit the inventors and innovators that added to the development of the lead-acid battery. The more modern developments are discussed in later chapters. Greater focus is placed on the lead-acid battery, because this design is the most common in automobiles worldwide. The descriptions and basics of the battery are covered for readers unfamiliar with this specific technology. Otherwise, you may wish to skip ahead unless you are a fan of history. Although many other important advances and developments were made to what would eventually be the battery used in modern automobiles, only the more notable advancements are discussed. The primary focus will be on differences in failure modes between DC and AC systems, general types of battery and electrical failure modes leading to fire, how to interpret electrical fires, determination of the primary failed part, and other skills the investigating engineer will require to perform technical failure mode analysis.

Vehicle Battery Fires: Why They Happen and How They Happen Chapter 1: History of the Battery Print ISBN: 978-0-7680-8143-5 eISBN: 978-0-7680-8361-3 DOI: 10.4271/R-443

Chapter 1 History of the Battery

The earliest example of a galvanic cell is the Baghdad Battery. The name comes from the collection of antiquities and artifacts in Mesopotamia during the Iranian dynasties of the Parthian period (approximately 250 BC to 250 AD). The artifacts are believed to be about 2000 years old [1-1]. The Baghdad Batteries were discovered in a village called Khujut Rabu, near Baghdad. They are terracotta jars, each fitted with a rolled-up sheet of copper surrounding an iron rod. The iron rod is suspended in the tube and jar through an asphalt stopper. Figure 1.1 is a reproduction of the Baghdad Battery [1-2]. Although no instructions were found with the Baghdad Batteries regarding their use, simply filling the jar with vinegar or any other electrolytic solution will cause the battery to produce approximately 1.1 V DC for two hours. Scientists speculate that the devices were used to electroplate one metal onto the surface of another, such as putting a layer of gold onto silver. This process is still in use in Iraq today. Some historical debate is ongoing as to the age of the Baghdad Batteries and the archeologist who discovered them. One account is that German archeologist Wilhelm Konig discovered them in 1938. However, the fact that the artifacts exist is proof of how long man has known how to generate electricity. Additionally, if the scientists' speculation is correct, then man also learned how to use the electricity produced.

Figure 1.1 Cutaway of the Baghdad Battery.

On another historical note, there is mention in a book entitled Agastya Samhita (Sanskrit, India) authored by a revered sage of the day named Agastya. The writings describe the construction of a battery by placing copper plates into an earthen pot, and covering it in copper sulfate and wet sawdust. Zinc powder is spread on the surface, and it is covered with mercury. Student reproductions of this early cell report that the cell will produce approximately 1.4 V DC. Note that Sanskrit is one of many Pan-Asian languages that predate the scientific method and newer traditions in

scientific documentation.

1.1 Early Beginnings and Experiments An early scientist to experiment with electricity is one of the United States' founding fathers, Benjamin Franklin. He was the first to use the term “battery.” Benjamin Franklin used the term “battery” to describe a set of capacitors he devised and fastened together for his experiments in electricity. His capacitors were sheets of glass coated with metal on both sides [1-3]. By connecting the capacitors together, he noted that the stored charge was “greater” when the assembly was discharged. Because voltmeters had not yet been developed, it is presumed that the spark produced by the capacitors was visibly greater as the number of capacitors hooked in series was discharged. The term “battery” has the generic meaning of “an array of similar things intended for use together” [1-4]. Benjamin Franklin thought that use of the term “battery” was most appropriate for his capacitor array because of the functioning similarities to an artillery battery. Thus, the term “battery” to refer to a collection of electrical devices was coined. In 1800, Alessandro Volta invented the first true battery that differed from the galvanic cell design. In Volta's design, shown in Figure 1.2, he piled copper plates in pairs with zinc discs. The discs were piled on top of each other, each separated by a layer of cloth or cellulosic material. Brine was added to the jar containing the piled plates to create the first “voltaic pile” battery. Volta continued experiments with various metals. Ultimately, he determined that zinc and silver gave off the greatest amount of current. Volta incorrectly believed that the current in his battery was the result of two different materials touching each other. This was an obsolete scientific theory known as “contact tension.” Because of Volta's belief in contact tension, he regarded the corrosion that occurred in his zinc plates as some type of unrelated flaw. He believed this flaw could be corrected by changing the materials used.

Figure 1.2 Volta pile battery.

While Volta was experimenting with his voltaic piles, he observed that the corrosion would occur on the zinc plate much faster as higher amounts of current were drawn through the plate. This negated the theory of contact tension. Rather, this suggested to Volta that the action of the corrosion was actually integral to the battery's ability to produce a current. This led to the rejection of Volta's contact tension theory in favor of the electrochemical theory. Volta's original pile model suffered from some technical issues. Two of the more common flaws the design experienced were the container leaking electrolyte and the creation of short circuits due to the discs being stacked one on top of the other. The weight of the discs would compress the cloth insulators, allowing one disc to touch the other. This problem was solved by a Scottish scientist named William Cruickshank. His solution stacked the plates on end inside a long box. This became known as the “trough battery,” and was the start of what the modern automobile battery would come to resemble. The biggest problem early cells had was low lifespan. The batteries of the day were all “primary” batteries. They could produce only a given amount of current before they ran down. A primary battery cannot be recharged. “Recharging” consisted of dumping the electrolyte, installing new plates, and pouring in more electrolyte. This was an expensive proposition for a device that only created an hour or two of electricity. A dozen or so mentionable improvements were made to galvanic cells and voltaic piles over the decades. However, two issues plagued all scientists studying the phenomena of electricity: the first was polarization. This phenomenon is a tiny film of bubbles forming on the copper. This steadily increased the internal resistance of the battery, eventually rendering it unable to produce current. The second issue was the phenomenon of localization. This presents as minute short circuits that form around the impurities in the zinc. They, in turn, would cause the zinc to degrade. These two problems were solved by William Sturgeon in 1835. Sturgeon found that amalgamated zinc did not suffer from local action. The amalgamation was the zinc plate that had its surface treated with mercury. By this time, the move away from the disproved contact tension theory was quite advanced in the scientific community. Electrochemical action was beginning to become understood and embraced by scientists. One of the first practical batteries was the Daniell cell. In 1836, a British chemist by the name of John Frederic Daniell found a way to eliminate the accumulation of hydrogen bubbles that formed in the Voltaic pile design. Daniell's solution was to use a second electrolyte to consume the hydrogen produced by the first (see Figure 1.3).

Figure 1.3 Schematic of the Daniell cell.

The Daniell cell consisted of a copper pot filled with a copper sulfate solution. In this solution, Daniell suspended a porous (unglazed) earthenware pot that contained sulfuric acid and a zinc electrode. The porous barrier allowed ions to pass through but kept the two solutions separate. This proved to be the first practical source of electricity. Figure 1.4 is a drawing of the Daniell cell. One of the greatest successes of the Daniell cell is that the electrolyte would deposit copper (a conductor) rather than hydrogen (an insulator) onto the cathode. This cell was a safe and less corrosive battery than previous devices. Of historical note, the Daniell cell was the device that provided the original basis for the definition of the volt. This is the unit of electromotive force in the International System of Units. The Daniell cell would reliably produce 1.10 V. This became the basis adopted by the International Conference of Electricians in 1881 that defined the volt [1-5], [1-6]. As our knowledge of electricity progressed, this gave rise to the new discipline of electrometallurgy [1-7]. The science of electroplating had already been known for approximately 2000 years. Increasing the amount of voltage and amperage available merely refined the knowledge. The development of metals using electricity was now the new horizon.

Figure 1.4 Drawing of the Daniell cell.

Most early battery designs were termed “wet cells.” These designs were impractical and hazardous. Moreover, the ability to produce current was degraded in cold and very hot climates. In extremely cold climates, the wet cells would freeze. The first “dry” battery is said to have been developed in 1887 by Japanese scientist Sakizou

Yai. The battery was known as the “Yai Dry Battery.” Yai's design overcame leakage and corrosion difficulties with the cathode by impregnating paraffin in a carbon rod. Zinc was used for the anode. A dry cell uses a paste for the electrolyte. The material is only moist enough to allow current to flow through it. The Yai Dry Battery was patented in the United States under patent numbers US 1328027 A (1920) and US 1431859 [1-8]. The first patent was issued for the improved battery casing. The second was issued for another improvement of the casing material, and use of a mixture of graphite and manganese peroxide. The Yai Dry Battery was used extensively in telecommunications. In residences and businesses alike, it was once popularly used to power the ringer on the telephone. The standard dry cell of today is the common zinc-carbon design. It consists of a zinc anode, usually in cylindrical form, with a carbon cathode central rod. The electrolyte commonly consists of ammonium chloride in paste form surrounding the zinc anode. A second paste of ammonium chloride and manganese dioxide surrounds the cathode. The latter paste acts as a depolarizer. Some designs replace the ammonium chloride with zinc chloride [1-9]. The following are common dry battery design types: Zinc-carbon Alkaline Lithium Mercury Silver oxide Nickel-cadmium Lithium-ion Nickel metal-hydride The first five cells listed are primary cells. These designs are made for single use only. If one were to try to recharge a primary cell, occasionally a slight increase in charge can occur. Regardless, the duration of the charge will be significantly less than when the battery was new. Nickel-cadmium cells, lithium-ion cells, and nickel metal-hydride cells are secondary batteries. These designs are rechargeable. The design issues for lithium-ion and nickel metal-

hydride batteries are discussed in a later chapter.

1.2 The Lead-Acid Battery The lead-acid battery was developed in 1859 by a French physicist named Gaston Planté. Planté was a professor of physics at The Polytechnic Association for the Development of Popular Instruction. Planté's design would go on to be the one selected for use in the vast majority of automotive applications. This is also the oldest type of secondary battery design. The primary advantage of the lead-acid battery design is its ability to deliver very high surge currents for short timeframes. This design feature was excellent for powering the high current demands of earlier starter motors. Later starter designs are more efficient. The lead-acid battery is inexpensive to produce and provides a reliable source of power. However, in overall considerations, the lead-acid design has a low energy-to-weight ratio. Planté's lead-acid battery design consisted of two sheets of lead separated by rubber strips and rolled into a spiral. Some of his experimental designs used cloth as the insulator. The spiral was immersed in a solution containing approximately 10% sulfuric acid. In 1860, Planté presented his design to the Bulgarian Academy of Sciences. His new design consisted of much the same materials as the first design. However, Planté had now gathered the negative and positive plates into a protective box with the terminals connected in parallel. This was the first design that could deliver remarkably large currents. It also began to resemble what would become the modern automotive battery. The lead-acid design can be demonstrated by using two ordinary sheets of lead that are separated while immersed in a sulfuric acid solution. However, this will only result in the production of one ampere for a short timeframe. Planté's design had found a way to increase the effective surface area. However, his design roughed up the surface of the lead to give it greater surface area. This design only resulted in slightly greater storage capacity. In 1880, a French chemical engineer named Camille Faure patented a method of coating lead plates with a paste of lead oxides, sulfuric acid, and water. The paste mixture was spread over a lead grid and then cured in a humid atmosphere with mild heat. This caused the paste to dry as a mixture of lead sulfates. Thus, the paste was converted into electrochemically active material that gave a substantial boost to the amount of current the plate could deliver. This design was presented to the French Academy of Sciences as a nine-cell lead-acid battery. This improvement in the lead-acid battery design made it marketable for use in electric vehicles, communication, and lighting.

In 1881, at the same time Faure was applying for a patent in France, an American inventor and entrepreneur named Charles F. Brush was applying for the exact same patent in the United States. U.S. Patent Number US 552425 A was granted to Faure on December 31, 1895 [1-10]. Faure's research was recognized as preceding Brush's. Table 1.1 shows historical developments in lead-acid battery designs. Faure's battery was also used to light up the streets of Paris electrically for the first time in history. In approximately the same timeframe, American inventor Thomas Edison was illuminating the streets around his Menlo Park, New Jersey, laboratory. However, as historical accounts would prove, DC electricity could not be transmitted over long distances as AC electricity could. Nikola Tesla, a Serbian-American electrical engineer, teamed up with George Westinghouse to develop what would eventually become the national electrical grid. Table 1.1 Historical Advancements in Lead-Acid Battery Designs



1.3 Early Lead-Acid Battery Designs One of the first new developments that moved the lead-acid battery toward resembling its modern cousin was the Gauntlet Motive Battery. This design was patented in the United States by American inventor Joe Brown, from Grass Valley, CA. Brown held several patents relating to his design. The patents most noted are CA 2697337 A1 (also published as US 20100239889) [1-21]. Brown's improvements included a substantially fluid-impervious case, an improved anode plate, and a cathode consisting of an array of elongated hollow spines, each spine of the array defining a top end and a distal-free end. The spines are electrically and mechanically interconnected at the top ends by an integral structure [1-21]. Brown's other improvements to the lead-acid battery were a substantially conductive bottomend cap that was electrically and mechanically interconnected with the spine-free ends so as to close and sequentially rigidly locate the free ends with respect with one another [1-21]. Another improvement in Brown's patent was a plurality of ion-permeable fabric covers substantially encasing the elongated spines. An electrolyte was in solution with water in the battery case such that the anode plate, gauntlet cathode array, bottom end cap, and fabric covers were all substantially received in the battery case [1-21]. Thus, with Brown's patented design improvements, the modern automotive lead-acid battery design began to take shape. The lead-acid battery design could now provide a platform for automotive use. It could sustain a small draw for several hours, provide large surge currents, was portable, and could be recharged by adding a generator to the gas engine of an automobile. In addition, it could be used to power an electric automobile. Figure 1.5 shows an early electric automobile—a 1916 Detroit electric 60985 Brougham.

Figure 1.5 1916 Detroit electric 60985 Brougham (©Steve Lagareca/123RF.com).

The first electric automobiles and vehicle designs date back as early as 1828. However, these were little more than large models of an actual automobile. While the designs did move under their own power, they were not practical for roadway transportation. The first known functional electric automobile was built in 1837 by a Scottish engineer, Robert Davidson of Aberdeen, Scotland. This vehicle was powered by galvanic cells. Davidson later went on to develop the first electric locomotive. He named his locomotive Galvani. The locomotive was exhibited at the Royal Scottish Society of Arts Exhibition in 1841. It was said to weigh seven tons and could haul a load of six tons at the rate of four miles per hour for a distance of one and one-half miles [1-22], [1-23]. As described, until Planté developed the lead-acid secondary battery with improvements by Faure, electric vehicles were little more than a curiosity. However, electric vehicles continued to be developed, including two-, three-, and four-wheel designs. Some other historical battery designs are notable. One is the chloride accumulator design; the other is the gel cell design. Both designs were by Exide Technologies, which still builds batteries today. Exide Technologies (both Inc. and Ltd.) was founded in 1888 by W. W. Gibbs. It was formerly

known as The Electric Storage Battery Company. What was to become the Chloride Accumulator Battery was produced by Gibbs using ideas and patents purchased from French inventor Clement Payden [1-24]. The Chloride Accumulator Battery was first used in electric streetcars in Philadelphia. Later uses were to power locomotives, passenger cars, surface boats, and telephone exchanges. Other applications were for consumer items such as an electric fan, sewing machines, and phonographs. In 1898, these batteries were used to power the first U.S. submarine [1-24]. With the turning of the new century, The Electric Storage Battery Company developed a battery with greater capacity and less weight than the Chloride Accumulator design. This led to a name change for the company to “Exide,” which is short for “Excellent Oxide” [1-24]. The name refers to the lead oxide developed by the company. Exide Technologies went on to develop a lead-acid battery that closely resembles modern designs. One of the first applications was to power the lights on a 1905 Buick. In 1912, Cadillac became the first battery-started car with an internal combustion engine. By 1915, electric-started engines had spread to trucks and were being phased-in on new automobiles [124]. The primary motivator for the development of electric-started internal combustion engines was the health problems caused by the starting of the engine. The hand crank used to start engines often would swing backward violently, breaking the arm of the driver. Exide batteries were the first used for electric-start engines, thus eliminating this hazard [1-24].

References 1-1. Peter James and Nick Thorpe, Ancient Inventions, New York, Ballantine Books, 1994, pp. 148-150. 1-2. Danielle Downs and Ava Meyerhoff, Doctoral Thesis, Smith College Museum of Ancient Inventions, 1999-2000. 1-3. Benjamin Franklin and Leonard W. Labaree, ed., The Papers of Benjamin Franklin, New Haven, Connecticut: Yale University Press, 1961, Volume three, p. 352. 1-4. The American Heritage College Dictionary, Third Edition, Boston & New York: Houghton Mifflin, 1993, p. 116. 1-5. Walter J. Hamer, Standard Cells: Their Construction, Maintenance, and Characteristics, http://www.nist.gov/calibrations/upload/mn84.pdf, US National Bureau of Standards, Monograph #84.

1-6. James N. Spencer, George M. Bodner, and Lyman H. Rickard, Chemistry, Structure, and Dynamics (Fifth Edition), John Wiley & Sons, 2010, p. 564. ISBN 9780470587119. 1-7. Alexander Watt and Philip Arnold, Electroplating and Electrorefining of Metals, Watchmaker Publishing, 2005, pp. 90-92. ISBN 1929148453. Reprint of an 1889 Volume. 1-8. US Patent Office, US 1328027A was granted on January 13, 1920. US 1431859 A was granted on October 10, 1922. 1-9. Battery Association of Japan, http://www.baj.or.jp/e/knowledge/history01.html, accessed September 10, 2014. 1-10. US Patent Office, US 552425 A, granted on December 31, 1895. 1-11. US Patent Office, US 333786 A, granted on January 5, 1886. 1-12. United Kingdom Patent Office, three patents issued to Alfred Tribe, number 1,587 granted on April 1, 1882, number 2,263 granted on May 11, 1882, and number 5,601 granted on November 24, 1882. All patents relate to improvements of a secondary lead-acid battery. 1-13. United States Patent Office, US 478661 A, granted on July 12, 1892. 1-14. United States Patent Office, US 2042840 A, granted on June 2, 1936. Patent was granted to Horace E. Haring. 1-15. United States Patent Office, US 3124488 A, granted on March 10, 1964. Patent was granted to Paul Ruetschi. 1-16. United States Patent Office, US 3057944 A, granted on October 9, 1962. Granted to Boris Cahan, Paul Ruetschi, and William Stanley. 1-17. United States Patent Office, US 2821565 A, granted on January 28, 1958. Granted to Jeanne Burbank. 1-18. United States Patent Office, US 7875486 B2, granted on January 25, 2011. Granted to Lukas Feiknecat. 1-19. United States Patent Office, US 3669746 A, granted on June 13, 1972, granted to John DeVitt and David McClellan. 1-20. Thomas Reddy, Linden’s Handbook of Batteries, 4th Edition, McGraw-Hill Education, 2010, Sections 1.1, 16.8, 16.9, 16.67, 16.74, 22.20, 26.2, 26.3-13, and 33.6. 1-21. US Patent Office, US 20100239899 and CA 2697337, granted on September 23, 2010.

1-22. Lance Day and Ian McNeil, Biographical Dictionary of the History of Technology, Routledge, 1995. ISBN 978-0-415-06042-4. 1-23. William Gordon, The Underground Electric: Our Home Railways, London: Frederick Wayne and Company, 1910, p.156. 1-24. “The History of Exide Technologies,” http://www.exide.com/Media/files/The%20History%20of%20Exide%20Technologies.pdf, 2010, Downloaded October 5, 2014.

Vehicle Battery Fires: Why They Happen and How They Happen Chapter 2: Battery Designs Print ISBN: 978-0-7680-8143-5 eISBN: 978-0-7680-8361-3 DOI: 10.4271/R-443

Chapter 2 Battery Designs

2.1 Basic Concepts Before discussing the basic concepts of the battery, some definitions and principles must be understood first: 1. Coulomb's law: The magnitude of the electrostatic force of interaction between two point charges is directly proportional to the scalar multiplication of the magnitudes of charges and inversely proportional to the square of the distance between them. The force is along the straight line joining them. If the two charges have the same sign, the electrostatic force between them is repulsive; if they have different signs, the force between them is attractive [2-1]. This law of physics is also known as Coulomb's “inverse-square law.” This law describes the electrostatic interaction between electrically charged particles. The law was first published in 1785 by French physicist, Charles Augustin de Coulomb. This theory is the basis for understanding electromagnetism. Coulomb's law is similar to Sir Isaac Newton's inverse-square law of gravitation. Application of Coulomb's law also will validate Gauss' law. Both principles of physics validate each other. Given the date of Coulomb's law, it has been heavily evaluated and tested by the scientific community. All observations and testing of the law have upheld the validity of the law. Coulomb published three reports on the dependence of the force between charged particles upon both distance and charge. These reports were essential to the development of electromagnetism. Coulomb used a torsion balance to study the attraction and repulsion forces of charged particles. He determined that the magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them [2-1].

2. Ohm's law: The current passing through a conductor between two points is directly proportional to the potential difference across the two points. Introduction of the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes the relationship [2-2]:

Figure 1.4 and Figure 2.1 are representations of the application of Ohm's law.

Figure 2.1 Ohm's law wheel.

While Ohm's law more directly affects the electrical design engineer, the field service engineer investigating an electrical fire in a product should be familiar with all electrical topics should the fire case he/she is investigating turn into a legal action. The investigating engineer might well be examined in a manner designed to challenge their electrical knowledge in an attempt to

limit or exclude testimony. 3. Joule heating: This process is also known as ohmic heating. It is the process whereby electrical current passes through a conductor that causes the electricity to be converted into heat. Joule's first law is as follows: P = VI where P is the power per unit of time that is converted from electrical energy to thermal energy I is the current traveling through the resistor or resistive element V is the voltage drop across the resistor or resistive element Thus, a joule is a measurement of power per second. It is a small unit of electrical work done by electrical power of one watt acting for one second. A joule is equal to approximately 0.74 foot-pounds [2-3]. While these laws are more design-oriented, the field service engineer investigating a battery fire or an electrical fire must be able to demonstrate a skill level fully fluent in DC electricity characteristics and properties should a fire case go to a Superior Court action. More will be discussed on this in chapter 7.

2.2 Elements of a Battery A battery is a device that converts the chemical energy stored in the electrolyte or active materials into electric energy by means of electrochemical oxidation reduction. This action is termed “redox.” The electrical energy is then used to create heat or work. The reaction for a battery involves the transfer of electrons in a circuit. Some measure of heat will occur. However, in a non-electrochemical redox, such as burning or rusting, the electrons will transfer as a result of heat. As the battery electrochemically converts chemical energy into electric energy, it is not subject to the limitations of the Carnot cycle (theoretical heat engine) dictated by the Second Law of Thermodynamics [2-4]. As previously discussed, primary cells are non-rechargeable. Secondary cells will accept a recharge. Recharging the battery is merely a reversal of the redox process. This type of reaction involves the transfer of electrons from one type of material to the other via an electrical circuit.

The cell consists of three components: 1. The anode or negative electrode. This is the reducing or fuel electrode, which gives up electrons to the external circuit. The anode will be oxidized during the electrochemical reaction. 2. The cathode or positive electrode. This is the oxidizing electrode, which accepts electrons from the external circuit and is reduced during the electrochemical reaction. 3. The electrolyte. This is the ionic conductor that provides the medium of exchange or transfer of electrons inside the cells between the anode and cathode. In a lead-acid battery, the electrolyte is typically a liquid such as water with dissolved sulfuric acid being the principal reaction agent. Other batteries will use dissolved salts, acids, or alkalis to impart ionic conductivity. In non-aqueous batteries, such as lithium ion, the liquid electrolyte is composed of an organic solvent, usually a mixture of ethylene and propylene carbonates and a lithium hexafluorophosphate salt. The most common modern design is the flooded-cell type. This can be both serviceable (water can be added) or maintenance-free (cell watering openings are sealed) designs. Another type of lead acid is the valve regulated (VRLA). VRLA come in two major types: absorbed glass mat (AGM) and gelled electrolyte, typically referred to as gel-cell. Except for the amount of acid, how it is held between the plates, and the venting system design, all lead-acid batteries share similar construction (see Figure 2.2).

Figure 2.2 Common flooded-cell battery.

Each 12-V lead-acid battery is made up of six cells in series. Each cell is composed of positive and negative plates separated by microporous separators and assembled in parallel configuration (all positive electrodes are connected together as are the negative electrodes). Each electrode is made up of a grid which is pasted with lead oxide to form a pasted plate electrode. Generally, each electrode is pasted with a mixture of lead oxide and electrochemically converted to sponge lead on the negative plate and lead dioxide on the positive. Both conversion reactions occur during the initial charging process in battery manufacture. This process is known as “formation.” The grids are composed of lead-calcium-tin and lead-antimony-tin alloys (with other minor alloying additions) to provide a mechanical framework for the plates and to conduct current in and out of the plate active materials. To reduce the rate of water loss due to formation of hydrogen and oxygen gases during the recharge phase of battery operation in auto applications, calcium is commonly alloyed into the grids instead of antimony. Antimony is generally used in batteries designed to be recycled (e.g., golf carts, marine cycling batteries, and personal mobility vehicles). Battery users should be aware that wet or flooded batteries can produce a potentially explosive range of hydrogen and oxygen gases during recharge. This includes calcium-lead

grid designs. Hydrogen gas can combust at 4% ratios with air and 2% with oxygen. Oxygen is another byproduct of battery charging. The outgassing of hydrogen and oxygen are greatest during high-current recharging. A competent source of ignition close enough to one of the cells can cause an explosion.

2.3 Lead-Acid Plate Designs As discussed earlier, Faure developed a pasted-plate grid design for his battery. Each of the plate grids, made by drilling into lead plate to form the grid, was plastered with layers of red lead and a sulfuric acid mix diluted to 33%. The porous paste was pressed into the holes in the grid and then tapered at the edges. The plates were hung in a humid environment with slight heating to dehydrate the paste [2-5]. In a lead-acid plate battery, the porous paste allows the acid to react with the active material inside the plate. The capacity of the battery is increased as the surface area of the plate is expanded. In this design, the positive plates are lead dioxide and the negative plates are sponge lead. The plates are stacked in groups alternating positive and negative plates. Each plate is surrounded by an “envelope” of separator material. This insulator allows for free flowing of the electrolyte in each cell and yet keeps the plates separate. The insulator enables ionic flow. One of the design issues faced by battery manufacturers is that the active material particles in both positive and negative plates increase in size as the active material converts to sulfate from the acid as the cell discharges. Conversely, the particles will decrease in size as a charge is absorbed. This action will cause a breakdown of the active material particles in the positive plates, and the plates will gradually shed the oxide and fail. Here, it is critical for the design engineer to give the insulator or separator enough room between each plate to allow for the expansion and contraction of the plates as the battery discharges and recharges. Additionally, room in the insulator or separator at the bottom must be made so as the tiny flakes of oxide are shed and drop to the bottom of the cell they are not allowed to pile up and touch the plate. If this occurs, that cell will develop an internal short that will cause the battery to discharge as the battery sits. Most automotive applications use “envelope” separators. This effectively eliminates this mode of shorting. Use of “envelope” separators in other battery applications (non-motive) are more susceptible to this type of shorting. If a maintenance-type of lead-acid battery is being tested for this type of shorting using the specific gravity method, the cell with the short will have the highest specific gravity for the longest timeframe as the battery discharges. The other cells “feed” the internal short, keeping the specific gravity of the electrolyte in the affected cell higher than the other cells as the battery loses its charge. This will also be true for multiple battery stationary installations.

In addition to lead oxide, the negative paste commonly contains carbon black, barium sulfate, and lignosulfonate. The barium sulfate acts as a seed crystal for the lead-to-lead sulfate reaction, and the lignosulfonate inhibits increases in crystal size. The latter also acts to inhibit reduction in negative material surface area, thereby maintaining electrical capacity through many discharge-recharge cycles. In essence, what happens as the lead-acid battery discharges is that the sulfuric acid in the electrolyte will embed its molecules into the oxide on the plates. This is principally why it is not a good idea to store any lead acid battery in a discharged state. The increased percentage of sulfuric acid being embedded into the lead oxide paste will expose the lead grid to greater percentages of acid. This will break down the grid more rapidly. The presence of lower voltage will accelerate the sulfation process [2-6]. Additionally, the sulfuric acid that reacted with the negative material upon discharge will result in lead sulfate crystal growth and loss of battery capacity, which is difficult to reverse.

2.4 Insulator and Separator Design Issues One of the primary design issues affecting insulator or separator designs is that the material must be porous enough to allow for ion passage, yet robust enough to withstand the expansion and contraction that occurs to the plates as the battery discharges and recharges. A second issue that occurs is as the plate degrades with normal use, dendrites will commonly form. The lignosulfonate prevents the negative plate from forming a solid mass during the discharge cycle. If a battery has a heavy plate mass for its size, the electrolyte will neutralize when the battery is totally discharged, and lead II will become soluble in the electrolyte. Dendrite growth occurs through the separators when the battery is charged and the lead II comes back out of the solution as lead 0 in the separator. The growth typically proceeds from the negative plate through the separator and into the positive plate. Dendrite growth is also referred to as “treeing” because the crystals have a tree-like form when viewed under a microscope. The dendrites are converted to lead on charging. The longer the battery stands in a discharged condition, the greater the number of dendrites and shorts. This process will repeat itself, and more dendrites will form and discharge the cell or cells when the battery is not being charged frequently. If space is insufficient between the plates to allow for the expansion and contraction of the plate, this creates the potential for the dendrites to compromise the insulator or separator designs. If the positive and negative plates are allowed to touch, an internal short could occur, which could lead to thermal runaway. Separators between the positive and negative plates prevent a short-circuit condition from occurring. Separators obstruct the flow of ions between the plates and increase the internal

resistance of the cell. Wood, rubber, glass fiber mat, cellulose, PVC, and polyethylene plastics are used to make separators. Microporous polyethylene separators with or without glass fiber mat and PVC or other materials are typically used for flooded designs and gel VRLA designs. The very fine glass fiber mat is the most common separator for AGM (absorbed or absorptive glass mat) VRLA designs. Wood was used in early designs. Unfortunately, wood degrades fairly rapidly when exposed to sulfuric acid. Rubber separators are stable when exposed to sulfuric acid. Rubber presents some electromechanical and electrochemical advantages that other materials cannot deliver. Effective separators must have a number of properties: Permeability Porosity Controlled distribution of pore size Mechanical strength Electrical resistance Ability to allow ionic conductivity Good resistance to the acidic condition of the electrolyte Ability to perform in a wide spectrum of climates Stability throughout the anticipated lifespan of the battery The general size of the insulator or separator must be larger (taller and wider) than the plate oxide layers or grid to avoid easy shorting paths.

2.5 Valve Regulated Lead-Acid Designs Valve regulated lead-acid (VRLA) battery designs (see Figure 2.3) are commonly referred to as “sealed” or “maintenance-free” batteries. Although the battery casing is sealed, which prevents additional water from being added, the casing does have a valve to release excessive pressure and gasses generated during normal charging conditions.

Figure 2.3 VRLA battery.

The VRLA battery casing has a gas collection manifold incorporated into the top. The manifold is intended to direct any gases produced during charging out through a flashback prevention safety subsystem. The safety subsystem consists of a pressure relief valve constructed from sintered porous polypropylene or a ceramic disc. The design provides a somewhat difficult path for the water vapor transmission between the cells (an undesired process). The condensate collection is minimal because of the very low gas evolution rates of the VRLA lead-acid design. These designs prevent water transmission between cells which, if permitted, can unbalance electrolyte concentration across the cells and result in shorter life. This is particularly true when the VRLA application is used in extreme climates. Extreme climate applications result in a shorter useful lifespan of the battery. Some VRLA designs are used for heavy industrial lead-acid flooded-cell batteries. These designs may be configured with more sophisticated individual cell vent designs with catalytic porous discs capable of recombining hydrogen and oxygen into water that returns to the cells. However, the vast majority of these industrial batteries are the maintenance type that require weekly “wetting” or hydrating of the cells with distilled water. More is discussed in section 2.11, which addresses industrial battery designs.

VRLA batteries exist in two configurations: gelled and AGM. Both configurations allow oxygen gas created at the positive plates during charging to migrate to the negative plates where it reacts with hydrogen ions to form water. This reaction dramatically reduces battery water loss. Both gelled and AGM batteries are sealed and use a one-way pressure relief valve to maintain a modest internal pressure. Typically, the pressure is below 10 psi to aid the water formation reaction. Batteries of this type are described as recombinant because of the formation of water during charging that results in very minimal gas formation and water loss. The following are features of a VRLA battery that differ from a typical flooded-cell battery: Exclusive use of lead-calcium rather than lead-antimony in the alloys of the grids. Sealed battery case with one-way pressure relief valve. No maintenance. Water is lost very slowly and cannot be added. No electrolyte seepage or residue. This allows use inside electronic and sensitive equipment. Can be designed to provide very good discharge-charge cycle life. Some designs can be mounted in any attitude except upside-down. Specific gravity of electrolyte is higher when new.

2.6 Gelled Electrolyte Lead-Acid Designs Gelled electrolyte batteries use silica particles added to the electrolyte to create a gelled material. The electrolyte is sulfuric acid based and has ionic transfer capabilities. The gel develops a network of fine cracks that allow oxygen gas created at the positive plates during charging to migrate to the negative plates where it reacts with hydrogen ions to form water, as described previously. These batteries are recombinant. The plates in a gelled battery will commonly be of a more robust design than standard floodedcell designs. The separators will not typically be constructed of polyethylene envelopes. Rather, the design will be a leaf-type from other specialized materials. The principal disadvantage of the gel battery is the slower rate of transfer of ions between positive and negative plates through the semisolid electrolyte. This results in a design that has higher internal resistance, and which cannot deliver the high current capabilities of a floodedcell or AGM design. The gel-cell design makes a better off-grid storage battery than other designs.

One area that the gel-cell battery can excel in is off-road applications. Specialty batteries for this application feature extremely robust case designs and valve designs that are less prone to dust plugging. The heavy vibration ranges found in off-road use do not cause the mechanical damage to a gel-cell battery that is commonly found in flooded-cell designs when used in offroad applications. In the early 1930s, Exide Company developed the gel-cell lead-acid battery. It was a natural extension of the company's chloride gel-cell accumulator battery. However, the battery suffered from two major issues: first, the electrolyte was prone to cracking in climate extremes. Second, motoring individuals of that time preferred to add water to the battery as part of maintenance that could be performed at home. The idea failed to find a market niche. Exide dropped the idea and never patented it. In 1982, a Russian engineer named Brajendra P. Varma was granted U.S. patent 4317872 A for a gel-cell battery that used an improved gel electrolyte. The novel separator material had a silicate component integrally mixed with an oxygen compound of boron that formed a microfiber mat. This development created an acceptable electrolyte that had stronger mechanical properties and that would produce a battery not suffering from the issues of earlier designs of Exide [2-7]. The patent was first assigned to Gould Inc. and was subsequently assigned to Exide. In essence, Exide bought their own idea back with some improvements. Also of note were gel-cell batteries sold by Sonnenschein of Germany. Sonnenschein developed successful commercial and storage batteries in the late 1960s. These batteries were for stationary use.

2.7 Absorbent (Absorptive) Glass Mat AGM batteries are recombinant designs that use a fine fiber glass mat separator and a stronger case to hold the battery plates and AGM separators in a compressed state. All electrolyte is liquid and is absorbed and held in the separators and plates of the battery with no excess liquid. Oxygen gas created at the positive plates during charging migrates through voids in the separators to the negative plates where it reacts with hydrogen ions to form water. The AGM design has only enough electrolyte to stay saturated. This also helps the electrolyte resist stratification in discharge-charge cycling. The AGM design differs from the flooded-cell design in this respect. Also, if an AGM battery container is punctured or cracked, electrolyte will not flow from the ruptured area. Figure 2.4 shows an exploded view of an AGM battery.

Figure 2.4 AGM battery detailed view.

The principal design advantages of an AGM battery are a more robust design, ability to withstand climate variances, and ability to operate in any position except upside-down. The battery is a sealed case design with an integral one-way regulator valve. The recombination reactions and low internal resistance also aid recharge and typically result in a higher operating state of charge than similar flooded-cell designs in controlled voltage charging conditions. Secondary advantages are that the thin nature of the fiber mats allows for more plates and provides very low resistance to current flow. This results in higher power density than flooded-cell designs. This feature can be valuable in many modern vehicle designs that require full battery voltage for modules to operate correctly during engine cranking or other highcurrent use states. An AGM battery will also operate in lower temperatures more satisfactorily than a similar flooded-cell design. Another advantage of the AGM design is that the compression of the plates and separators results in a mechanically strong battery. It will have greater resistance to vibration in service. The fiber mat prevents sloshing of the electrolyte compared to a flooded-cell design. Another advantage is that the electrolyte resists stratification when the battery is stored over long periods. One issue of which the service engineer should be aware is the visual appearance of an AGM battery. These designs commonly have bulging sides in the rectangles that comprise their cells, even when new. They are built that way. It is a normal visual appearance for the ends to bulge.

By comparison, if a flooded-cell battery were to display similar bulging sides to the rectangles that comprise their cells, this is an indicator that the battery has been overcharged. To prevent the formation of hydrogen gas during the discharge phase, calcium is commonly alloyed into the plates to absorb the gas. However, the production of a potentially explosive range of hydrogen gas is possible during a state of a high rate of discharge. Hydrogen gas can combust down to 4% ratios of fuel to air. The term “maintenance free” is somewhat of a misnomer. Granted, a VRLA design will lose electrolyte like a flooded-cell design. However, it loses electrolyte at a much slower pace. Regardless, the electrolyte loss does occur over time and is accelerated by operation in hightemperature environments. As the electrolyte is lost, the affected cells will dry out and lose capacity. The VRLA design will suffer many of the same failure modes as a flooded-cell design when subjected to inadequate charging, overcharge, or standing while discharged. Note that on modern vehicles with an engine control module (ECM) or powertrain control module (PCM) to operate the engine, parasitic drain on the battery will always occur unless the fuse for the ECM/PCM is removed from the fuse panel. A common practice by manufacturers is to tape the correct fuse to the inside of the fuse panel lid. The fuse is inserted into the correction position when the vehicle is readied for sale. If a vehicle is to be stored for any length of time, it is a good idea to remove the ECM/PCM fuse to prevent the parasitic draw.

2.8 Deep-Cycle Battery Designs The deep-cycle design is accomplished by the addition of antimony, tin, and arsenic to the lead in grids of the lead plates of the battery to increase strength and aid in manufacturing of the plate grid. This alloying also makes the lead harder and the positive material less prone to particle size breakdown with discharge-recharge cycling. The use of these alloys increases the usable life of the lead plates, but it also expands the outgassing and water loss, making it necessary to add water to maintain proper battery electrolyte levels and battery life. These batteries also employ special positive and negative paste formulations and applicationspecific separators to provide the life desired in deep-cycle applications. VRLA, gel-cell, and AGM batteries are also used for certain deep-cycle applications.

2.9 Advanced Lead-Acid Battery Designs UltraBattery®: A promising new development in lead-acid battery designs is the combination of the lead-acid battery with a carbon electrode material as part of the electrode arrangement. The UltraBattery® was invented by CSIRO of Australia. It was subsequently manufactured by

the Furukawa Battery Company and also by East Penn. The technology is licensed by CSIRO [2-8]. This battery design is one of the advanced lead-acid battery technologies that might find an application and market in the hybrid arena. More specifically, it might find an application in the medium-duty hybrid or, possibly, the full hybrid market. UltraBattery® is being manufactured in both the VRLA and flooded-cell version. The flooded version falls into a new category: an extended-life flooded (ELF) design. The ELF design is also being developed for hybrid micro-car configurations. This design has full stop-start capabilities. The traditional lead-acid battery design is not suited for this type of duty cycle requirement. One of the principal claims by the manufacturer of the UltraBattery® is that the design is 70% cheaper to produce than current hybrid electric vehicle (HEV) batteries. The UltraBattery® is currently undergoing road trials in a Honda Insight HEV with good results [2-8]. If a conventional lead-acid battery design is used in a hybrid application, the battery will suffer from issues such as stratification of the electrolyte, rapid sulfation of the negative material, and shedding of the active material from the plates. An ELF battery has additional additives in the negative and positive plates and uses a scrim material over the plates to apply pressure to the active materials to provide better performance and life. An ELF design was developed to provide a lower-cost design but with reduced performance compared to a VRLA-AGM design. These designs were embraced by European automotive manufacturers as a safer battery and one with a longer life. In addition to the VRLA-AGM being more expensive than the ELF, the former is not yet capable of performing well in medium-hybrid applications. Firefly Energy: The Firefly Energy battery is based upon a lead-acid variant that is lighter, longer living, and has higher material utilization than current lead-acid batteries. This design is one of the few that can operate for extended timeframes on a partial state-of-charge without significant degradation [2-8]. The Firefly design incorporates a carbon-foam electrode for the negative plates. This gives it performance comparable to a NiMH battery but with lower manufacturing costs. Firefly was a spinoff company of Caterpillar. Unfortunately, the company went into bankruptcy in 2010. The company was purchased from bankruptcy by new owners, and it is now operating under the name Firefly International Energy. The battery design was renamed Oasis. Some of these designs are still sold in the U.S. market. However, most of the production is sold overseas.

Atraverda Bipolar: Similar to the Firefly Energy design, the Atraverda battery is based upon lead-acid technology. This design uses a proprietary titanium suboxide ceramic structure. The structure, which is called Ebonex®, is used in the bipole substrate material of a bipolar battery. The Ebonex® particles are in a polymer matrix bipolar substrate that holds a thin lead alloy foil on the external surfaces. Positive paste is applied to one face of the bipole and negative paste to the other face. This design is reported to produce 50-60 W·h/kg, which is approximately 30% greater than is produced by a conventional lead-acid battery design [2-8]. Axion Power: The Axion Power E3 Supercell® is a hybrid battery/ultracapacitor in which the positive electrode consists of standard lead dioxide and the negative electrode is activated carbon. The assembly process is similar to conventional lead-acid designs. The Axion Power battery offers faster recharge times and longer cycle life given repeated deep discharges than what is possible for conventional lead-acid designs. As described earlier, a conventional lead-acid design is sluggish compared to ultracapacitors. The lead-carbon design opens the door for use in micro-hybrid vehicles employing various energy saving strategies such as start/stop and opportunity or regenerative charging. Moreover, the Axion Power battery greatly lowers the lead content in the negative plate. This results in a weight reduction of approximately 30% compared to conventional lead-acid battery designs. However, it also reduces the specific energy to 15-25 W·h/kg, down from 30-50 W·h/kg commonly delivered by conventional lead-acid designs [2-8]. EEStor®: This battery design is based on a modified barium titanate ceramic powder. The design claims a specific energy of up to 280 W·h/kg, which is considerably higher than for lithium-ion. The EEStor® battery is a new design. As of the time of this writing, the company had not released much media or design information. The company claims the EEStor® weighs one-tenth of the weight of a similar NiMH battery in a hybrid application, and features no deep-cycle wear-down, three-to-six minute charge time, no hazardous material contained within the design, and similar manufacturing costs compared to a conventional lead-acid design. The self-discharge rate is claimed to be only 0.02% per month, which is a fraction of that for lead-acid and lithium-ion [2-8].

2.10 Dual Battery Technology for Hybrid and All-Electric Vehicles Using Stop/Start Technology Johnson Controls unveiled a new prototype battery at the 2015 North American Auto Show. The new advanced battery is comprised of a lithium-ion battery inside an AGM lead-acid or an ELF battery. The design was in the prototype phase when the press announcement was released. The design is slated to come to market in 2018.

Johnson Controls and Toshiba are collaborating on a lithium-titanate cell design. The lithiumtitanate chemistry is effective for fast recharging under a wide range of temperatures. The lithium-titanate battery is effective at taking a rapid charge. Systems such as regenerative braking will add charge to the battery in a short timeframe. This will maintain the voltage at higher levels where the AGM battery will deliver deep surge currents to support loads that are applied to the drive motor for instances such as when climbing a hill. The AGM battery will also support loads such as the headlamps, navigation, heating, ventilation, and air conditioning (HVAC) fan motor, and infotainment systems. For hybrid systems, this design also allows the engine to stay off for longer periods of time.

2.11 Casing Design Considerations for Forklifts and Heavy Equipment One issue faced by forklift and heavy equipment batteries is that of vibration. Forklifts, particularly yard or outdoor forklifts, will suffer oligocyclic stress levels. A standard automotive battery casing will not withstand such vibrations. The casing will crack and leak over a short period of use. The battery casing of any off-road vehicle or equipment will be designed much thicker and tougher than the standard automotive battery. These batteries are highly specialized. They can only be procured from a manufacturer that designs, or dealers that sell, this type of specialty battery. One industry that requires specialty casing designs is the food distribution industry. Electric forklifts must be used around the handling of food items. Gas-powered forklifts cannot be used around food distribution operations because the emissions may contaminate the food. An electric forklift will commonly run on 24-, 36-, 48-, or 72-V platforms. The battery casing is generally a large steel box that holds all the individual cells. The individual cells are also steel boxes located within the larger casing box. The individual cells are hooked up into series and parallel circuits to attain the operating voltage and amperage required by the electric vehicle.

Figure 2.5 Deep-cycle industrial flooded-cell battery.

Figure 2.5 depicts a 72-V industrial flooded-cell battery. This is a deep-cycle design. It is also the largest variety of this type of battery. This design is commonly found on electric buses, heavy yard tugs, and parking lot trolleys. Specialized training and care is required by the engineer working with these batteries because there is a lethal potential to the handler should a circuit occur through the human body. Another precaution when the engineer is working with this type of battery design is that the battery cells will require rehydration on a weekly basis. Deep-cycle use tends to result in water loss from the electrolyte due to electrolysis of the water. Electrolysis is the conversion of water to hydrogen and oxygen during the end of charge when gassing is used to mix the electrolyte and control density stratification. The portion of the electrolyte that has heavier specific gravity will tend to stay at the bottom of the cell if charging does not result in enough gassing to mix the electrolyte. A forklift battery or any deep-cycle battery should not be in a charging cycle when water is added. The electric forklift battery design also has a much greater potential for damage to the equipment should the charge be run low by the operator. An electric forklift battery should be able to deliver eight hours of continuous use. If the electric forklift begins to run slow, it is a common practice among warehouse forklift operators to just keep running the unit until it will not move. Should this occur, the engineer should not be surprised when he or she removes the deck plate to find the unit has blown a 5000- or 10,000-A main fuse. The fuses are located in a sealed box because they are bars of copper with serrated edges. Molten copper droplets are spewed about when one of these large fuses blows. Common sense dictates that when an engineer encounters a blown 5000-10,000-A fuse,

electrical fire potential preceded the blowing of the fuse. The fuses on electric forklifts are all a slow-blow design. The unit should be checked over carefully before being returned to service after charging the battery and replacing the fuse. The same common-sense approach is required when dealing with all-electric and hybridelectric automotive batteries. Most hybrid platforms operate on 125- to 650-V DC designs. This level of current is lethal. If the investigating engineer lacks proper training on how to approach hybrid vehicles safely, then the assignment should be given to a properly trained engineer because of the dangers presented with high-voltage, high-current batteries.

2.12 Chemistry of the Lead-Acid Plate Design Starting out with a full charge, the electrolyte will have a specific gravity of approximately 1.28. As the cell discharges, both electrodes are converted to lead sulfate. This process reverses upon charging the cell:

As discussed previously, the lead-acid battery design uses a lead grid structure for the positive plate upon which lead oxide is pasted. The high surface-area of the paste is due to its porous structure. Different types of lead oxide paste are used in different plate designs. Similarly, the negative plate is a highly porous metallic lead commonly referred to as “sponge” lead. This forms the negative active material. The addition of antimony, even in low concentrations, in the construction of the lead plates will greatly increase their water loss rate. During discharge of the battery, the H+ produced at the negative plates and from the electrolyte solution migrates to the positive plates where it is consumed. The HSO4− will be consumed at both plates. The reverse of this occurs during charging. Since the specific gravity of the sulfuric acid solution concentration is higher during recharge,

the sulfuric acid will diffuse out of the active plate materials relatively quickly. Therefore, a flooded-cell design or liquid-medium design will tend to rapidly discharge and recharge more efficiently than a gel electrolyte because of the slower diffusion of the sulfuric acid in the gel. The ratios of the reactants and curing conditions of the lead oxides pasted upon the grid surfaces will affect the development or formation of crystallinity and pore structure [2-4]. The electrolyte is a sulfuric acid solution, typically possessing a specific gravity of approximately 1.28 or 37% acid by weight in a fully charged state. As the battery discharges, the specific gravity of the electrolyte will drop because the sulfuric acid molecules have embedded themselves into the lead oxide on the positive plate. The actual ratio of sulfuric acid to water will vary depending on the manufacturer of the battery. As shown in the examples above, the basic electrode processes contained in the positive and negative electrodes involve a dissolution precipitation mechanism. It is not a solid-state ion transport or film formation mechanism. [2-4]. As cell charge approaches a full-charge state, the sulfuric acid molecules are released from the oxide paste and the majority of the PbSO4 has converted to Pb or PbO2, the cell voltage increases greatly beyond the gassing voltage, and almost all of the charging current is applied to gassing. The cell will begin production of hydrogen and oxygen gasses. This results in the loss of water. A simple method of determining that one or more cells of a lead-acid battery have developed a short or there is too great of an ionic flow through the separator or insulator is if the suspect battery is placed on a charger that is set for 20 to 50 A. The affected cell(s) will immediately begin boiling the electrolyte. Visible production of bubbles in the affected cell(s) is quite evident. This only applies to battery casing designs in which the caps can be removed to add water to the cells. A second point to observe is that the affected cells will produce a copious quantity of bubbles (not just one or two bubbles) as the charger is charging the battery. Production of a bubble or two in a cell is normal. Copious bubbling or boiling is indicative of a shorted cell. If the shorted cell is allowed to continue in service, this may lead to either an unreliable battery that discharges greatly as it sits or one that suffers a thermal runaway event. If a battery connected to a charger begins to boil one of the cells (caps off), then the charger should be turned off and removed from the defective battery. Do not remove the charger while it is still turned on. The resultant spark may cause the outgassing hydrogen to ignite, exploding the battery. Sulfation:

Lead-acid batteries lose the ability to accept a charge when discharged for too long of a timeframe. As previously mentioned, a process known as sulfation occurs over time and duty cycles. Sulfation is the formation of lead sulfate crystals in the active plate materials. The lead and lead dioxides react with the sulfuric acid in the electrolyte to form lead sulfate as the battery discharges. The lead sulfate first forms in a finely divided, amorphous state that easily reverts to lead dioxide, lead, and sulfuric acid when the battery is recharged [2-4]. However, after sitting in a discharged condition for a long time, very large lead sulfate crystals will form in the negative plates, and the battery will be difficult to fully recharge without a significant amount of discharge-charge cycling. The positive plates show the same effect to a lesser degree. As batteries are operated through numerous cycles, some of the lead sulfate is not recombined into the electrolyte. This material slowly converts to a crystalline state that no longer reconverts on recharging. Thus, not all the lead is returned to the battery plates as the battery cycles increase. The amount of usable material to generate electricity degrades over time. The sulfation crystals will be deposited upon the plates or will slough off into the bottom of the battery container. This action can reduce or “plug” the porosity of the plate material, reducing the amount available for discharge reactions. The rate of sulfation greatly increases as the battery operating voltage decreases [2-4]. This results in loss of capacity from the battery. Desulfation: Desulfation is the process of reversing the sulfation in a lead-acid battery. Many battery charging designs use a continuous feed of current. Some modern designs have turned to pulse charging. The desulfation of the battery will occur as the battery accepts a charge. As described, the crystals dissolve back into the electrolyte as the electrolyte is charged. However, if the battery is charged at too great a rate, then heat will build [2-4]. The excessive heat from charging at too great a rate will also cause a high rate of hydrogen outgassing. This has the potential for creating an explosive environment. Constant-Potential Charging is characterized by a constant-potential charging method. This method of recharging the battery has a current limit that is maintained until a predetermined voltage is reached. The current is then cut back. This approach is common to industrial applications. Modified-Constant Charging is used for on-road uses in which the charging applications are tied to the battery. This approach is sometimes referred to as float charging.

The battery charge is merely reduced when the battery approaches a full charge state. In automotive applications, the charge voltage is constant, but the current amount allowed into the battery is determined by the voltage regulator. Some manufacturers have turned to pulse charging or pulse conditioning designs. This approach uses high-current pulses produced between the terminals of the battery. The theory behind this approach is that the pulses must last longer than the resonant frequency of the battery. Short pulses merely feed wasted energy into the battery. The pulses are lost to the resistive components of this resonant circuit. Thus, little current is restored into the battery. Depending on the battery design, the pulse charging approach will vary the widths and frequency of the high-current pulses [2-4]. The charging design selected must be considered optimal for the device being designed (or redesigned). The battery voltage and charge must be maintained without excessive heat generation or excessive outgassing generation. The type of charger employed to give the battery the longest life expectancy should be matched to the battery's needs and the anticipated use of the design. Design factors should include a consideration of the greatest drain on current availability and whether that drain will affect other devices. A lead-acid battery that has sat unused for a long period of time is a prime candidate for sulfation of the plates. Should sulfation completely cover any one plate, the battery will no longer be acceptable for automotive use. Simply put, adding the electrolyte to a lead-acid battery is much like being born. The electrodes will be subjected to sulfation from the moment the electrolyte is poured into the battery. If the battery is used in temperate climates on a regular basis where the nominal charge is maintained above 10.5 V, it should have the approximate lifespan (provided that an internal failure does not occur) stamped on the label. If the battery is charged and then just placed on a shelf, the sulfation process will be accelerated because the cells will self-discharge to the air, lowering the voltage in the cells. Sulfation rates will increase. If a lead-acid battery is to be stored for any length of time, use of a battery tender is a common approach to prevent sulfation of the plates. A battery tender is a very small battery charger with a sensitive voltage regulator built into the design. Generally, it is a small device no larger than a few cubic inches. Typically, a battery tender will have an input of 110 V AC with an output of 2 to 3 A DC current at approximately 13 to 13.5 V. The sensitive design of the voltage regulator built into the tender will cut back current production to a level that is barely above the amount lost to self-discharge by the battery. Some models may have a slightly higher charge rate voltage.

By keeping the voltage topped up, the battery tender reduces plate sulfation significantly. However, no battery design will last forever. Over time and duty cycles, the internal resistance of the battery will increase or sulfation of the plates will occur. The battery tender merely allows the battery to sustain a charge for a longer period of time while the battery is not in use. A battery tender design typically uses a trickle charge approach. Plate Thickness: The service life of a lead-acid battery can be directly linked to the plate size—in particular, the positive plate. The thicker the plate is, the longer the lifespan of the battery will be. The weight of the battery is a good indicator of the capacity. The heavier the battery is, the longer the lifespan will typically be. The ratios of the reactants and the curing conditions (temperature, humidity, and time) affect the development of crystallinity and pore structure of the plate. The cured plate consists of lead sulfate, lead oxide, and some residual lead. Generally, residual lead is less than 5%. The effectiveness of the positive plate active material is directly tied to the lifespan of the battery [2-4]. As described, a lead-acid battery alternates between embedding the sulfuric acid into and out of the plate oxide. This process gradually causes loss of plate material. The sediment falls to the bottom of the battery box. Should this pile of flaked material rise to the point where it is touching two or more plates, an internal short will develop. The plates of automotive (cranking) batteries are generally about 0.04 in (1 mm) thick. This does not count the thickness of the oxide paste. A typical golf cart battery will have plates that are between 0.07 and 0.11 in (1.8 and 2.8 mm) thick. Forklift batteries may have plates that exceed 0.25 in (6 mm) [2-4]. While weight is a common design concern on automobiles, it is of little concern on golf carts or electric forklifts. Automotive applications are subject to Corporate Average Fuel Economy (CAFE) standards. The logic is simple: the lighter the automobile, the better the gas mileage. Forklifts and general purpose electric vehicles, such as an electric yard tug, are not subject to CAFE standards. Thus, weight of the battery is of little concern to the designers of this type of equipment.

References 2-1. Charles Augustin de Coulomb, Premier Memoire sur l’electricite et le magnetisme, Histoire de L’Academie Royale des Sciences, 1785, p. 574.

2-2. Oliver Heaviside, Electrical Papers, Macmillan and Co., (1894) reprint, p. 283. ISBN 08218-2840-1. 2-3. The Lincoln Library of Essential Information, Buffalo, New York: The Frontier Press Company, 1926, p. 948. 2-4. Thomas Reddy, Linden’s Handbook of Batteries, 4th Edition, McGraw-Hill Education, 2010, Sections 1.1, 16.8, 16.9, 16.67, 16.74, 22.20, 26.2, 26.3-13, and 33.6. 2-5. US Patent Office, US 552425 A, granted on December 31, 1895. 2-6. Yuasa Battery Technical Manual, Yuasa Battery Company, Reading, PA, Revised Edition,Copyright 2004, p. 2. 2-7. United States Patent Office, US 4317872 A, granted on March 2, 1982, granted to Brajendra P. Varma. 2-8. Battery University, BU-202: New Lead Acid Systems, http://batteryuniversity.com/learn/article/new_lead_acid_systems, and BU-308: Availability of Lithium, http://batteryuniversity.com/learn/article/availability_of_lithium, Downloaded December 19, 2014.

Vehicle Battery Fires: Why They Happen and How They Happen Chapter 3: Battery Location Design Issues Print ISBN: 978-0-7680-8143-5 eISBN: 978-0-7680-8361-3 DOI: 10.4271/R-443

Chapter 3 Battery Location Design Issues

3.1 Importance of Battery Location for Early Designs As discussed, the lead-acid battery is the battery of choice among automobile manufacturers despite the low weight-to-energy ratio. However, the physical location of the battery within the vehicle is a subject of debate. Early battery design location was a compartment built under the feet of the front passenger. A small compartment was built into the floor pan. To access the battery, the mat or carpeting was moved back, and the hatch was unlatched and lifted to reveal the battery. It is presumed that the principal reason for locating the battery in a compartment under the front passenger floor is twofold: first, this area allows the shortest distance between the battery cathode and the B+ terminal on the starter. DC electricity does not flow over long distances well, even when oversized cables are employed. Early electric starter motors were not particularly efficient. This issue would sometimes result in the ignition coil suffering from voltage drop. In turn, the ignition coil would produce a poor spark, making starting on a cold morning difficult. Second, the early automobile manufacturers realized the potential for battery explosion. The design concept located the battery where it had the least potential for damage or injury to passengers should an explosion occur. Recall that many vehicles of early design would locate the gas tank in close proximity to the engine compartment. Should an explosion occur under the hood, this had the potential for causing immolation of the driver and passengers. The vast majority of these early designs used a manual starter engagement gear. These designs had no solenoid or Bendix® starter drive. The Bendix Corporation was the first to develop a design that incorporated both a solenoid switch to handle the high current draw and a lever to move the drive gear forward to engage on the flywheel ring gear. The first designs included a manual engagement switch and gear that were located next to the driver pedal. The driver angled his or her foot over to depress both the starter switch and the accelerator simultaneously to start the engine.

Also of note was that the vast majority of automobiles were equipped with an inline sixcylinder engine. The starter was similarly located within a foot or two on all models. Whether the starter was mounted to the left side or right side of the engine, the battery B+ cable was only a foot or two longer when the starter was located on the far side of the engine compared to from the battery well by the front passengers' feet. Thus, the first considerations of the design engineer were to locate the battery as close as possible to the engine to minimize voltage loss due to “line drop” and reduce damage should an explosion of the battery occur. The design engineer did not wish to spray electrolyte all over the passengers nor to cause the gasoline tank to breach should the battery explode.

3.2 Design Issues for Later Model Vehicles As discussed, lead-acid battery designs do not function well in climate extremes. This includes the heat generated under the front hood by modern engines. The average ambient air temperature that occurs under the hood of any given modern vehicle is approximately 275° to 300°F. This is a typical heat measurement on a 70°F day. Hot spots will be present within the general ambient air inside an engine compartment. The air will become hotter when measurements are taken in close proximity to the exhaust system. If any given lead-acid battery design is subjected to these temperatures, this will cause the battery to suffer accelerated degradation of the electrolyte and accelerated sulfating of the plates. To combat battery degradation issues, automobile designers have shifted the physical location of the battery. These designs include: 1. Forward portion of the engine compartment with a fresh air duct or grille opening blowing ambient air over the battery. Location is high in the engine compartment in this example. 2. Rear portion of the engine compartment. Typical locations are away from the engine and as close to the joint of the firewall to apron (either left or right side) as possible. Design considerations here locate the battery as far from the exhaust manifold as possible. 3. Moving the battery to a well in the trunk. In this design, a larger battery cable will route to the engine compartment. Typically, a “jumper” lug arrangement will be incorporated to allow for manual jumping of the battery from the engine compartment. This is done for three reasons: most of these vehicles will have an electric trunk release with no manual exterior lock. Thus, jumping a dead battery will prove problematic.

The second reason also has to do with ease of jumping a dead battery because typically it is easier for the good vehicle to jump the bad vehicle while the engine compartments are close together. Third, most of these designs will incorporate a “jumper” lug in the engine compartment. This provides a shorter path to the starter motor. More current is available to the starter from the vehicle providing the jump start. Notably, moving the battery into the trunk will provide the greatest environment of temperature stability for the battery. Even though there is no direct heating into the trunk area of any vehicle currently sold in the U.S. market, there is indirect heating from the air that escapes from the passenger area into the trunk. Similarly, air conditioned air will seep into the trunk on hot days. There is no engine heat to contend with. It should be noted that most manufacturers that locate the battery in the trunk will also commonly equip that vehicle with an AGM type of battery. As discussed earlier, the AGM battery will commonly upgrade the battery design with a couple of extra plates per cell. Adding plates increases capacity and rate capability compared to a flooded-cell design. So even though the voltage drop is greater because the battery is in the trunk, a higher current is available to power the accessories and starter motor properly. Thus, the AGM battery design is proving to be the most robust and safe design of all the design choices available to the design engineer. The greater the amount of telematics and electronics that are equipped on modern vehicles, the greater the demands that are placed upon the battery and charging system. However, the AGM design is also among the most expensive on the market. The single biggest disadvantage locating the battery in the trunk poses is the distance the heavy current for the starter and charging system is required to travel to reach or depart from the battery. This disadvantage is overcome somewhat by increasing the American wire gauge (AWG-SAE) size or the cross sectional area (CSA-metric) of the cable. The second biggest disadvantage in locating the battery in the trunk is that the materials comprising the trunk trim and spare tire cover do not have to be made in compliance with FMVSS 302-Interior Flammability. Moreover, consumers will commonly carry all types of combustibles in the trunk. A trunk fire caused by a battery can result in a high-order fire. Finally, the gas tank fill neck is generally located near the trunk on many models. This has the potential for creating a gas tank fire should a trunk fire occur. The greater BTU load from a gasoline fire may well destroy all the fire evidence to the point that a fire cause and origin diagnosis with 100% certainty is not possible. 4. Inside a compartment built under the driver seat or passenger seat. In this example, the seat must be removed, a “U” shape cut into the carpeting to access the hatch, and the battery hatch opened to access the battery. Please note: it is best to look under the vehicle

to determine where the battery compartment is located so time is not wasted by removing the wrong seat or the carpet is not cut at the incorrect location. 5. Protective shields are used over the battery. These can be found on all of the designs listed here. For the batteries physically located within the engine compartment, the shield designs will commonly be to block heat. The closer the battery is located to the exhaust system, the more common heat shields of a reflective variety will be employed. Some manufacturers have used a metal compartment at the firewall and apron to shield the battery from engine heat. Some of the shield designs include a battery box with a removable lid similar to those used on marine applications. Often, convolute conduit or heat shield material over the top of the battery cables is incorporated as additional protection from heat. The design engineer may select a combination of shielding and location to satisfy the demands of the vehicle model being designed. For example, a battery complete casing would be desirable for a battery mounted in the trunk. Alternatively, some type of secure convenience tray cover may be used. Given that batteries have a propensity for outgassing corrosive vapors and emitting microscopic particulate matter, covering the battery from contact with any consumer items is a consideration. Moreover, the terminals need to be shielded from accidental shorting from a loose metal object rolling around in the trunk. One innovation by GM is with the 2014 Camaro model. The vehicle is no longer equipped with a spare tire. The battery has been relocated in the trunk spare tire well. Fusible links are mounted to the battery B+ cable for the power distribution module and alternator. An overcurrent field-effect loop is used to determine if current moving to or from the battery is too high. This device will signal a cutback. In addition, the battery B+ cable has a jumper lug in the engine compartment on the left side. A high-impact foam cover is placed over the battery, and a tire repair and inflator kit are located next to the battery cover. A conventional spare-tire fiberboard cover is then placed over the assembly and connected with a threaded fastener. This approach places the battery in a well-protected area, which is covered and secured so that a battery explosion has minimal injury potential; circuit over-current protective devices are present, and the battery is located in a place that allows for easy load testing and replacement of the battery. In the process, GM has eliminated the cost of a spare tire and tire tool set. This is a considerable savings in cost and weight. Figure 3.1, Figure 3.2, Figure 3.3, Figure 3.4, and Figure 3.5 show battery and safety components in a 2014 Camaro trunk.

Figure 3.1 Outer battery cover in trunk.

Figure 3.2 Inner battery cover in trunk.

Figure 3.3 Battery.

Figure 3.4 Stand-alone control voltage regular sensor.

Figure 3.5 Current overload fuses.

3.3 Design Issues for Components Surrounding the Battery Numerous design issues must be considered for locating the battery. Some of the larger design issues are as follows: 1. Lead-acid batteries will commonly outgas a combination of oxygen, vaporous sulfuric acid, hydrogen sulfide, and microscopic lead oxide particulate matter that is small enough

to float in the outgassing vapor mass. These vapors outgassing from the battery vent or casing are heavier than air [3-1]. Moreover, the fumes do not disperse quickly when the vehicle is parked. An issue compounding this problem is the fact that the battery may continue to outgas fumes after the engine is shut down and the vehicle is parked. This is due to the residual heat built up in the battery mass and the mass of the engine. This phenomenon is commonly called “heat soak.” A shorted cell also will expand the amount of outgassing vapors, as well as increase the charge rate to the other cells. An example is the division of 12.5 V by five cells vs. six cells. Because the sulfuric acid vapors are heavier than air [3-1], they will tend to cling onto and around the electronic components located near the battery. Over time, the vapors will tend to accumulate. This will pose corrosion issues for all components that the vapors touch. It can also lead to back-feed issues in the electronics and shunt currents running along the body. This is mostly seen in higher voltage applications. For example, a bank of relays is located at the base of the battery (see Figure 3.6 and Figure 3.7). This can lead to one or more of the relays suffering “bad contact” issues or the connector at the base of the relay becoming corroded. Both conditions will cause the relay to stop working. Sometimes, a large power connector is located underneath the battery pedestal or passes near the battery. The same phenomena of corrosion can occur to the power connector as to the relays. Either the engine stops running or some of the electronics stop working when this issue crops up. 2. The manufacturer locates the power distribution module directly rearward of the battery. Unless the unit is sealed well, the corrosive vapors can ingress into the power distribution module over time. This can lead to internal resistive shorting inside the power distribution module, which can cause the unit to catch fire. This may well be one of the reasons so many vehicle fires can be traced back to a failure from within the power distribution module. Figure 3.8 shows electrolyte accumulation on the PDM casing of a vehicle. Note the moist accumulation on the power distribution module box from the outgassing of the battery.

Figure 3.6 Battery positive terminal next to PDM.

Figure 3.7 Power relays next to battery.

This particular failure mode leading to fire can be exacerbated if the lid to the power

distribution module has fallen off the module due to the poor design of the lid holddowns, or if someone has inadvertently left the lid off when servicing one of the fuses or relays. In this case, moisture and road grime are also allowed to enter the power distribution module via the openings of the top. Road grime conducts electricity. It is comprised of moisture, various salts, carbon, and powdered metals such as the steel belts from worn tires and metallic brake pads. If moisture and road grime are allowed to accumulate over an exposed power distribution module, a failure leading to fire increases exponentially. This is one issue the investigating engineer should examine with care when electrical fire from a power distribution module is suspected: determine if the lid for the power distribution module was in place before the outbreak of fire. Determining that the failure leading to fire was caused by the underhood power distribution module and not the dashboard fuse panel can be evidenced by Figure 3.9. Note that one of the two battery B+ cables shows high electrical heat where the other does not. The larger one that shows the high electrical heat is the one that routes from the positive terminal of the battery. The second cable routes to the fuse panel on the left side of the dashboard. The fact that one B+ cable is damaged by electrical heat yet the other is not indicates that the failure mode is from within the power distribution module and not from the fuse panel.

Figure 3.8 Electrolyte accumulation on a PDM casing.

Figure 3.9 Battery B+ cable routing to PDM.

Destructive levels of current flowed through the main B+ cable to the B+ terminal on the power distribution module. Note that the B+ cable to the fuse panel on the left side of the dashboard shows ruddy-red discoloration but no disorganization of the cable strands. This is proof that the cable was brought near its melting point by convective heat. The main B+ cable has been damaged by electrical heat. Both are located inches from each other. Therefore, they would both be subjected to the same amount of convective heat. 3. A design issue that exists and which can lead to electrical fire is the design engineer failing to add sufficient hold-downs or stand-offs to prevent a battery B+ cable from chafing against a negative body surface or AC pipe. Figure 3.10 depicts a battery B+ cable that left the factory missing the plastic “stand-off” that holds the battery cable away from the AC pipe. Although not currently an issue, this type of error can lead to a fire. Thus, a $0.50 error has the potential at minimum for burning a vehicle. If the fire occurred when the vehicle was garaged for the night, it would have the potential for burning down a house.

Figure 3.10 B+ cable resting on AC pipe.

In the example of a battery B+ cable shorting out against an aluminum AC pipe, the investigating engineer should be aware that the AC system contains pressure at all times (unless Freon charge has been lost due to leakage). Moreover, polyalkalene glycol (PAG) oil generally is circulating in the AC system. The electrical arcs that occur when a battery B+ cable shorts out against the pipe will cause the spewing bits of flaming PAG oil to be discharged. These flaming bits of oil can start fires on the surfaces they land upon. Thus, not only is the shorting battery B+ cable a source of electrical heat, when it shorted against the grounded AC pipe, a second fuel was added in the form of flaming PAG oil bits created by the arcing B+ cable that has breached a hole in the AC pipe. The investigating engineer must be able to grasp the “big picture” that is presented by the remaining fire evidence. In the example depicted in Figure 3.11 and Figure 3.12, the wiring harness is resting on the AC pipe above the transmission. When the wiring harness was pulled back, it was revealed that the harness had been chafing on the AC pipe. Mechanical friction damage occurred to the convolute conduit, commonly termed “crinkle tube,” and to the AC pipe. Should the chafing continue, this could very well lead to a PAG oil and electrical short fire.

Figure 3.11 Wiring harness chafing on AC pipe.

4. One design issue applies to all vehicles: servicing the battery. Without question, the battery will eventually need replacing in the lifetime of the vehicle. Access to the battery must allow for removal and installation of the battery without injury to the service technician. Depending on battery group number, a lead-acid battery can be heavy to lift from an awkward position. Germane to the servicing of the battery is the design issue of servicing the battery cable terminals and the battery lugs. The battery cable end should be designed to be serviced easily. Another concern is the potential replacement of the battery cable terminal should corrosion damage the first one. One design opportunity that seems to be missed by many design engineers is to create a replacement OEM part in case the original battery cable terminal becomes worn out or damaged. However, a few manufacturers are now coming to realize the advantage of a replacement cable end as an assist to the dealer's service department. As a general rule, the only service option is to replace the entire cable. Sometimes, this involves having to rewire the entire engine compartment because the battery B+ cable is integral to the engine compartment wiring harness. This is not an economically viable option for most consumers. Therefore, aftermarket cable ends are installed by service technicians. An OEM part sale and service revenue at the dealer is lost when a replacement cable end is

unavailable.

Figure 3.12 Mark on wiring harness from chafing.

5. Another current design issue concerns the newer “pre-fuse” module (exploding squib) located at the battery B+ terminal. The B+ cable actually routes through the pre-fuse module before heading to the engine and power distribution module. These modules operate with the SRS system. The SRS module commands the pre-fuse module to explode. This parts the battery B+ cable so that a post-collision electrical fire is eliminated. Figure

3.13 and Figure 3.14 depict a battery “pre-fuse” module that has failed and caught fire. Figure 3.15 depicts the negative battery cable. The negative connection to cause the fire on the positive side at the “pre-fuse” module clearly did not flow from this cable. The module shorted internally. Both ends of the B+ cable affix to the “pre-fuse” module. Figure 3.16 is what a new pre-fuse module looks like. Some will mount on top of the battery as this exemplar or they may mount to the side of the battery as in Figure 3.13 and Figure 3.14.

Figure 3.13 Pre-fuse module failure.

Figure 3.14 Pre-fuse module failure.

Figure 3.15 Negative cable on battery.

Figure 3.16 Pre-fuse module.

The pre-fuse module must be located in fairly close proximity to the battery. It is unacceptable for any length of B+ cable to be dangling after the pre-fuse module has exploded its squib. Therefore, this module will tend to suffer corrosion degradation from the battery outgassing corrosive gasses. Use of the AGM battery design will minimize the outgassing vapors. Again, the cost of a pre-fuse module should be taken into design consideration. Because these modules are a safety item, the price generally is fairly expensive. Having to replace the pre-fuse module because of ordinary maintenance might cause the consumer to consider another manufacturer when it comes time to purchase another vehicle. 6. The battery location must not be such that the positive terminal cannot short out against the vehicle body. Similarly, a vehicle structure cannot be allowed to touch both of the battery terminals. If the battery cables are designed to route the negative with the positive cable, the design engineer should call for a robust insulation for the cables. One famous example of an erroneous battery location design issue is very early Volkswagen models that located the battery under the rear seat. The very early models did not have a battery case. The rear seat springs would weaken with age. When a passenger was seated or heavy cargo was placed in the rear seat above the battery, the seat springs would contact both of the battery terminals, setting the rear seat on fire. The later (but still

early) designs, through the demise of air-cooled engines in the U.S. market, incorporated a plastic shield over the positive terminal. Unfortunately, this shield had a tendency to fall off or be left off by a technician. Because of the erratic nature of electrical fire, the experience level of the investigating engineer becomes paramount. Any engineer is only capable of responding to their level of training. The root causes of failure modes of electrical and electronic components must be fully understood or the diagnosis may well correct the symptom but fail to address the primary cause. In this case, field experience cannot be replaced by classroom training or the reading of a book. Books and classroom training can only provide the basic building blocks upon which field experience is gained. Experience refines the training.

Figure 3.17 Stand-alone control voltage regulator.

Figure 3.18 Heat damaged battery terminal protector.

Figure 3.19 Melted battery from over-cranking.

Figure 3.17 depicts the voltage monitor module (works with alternator). Both of the wires had melted their insulation from the wires. This is a very minor electrical fire as defined by the

National Highway Traffic and Safety Administration (NHTSA). The investigating engineer should be familiar with voltage monitor modules and explain the theory and operation as well as the failure mode in the fire report. Figure 3.18 and Figure 3.19 depict a lead-acid battery that has overheated and melted due to the owner of the vehicle continuously cranking the starter until the fire started. Essentially, the plates overheated and melted the battery top. The engine would not start so the owner just kept cranking the starter until smoke was observed coming out from under the hood. Note the evidence of electrical heat on the red weather cover of the B+ terminal. However, neither of the battery lugs melted.

Vehicle Battery Fires: Why They Happen and How They Happen Chapter 4: Direct and Alternating Current Print ISBN: 978-0-7680-8143-5 eISBN: 978-0-7680-8361-3 DOI: 10.4271/R-443

Chapter 4 Direct and Alternating Current

4.1 Generators and Alternators Modern automobiles generate both DC and AC current. If the vehicle is an American model built before approximately 1955 and 1959, then a generator may be found under the hood. By 1960, all American models had switched over to alternators, and the 6-V DC platform had been discontinued. Import models used generators up to approximately the 1969-1970 model years. Some import models used the 6-V platform up to approximately the 1966-1967 model years. By 1970, the vast majority of models had switched over to the 12-V DC platform charged by an alternator. Both an alternator and a generator perform the same function—they generate electricity. The biggest difference is that the generator will produce DC from the alternating polarity magnets that make up the armature. The current is delivered out of the armature via carbon brushes. Essentially, a generator is much like an electric motor. It will produce DC electricity when rotated by an engine, or, when power is applied in the correct polarity, a generator will rotate like an electric motor. An alternator differs from a generator in that it produces AC electricity from its field windings. The AC electricity must be rectified via use of a diode bridge. The biggest advantage an alternator has over a generator is that it will produce peak voltage and higher currents at lower revolutions per minute (RPM). An alternator will not rotate like a generator if current is supplied to the correct terminals. Many types of alternators are on the market. The principal design types are compact clawpole, windingless rotor, salient-pole, and compact liquid cooled. Alternators can be single phase or triple phase. Most automotive alternators will produce approximately 85 A in modern vehicle applications. These units are capable of amperage spikes of up to approximately 125 A without damaging the alternator or voltage regulator. The easiest way to determine if the alternator on a vehicle engine that has caught fire is an average output model or a high-amperage output model is the size of the B+ terminal on the back of the alternator. The average units will be equipped with a 1/4 in (6 mm) terminal bolt.

High-output alternators (over 100A RMS) will have a 5/16 in (8 mm) terminal bolt. This observation will hold true for the vast majority of alternator designs regardless of manufacturer. Many drivers remember the headlamps dimming at idle for vehicles equipped with a generator. As soon as the RPMs were increased, the headlamps increased in brilliance. On vehicles equipped with an alternator, no voltage loss is observable at idle at the headlamps. Other sources of AC are the inverter used on hybrid designs. In this application, the highvoltage battery cables are completely isolated from the 12-V DC vehicle platform. The highvoltage battery sends the DC current to the inverter, which converts it to AC to power the hybrid motor. Hybrid vehicles are discussed in a later chapter. The only other sources of AC found in automotive applications are sensors that generate an AC wave and 12-V DC to 110-V AC power inverters sometimes found in vehicles that are used for camping or off-road use. Some manufacturers have equipped such inverters on the vehicles as OEM equipment. The investigating engineer should have a solid understanding of charging systems. The discussion point here is that the investigating engineer must know the basics of how an alternator or generator operates, and what a failed alternator leading to fire should look like and how to diagnose such a failure. For example, the diode bridge inside the voltage regulator on an alternator has failed, causing a fire. Figure 4.1 and Figure 4.2 depict a failed alternator that the diode bridge has allowed reverse current into the field windings. Note how the alternator casing itself is showing signs of heat, heat cracking, and shrinkage. Note the heat is present in small nooks in the alternator casing where convective heat from the engine fire would not normally present. However, the alternator bracket itself shows none of the similar signs of heat. The alternator mount bracket reflects virtually no heat impingement, yet the alternator casing has begun to melt. Due to sheer mass, most alternators will survive engine fires largely intact.

Figure 4.1 Melted alternator housing from failed diode bridge.

Figure 4.2 Melted alternator housing from failed diode bridge.

Figure 4.3 Car after house fire.

Figure 4.4 Alternator intact after house fire.

Compare Figure 4.1 and Figure 4.2 with Figure 4.3 and Figure 4.4. The latter two are an example of a vehicle involved in a house fire while parked in the garage. The vehicle did not start the fire. However, even with such a high level of destruction, note that the alternator has

survived relatively intact. The alternator casing does not reflect the same type of damage as in Figure 4.1 and Figure 4.2 for the alternator that suffered an internal electrical failure.

4.2 Electron Flow The electron flow argument has been ongoing since the 17th century. The Conventional Flow Rotation theory and the Electron Flow theory are at odds with each other. Figure 4.5 and Figure 4.6 illustrate the Conventional Flow Rotation theory and the Electron Flow theory, respectively.

Figure 4.5 Conventional electron flow.

Figure 4.6 Electron flow.

One of the first erroneous conjectures on the flow of electrons was from Benjamin Franklin. He (incorrectly) reasoned because the terms “negative” and “positive” are from the human vernacular of that time period with “negative” referring to a deficit and “positive” referring to a surplus, then these terms could be applied to electron flow. The terms have no meaning beyond the conventions of our own language and scientific description. The words “black” and “white” may easily have been substituted. Franklin reasoned that “negative” is associated with a deficiency. Therefore, electrons flowed from the positive to the negative. His reasoning was the positive had a surplus of electrons, therefore, the flow must be from the surplus to the deficit. By the time the true direction of electron flow was established by the scientific community, the terms “negative” and “positive” had already been accepted and commonly used. Because this book will focus on failure modes of DC systems, the argument between Conventional Flow Notation theory and Electron Flow Notation theory is moot. The main cause of electrical fires is either a resistive short-to-ground or a direct short-to-ground. In either case, electrical heat is generated. How the electrons flow in this example is irrelevant.

4.3 Battery Ratings Lead-acid batteries are rated using differing methods for the various markets in the automotive world. The following are the most common methods for rating battery capacity: Cold Cranking Amps. This method is also referred to as Cranking Performance. A figure will be printed on the battery label that will state the cold cranking ampere (CCA)

rating. Common automotive batteries run between approximately 600 and 750 cold cranking amps. For example, the battery has 650 CCA printed on the label. This means the battery is capable of sustaining 650 A at 0°F (−18°C) while still maintaining a voltage across the terminals of not less than 7.2 V. Reserve Capacity. The reserve capacity is listed in minutes, such as 39, 86, 100, or longer. This is a measurement of the length of time a 12-V battery can deliver 25 A while still maintaining a terminal voltage of at least 10.2 A at an ambient temperature of 80°F (27°C). Ampere-Hour. This method rates a battery capacity based on a 20-hour rate. This represents the steady current a battery can deliver for 20 hours at a temperature of 80°F (27°C) without terminal voltage dropping below 10.5 V for a 12-V battery. Watts. This method is a measurement of a battery cranking power available at 0°F (−18°C) to crank an engine over. Amperes are units of measure of the amount of current flowing in a closed circuit, and voltage is the electrical pressure or force applied to the circuit. Under Ohm's Law, V × I = W (volts × amps = watts). The watt rating is identical to the cold cranking amps method. As the reader may have noticed, all the battery capacity methods involve performance at a given temperature. As previously discussed, a lead-acid battery does not perform well in extreme climates. Thus, the location of the battery within the vehicle is very much an issue to address.

4.4 Failure Mode Differences between AC and DC Electricity The most common platforms for automotive designs are 6-V DC, 12-V DC, and 24-V DC (military and heavy-truck application) systems. For a period of time, there was talk among designers of moving to a 42-V platform to accommodate greater CAFE ratings by making more accessories powered by an electric motor than a fan belt. This platform either still remains in the planning stage or has been canceled altogether [4-1]. SAE had discussed changeover to the 42-V platform as early as 1988. The theorized systems would be configured with a lithium-ion battery that produced a nominal voltage of 42 V. The charging system would have operated on 50 V. The purpose of this limit was to stay under the safety shock hazard of 60 V [4-1]. Electric vehicles will operate most commonly on 24-, 36-, 48-, and 72-V DC designs. Hybrid battery platforms range from early systems that operated on 125 V DC up to a high of 650 V DC. This new 650-V platform appeared on the 2015 Toyota Prius. As hybrid designs are

refined, the platforms will likely grow in energy density and voltage. More is discussed on this topic in chapter 6. One of the biggest safety issues facing the investigating engineer while working with one of these high-voltage systems is to make absolutely sure that the high-voltage battery has been disconnected or completely discharged before performing work on that type vehicle. DC electricity has a lethal component that is not found in AC electricity: the ability to paralyze the muscles of a human [4-2]. Accidental contact with both conductors of a high-voltage DC system can be deadly. DC current has the capacity to cause paralysis, such that the person cannot let go of the wires, because the human body works on DC electricity [4-2]. The electrical shock will be of far greater duration. Six-volt DC systems were the norm until approximately 1955-57 on American models. Some non-American vehicles used the 6-V system until approximately 1967-68 model years. One of the biggest issues facing the 6-V platform was low voltage. If the system were to lose 1 to 2 V due to resistance from old age or micro-corrosion in a circuit, the circuit would not perform correctly. Examples to be pointed out are dim bulbs or electric motors that rotated too slowly. Low-voltage circuit overheating issues occurred during starting on cold mornings. The slower an electric motor revolves the armature, the closer that circuit will move toward “locked rotor amperage.” This is a fire hazard in any motorized electrical circuit. Moreover, if the starter was taking too much voltage and amperage from the battery to rotate the engine during starting, the amount of voltage available at the ignition coil could drop so low that an inefficient spark was generated. Starting the engine was problematic. The 12-V platform has performed much more reliably than the earlier 6-V system. The engine would start even in cold climates. Light bulbs would not dim at idle. More accessories could be added for the convenience of the motorist. Notably, the vast majority of early circuits were analog in design. Modern platforms are digital circuits controlling analog ones. One of the biggest differences in analyzing DC electrical fire from AC electrical fire is the use of stranded wire for automotive designs. Stranded wire is required in automotive applications because of vibration and flexing factors. Solid core wire is used primarily in houses. However, it will be found in recreational vehicles of all makes and models. Solid core wire does not tolerate vibration well. It will develop bad connections quickly unless anchored carefully. Even when anchored well, solid core wire still does not tolerate the vibration and flex that accompanies the operation of a recreational vehicle. The second greatest difference between AC and DC electrical failures leading to fire is the speed at which the failure occurs. In AC residential and recreational vehicle AC systems, the

unit will be plugged into the electrical grid. Not all campsites have RV plug-in capability. However, the vast majority of RVs do have an on-board generator to supply both DC and AC current. The ability of a steady source of 110-V AC current to create electrical heat leading to auto ignition will occur at a much greater pace than most systems. Several battery systems, including lithium-ion, nickel metal hydride, and lead-acid, can either supply the secondary fuel or be decomposed to be the secondary fuel that may exceed an AC current initiation of a fire. Moreover, the 110-V AC system will not run out of electrons. It will continue to supply the failure until the circuit breaker trips or the power wire melts in two. A DC battery failure only has the supply of electrons from the electrolyte and plates to give up. If fuel to propagate the fire is not present in the area of failure of a DC system before a battery runs out of charge, then all that will occur is a good deal of smoke from the affected insulation. It is possible that the first fuel to assist in the onset of flaming combustion is actually the outgassing volatile organic compounds contained in the insulation of the wire. However, a secondary fuel must still be in close proximity to propagate the fire. In the first example, all that happens when the circuit failure occurs is a quantity of smoke. In the second example, the smoke actually ignites for a brief period of time. Thus, the DC system failure must reach the auto ignition point and have a secondary fuel present in close proximity as requisites to propagate a fire in a much shorter timeframe than an AC system with a constant electrical supply. Similarly, the AC system must also have a fuel in close proximity to the failure. However, the speed at which the AC system can reach and maintain auto ignition temperatures is considerably faster and more robust than DC systems. One unique issue of battery fires is the internal capacity of the battery. All batteries lose capacity with age, use, and duty cycles. As the ability of the battery to store and give up its charge decreases, so does its ability to start a fire. Age and condition of the battery should be one area of investigation to be explored. For example, a lithium-ion battery with only a 30% charge is capable of being both a competent source of ignition and a secondary source of fuel. A second distinctive issue in a DC system failure leading to fire is the fact that hydrogen outgasses from the battery cells as the electron demand increases. The battery has the potential for explosion where an AC system failure does not. A third unique issue in a DC system failure leading to fire is the propensity for the electrical failure to follow Ohm's Law. The signs of electrical heat will be present at the site of the failure. The lower the resistance at the failure site, the greater the potential for ohmic heating to occur. As discussed, a dead short- and a resistive short-to-ground can both cause electrical heat. Resistive heat commonly occurs over a longer timeframe. As the circuit continues to overheat and lose resistance, if a dead short were to develop, the

fuse protecting the circuit will blow, cutting off the current. If the circuit continues to overheat with resistance, then the fire will occur at the failure site, and heat will be generated at the fuse supplying the circuit with current.

Figure 4.7 Melted dashboard.

Figure 4.8 Melted PDM at cigar fuse holder.

Figure 4.9 Scorched PDM lid.

Figure 4.10 Label for cigar lighter socket that failed.

Figure 4.7, Figure 4.8, Figure 4.9, and Figure 4.10 depict the normal failure mode for an electrical fire in the dashboard. This particular unit was an SUV heavily modified for off-road use. While the failure mode was traced back to one of the power sockets (cigar lighter) and the vehicle was barely out of warranty when the failure occurred, this case was deemed a poor candidate for subrogation because the cause of the cigar lighter failure leading to fire cannot be determined with 100% certainty. The failure may have been a latent defect from manufacture or it could have been a defect caused by severe service while off-roading. Subrogation is the legal process whereby the insurance carrier files a lawsuit in an effort to be reimbursed for the sums paid to their insured. The insured had filed a claim for damage from a defective product that caused the loss. The carrier paid the claim and now seeks to recover from the manufacturer that built the defective product. If solid proof of precisely what caused the fire cannot be determined with a strong degree of scientific certainty, then subrogation is not recommended. The point in this example is that the DC electrical failure mode leading to fire presented most heavily at the dashboard site of the failure and at the fuse supplying current to that circuit. The dashboard caught fire from the failed cigar lighter, and the power distribution module melted around the fuse supplying current for that circuit. This is a standard failure mode for DC electrical fires: fire or heat occurs at the site of the failure, at the source for that circuit, and then it will melt to the center of the affected wiring. DC electrical heat from a high-resistance

failure is localized in nature.

4.5 Charging of a Lead-Acid Battery Before discussing lead-acid battery issues, the investigating engineer should be familiar with Faraday's First and Second Laws of Electrolysis. Michael Faraday was an electrochemical engineer in the mid-1800s. He wrote his First and Second Laws of Electrolysis in a series of research papers published in 1834 [4-3]. Faraday also developed what went on to become the common ignition coil. He discovered that a coil of wire wrapped around a core would store a “field” charge. When the continuity of the circuit was interrupted, this caused the field charge in the coil to collapse. This in turn caused an exponential increase of the available voltage to create a spark from the center core of the coil. Faraday's work with field effect and ignition coils as well as the other Faraday Laws that were developed around this research should not be confused with his laws on electrolysis. Faraday's First Law of Electrolysis: “The mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electricity transferred at that electrode. Quantity of electricity refers to the quantity of electrical charge, typically measured in coulombs.” [4-3] Faraday's Second Law of Electrolysis: “For a given quantity of DC electricity (electric charge), the mass of an elemental material altered at an electrode is directly proportional to the element's equivalent weight. The equivalent weight of a substance is equal to its molar mass divided by the change in oxidation state it undergoes upon electrolysis (often equal to its charge or valence).” [4-3] Faraday's Laws can be summarized by the following formula:



For Faraday's First Law, M, F, and z are constants. The larger the value of Q, the larger m will be.

For Faraday's Second Law, Q, F, and z are constants. The larger the value of M / z (equivalent weight), the larger M will be. For an element, the equivalent weight is the quantity that combines with or replaces 1.007977 grams of hydrogen or 7.9997 grams of oxygen. Alternatively, equivalent weight is the weight of an element that is liberated in an electrolysis (chemical reaction caused by electrical current) by the passage of 9.64853399(24) x 104 coulombs of electricity. The equivalent weight of an element is its gram atomic weight divided by its valence (combining power) [4-3]. While much of Faraday's research was theoretical, the investigating engineer should have an understanding of the laws and how electrolysis can affect circuits and a lead-acid battery in an automotive application. The investigating engineer must be able to identify an electrical connection that has suffered electrolysis. Electrolysis will first present as a bad or intermittently bad connection. Many times, corrosion is present. As the connection degrades, heat will build at the site. If the circuit has sufficient current flow through it to create heat, there is a potential for fire at the bad connection. Additionally, the investigating engineer should be able to cite the correct references and describe the precise failure mode provided that sufficient fire evidence remains. Electrolytic corrosion is an ongoing issue for automobiles and heavy trucks. Any given lead-acid battery design must be charged in stages. Pulse charging and constantcurrent charging were briefly touched upon in section 2.12. The following discussion elaborates upon the topic. This section examines the different methods of charging and why some of the systems work better than others. The focus will be upon closed-loop techniques that communicate with the battery and terminate charge when certain responses occur. If outgassing and plate corrosion can be controlled, the battery will have a longer lifespan. When a battery is overcharged, it heats, outgasses, and consumes water. Notably, overcharging will cause expansion of the battery and its components. In turn, this restricts the channels that are carrying water molecules on their way to become electrolyzed to hydrogen at the surface of the negative plate. This process is subject to Faraday's First and Second Laws of Electrolysis. Simply put, if the top-of-charge is limited to a voltage of approximately 2.55 V DC per cell, this will reduce the water lost per cell dramatically. The battery will last considerably longer [4-4]. Lead-acid charging uses a voltage-based algorithm that is similar to lithium-ion. The charge time of a sealed lead-acid battery is approximately 12-16 hours for automotive designs and up

to 36-48 hours for large stationary batteries. A constant charging current rate can be used until the cells reach a specified voltage; then a common adaptive strategy is to use a current taper. Lead-acid batteries can continue to be charged at a low rate matching the regeneration cycle. Lithium-ion batteries must have the charging terminated when the capacity reaches 100%. With employment of higher charge currents and multi-stage charge methods, the charge time can be reduced to 10 hours or less. However, the topping charge may not be complete. As discussed, lead-acid is sluggish to accept a charge and cannot be charged as rapidly as other battery systems. Lead-acid batteries should be charged in three stages, as listed here and shown in Figure 4.11: Constant-current charge. The constant-current charge applies the bulk of the charge and takes up roughly half of the required time to charge the battery. Topping charge and float charge. The topping charge continues at a lower charge current and provides saturation. The float charge compensates for the loss caused by self-discharge [4-4].

Figure 4.11 Battery charging stages.

During the constant charge stage, the battery charges to 70% in 5-8 hours. The remaining 30% of the time is filled with the slower topping charge. This allows the cations and anions to embed fully into the electrolyte and plates. The float charge is provided by a separate battery tender. This stage maintains the battery at full charge. The switch between the constant charge and the topping charge phases will occur seamlessly when the battery reaches a set voltage limit. The current from the charger will drop as the battery starts to saturate. When full charge is reached, the current will drop to approximately the 3% level of the rated current for that battery. If a cell is shorted within the battery, it is possible the battery will never attain the low-saturation current. The correct setting of the charge voltage is critical. The ideal range is from 2.30 to 2.55 V per cell. Correct voltage threshold is a compromise. On one hand, the battery wants to be fully charged to get maximum capacity and avoid sulfation on the negative plates. On the other hand, an over-saturated condition causes grid corrosion on the positive plate and induces outgassing.

To make matters worse, the temperature of the battery changes during charging, making it even more difficult for the charger to provide the correct voltage setting [4-4]. Once the battery is fully charged through saturation, the battery should not dwell at the topping voltage for more than 48 hours and must be reduced to the float voltage level. The longer the charger is left charging even at lower amperage range, the more heat builds within the battery. This is especially critical for sealed and VRLA designs because these systems are less able to tolerate overcharge than a flooded-cell design. The recommended voltage for sealed and VRLA designs is 2.25 to 2.27 V per cell [4-4]. AGM-VRLA designs produce higher voltages in the range of 2.4 to 2.7, which are temperature dependent. As discussed, a flooded-cell design presents overcharging with bulging sides of the casing ends and sides. The AGM design has bulging sides as a design characteristic. It should be noted that not all chargers feature a float charge option. If the charger being used does not have a float charge feature, the charger should be set on topping charge until the battery is fully charged. Then the charger should be removed from the battery. If the vehicle is not going to be used regularly, then a battery tender should be affixed to provide the float charge. A battery tender is a small device that most commonly has a 110-V AC input with a 2 to 3 A output. These units are also configured with a very sensitive voltage regulator. The purpose of the tender is to cut back the charge to almost equal the amount lost to self-discharge in air. Note, there are specialized battery tenders that have an AGM setting for use on AGM battery designs. This topping charge will maximize the battery charge without creating heat. Age is an important issue for setting the charger correctly. As discussed, batteries wear down with age and duty cycles. For lead-acid batteries, sulfation of the plates will occur. However, sulfation rates between the plates differ. Therefore, each plate will have different charge rates because each is affected by sulfation differently. This may cause one plate to undercharge while another overcharges. Ripple voltage may also occur, especially on larger battery installations. The voltage peak of the ripple constitutes an overcharge, albeit one of short duration. The overcharge will cause hydrogen gas to be released. The valleys of the ripple constitute an undercharge. This creates a “starved” state that results in electrolyte depletion. Commonly, manufacturers of chargers will limit the ripple to 5%. A great deal less information is available on the pulse charging of a lead-acid battery. Clearly, advantages exist in terms of lower sulfation. However, manufacturers and service technicians are divided on the benefits. The results are inconclusive. If sulfation could be measured with

accuracy and the pulse charges applied as a corrective service, then the remedy could be beneficial [4-4]. Unfortunately, sulfation cannot be measured accurately. Any attempt would just be a wild guess. The battery must be disassembled to measure sulfation on each plate. Obviously, this is not a feasible approach. In stationary battery installations or industrial (electric forklift, yard tug) battery applications, the battery is commonly kept on float charge. The charger switches off for industrial applications after the topping charge moves to the float charge for a short period. This is to reduce stress within the battery. What is termed the hysteresis charge disconnects the float charge when the battery is full [4-4]. A lead-acid battery must be always stored in a charged state. A topping charge should be applied every six months or a float charge applied continuously to prevent the cell voltage from dropping below 2.1 V per cell. With an AGM design, the requirements can be relaxed somewhat. However, all battery designs will self-discharge over time. The less charge the battery contains, the greater the concentration of sulfuric acid is within the positive plates. This accelerates degradation. If the battery is being stored with a modern vehicle, then the battery cables should be disconnected. All modern fuel-injected vehicles require battery memory to maintain engine computer (ECM) settings. An average lead-acid battery will only last one month to 45 days before the charge runs dead due to the parasitic draw from the engine computer's memory. A common technique employed by automobile manufacturers and service technicians is to remove the ECM fuse and tape it to the fuse box lid while the vehicle is being stored. The following are some guidelines for charging lead-acid batteries: Charge battery in a well-ventilated area. Hydrogen gas is explosive. Select the appropriate charge program for flooded, gel-cell, and AGM designs. Check the battery manufacturer guidelines. Charge lead-acid batteries after each use, or if on a vehicle, make sure the alternator is operating correctly. Proper charging will reduce sulfation. Top up cell water to designated level after charging. Overfilling a discharged battery can result in acid spillage. If battery cell is found dry to the point the insulators protrude above the electrolyte, fill to just above insulators before charging. Formation of copious amounts of bubbles in a single cell of a flooded-cell design indicates the battery is suffering a shorted cell. Do not attempt to charge battery. Battery

should be replaced. Formation of some bubbles is normal for a flooded-cell design. The amount of bubbles observed will increase as battery reaches full-charge state. Reduce float charge if the ambient temperature is higher than 85°F (29°C). Do not allow lead-acid to freeze. A discharged battery freezes sooner than one that is fully charged. Never attempt to charge a frozen battery. Do not charge at temperatures above 120°F (49°C). Beware of overcharging any lead-acid battery under any conditions because the battery can outgas hydrogen, collect hydrogen in the cell top airspace, and if any part overheats, hydrogen can cause the battery to explode (see Figure 4.12). Hydrogen can also be ignited by the spark of attaching or removing the charger clamps. Make sure the charger is off before removing or attaching the clamps.

Figure 4.12 Exploded lead-acid battery. (Courtesy of 123RF.com)

References

4-1. SAE Standard J2622_200304, 2003, Battery Connections for the 42 Volt Electrical Systems Tests and General Performance Requirements, SAE International, Warrendale, PA, 2003. 4-2. Carl R. Nave and Brenda C. Nave, Physics for the Health Sciences, Third Edition, published by W. B. Saunders, 1985. 4-3. Rosemary Gene Ehl and Aaron Ihde, “Faraday’s Electrochemical Laws and the Determination of Equivalent Weights,” Journal of Chemical Education, 1954, pp. 226-232. 4-4. Battery University, BU-202: New Lead Acid Systems, http://batteryuniversity.com/learn/article/new_lead_acid_systems, and BU-308: Availability of Lithium, http://batteryuniversity.com/learn/article/availability_of_lithium, Downloaded December 19, 2014.

Vehicle Battery Fires: Why They Happen and How They Happen Chapter 5: Lithium Batteries Print ISBN: 978-0-7680-8143-5 eISBN: 978-0-7680-8361-3 DOI: 10.4271/R-443

Chapter 5 Lithium Batteries

Lithium and lithium-ion batteries are currently in production using various chemistries. Some of the more common designs are discussed even though they may not now be equipped on production vehicles. The fact is, there is not enough lithium in the world as a mineral to sustain current consumption indefinitely. If shortages of one material develop, then different chemistries may be substituted. Approximately 70% of the world's lithium is extracted from salt lakes or the brine beneath salt lakes. The remainder is mined from hard rock. Currently, there are designs to extract lithium from seawater. However, these designs were not commercially feasible as of the date of this publication. Most of the known supply of the world's lithium is in Bolivia, Argentina, Chile, Australia, and China [5-1]. Lesser supplies are available in the United States. It takes approximately 750 tons of brine and 24 months of time to extract one ton of lithium. Lithium can be recycled an unlimited number of times. Twenty tons of spent Li-ion batteries will yield approximately one ton of recycled lithium. However, recycling can be more expensive than mining or extracting new lithium [5-1]. On average, the world consumes approximately 90,000 metric tons of lithium per year. Of this figure, approximately 26% is used in making batteries [5-1]. For the average full-electric hybrid configured with a Li-ion battery, approximately 9 lb (4 kg) of lithium is used. The Chinese believe the world will soon be universally powered by Li-ion cars. Should world consumption rise to supply this level, then shortages will be imminent [5-1]. Even with oil prices fluctuating to historic lows, the position of electrifying all automobiles is still relevant. Secondary considerations are that cobalt is expensive and subject to the same shortages, and, although not as expensive as cobalt, graphite is also subject to the same shortages. Both of these materials are used in anode materials of Li-ion batteries. A full-electric hybrid Li-ion battery uses approximately 55 lb (25 kg) of these materials [5-1].

5.1 Lithium Primary Batteries

A lithium battery is a primary battery design. Lithium batteries are disposable batteries that contain lithium metal or lithium compounds as the anode. These batteries stand apart from other lithium batteries and lead-acid batteries. The principal advantage is high energy-toweight ratio. However, the downside is they are expensive to produce per unit. Depending on the design and chemical compounds used, a primary lithium battery can produce levels from 1.5 to 4.6 V. The term “lithium battery” applies to a group of different chemistries that are used to construct many types of cathodes and electrolytes. The average primary lithium battery will contain approximately 0.15 to 0.3 kg of lithium per kW·h. The most common type of primary lithium battery is comprised of a metallic lithium used for the anode and manganese dioxide for the cathode. The electrolyte is a dissolved salt of lithium that was reduced using an organic solvent. These primary lithium batteries have a coarse-grained lithium salt in the electrolyte solution. This graining of the salt has been known to degrade the insulator. Also, improper handling and storage of the batteries can cause damage to the insulator. A compromised insulator that allows too much ionic flow will cause a thermal runaway of the cell, possibly leading to fire. It is a consumer product and generally is handled fairly roughly. This adds to the potential failure issue. The following discussion merely lists the types of lithium battery designs. Most of these designs do not currently appear on vehicle models or hybrids. However, the investigating engineer should be familiar with the basic chemistry should these designs begin finding applications in telematics, personal electronics the consumer has in the car, wired accessories, and other areas in vehicles.

5.2 Lithium-Ion Thionyl Chloride Cell This is a different type of lithium-ion cell design (Li-SOCl2) that generally is not sold in the consumer market. Rather, these batteries find greater use in commercial and industrial applications, or they are installed in a fashion whereby the battery is precluded from being replaced by the consumer. This design has a high-energy density. It will deliver 3.5 V at 500 to 700 W·h/kg [5-2]. The cell has a liquid cathode. The electrolyte contains a liquid mixture of lithium tetrachloraluminate in thionyl chloride (LiAlCl4). A porous carbon material serves as the cathode current collector that receives electrons from the external circuit. Lithium-thionyl chloride batteries are well suited to extremely low-current applications where long life is necessary. One example of this application is the back-up battery found in alarm systems [5-2].

The electrolyte is toxic and will react with water. Low-current cells are also used in consumer electronics. High-current cells are used in military applications. This design suffers from high impedance when stored for long periods. The chemistry will form a “passivation” layer upon the anode. This either can lead to a dead battery that will not take a charge or delayed voltage delivery upon command from the circuit. Due to the high cost and safety concerns, this design likely will not be used in consumer vehicle applications, including hybrids [5-2]. A variant on this design uses thionyl chloride with bromine chloride as a liquid cathode. This design produces a larger “surface charge” of 3.9 V at initial drain on a fully charged battery. The voltage will drop back down to 3.5 V after the bromine chloride is consumed during the first 10-20% of discharge. This design is believed to be safer than ordinary thionyl chloride [5-2]. A second variant of this chemistry exists configured with a sulfuryl chloride cathode. It is similar in design to thionyl chloride. However, discharge does not result in build-up of elemental sulfur. Elemental sulfur is believed to be a contributing factor in hazardous reactions leading to thermal runaway. Therefore, sulfuryl chloride batteries may be safer. One issue with the sulfuryl chloride chemistry is the tendency of the electrolyte to corrode the lithium anodes, reducing shelf life. Sulfuryl chloride gives off less maximum current than thionyl chloride designs due to the polarization of the carbon cathode. Sulfuryl chloride will react violently when it comes in contact with water. Contact with water will cause the battery to outgas hydrogen chloride and sulfuric acid [5-2].

5.3 Lithium-Ion Perchlorate Manganese Oxide Cell This type of lithium cell is characterized by a heat-treated manganese dioxide cathode. The electrolyte is lithium perchlorate in propylene carbonate and dimethoxyethane (Li-MnO2) [53]. This design produces a nominal voltage of approximately 3 V at 280 W·h/kg. This cell is the most common consumer-grade battery, and it makes up approximately 80% of the lithium battery market. The design uses inexpensive materials. It is well-suited for lowdrain, long-life, low-cost applications. It also has a high energy density. Operational temperature ranges from −22°F (−30°C) to +140°F (+60°C). The cell is capable of delivering high-pulse currents [5-3]. As with most lithium batteries, with age, the internal impedance rises and the terminal voltage decreases. This design has a high self-discharge rate when exposed to high ambient temperatures.

5.4 Lithium Tetrafluoroborate with Carbon Monofluoride Cathode The cathode material is formed by high-temperature intercalation of fluorine gas into graphite powder—Li-(CF)x. Compared to manganese dioxide, it will produce the same nominal voltage. However, it produces it more reliably [5-3]. It is used in low-to-moderate current applications such as a clock or a battery used to power random access memory. Some military applications of this battery design are currently employed. This design produces approximately 3 V at 360 to 500 W·h/kg [5-4]. This design possesses a very limited self-discharge rate. Testing has shown less than 5% per year of self-discharge at 140°F and less than 1% self-discharge at 185°F. The cell was developed in the 1970s by Matsushita Electric Works (now Panasonic Corporation) [5-3]. It is principally used in consumer devices that require a very low selfdischarge rate at temperature extremes. It will reliably produce 3 V in an environment of 176°F (80°C) [5-4].

5.5 Lithium-Iron Disulfide The cathode material is comprised of iron disulfide (Li-FeS2). The electrolyte is propylene carbonate, dioxolane, and dimethoxyethane. The lithium-iron design is termed “voltage compatible” lithium because it can work as a replacement for alkaline batteries with its 1.5-V nominal voltage. This design will deliver approximately 1.8 V at 297 W·h/kg [5-5]. This design is compatible with AA and AAA battery sizes. Energizer® lithium-ion batteries use this chemistry because the design has a lifespan of approximately 2.5 times higher than comparable alkaline batteries due to its low self-discharge rate. It can produce high-surge currents for its size. Shelf life is approximately 10-20 years of storage. The cathode is designed from a paste of iron sulfide powder mixed with powdered graphite [5-5].

5.6 Lithium-Air Battery The lithium-air battery is a metal-air battery chemistry that uses the oxidation of the lithium at the anode and reduction of the oxygen at the cathode to induce current flow [5-4]. The battery gains this advantage in current by use of the oxygen from air rather than from an oxidizer stored in the electrolyte. This design was originally proposed for use in electric vehicles as early as the 1970s. Li-air batteries captured the interest of the scientific community due to advances in materials

technology and to satisfy the demand for an environmentally safe energy source. The appeal of the lithium-air battery is the very high-energy density of the design. The lithiumair design has an energy density per kilogram that is very similar to gasoline. Note: the average blend of gasoline will deliver approximately 20,000 BTU per lb (40,000 BTU/kg). The average density of gasoline is approximately 13 kW·h/kg for liquid gasoline. This reduces to approximately 1.7 kW·h/kg at the wheels (brake horsepower). The theoretical energy density of a lithium-air battery is approximately 12 kW·h/kg (43.2 MJ/kg). The theory holds that the same 1.7 kW·h/kg at the wheels is potentially attainable given the higher efficiency of electric motors to drive the wheels. The way the lithium-air battery operates is via a cathode that is constructed from a porous carbon electrode and a gel polymer electrolyte membrane that serves as both the separator and ion-transporting medium [5-4]. Under discharge, this oxygen was reduced, and the products were stored in the pores of the carbon electrode. Essentially, the lithium is oxidized at the anode, forming lithium ions and electrons. The electrons follow the external circuit and perform electric work. The lithium ions migrate across the electrolyte to reduce the oxygen at the cathode. When an externally applied potential through the separator via the electrolyte is greater than the standard potential for the discharge reaction, lithium metal is plated out of the anode, and oxygen is generated at the cathode [5-4]. However, this technology is still not commercially feasible or viable as of the date of this writing. Some scientists consider this technology too unstable to allow outside of a lab. Vibratory-caused thermal runaway events of significant proportions are a distinct possibility from a Li-air battery. A major motivating factor in the development of the technology is from the automotive sector.

5.7 Future Battery and Super-Capacitor Designs Graphene is a promising new technology. Graphene was “officially” invented in 2004, and its inventors received the Nobel Peace Prize in 2010. It was first developed from graphite using Scotch® tape to pull decreasingly smaller layers from the graphite until only a single layer could be removed using the tape. Drs. Andre Geim and Konstantin Novoselov, both of University of Manchester, UK, were awarded the Nobel Peace Prize in 2010 “for groundbreaking experiments regarding the twodimensional material graphene.” Drs. Greim and Novoselov have often been asked by the media as to why they never patented their work and research in graphene. As the story goes, when queried, both would respond that

an attorney for a high-tech company warned them that they would seek all permutations of a graphene patent. Both would spend the rest of their lives and entire fortunes in court fighting for the patent. Being from academia, Drs. Greim and Novoselov made the decision to pursue research and not engage in a protracted court fight. However, two patents were issued prior to 2004 regarding the production of graphene. The first is U.S. patent number 6872330 B2 applied for on May 30, 2002 and issued on March 29, 2005 to inventors Drs. Richard Kraner, Julia Mack, and Lisa Viculis [5-6]. The second is U.S. patent number 7071258 applied for on October 21, 2002 and issued on July 4, 2006 to inventors Drs. Bor Z. Jang and Wen C. Huang [5-7]. Both of the U.S. patents were applied for a full two years prior to Drs. Greim and Novoselov's research. U.S. patent 6872330 B2 was the first one issued regarding the chemical manufacture of nanostructured materials. This patent contains actual images of produced sheets of graphene with a description of the manufacturing process. U.S. patent 7071258 contains a drawing of multi-walled carbon nanotubes that can be unrolled into monolayer and multilayer nano-scaled graphene sheets (see Figure 5.1).

Figure 5.1 Rolled graphene.

The reason that two seemingly identical patents were issued illustrates one of the problems that academia and other inventors face. Each patent was submitted within months of each other. As the patent application was winding its way through the U.S. Patent and Trademark Office, it was a case of one hand not knowing what the other was doing. Thus, two patents were issued for the same process.

U.S. patent 6872330 B2 was the first to be issued. Therefore, the true credit for development of manufacturing processes for graphene belongs to Drs. Kaner, Mack, and Viculis. It should be noted that graphene itself cannot be patented. If some material or invention has been reported in scientific literature, then that material or invention cannot be patented. This is one of the reasons why graphene itself cannot be patented. Both patents held refer to the production methodology, not to the actual synthesis of graphene itself. Both patents further describe the production of the graphene nanotubes, nanorods, nanoscrolls, or nano-scale sheets as being produced with single-layer parallel planes of graphite that have one value of width or length below 100 nm thickness. The patents describe the process of partially or fully carbonizing a precursor polymer, or heat-treating petroleum or coal tar pitch to produce the polymeric carbon containing micron- and/or nanometer-scaled graphite crystallites within the polymeric carbon. Finally, both patents describe the process of exfoliation of the graphite crystallites to produce nano-scaled graphene sheets [5-6], [5-7]. Currently, over 25 patents have been granted for anticipated uses of graphene in different products and processes. Graphene has since been synthesized in various shapes and sizes in labs. It is a twodimensional matrix of a single layer of atoms that is capable of embedding other molecules into the matrix that would, otherwise, be too brittle to act alone in an electrolyte. The layered lattice construction of the nano-sheets allows for the increase in capacitor or battery energy storage.

Figure 5.2 Graphene transferred onto transmission electron microscopy (TEM) grids.

Figure 5.3 Graphene matrix.

Figure 5.2 and Figure 5.3 depict microscopic photographs of graphene. Note the matrix pattern on Figure 5.3. Figure 5.4 depicts a microscopic photograph of a sulfur molecule being inserted into the graphene matrix. Graphene has a distinct advantage in that it is a conductor and not an insulator. As a conductor of heat, it outperforms all other known materials. This feature aids in the construction of capacitors and battery designs. This conductive action will open the doors to new chemistries in Li-ion batteries. However, it also lends itself to application in “super capacitors.” Currently, in some Asian nations, city transit buses are powered by large banks of “super capacitors.” This type of electric bus can be found in major cities such as Shanghai, Beijing, Saigon, Tokyo, and many others.

Figure 5.4 Molecule being inserted into graphene matrix.

Think of banks of “super capacitors” as devices that both store and discharge large quantities of current. Consider the current stored in a super capacitor bank as liquid stored in a bucket. Consider electricity stored in a battery as liquid stored in a bottle. The bucket will empty its contents much more quickly than the bottle. Given a large hose, the bucket also can be filled much more quickly than the bottle. Simply put, this analogy is the essence of the difference between a super capacitor and a battery. This is the principal advantage of use of graphene as the matrix or lattice of a super capacitor: It gives up large quantities of current and can restore the used current much more quickly than the jelly electrolyte of a Li-ion battery. The current design target for the super-capacitor buses being tested in Shanghai, China is an operational run time of approximately 20 miles with a recharge time of approximately two minutes. Charging stations are scattered across the city near the bus stops. An umbrella charging system rises from the roof of the bus to touch the charging cables at the bus stop. The

timeframe the passengers require to disembark and new passengers need to board is typically longer than the time required to recharge the capacitor array. Thus, the new super-capacitor bus can complete a 40-mile route with only two recharge cycles. Battery powered and super capacitor-powered buses are currently being tested in various markets in many countries. Figure 5.5 shows a Chinese super-capacitor electric bus. One of the more promising applications of graphene is in the Li-ion-sulfur battery. Sulfur by itself is a brittle molecule. It is not suitable for use in electrolyte because it causes the electrolyte to become too unstable. This disallows use of this element in a vehicle battery without a mechanism of stabilizing the sulfur molecule. Thermal runaway is a significant design flaw at this stage of development. However, graphene shows a good deal of promise as being the flexible and strong medium where nano-sized particles of sulfur can be held in the graphene matrix. The graphene matrix or lattice will allow resolution of vibratory issues. A Li-ion-sulfur battery shows promise for a greater weight-to-energy ratio. Graphene is very lightweight and strong. It has amazing strength for the molecular size. The current issue facing the commercial application is the manufacture of the larger sheet sizes required to make a battery plate. Graphene production is currently not in the development stage where large batteries or super capacitors exist. Only small prototype capacitors and batteries in labs are available for study.

Figure 5.5 Chinese super-capacitor electric bus.

However, given the nano-sized surface of graphene, this opens the doors to building a large battery or capacitor sheet with sufficient surface area to accept a large charge. Current dual-

layer capacitors can be replaced by multiple-layer capacitors to add to the energy-to-weight ratio.

5.8 Failure Characteristics and Issues A lithium-metal or lithium-ion battery can be configured into differing packages. A single cell can be round and cylindrical or flat and square or rectangular. Some designs are flat aluminum “pouches.” The designs will likely continue to adapt because the product “designs” the battery, not vice-versa. While most of the designs and chemistries described here are currently used in consumer electronics and some other applications, similar designs also are used in limited production vehicle models. Notably, greater electrification of vehicles and more telematics are expected to grow in market share of future vehicle models. A second consideration is the fact that consumers add optional equipment and use the power sockets to charge consumer electronics. In such an example, these battery Li designs will be found at the site of a vehicle fire. The burden upon the investigating engineer assigned to diagnose a vehicle fire is to troubleshoot the nature of the failure and approximate the area of origin. Determinations must be made as to the possibility of the fire having been started by an item of consumer electronics or an OEM product. Was the product being charged from a power socket or was it hard wired to the vehicle? What type of circuit protection was the vehicle equipped with? Proper troubleshooting methodology will require the engineer to have training in what the failure modes from consumer electronics should look like.

Figure 5.6 Li-ion cell fire.

Figure 5.7 Li-ion cell fire.

Figure 5.8 Li-ion cell fire.

Figure 5.9 Li-ion cell fire.

Figure 5.10 Li-ion cell fire.

Figure 5.11 Li-ion cell fire.

Figure 5.6, Figure 5.7, Figure 5.8, Figure 5.9, Figure 5.10, and Figure 5.11 depict x-rays of a battery pack that was in a laptop computer being charged from a vehicle power socket. The laptop was merely sitting on top of the passenger seat when the thermal runaway event occurred. Damage to the seat was minimal. Basically, the thermal runaway of the computer

battery pack only melted a hole in the seat foam. However, smoke damage totaled the vehicle. Figure 5.6 and Figure 5.7 depict one of the batteries that was not affected by the thermal runaway event. This is a cylindrical “jelly roll” electrolyte and cell design. Note that the cathode is located correctly and the anode wraps are arranged in an undisturbed spiral wind. Figure 5.8 depicts the fusible discs and cathode “hat” as a normal cell should appear. Note the positioning of the fusible discs. No warping or distortion has occurred. Figure 5.9 depicts one of the cells from the battery pack that did suffer an internal failure that led to the fire. Note the shape of the end of the anode. Parts of the anode are destroyed. The “splatter” appearing in the x-ray is the anode material that melted in the violent reaction. Figure 5.10 and Figure 5.11 depict that same cell unrolled on an inspection table. Note the eroded end of the anode, the heat “stripe” down the center of the copper anode, and the charred remains of the electrolyte and insulator. If Figure 4.11 is examined carefully, a piece of the anode can be seen stuck to the center of the cathode, with a notch out of the anode material that matches the piece stuck to the cathode. Also note that one end of the cathode has eroded compared to the other end. Figure 5.9, Figure 5.10, and Figure 5.11 are all signs of a Li battery pack that has suffered a thermal runaway event. The battery separator failed, allowing heat to build along the surface of the anode, and the “jelly” roll began to decompose the electrolyte, causing the outgassing of combustible volatile organic compound (VOC) vapors. The ignition then occurred when heat was great enough or an internal spark initiated. The battery suffered a violent reaction that resulted in a cascading thermal event at the time the proper air-fuel mixture was reached. This affected some of the other batteries in the same pack as the battery set itself on fire. The vehicle was subsequently affected. The investigating engineer will see similar signs on other Li battery packs that have suffered a thermal runaway event. In some situations involving battery packs, the failure of one battery can become the competent ignition source, with the subsequent propagation of remaining cells becoming the secondary and tertiary fuels. Generally speaking, when a piece of consumer electronics is being recharged in a vehicle power socket, and a thermal runaway event occurs to that battery pack, the burn pattern on the vehicle will be moving away from where the consumer electronics were plugged into the socket. However, if a bad connection exists at the power socket, then it is possible that the fire will start at the power socket. In this example, the consumer electronics will likely not show the same signs of a thermal runaway event from the battery pack. Because of their nature to store energy, batteries can initiate a fire regardless of whether they are being charged or in the

middle of a discharge. The investigating engineer should be familiar with this type of failure mode. The report should document the failure properly as not being caused by the vehicle itself. Finally, the report should state precisely how the thermal runaway event is opined to have occurred. Some additional factors may also be relevant to the fire event. An example would be a piece of consumer electronics being recharged sitting in the sun on the top of the dashboard on a hot day. This could well have been a contributory factor in the thermal runaway event leading to fire, because the windshield can magnify the heat of the sun. One of the issues impacting the investigating engineer when a vehicle fire occurs due to a failure of the vehicle battery or its electrical system happens when the battery is likely not in factory-new condition. All batteries will suffer degradation through age and duty cycles. This will directly affect the ability of the battery to deliver current. In simple terms, in a fire investigation, the responsible engineer must be able to determine if the battery is so worn that it is not capable of delivering sufficient heat to start a fire. There are innumerable charts available from different types of battery testing depicting all manner of discharge or charge curves. However, these data are merely from testing by design engineers performed in a lab setting using new batteries. These are of little use in the field analysis. The practice of material “doping” is common among battery designers and chemists. This is an attempt to boost the nominal voltage or current available to the circuit. As noted, a battery is capable of attaining a “surface charge” that is higher than the average voltage at the circuit after the surface charge has been consumed. One caveat is that lab testing has little to do with determination of the primary failed part leading to fire while in the field. It may not be a good idea to use lab battery data for field failure determinations. However, if a design defect investigation is being conducted, then the data would be applicable.

References 5-1. Battery University, BU-202: New Lead Acid Systems, http://batteryuniversity.com/learn/article/new_lead_acid_systems, and BU-308: Availability of Lithium, http://batteryuniversity.com/learn/article/availability_of_lithium, Downloaded December 19, 2014. 5-2. Lithium Carbon Monofluoride Coin Cells in Real-Time Clock and Memory Back-up Applications, Archived in 2007 from rayovac.com. Rayovac® Corporation. 5-3.

Panasonic

Electronic

Components

-

Panasonic

Industrial

Devices,

http://www.panasonic.com/industrial/batteries-oem/primary-coin-cylindrical/br-cr.aspx, Downloaded December 30, 2014. 5-4. Thomas Reddy, Linden’s Handbook of Batteries, 4th Edition, McGraw-Hill Education, 2010, Sections 1.1, 16.8, 16.9, 16.67, 16.74, 22.20, 26.2, 26.3-13, and 33.6. 5-5. “Energizer Cylindrical Primary Lithium Handbook and Application Manual,” http://data.energizer.com/PDFs/lithiuml91l92_appman.pdf, Downloaded December 2014. 5-6. United States Patent Office, US 6872330 B2, granted on March 29, 2005, granted to Julia J. Mack, Lisa M. Viculis, and Richard B. Kraner. 5-7. US Patent Office, US 7071258, granted on July 4, 2006. Also issued under US 20060216222.

Vehicle Battery Fires: Why They Happen and How They Happen Chapter 6: Nickel-Metal Hydride Battery Print ISBN: 978-0-7680-8143-5 eISBN: 978-0-7680-8361-3 DOI: 10.4271/R-443

Chapter 6 Nickel-Metal Hydride Battery

Early hybrid-electric vehicle (HEV) designs placed greater emphasis on the use of nickelmetal hydride batteries than did plug-in hybrid electric vehicle (PHEV) or all-electric vehicle (EV) designs. One good solution to the high discharge and quick charge demands of the HEV design is the nickel-metal hydride (NiMH) battery. For HEV applications, the typical NiMH battery pack will have a specific energy density in approximately the 45 W·h/kg range, and will have attained a specific power of about 1000 to 1300 W/kg [6-1]. The NiMH design is no different from a lead-acid one. The same rules of battery construction apply. The only difference is that the electrolyte, which causes the reaction, is an alkaline and not an acid. One disadvantage of the NiMH design is the tendency to self-discharge at a greater rate than other designs. The NiMH design simply loses electrons to parasitic reactions that normally occur in the chemistry of the battery. These parasitic reactions will speed up with increases in temperature. They will decrease as the state of charge in the battery decreases. If a NiMH battery leaks for any reason, the clean-up technique preferred is the use of boric acid, eye protection, and toxicological gloves. Disposable overalls or a rubber apron are also a good idea. The boric acid is mixed with water to create a fairly strong solution of liquid. This is applied to the leaking electrolyte. The electrolyte will become neutralized and can now be cleaned up. All of the battery assembly is still considered hazardous waste. Disposal must be performed per local or state regulations.

6.1 Hybrid Electric Vehicles 6.1.1 The Beginnings of Hybrid Vehicles While the actual beginning of the hybrid vehicle movement in the United States is a subject of debate, the Partnership for a New Generation of Vehicles was formed in 1993. The organization involved eight federal agencies [6-2], national laboratory universities, and the United States Council for Automotive Research (USCAR). USCAR was composed of DaimlerChrysler, Ford Motor Company, and General Motors Corporation.

The principal goal of the PNGV was to produce an extremely fuel-efficient vehicle that was ready for market by 2003. The stated goal was a gas mileage of up to 80 mpg. Three experimental vehicles were produced: GM produced the Precept model that achieved 80 mpg. Ford made the Prodigy that obtained 72 mpg. DaimlerChrysler created the Intrepid ESX III which got 72 mpg. The PNGV program was canceled by the Bush Administration in 2001 at the request of the automakers. The FreedomCAR and Vehicle Technologies (FCVT) program supplanted the PNGV, also by order of the Bush Administration. The goal of FCVT is to advance the nation's economic, environmental, and energy security by supporting local programs and practices that reduce the nation's dependence on foreign oil. To that end, the Clean Cities Program was started. The Clean Cities Program is a coalition of 80 volunteer organizations that develop public and private partnerships to promote alternative fuels and vehicles, fuel blends, enhanced fuel economy, and hybrid vehicles, and to reduce the amount of time gasoline and diesel engines spend when idling. One interesting fact about all hybrids with gasoline engines incorporated in the design is that the majority of the savings on gas mileage is because the vehicle will shut off the gas engine at stop lights or stop signs. The shut-down of the gas engine at idle saves an amazing amount of gasoline. Heavy trucks also consume large quantities of fuel while idling. Whether it is waiting to load, idling the engine at a truck stop, or sitting at stop lights, the amount of fuel consumed is considerable. Given that the average heavy truck engine only obtains approximately 5-6 mpg, any savings is welcome. One of the issues of HEV cars that is studied by automobile manufacturers is the power-toenergy ratio (P/E) of 40. Quite literally, manufacturers calculate cost in terms of available power in $/kW. Therefore, whatever design is considered must produce significant savings so as to outweigh the costs. Whether or not the hybrid vehicle is a satisfactory and marketable product without the federal subsidies remains to be determined.

6.1.2 Types of Hybrid Vehicles The following paragraphs highlight various operating modes of hybrid vehicles: Micro Hybrid. A micro hybrid uses stop/start technology. With this technology, the internal combustion engine (ICE) shuts down upon stopping, thereby reducing fuel consumption and emitting less pollution while stopped. One fact of which the vast majority of consumers and

engineers are now aware is that the stop/start technology is one of the biggest reasons that any type of gas-powered combination hybrid obtains such good gas mileage figures. The amount of gasoline consumed while sitting at traffic lights and stop signs is staggering when entire vehicle model lines are considered. The micro-hybrid design is commonly configured with regenerative braking. The regenerative braking mode only has the propensity for keeping the voltage available from the battery higher at any given point in the operation cycle. On a side note, in electric vehicles configured with silicon controlled rectifier (SCR) technology, regenerative braking is viewed as an undesirable feature. General Electric Corporation holds the vast majority of patents controlling SCR technology. In SCR circuits, the regenerative braking is referred to as “fly-back current.” GE uses diodes to turn “fly-back current” into heat when the electric vehicle is decelerating. The micro-hybrid vehicle will not be capable of providing propulsion without the ICE. The system consists of a 42-V battery and an electric motor coupled with a lead-acid battery. This type of hybrid operates in a charge-sustaining mode and is widely used by European automobile manufacturers [6-1]. These vehicles are not commonly found in the U.S. market, except for use as golf carts and “neighborhood friendly” vehicles. Note that the motor vehicle code in most states allows for the use of electric- or gas-powered low-speed vehicles. If allowed, the motor vehicle code permits local municipalities to regulate low-speed vehicles to operate on given routes through residential neighborhoods as long as the vehicle meets certain requirements. Some examples are headlights, turn signals, tail lights, brake lights, horn, doors, or a chain over the door aperture. These micro-hybrid vehicles will be found in private “compound” residence tracts such as ones built around a golf course, in areas with high populations of active senior citizens that need to get to a market but no longer drive standard automobiles, etc. These “neighborhood friendly” vehicles are not allowed on freeways because most models do not go faster than approximately 15 mph. These designs differ slightly from the micro-hybrid models sold for the European market. Mild Hybrid. A mild hybrid also uses stop/start technology. This design is not capable of providing any propulsion of the vehicle without the ICE. It is also configured with regenerative braking. The system design differs from the micro hybrid in that the mild hybrid can provide some level of power assist to the ICE, and the system operates at a higher voltage. The platform the voltage operates upon varies from approximately 125 to 650 V [6-1]. Full Hybrid. A full hybrid incorporates the same features as found on micro and mild hybrids. The main difference is that this design adds a limited range of pure electric propulsion without the aid of the ICE. Generally, the vehicle will drive up to five miles at speeds of under 35 mph. Some modern full hybrids are advertising ranges of 30+ miles before the ICE engages. The

most common voltage platforms operate on 200 to 650 V [6-1]. Plug-In Hybrid. A plug-in hybrid is a full hybrid but with a larger driving range in pure electric mode. It uses the same features found on the other hybrids with regard to stop/start and regenerative braking. After a full charge with a “topping charge” is delivered by plugging the vehicle in overnight, the battery drive will deliver up to a 40-mile range at speeds of 35 mph before the ICE engages automatically, adding to the propulsion of the vehicle [6-1]. Because of the ability to drive in purely electric mode, this design of hybrid operates in both the charge-sustained mode and the charge-depletion mode. This dual-mode operation places a good deal of stress upon the battery [6-1]. This will clearly affect cycle life of the battery design. As with most vehicles, the design of the vehicle dictates the battery design. Notably, Toyota hybrid products will be configured with replaceable cells and inverters that can be rebuilt. This refinement was slated for phase-in starting in 2016. The refinement will improve customer satisfaction and reduce warranty costs associated with battery and inverter replacement. Obviously, this platform will change as battery development evolves. Charge-Depletion and Charge-Sustained Modes. Charge-depletion hybrid vehicles are designed to have a certain vehicle range when driven in purely electric drive mode. In this mode, the least amount of emissions is produced per mile driven [6-1] (i.e., zero emissions). Notably, this only addresses the electricity stored in the battery. This zero emission figure does not consider the air pollution caused by the generating of power to the national grid. It also fails to consider the costs to mine or produce the fuel on which the powerplant operates. However, as with all batteries, as the voltage decreases the current increases. Therefore, this design must have a charge depletion limiter. In simpler terms, the battery on this design will stop providing current to the circuit when it depletes to approximately 80 to 90% state of charge, with some designs down to 40%. Note that some designs will allow a threshold of 3 to 5% before battery shut-down. Charge-sustained mode is a concept in which the vehicle is designed to be operated under the various other modes of propulsion than purely electric. Another feature is for the hybridelectric motor to assist in acceleration and wide-open throttle (WOT) mode. The value of the throttle position sensor signals the ECM when the accelerator pedal is at full throttle. The ECM responds by giving the ICE full acceleration and engaging the hybrid motor as well. The concept is that ICEs are not efficient in stop/start driving. However, on freeway or highspeed driving, the ICE efficiency is improved. The addition of electric motive power, when required, will increase mpg. One other feature to the ICEs equipped on any model hybrid is that the displacement of the ICE is not large. The typical ICE equipped on a hybrid will be less

than 1500 cc's. Three basic types of hybrid-electric vehicle (HEV) configurations currently are available commercially: First is the series HEV. This model is configured with a gas engine/generator combination that produces current for the battery. The battery sends the high-voltage current to the inverter. The inverter then converts it to AC electricity for use in the electric motor. The electric motor connects directly to a differential or a wheel to provide motive force. Second is the parallel HEV. This model is configured with a gas engine and electric motor/generator combination. The high-voltage battery sends current to the electric motor. These together send power to the transmission. The gas engine may or may not operate during certain phases on this design. Most of these designs are stop/start types for the gas engine. Third is the series-parallel HEV. This model is configured with a gas engine and electric motor combination that feeds power into a transmission. A generator is separate from the electric motor. Most of these designs are also stop/start types for the gas engine.

References 6-1. Thomas Reddy, Linden’s Handbook of Batteries, 4th Edition, McGraw-Hill Education, 2010, Sections 1.1, 16.8, 16.9, 16.67, 16.74, 22.20, 26.2, 26.3-13, and 33.6. 6-2. Departments of Commerce, Energy, Defense, Interior, Transportation, the National Science Foundation (NSF), National Aeronautics and Space Administration (NASA), and Environmental Protection Agency (EPA).

Vehicle Battery Fires: Why They Happen and How They Happen Chapter 7: Automotive Electrical Fire Science Print ISBN: 978-0-7680-8143-5 eISBN: 978-0-7680-8361-3 DOI: 10.4271/R-443

Chapter 7 Automotive Electrical Fire Science

7.1 Automotive Fire Science Terms Before beginning a discussion of electrical systems and battery fire, the investigating engineer should have a solid understanding of some terms and definitions for fire science. There should also be a solid knowledge base of how and why fire propagates in various automotive and truck designs. The investigating engineer should read through the Glossary of terms and explanations provided at the conclusion of this book. Many individuals will be unfamiliar with the terms. In addition, the terms can have a second meaning when used in the context of a fire. Some of the issues discussed have the potential for destroying the fire case when the rules for handling fire evidence are not followed.

7.2 A Word about Safety Vehicle fire investigation involves dealing with a hazardous substance: small particulate matter. When vehicles suffer a large-order fire, the fibers embedded into the polymeric or nanocomposite plastics will be affected and freed. These tiny shards of particulate fibers that were formerly buried inside a plastic formula, as well as the secondary remnants of burned components, will fly up and float in the air around a burned vehicle. Breathing these shards is hazardous to the health. While there is not a great deal of research on the subject, the particulate matter can cause diseases such as silicosis or various types of cancer. Safety measures such as a painter's rubber mask, welder's gloves with a long cuff, and disposable coveralls are highly recommended to protect the investigating engineer that is sifting through remaining fire evidence to find the primary failed part. The painter's mask should be discarded when the outer “pre-filters” begin to show some soot accumulation. The disposable coveralls should be disposed of after each use. The welder's gloves should be placed in a large zip lock bag. The gloves and mask may be reused until they are too dirty for further use. If a hybrid vehicle is being approached, the high-voltage battery pack must be disabled. Two methods can be used to render the high-voltage battery safe: first, pull the service “grip” or

rotate the safety switch to the “off” position. These safety devices are generally located on the casing of the high-voltage battery pack. Sometimes, the safety switch or grip is located on a snorkel that attaches to the battery casing at one end and locates the other end at an easy-toaccess point. Second, remove or cut the positive and negative 12-V DC cranking battery cables for mild and micro-hybrids. This battery generally controls the battery module inside the high-voltage battery pack. Cutting the 12-V supply to this module generally forces the module to open the latching relays for the high-voltage positive and negative cables. It is highly recommended that a voltmeter be connected from each high-voltage terminal to ground as well as a measurement of current taken to determine if the battery is in stable condition. Otherwise, a secondary fire or electrocution is possible. Currently, the high-voltage cables are universally sheathed in a bright orange convolute conduit or solid conduit with bright orange ends. The high-voltage ground cable is not connected to the vehicle body. It is a dedicated cable connected to the inverter. The investigating engineer should beware: the high voltage and current produced by hybrid battery packs is of lethal levels. Extreme caution should be exercised at all times when dealing with this product.

7.3 FMVSS 302—Interior Flammability The Federal Motor Vehicle Safety Section (FMVSS) codes are law. This set of codes can be found in The Federal Code of Regulations, Title 49, Section 571; the subsections 101, 102, 103, etc. are the individual FMVSS codes. FMVSS 302 essentially states that any material located within 13 mm (½ in) of the airspace of the passenger seating area cannot consist of any material that burns at a rate of greater than 102 mm per minute. This code section went into effect April 1971. Basically, this was one of the first actions from the National Highway Traffic and Safety Administration (NHTSA). The purpose of the code was to make vehicles resistant to ignition by cigarettes and matches. FMVSS 302 establishes the minimum flammability or combustibility resistance standards for any vehicle sold in the U.S. market. This standard applies to all vehicles sold in the U.S. market with a gross weight rating of less than 10,000 lb. Specifically, FMVSS 302 stipulates that the following components must be compliant: seat cushions seat backs seat belts

headlining convertible tops arm rests all trim panels including door, front, rear, and side panels compartment shelves head restraints floor coverings sun visors curtains wheelhouse coverings engine compartment covers mattress covers any other materials including padding and crash deployment elements that are designed to absorb energy on contact by occupants in the event of a crash. Section 4.2 of the FMVSS 302 code also requires that “any portion of a single or composite material which is within 13 mm of the occupant compartment air space shall meet the requirements of Section 4.3.” The most important section of FMVSS 302 is Section 4.3. Section 4.3(a) is the section that requires that all of the material components mentioned shall not burn, nor transmit a flame across its surface, at a rate of more than 102 mm per minute. This is important because it establishes a timeline of burn resistance that may be employed in the fire investigation. The testing methodology for this code states that a ½-in square piece of material about a foot long is suspended, horizontally oriented, in a specified test oven. It can burn at any rate less than 102 mm per minute. However, bear in mind that the testing performed in the lab is not necessarily how the product will perform in an actual vehicle fire. In other words, a high-order fire, originating or involving a flammable liquid such as gasoline, will create a condition in which the seat foam or other interior material is consumed at a much faster timeframe than what the code calls for because the initial BTU load is greater.

7.4 Society of Automotive Engineers Standard J369 SAE J369 was originally issued by SAE in March 1969. This was approximately two years before FMVSS 302 was established by NHTSA. The J369 standard is the basis upon which FMVSS 302 was modeled. Unfortunately, the FMVSS 302 standard has never been re-visited nor revised since inception. By contrast, the J369 standard has been re-visited and revised several times over the decades. The standard was improved and redefined as advances in plastics, polymeric composites, and nanocomposites have developed. Most notably, J369 forms three classifications of plastics, where FMVSS 302 does not. These classes are as follows: Does not ignite (DNI). This material does not support the combustion during or following the 15-second ignition period and does not transmit a flame front across either surface to the demarcation line for the test piece. This means that fire snuffs out before the 60 seconds of the test timeframe has expired. Self-extinguishing (SE). This material ignites on either surface, but the flame extinguishes itself before reaching the demarcation for the test piece. Self-extinguishing/no burn rate (SE/NBR). This material stops burning before it has burned for 60 seconds from start of ignition and has burned more than 50.8 mm [7-1]. The most significant difference between FMVSS 302 and J369 is the testing orientation of the test material. The FMVSS 302 code requires horizontal orientation inside the test oven. SAE J369 standard holds that the material being tested is oriented in a vertical manner inside the same test oven. Otherwise, the testing protocols are nearly identical.

7.5 Society of Automotive Engineers Standard J1344 SAE International has always moved to study safety issues for the ground transportation industry. A ground transportation standard designation begins with a “J.” SAE J1344 was first issued in October 1980. Primarily, this standard was issued in response to ISO Standard 14004. Recycling of plastics was readily becoming a large industry and issue in the European market. Nations were erecting tariffs that stated in essence that the country of origin for a vehicle will be the nation of disposal. If the vehicle were to be disposed of in another market, then the automobile manufacturer paid a fee to the country of disposal. Thus, some system of universal identification of materials was developed so the various polymeric composites could be sorted into piles of matching materials for recycling.

J1344 was also developed in response to the need to standardize identification of the polymeric materials in the U.S. market. This assists the investigating engineer in identifying the combustible properties of the polymeric composites. The same standard assists technicians and service engineers in identifying the polymeric composites that could be repaired and repainted. Note that many polymeric composites can be repaired using a hot air gun and correct plastic rod approach. The repair method is similar to brazing steel. Although no law requires the identification of the material to be cast into the part, the automobile manufacturers all comply as a general rule. The identification systems used are as follows:

Polypropylene. This denotation appears with header points.

Polypropylene plus rock talcum in a 40% ratio mix. Polyamide 66. This denotation appears without any header points or box. PA66 There can also be a notation of the polymeric composite surrounded by a rectangular box. Another factor to note is that many vendors of polymeric composite parts to a manufacturer will commonly place either a date stamping or a date matrix cast into the part. Often, the part is dated. This date stamp or matrix can be used by the investigating engineer to determine if the vehicle has ever been worked on to repair collision damage, or if a component was replaced. The date of manufacture listed on the component should be within approximately one month of the build date of the vehicle. The investigating engineer will also need to identify polymeric and composite materials correctly. The point at this junction is that the FMVSS 302 code establishes the minimum or “floor” standards that a vehicle that is sold in the U.S. market must possess. Manufacturers are free to design plastics that far exceed the minimum requirements. They simply are barred from lawfully selling a vehicle that contains plastics that burn at a rate greater than the minimum standards. The investigating engineer will also realize after a number of inspections that polymeric composites and nanocomposites have a much lower BTU load potential than entry-level polymeric composites. The ability for the flaming combustion to transfer heat is greatly diminished as the plastic formulas become more advanced into the polymeric and nanocomposite materials.

7.6 Fire Analysis of a Vehicle The first rule of vehicle fire analysis is that there are no absolute rules. Fire is both a random

and chaotic event. Failure modes do not always occur identically, even if the same part on two of the same models for a given make are involved. One identical failure could lead to a largeorder fire, and a second similar fire due to the same failure on a similar vehicle could lead to a small-order fire. This publication will focus on electrical system failures leading to fire and how to diagnose the primary failed part with reasonable certainty. Unless a fire occurs in two identical models, the chance is excellent that the polymeric composites vary in composition and combustion properties. An example is an electric window switch design that has developed into a significant percentage of warranty charges and failures leading to fire. Even though the failure mode has sourced from the same switch assembly, not every failure leads to fire. Many of the warranty charges may include a description from the owner stating that smoke was observed shortly before or just as the switch failed. Even among the group of failures that do lead to fire, there will rarely be the same degree of fire in each event. The investigating engineer may begin to see a pattern to similar failures leading to fire. There may well be similarities in the burn patterns. However, each investigation has to be approached as a unique event. There may also be a mitigating factor or factors present that caused the failure leading to fire to propagate to the degree where the entire vehicle was immolated. For example, the same electric window switch failure catches the door panel on fire. The owner has a bag of snack chips in the door pocket. The presence of snack chips in an automotive fire will cause significant propagation of the fire because the oil leaches out of the snack chips, and the paper (or mylar) of the package both combine to cause a fire that engulfs the interior. This might lead an inexperienced investigating engineer to reach an erroneous conclusion that the cause of the fire was from another source than the failed window switch. This fire was so much more significant in degree that the engineer does not associate it with the other window switch fires for which he/she has been assigned to investigate the cause and origin. The ability to interview the vehicle owner or driver may lead to information that some combustible products were stored in the door pocket.

7.6.1 Compartmentalization All vehicles are built in compartments. However, the configurations of the compartments differ. Vehicle designs vary from a coupe to a cargo van. Even among similar vehicles, the designs of the compartments are not the same.

Thus, one of the first tasks faced by the investigating engineer is to establish the fire pattern. The second task is to determine the fire level in the vehicle: did the fire begin on top of a structure, mid-engine, mid-dashboard, under a seat, in the trunk, or under the vehicle, etc.? Because of compartmentalization, the locations of varying on-board normal levels of combustible and flammable liquids, and other variables, the first task is to define the fire type and the burn pattern within the vehicle. Vehicles burn in a different manner than buildings. For example: take three stucco and wood houses. If three similar houses were next to each other, the chances that the combustible materials located within the houses are also going to be similar are high. With vehicles, the similarity is limited to three of the exact same models by the exact same manufacturer. Materials and configurations can change dramatically on different models. Therefore, the burn patterns will not be the same. Conventional fire science does not adapt readily to automotive fire. Conventional fire science, as applied to structure fire, will state words to the effect that a burn pattern is defined as moving from the area of least destruction to the area of greatest destruction. Vehicle fire burn patterns are most commonly just the opposite. Again, the key word is “commonly.” The materials that make up the average vehicle resist fire spread. The vehicle will not want to sustain flaming combustion until an exceptional level of heat is achieved that is capable of removing any thermal inertia (resistance to burning). Thus, the area of greatest destruction is generally the area of origin.

Figure 7.1 Figure caused by pre-fuse module failure.

Figure 7.2 Figure caused by pre-fuse module failure.

Figure 7.3 Pre-fuse fire.

Again, the key word to the previous paragraph is “generally.” Recall the statement, “there are no absolutes.” There is no step-by-step guide on how to diagnose a vehicle fire down to the primary failed part. The investigating engineer should realize that an FMEA approach will not succeed. Even the Scientific Method will not always arrive at the correct diagnosis with 100% certainty. Figure 7.1 and Figure 7.2 depict an electrical fire in a high-line vehicle. This is the engine compartment fire that started due to the same failed pre-fuse module depicted in Figure 7.3. In this example, the pre-fuse module failed while the vehicle was parked and unoccupied. By definition, this fire was electrical in nature. Note that the burn pattern area of origin is from the battery area in the right rear of the engine compartment, across the top of the engine, yet the power distribution module next to the left hood hinge is not damaged by the heat. Clearly, the area of origin is at the right rear propagating forward and to the left. The amount of damaged components is less as the pattern moves across the top of the engine. From this fire evidence, it can be deduced that a, the fire was electrical in nature, and b, the vehicle being inspected is configured with blended polyamide (), a reinforced blend, highly crosslinked polypropylene (), or a nanocomposite such as polypropylene mixed with rock talcum (). Regardless of material, it is clear from the photograph that the polymeric materials located under the hood are not very combustible. This particular fire flared up in the night and then snuffed itself out. The owner came out in the morning to find the damage that occurred. This is also a demonstration of the plastic classification defined in

SAE J369. These plastics are classified as Self-Extinguishing/No Burn Rate (SE/NBR). This particular case demonstrates both burn pattern and fire level within the engine compartment. The burn pattern is clearly from right-to-left and across the top of the engine. The tightly sealed engine compartment prevented the fire propagation to the interior. These figures denote three separate issues that should be addressed in the investigating engineer's report. A second issue to consider in defining the fire is the propagation and intensity of the fire. This becomes an area where the investigating engineer's field experience will come into play. The more the engineer deals with diagnosis of vehicle fire, the greater his or her experience level will rise. Going back to the fire example in Figure 7.1, Figure 7.2, and Figure 7.3, the fire evidence in Figure 7.3 indicates that the pre-fuse module failed internally. That is to say, a path to ground was found from within the module. Note that all computer control modules in a vehicle will require both positive and negative wires to make the module operate. The negative battery cable (B-) did not provide the path to ground directly. Otherwise, had the negative cable been a significant contributor to the failed pre-fuse module, the expected outcome would be some or all of the insulation having melted from the B- cable. However, as depicted, the cable insulation is largely intact.

7.6.2 Engine Compartment The average vehicle will contain the following as normal levels of underhood fluids available to propagate fire: 1. Gasoline. Earlier fuel injection models will use both a fuel feed rail and a fuel return rail. Later model designs moved to a larger fuel feed or supply rail. The return fuel rail has been discontinued. Both designs will use a “quick connector.” Both designs will also incorporate a rubber flex line. Obviously, gasoline will possess the greatest BTU load of any of the normal on-board fluids. The typical gasoline blend will contain approximately 20,000 BTUs per lb. This will cause the greatest propagation of the fire should the system rupture and dump the contents of the fuel rail into the fire. Gasoline is the most difficult of normal underhood fluids to auto ignite on a hot exhaust. However, as described, gasoline leaks will fill the engine compartment with highly flammable vapors that can be ignited by any spark, such as occurs at the brush end of the alternator. 2. Brake fluid. Brake fluid is the easiest normal underhood fluid to auto ignite on a hot

exhaust. Additionally, if a failed power distribution module or other power wire failure leading to the fire is located near the brake fluid reservoir, this will convert a low-order fire into a large-order fire. One famous example of the brake fluid playing a part in the propagation of electrical fires was the Ford cruise control deceleration switch recall. In that case, the switch was a diaphragm-type of switch in which brake fluid pressure activated the switch. One leg of the two wires affixed to the switch was hot regardless of ignition key position. When a failure occurred, the brake fluid was nearby to create a high-order fire. Approximately one quart of brake fluid is contained in the average brake master cylinder. 3. Transmission and power steering fluid. Transmission and power steering fluid will auto ignite easily on a hot exhaust. However, the quantity contacting the hot exhaust will have a distinct effect on auto ignition. Auto ignition occurs in the vapors that leave the fluid as some is splashed onto the hot exhaust. If a significant quantity of fluid leaks and contacts the exhaust, this has the effect of cooling the exhaust to the point where auto ignition is difficult. Power steering fluid has much the same properties as transmission fluid. Many times, transmission fluid is used for power steering fluid. Approximately one quart of fluid, total, is in the average power steering system. The transmission will hold approximately seven to eleven quarts total. However, when a leak occurs in one of the cooler lines, the system will pump fluid until the sump runs dry. This drains approximately half the fluid out of the transmission. The other half will remain inside the torque converter. The amount leaked will vary. Full-synthetic blends of transmission fluid will not auto ignite easily. See discussion in number 5 on full-synthetic engine oils. 4. Coolant. Coolant blends consist of ethylene glycol, propylene glycol, OAT, and H-OAT blends. Ethylene glycol blends are by far the most common. It should be noted that most automobile manufacturers will ship their vehicles from the factory with a coolant-towater ratio that is just below the threshold for auto ignition. In this example, the coolant will only steam off and leave a white residue on the hot exhaust. If the fluid auto ignites, the investigating engineer should take a sample from inside the block if an uncontaminated sample can be obtained and check to determine the coolant-to-water ratio. Propylene glycol is not chemically the same as ethylene glycol. It is sold as the “environmentally friendly” coolant. It possesses greater properties of auto ignition as

does its cousin, ethylene glycol. Organic Acid Technology (OAT) and Hybrid Organic Acid Technology (H-OAT) coolant blends contain sebacate, 2-ethylhexanoic (2-EHA) acids, and other organic acids, but no silicates or phosphates like those commonly found in ethylene glycol blends. H-OAT coolant blends will include a small amount of silicates or phosphates. The OAT and HOAT coolant blends will commonly be dyed red, orange, or pink. The investigating engineer will soon realize the greater potential for combustion that OAT and H-OAT equipped vehicles will have. Many times, the radiator has melted away on engine fires containing OAT and H-OAT blends. Additionally, these blends can auto ignite when exposed to temperatures of 350° to 450°F [7-2]. 5. Engine oil. Petroleum-based engine oil will auto ignite on a hot exhaust. Again, the quantity leaked onto the hot exhaust will have a direct effect on the ability of the oil to outgas volatile organic vapors that can auto ignite. One type of engine oil that will not easily auto ignite on a hot exhaust is full synthetic. These oils contain highly refined components of petroleum oil, not oil itself. Mostly, the different blends contain gas-to-liquid compounds from methane blended with polyalphaolefins (PAO), esthers, and proprietary formulas. The average temperature requirements for auto ignition range from 600° to 800°F. The average exhaust temperature of a fully warmed engine (one hour driving on roadway) has been measured at 450° to 500°F for the average vehicle at the catalytic converter housing [7-3]. Full-synthetic motor oils do not ignite or burn well under normal operating conditions. Greater sustained temperatures are required for ignition. An example would be a misfiring engine causing the catalytic converter to overheat. If full-synthetic oil were to contact the catalytic converter surface with elevated temperatures due to the misfire, auto ignition temperatures will be reached for most blends of full-synthetic oil. The oil will ignite with orange-yellow flames of moderate duration. The flaming combustion residue will consist of an outline where the oil contacted the exhaust surface that ignited it, and a greasy smoke residue will be left behind. Full-synthetic oils will auto ignite. The formulas merely auto ignite at greater temperatures than petroleum oils. Thus, the engine compartment contains combustible fluids, flammable fluid (gasoline), and a potential ignition source for when the vehicle is parked and unoccupied. If the fire originates from the power distribution module, the flaming combustion must get to and cause a leak from one of the combustible fluids normally in the engine compartment to start a large-order fire. Clearly, if the outbreak of fire is from a vehicle that is parked, unoccupied, and the engine has been off for at least 20 minutes, then the only possible source of an on-board accidental fire is

electrical. One issue that is not understood very well in fire science when dealing with engines is a phenomenon called heat soak. Heat soak occurs when a vehicle is stopped after being operated. For a brief period of time, the exterior temperature of the engine assembly, exhaust system, and catalytic converter will actually rise. This is due to the fact that cooling air is no longer blowing over the assemblies. The heat stored in the mass of the engine or exhaust system will be released and rise to the surface of the assembly. This can create auto ignition a few minutes after the engine is shut down. For example, a vehicle is being operated with a power steering fluid leak. Power steering fluid is dripping onto the hot exhaust as the vehicle drives down the roadway. The air flow over the engine is blowing away the combustible vapors. Once the vehicle parks, the vapors are allowed to collect. The skin temperature of the exhaust system will rise sufficiently to cause the outgassing vapors to auto ignite. A fire starts in a timeframe after engine shut-down. Thus, an important tool for the investigating engineer is to establish a timeline for precisely how long the vehicle was parked before ignition occurred.

7.7 Electrical Fire Analysis Copper stranded wire is the most common to be used in automotive applications. As discussed, solid core wire is not suitable due to vibration. In researching for this publication, various wire manufacturers were contacted and interviewed for information about the copper alloys and insulations used by the different manufacturers. The overall reply from wire factory engineers were words to the effect that “we produce wire and insulation per the manufacturer specifications.” In other words, no one specific alloy of wire is used by automobile manufacturers. Although similar, the alloys will vary, as will the type of insulation. Thus, the investigating engineer will only have general guidelines to work by because the engineering specifications will not be known. However, several signs that are present on failed electrical circuits and wiring will appear common among electrical failures leading to fire. Parts warranty replacement information is one of the guidelines that a factory engineer will have access to where others from outside the automotive industry do not. If a given part is suspected of causing the fire, warranty replacement numbers can be consulted to determine if a pattern or unexpectedly high number of warranty failure has occurred. Other internal

information also may be available to the investigating engineer, such as other fires with a “cause undetermined” report that have occurred on similar vehicles with similar fire patterns. As another issue, the percentage of failed parts that constitute a design flaw is generally considered to be greater than 1% of sold units. A failure rate of greater than 2% likely will cause the failure rate to become a subject of interest by NHTSA. The failure rate threshold for ordering a recall was the subject of a lawsuit against NHTSA some years ago. Until being sued, NHTSA used the 1% rule as the threshold for ordering a recall. The lawsuit accused NHTSA of using an “arbitrary” percentile. In response, the NHTSA now does not publish any given percentage of failed parts as the “trigger” value for a recall. Rather, new rules were established where a recall could be ordered on a vehicle population in which only a few units failed, causing a fire or other significant safety hazard. As of the date of this publication, the new regulations were being signed into law. The date of the final proposal to change the Federal Code of Regulations, Title 49, Sections 573, 577, and 579 was August 9, 2013. Any proposed changes had to be submitted by the automobile, heavy truck, or equipment manufacturer within one year of that date, or the wording of the proposal was forwarded to Congress. As a general rule, NHTSA proposed regulations are rubberstamped into law. Essentially, this proposal established Early Warning Reporting, Foreign Defect Reporting, and Motor Vehicle and Equipment Recall Regulations. The report proposal was numbered RIN 2127-0068; Notice two. Fire was only one of the areas addressed in the proposal. The nexus of the proposal was the establishment of the Early Warning Reporting process. As discussed, electrical failure leading to fire can present in a variety of ways. One of the peculiar facts about technical analysis is that the answer to the same question could very well be both “yes” and “no.” Given facts of one nature, the answer will be “yes.” Change a few of those facts in a minor manner and the answer will become “no.” Thus, defining the fire by pattern, available fuels, outside influences, and facts of loss becomes the first requirement of any fire investigation. If the vehicle were located inside a house garage when the fire occurred, the fire evidence may or may not be destroyed to the point where a determination of the primary failed part can be made with any degree of certainty. The “cause undetermined” fire report skews the number of vehicle fires reported to NHTSA because the manufacturer is unable to determine if the vehicle was the cause or victim of the fire. It is always best for one to be standing on the Rock of Gibraltar with the evidence collected in a fire investigation. Sometimes, it is possible to determine precisely what occurred to cause the fire. When certainty is not 100%, then the phrase “there is a substantial probability” is applied as to the part believed to have failed causing the fire. As noted, with electrical fires,

one of the difficult issues is that the part that failed and caused the fire was the part that received the most heat damage for the longest timeframe. Not much of that part may be left to examine. One highly documented example of this process is the Ford cruise control deceleration switch that led to a recall. At first, it was believed that the power distribution module was the primary failed part because it was located very near the brake fluid reservoir. As the number of fires increased, Ford engineers began seeking out similar units that had not yet caught fire to study for determination of precisely what was the primary failed part. Figure 7.4 shows the master cylinder guide boss where the cruise control deceleration switch screwed into the master cylinder on a Ford truck. Note the heat cracking on the guide boss and the melted interior of the guide boss hole. Figure 7.5 is the cruise control deceleration switch from that guide boss. Note that it shows some heat damage, and melted aluminum is stuck to the threads of the switch. It should also be noted that the cruise control deceleration switch has a single AWG #16 power wire that is protected by a 20-A fuse. The #16 wire conducted enough current to heat the aluminum sufficiently to cause the aluminum switch mount boss to crack and transfer melted aluminum to the switch, yet it did not cause the fuse to blow.

Figure 7.4 Cruise control switch mount on master cylinder.

Figure 7.5 Cruise control switch.

In this particular case, the owner of the vehicle was sitting a few yards from the vehicle when smoke was observed. The fire was extinguished by using a garden hose within a very short time. This is why the evidence is in very good condition. As the investigation progressed, Ford engineers began to realize that the failure mechanism was a confluence of factors surrounding the cruise control deceleration switch. As the switch failure was studied, the number of affected vehicles expanded exponentially. Thus, what started out as a small recall ended up covering over 10 years of production of various Ford models equipped with this switch design. In this example, the Rock of Gibraltar evidence did not source from the failed units. Rather, the data were gathered from working units that had not yet caught fire. Cruise control deceleration switches were recovered from working vehicles that had accumulated brake fluid under the weather boot from a leaking diaphragm inside the switch. As soon as brake fluid and road grime accumulated to the point that a path to ground was made between the switch and the body of the brake master cylinder, the wiring to the switch began to overheat. Eventually, a fire would start. The point of the argument at this junction is that it does not matter which side of the rock was ascended, Ford engineers were now standing on the Rock of Gibraltar. The primary failed part was determined with 100% accuracy.

7.8 Signs of Electrical Heat

One of the biggest issues facing the investigating engineer is the lack of vehicle fire training available at the collegiate level. No textbook is available that discusses the topic in conjunction with any college or university program. Some fire science programs touch on the topic of vehicle fire analysis. However, limited data or publications on the topic are available. Procuring vehicles for fire testing, and deliberately forcing a system failure leading to fire for each mode of failure and model involved, is patently cost prohibitive. For any such testing performed by a manufacturer or vendor for the manufacturer, the data remain proprietary. Thus, the best teaching method for the investigating engineer is field study. Many manufacturers have trained personnel that accompany in-training engineers on field assignments to instruct in proper methodology in recognizing product failure leading to fire. The point is, available training in either classroom or field casework is limited. As described, vehicle fire science has no absolutes. Electrical heat leading to fire can present in a different manner even when the failure mode is similar between two vehicle fires. Another point to note is that the battery or B+ cables are attacked during the fire event. If the battery has not given up all its electrons, then it becomes a source of heat that can cause signs of electrical failure during the fire event. The original fire event becomes a cascading thermal event. It is up to the investigating engineer to determine what issues are causes or contributing factors in the fire, and what fire evidence was a victim of the fire. Some of the common signs of electrical heat leading to fire are described in the following sections.

7.8.1 Battery Plates In cases of electrical fire where the electrical discharge is causing high heat loading at the battery, the investigating engineer may see discoloration on the individual plates. This will appear as heated marks from the positive plate grid through the oxide paste on the plate.

Figure 7.6 Overheated lead-acid battery grid.

Figure 7.7 Overheated lead-acid battery grid.

Figure 7.8 Overheated lead-acid battery grid.

Figure 7.9 Overheated lead-acid battery grid.

Figure 7.6, Figure 7.7, Figure 7.8, and Figure 7.9 depict a battery that has suffered high electrical heat draw. Note the heat imprint left by the overheated grid plates. Also, note in Figure 7.9 that the plate separator is being held back, revealing the overheated grid plate behind it. Clearly, a current over-draw from the battery B+ cable has caused the excessive heat from the draw the failed component placed on the battery. The B+ plate overheated, causing the grid-type burn pattern on the lead oxide paste. However, the same grid burn pattern does not appear on the separator. This is solid proof that the electrical heat was from the grid and not convective heat from the engine compartment. In this particular example, the neighbor observed the vehicle start to catch fire. The neighbor ran over to the owner's residence to notify them about the vehicle catching fire. The vehicle had been parked and unoccupied for approximately two hours when the fire occurred. Generally, when this type of evidence is recovered from a vehicle fire, this indicates the battery exploded as part of the event. The battery remnants were recovered from down below the battery pedestal. The parts of the battery were reassembled into approximate order and then photographed as depicted. When the investigating engineer encounters grid heat patterns on the remains of the positive plates, this is a solid sign that high electrical current was drawn from the battery. This, in turn, caused the battery plates to overheat in a thermal runaway event. As a general rule, batteries

commonly give up their charge early-on in an electrical fire.

7.8.2 Shrunken or Exploded Remnants of Battery Lugs Other signs that the battery has suffered an explosion or a thermal runaway event are melted or shrunken battery lugs and poor condition of the casing remains. In some examples, the signs of battery explosion are extreme. As a general rule, most of the battery will survive the majority of engine compartment fires. One complicating factor is if the vehicle is located within a garage or other structure that caught fire as a result of the fire. In such a case, the overall damage level will be greater, but the signs that the fire was electrical in nature may still present. The investigating engineer first must separate the fire evidence. The area-of-origin evidence must be separated from the convective-heat-damage evidence.

Figure 7.10 Exploded lead-acid battery.

Figure 7.11 Exploded lead-acid battery.

Figure 7.12 Exploded lead-acid battery.

Figure 7.13 Exploded lead-acid battery grid.

Figure 7.10 depicts a brand-new exploded battery. This battery was purchased and installed earlier in the day. The vehicle caught fire in the residence carport at night. Note that the battery plates are not lined up evenly. Some of the plates were located on the floor alongside the battery pedestal. Also note that the battery tray is bent and the battery cable terminals were torn away from the cables when the battery exploded. The battery positive B+ cable and the battery negative B- cable run together in a conduit to the rear of the engine. The battery pedestal is located in the right front of the engine compartment. Note in Figure 7.10 how both the negative and positive cables have turned a ruddy-red discoloration and both ends are ripped. The other cable appearing in the photograph is a body ground. Note how this cable is not as badly discolored as the B+ and B- cables. Obviously, less current flowed through this cable. In this example both the B+ and B- cables routed together in a conduit terminating at the starter motor. The ground wire on the right is a body ground. Figure 7.11 shows the battery positive lug assembly. The battery exploded, sending the positive lug, sensor mounting flange, and battery cable end flying. The cable itself was ripped in the process. Note the ruddy-red discoloration to the battery B+ cable that routes to the starter solenoid. However, the smaller B+ cable that routes to the power distribution module to provide power is not nearly as discolored. This indicates that the electrical heat presented in the main B+ cable because the electrical short occurred in this cable. The short did not occur from the

power distribution module. Note how the power distribution cable loops over the B+ cable in Figure 7.11. Both connect to the battery positive lug, yet only one of the cables shows signs of high electrical heat. Figure 7.12 shows the battery remnants after they were removed from the front of the vehicle and placed on the trunk. This is a normal appearance for an exploded battery. Figure 7.13 depicts the battery B+ positive cable in an up-close view. Note the ruddy-red discoloration and the frayed cable strands. These are both signs of high electrical heat. More will be discussed on cable bundles in this chapter. One final point to note with battery explosions is that most lead-acid battery designs will incorporate six sealed chambers to house the plates and electrolyte (see Figure 7.14). The positive and negative electrodes pass through each chamber wall in a sealed manner. If a short in the battery circuit is causing the build-up of hydrogen in the cells, this creates the potential for any one of the cells or all six cells to explode when the ratio of hydrogen-to-oxygen and a competent ignition occurs. The source of competent ignition does not have to be electrical. For example, a shorting battery has caused the cells to produce excess hydrogen. The flaming combustion has compromised the casing of one of the cells, but the battery did not explode. However, this leaves the adjoining cells still containing hydrogen and the potential for explosion. Thus, it is not entirely unusual to see just one end or part of a battery exploded in a vehicle fire.

Figure 7.14 Cutaway view of lead-acid battery.

Figure 7.15 Shrunken battery terminal.

Figure 7.16 Shrunken battery terminal.

Figure 7.15 and Figure 7.16 show a burned battery from an engine compartment fire. Note that the terminal surrounding the battery positive lug has shrunk from its original dimension. The battery cable clamp still surrounds the positive terminal post. Also note that the negative lug has completely melted away. The battery cable clamps will commonly protect a battery lug from convective heat. When shrunken lugs such as those depicted in Figure 7.15 and Figure 7.16 are present, then the fire had an electrical component to it that caused the high electrical heat. Clearly, this type of damage cannot be caused by convective heat without similar damage to the clamp.

7.8.3 Battery Explosion Caused by Outside Influence In this example, the outside influence is that the fire was incendiary in nature. The vehicle was driven to a site out in the desert. A copious quantity of accelerant, such as gasoline, was poured over the entire vehicle and subsequently ignited.

Figure 7.17 Left front corner of engine compartment after vehicle recovered.

Figure 7.18 Battery B+ cable.

Figure 7.19 Exploded battery remains.

Figure 7.20 Exploded battery remains.

Figure 7.21 Exploded battery remains.

Figure 7.22 Exploded battery remains.

Figure 7.23 Exploded battery remains.

Figure 7.24 Exploded battery remains.

Figure 7.25 Exploded battery remains.

The battery and cables were subjected to extreme destructive outside influences. The battery B+ cables were attacked by flaming combustion, causing the insulation to short out against any available B- surface. Additionally, the battery case was being attacked itself by extreme convective heat. The combination of the two influences caused the battery to explode with extreme force (that is, relative to the force typically exhibited by an exploding battery). Figure 7.17 depicts the left front corner of the engine compartment after the vehicle was recovered. The remains of the battery can be seen in the left front corner. Figure 7.18 shows the battery B+ cable as it appears stretched out from the fire debris. Note that the battery terminal cable end is relatively intact. There is the familiar ruddy-red discoloration of the cable braids near the battery terminal end, the cable braids have begun to unravel near the site of the heat, and the copper cable resumes its original color the closer it gets to the starter. What this indicates is that the site of the first insulation failure was not far from the battery B+ cable clamp. It also indicates that convective heat is not effective at causing the cable to reach the melting point for copper. The entire length of the B+ cable was subjected to the same amount of BTU heat release, yet only the portion closest to the battery B+ lug presents the ruddy-red signs of high heat. Figure 7.19, Figure 7.20, Figure 7.21, Figure 7.22, Figure 7.23, Figure 7.24, and Figure 7.25 depict the exploded battery remains around the engine compartment and the remains of the

battery casing after the plate and other fire debris were lifted out of the way. Note the positioning of the exploded remains and the curvature of the clump of plates that were flung against the transmission. Figure 7.24 shows the battery B+ cable that was formerly affixed to the firewall with the other cables appearing in the photograph. Also note that the quick coupler for the fuel rail has not separated. The cables are blocking the view of the fact that the plastic intake manifold was consumed. The intake manifold, which was formerly located just behind the point where the cables dropped down to as the fire attacked the wiring harness, anchors to the firewall. The only things that remained of the intake manifold were the mount bolts. Note the heat pattern across the B+ cable that was in the wiring bundle affected. All of the cable strands and braids are intact and do not show the characteristic damage of electrical heat. However, the top of the B+ cable does reflect that convective heat has impinged some of the cable sufficiently for the top half of the B+ cable to turn the characteristic ruddy-red color most associated with electrical heat. This is another example of the importance of unbiased fact gathering required by the investigating engineer. This fire was not accidental. However, some of the signs of electrical thermal runaway are present. This example also underscores the importance of forming a diagnosis based upon the totality of the evidence and not just one piece or a limited number of pieces of evidence. Figure 7.25 depicts the pieces of the battery remains collected and placed on the trunk lid. Note the curved damage to the grids on the clump of plates that was flung against the transmission. Also note how the battery remains present both high electrical heat damage and convective heat damage. The convective heat damage would clearly have had to occur after the battery exploded. The two examples of exploded batteries also show how two different batteries can explode in distinctly different manners. One battery exploded because the insulation between the B+ and B- cables became compromised after a battery replacement that had been performed only hours before the failure occurred. The second battery exploded due to the outside influence of the entire vehicle being subjected to a heavy incendiary fire. Both cases caused the electrolyte to outgas hydrogen and oxygen to the point of ignition. The only difference in the second example was that the battery casing was subjected to extreme convective heat from the burning accelerant in addition to electrical heat caused by compromised B+ insulation as the fire progressed. This convective heat plus the electrical heat caused the battery electrolyte to outgas greater quantities of hydrogen in the timeframe very shortly preceding the explosion. Obviously,

production of hydrogen gas becomes a non-issue after the battery casing explodes. Therefore, for the explosion to be of such a greater force, then the collection of hydrogen gas inside the battery casing in the second example had to be greater in order to cause the damage pattern observed.

7.8.4 Discoloration, Bundle De-stranding, and Fraying of Cables Copper is a “red” metal by metallurgical definition. Most copper alloys will have a melting point of approximately 1900° to 2000°F [7-4]. As discussed, the normal convective heat will not easily cause the necessary temperatures leading copper to become heated to the point that it will turn ruddy red. Electrical heat is far more efficient at causing the heat required to bring the copper wire close to its melting point. Compare the impingement of heat upon a wiring cable or bundle to the roasting of a hot dog over a camp fire. The hot dog is inserted onto a metal rod to hold out over the fire. Ordinary, not enhanced, flames will burn at approximately 2000° to 2200°F. There will certainly be 2000°F air convecting around the hot dog. Will the hot dog immediately become seared and done within a 10-second timeframe? Will it be done within a 30-second timeframe? Will the metal rod the hot dog is skewered upon turn red-hot in the same time frame? The answer is no because insufficient heat exposure time has occurred. Convective heat in that example is insufficient to cook the hot dog or heat the rod in such a short time. If the hypothetical theory is expanded by throwing some gasoline onto the camp fire (not recommended), the intensity of the BTU load is now expanded exponentially. Will the hot dog now cook in a matter of seconds? Will the steel rod turn red-hot? The answer is still no. Convective heat lacks the ability to effectively transfer heat in this manner to such a small and cylindrical surface. Eventually, the hot dog will become seared, and the exposed part of the rod will turn red-hot, but it will take longer than a few seconds. The timeframe will be reduced because of the increased BTU load, but the cooking and turning the rod red-hot will still take some time. The point of the discussion here is for the investigating engineer to examine the fire evidence under the hood, determine what combustible fluids were contributors to the BTU load, and approximate the amount of fuel load available. The design of the hood will also have to be examined. The angle and composition of front hoods vary widely with design models. This can have an effect on the overall burn pattern due to the ability of the hood to direct the flaming combustion. The following examples will each affect the fire in a different manner:

A steel hood will not melt in an engine fire. It will direct the flames across the top of the engine to potentially affect other fluids, components, structures, and polymeric composites. Sometimes a steel hood will angle downward sharply, such as with a minivan. This will direct the heat in a different manner than a hood that affixes with less of an angle, such as a large sedan. An aluminum hood will do the same, but to a much lesser degree, because aluminum hoods tend to melt through on high-order engine compartment fires. The heat plume is allowed to rise away from the engine as the hood melts. A fiberglass hood will affect the burn pattern the most because it heats to the point of catching fire, which adds to the available BTU load. An SMC (sheet molded compound) hood tends to not deliver the same BTU load as does flaming fiberglass. SMC is a tough cousin to fiberglass gloss cloth or chopper gun systems. The resin is different, and the components are generally formed under pressure. (See GM products such as Camaro or Saturn models.) Aftermarket carbon fiber hoods will act in a similar manner to SMC hoods. Less damage may very well occur depending on the formula and processes used by the aftermarket supplier. This discussion begs the question of why would convective heat impingement upon a battery cable during an engine compartment fire obtain the necessary timeframe and heat to cause the copper to reach a temperature very close to its melting point? The answer is that convective heat does not reach the 1900° to 2000°F internal temperature of the copper for a very long timeframe. It can happen. However, electrical heat is much more efficient at making the copper reach its melting point. Copper is heat-treatable, and much like steel, will be tempered [7-4]. Heat-treating codes for copper and copper alloys are also addressed in the ASTM B601 standard. A second issue facing the investigating engineer is regarding recognizing fusible link wire. This is an alloy of copper with a proprietary amount of tin. Tin melts between 350° and 400°F. When alloyed with copper, the overall melting point is lowered. A common place to find fusible link wire is for the battery B+ cable on the alternator, attached at the starter B+ lug, or used in power distribution modules.

Figure 7.26 Electrical fire with melted fusible link.

Figure 7.27 Close-up view of electrical fire with melted fusible link.

Figure 7.26 shows a battery B+ cable and the ring terminal of what used to be the “jumper lug” located just to the left of the alternator. Figure 7.27 depicts a close-up view of the melted fusible link end and the B+ terminal of the “jumper lug.” Note that the ring terminal being held has an eyelet with no wire attached. This was formerly the B+ cable that routed to the B+ terminal located on the back of the alternator. This cable is a fusible link that melted through. Note the familiar ruddy-red discoloration and characteristic de-bundling of the battery B+ cable strands. Therefore, it is incumbent upon the investigating engineer to determine if the affected copper cable has suffered convective heat or electrical heat to cause it to turn a ruddy red in color. Figure 7.28 depicts the B+ battery cable that formerly routed to a failed radiator electric fan. Note the same ruddy-red discoloration, cable strand de-bundling, and the frayed areas that were caused by electrical heat. Figure 7.29 shows that same B+ cable slightly further back from the area depicted in Figure 7.28. Note the spot of melted aluminum stuck to the copper strands. This was caused by contact with an AC tube.

Figure 7.28 Electrical fire from failed radiator fan.

Figure 7.29 Electrical fire from failed radiator fan.

Figure 7.30 Electrical fire from failed radiator fan.

Figure 7.31 Failed radiator fan motor.

Figure 7.32 Defective same-model radiator fan that failed but did not catch fire.

Figure 7.30 is an interesting photograph because it depicts that same power cable. The far right

side of the cable reflects the ruddy-red discoloration from the excessive draw caused by “locked rotor amperage” from the seized electric radiator fan motor. Note how the ruddy-red discoloration changes hue as the cable moves off the photograph to the left. The left-side portion of this same B+ cable only shows the normal copper color, where the right side of the same cable shows electrical heat. Also note how the cable bundling has resumed normal order and twisting compared to the area of electrical heat damage. The important point that Figure 7.30 shows is the normal appearance at one end of the cable. Moving to the right of the cable in the photograph, the hue begins changing from gold-colored copper to increasingly greater shades of ruddy red approaching the end of the cable that formerly affixed to the failed radiator fan motor. This is proof positive that electrical heat presents at the site of failure and then moves toward the battery or controller, proving that the destructive levels of current in the failed circuit are localized. Unfortunately, in this example, the battery is located in the trunk. The trunk can only be opened via electric lock, physical defeat of the latch, or removal of the back seat and reaching in with a suitable tool to pull the child lock release. The attorney representing the owner of the vehicle would not allow any of the above. Photographs of the battery end of that same cable were not available. Figure 7.31 depicts the failed radiator fan motor. Note that the only cable remaining is a piece of the negative B- cable. Figure 7.32 shows a defective same-model radiator fan that merely failed but did not catch fire. Note the organizing of where the cables should affix. The positive end is on the right and the negative is on the left. The plastic housing cover identifies the different cable positions. Figure 7.33, Figure 7.34, and Figure 7.35 depict a failed driver module for a high-intensity discharge Xenon headlamp. Note that the two power wires for the headlamp did not turn the familiar ruddy-red discoloration, yet the fraying of the copper strands and formation of black oxide still are present. Black oxide formation is another sign of high electrical heat on copper strands. Compare the appearance of the high-current lamp wires with the appearance of the driver activation wiring and communication lines. The activation and communication wiring still has order to the strand bundles. However, given the small AWG size, the convective heat was able to impart sufficient heat to bring the temperature of the copper near its melting point.

Figure 7.33 Melted headlamp driver module.

Figure 7.34 Melted headlamp driver module.

Figure 7.35 Melted headlamp driver module.

Figure 7.36, Figure 7.37, Figure 7.38, Figure 7.39, Figure 7.40, and Figure 7.41 depict a highintensity discharge headlamp fire and the surrounding components. Also shown in the figures are the power distribution lid that was removed to reveal no electrical heat from inside the module, and the discoloration of the actual terminals that affix to the headlamp lugs. Note in Figure 7.41 that the wiring for that connector shows the familiar de-bundling and fraying of the strands, but on a lesser scale. Figure 7.41 reveals that the same connector shows signs of electrical heat where the metal of the female terminal has suffered electrical heat to the point that the temper began to rise out of the metal.

Figure 7.36 Melted high-discharge headlamp.

Figure 7.37 Melted high-discharge headlamp.

Figure 7.38 Melted high-discharge headlamp.

Figure 7.39 Melted high-discharge headlamp.

Figure 7.40 Melted high-discharge headlamp.

Figure 7.41 Melted high-discharge headlamp.

A potential contributing factor is repeated heat cycles over time. For example, a female pushon connector has a slightly bad connection. Over time, resistance develops and the circuit begins to heat each time it is used. The grip of the female connector on the male half will

loosen with heat. The process progresses until the circuit fails or fire develops. The tightness of the connectors should be checked by the investigating engineer on circuit failures leading to overheated circuits. Figure 7.42 and Figure 7.43 depict the power wire (B+) for a power distribution module fire on an older model vehicle. Note that the characteristic ruddy-red color is not as prominent as the other examples. However, some red discoloration is visible along with some black-oxide discoloration, such as seen in Figure 7.33 and Figure 7.34. The characteristic de-bundling and parting of the metal strands in the wire is prominent. Figure 7.44 and Figure 7.45 depict the power distribution module power wire (B+). Note the heavy ruddy-red discoloration of the cable strands. Significant de-bundling of the cable strands can also be seen. In this example, the power distribution module was consumed. Part of the bus bar from inside the module is visible in Figure 7.44. The cable damage is higher in this example because the power distribution module remains dislodged from its anchor on the apron. The cable strands became more distorted when the module fell down after its mount melted.

Figure 7.42 Overheated PDM cable.

Figure 7.43 Overheated PDM cable.

Figure 7.44 Melted PDM cable with red discoloration.

Figure 7.45 Melted PDM cable with red discoloration.

Figure 7.46 Melted alternator B+ cable.

Figure 7.47 Melted alternator B+ cable.

Figure 7.48 Melted alternator B+ cable.

Figure 7.49 Melted alternator B+ cable.

Figure 7.50 Melted alternator B+ cable.

Figure 7.46 shows the battery B+ cable that routes to the alternator. This vehicle suffered an alternator fire. Reverse voltage was allowed into the alternator field windings where the B+

current found a path to ground. Note the familiar ruddy-red discoloration. However, the debundling of the strands is not as pronounced as in the other examples. Figure 7.47 depicts the battery B+ cable at the battery. Note that this cable has only been damaged by electrical heat but to a much lesser degree. Also, the de-bundling of the strands is much less pronounced. Figure 7.48 shows the battery B+ cable that routes to the power distribution module. Note that all the wires that appear around the B+ wire show the same ruddy-red discoloration, and the B+ cable has started to melt. This is not due to electrical heat. This model vehicle is equipped with a hydro-boost power brake booster. The system is powered by the power steering pump. The system leaked an amount of power steering fluid underneath the wire that shows the melted droplets beginning to form. This is convective heat damage to copper wiring. Note the differences between Figure 7.48 and Figure 7.49. The arc bead in Figure 7.48 is associated with an electrical short-to-ground, while the melted copper in Figure 7.49 is caused by convective heat. Figure 7.50 shows the battery on the vehicle. Note that the battery has exploded, the positive and negative terminals are melted away, and heat is showing from the positive grid that was exposed when the battery exploded. The heat on the grid, along the top of the grid, and the top of the separator, is from high electrical heat draw. As the case was consumed by convective heat, this would have added to the appearance of the damage. Compare this photograph with Figure 7.6, Figure 7.7, Figure 7.8, and Figure 7.9. This battery grid pattern is fairly common when a high electrical current draw involving electrical heat occurs to a battery.

7.8.5 Heavy-Duty Applications The same signs of high electrical heat will also apply in heavy-duty battery applications such as found on heavy trucks, transit buses, recreational vehicles, and farm equipment. As a general rule, the damage level will be greater due to the fact that larger-capacity and multiple battery systems can be equipped. The investigating engineer should be familiar with the signs of heavy-duty battery system failures. The biggest differences are the size of the battery B+ cables and the strand construction. As AWG stranded copper cables increase in size, the construction will commonly be smaller individual strands that have been braided into larger bundles. The bundles are then wound or braided into the final AWG size that the design specifications require. The same debundling of the cable bundles, fraying of the strands, and discoloration of the copper will occur.

Figure 7.51 Heavy-duty electrical fire.

Figure 7.52 Melted components as found.

Figure 7.53 DC to AC inverter.

Figure 7.54 Burned section of inverter.

Figure 7.55 Electrical heat damage to battery cables on inverter.

Figure 7.56 Battery on/off switches.

Figure 7.51 is the subject vehicle that suffered an electrical failure. This is a transit bus that was waiting for the parties to return from a casino. The driver was operating the 110-V AC inverter to power the blowers while the vehicle idled. The inverter was the primary failed part. The broken window on the bus was the result of an over-eager fireman. The air vents

pass through this area. Firemen are trained to chop walls apart seeking hidden fire. It was unnecessary in this case. Figure 7.52 shows the cargo box as found upon first inspection. The fire was “overhauled” by the fire department prior to the inspection. The contents of the cargo box were replaced into the box by the fire department prior to the bus being towed back to the bus yard. Figure 7.53 and Figure 7.54 depict the inverter unit that failed. Figure 7.55 shows the portion of the inverter where the battery B+ and B- cables enter the unit. Note the ruddy-red discoloration, the dark discoloration, and the de-bundling of the cable strands. Clearly, these are signs of high electrical heat. Figure 7.56 shows the battery switches for turning off the B+ current when the bus is being stored. These are to prevent a dead battery due to parasitic draw.

Figure 7.57 Affected battery cables set out on ground.

Figure 7.58 Signs of high electrical heat.

Figure 7.59 Evidence of high electrical heat.

Figure 7.60 Close-up of high electrical heat damage on cable.

Figure 7.61 Signs of high electrical heat.

Figure 7.62 Indications of high electrical heat.

Figure 7.63 Not all battery cables in the circuit are affected.

Figure 7.64 Cable affected at one end but not the other.

Figure 7.65 Both batteries.

Figure 7.66 Inside battery. Note that this one is not damaged.

Figure 7.67 Burn pattern on wall of electrical box.

Figure 7.68 Left wall of electrical box.

Figure 7.69 Burn pattern on rear wall of electrical box indicates direction of fire travel.

Figure 7.57 depicts the battery cables and wiring that was cut from the bus by the fire

department. Note that the overall condition includes wiring that is not damaged, and some that clearly has suffered electrical heat. Figure 7.58, Figure 7.59, Figure 7.60, Figure 7.61, and Figure 7.62 depict electrical heat on the battery B+ and B- cables. Note the familiar ruddy-red discoloration, the de-bundling of the cable braids, and signs of high electrical heat exposure. Figure 7.63 and Figure 7.64 depict two ends of the same cable. Note that one end presents all the signs of high electrical heat. However, the other end of the same cable is relatively intact. This is further proof of the localized heat that electrical fires present. Figure 7.65 and Figure 7.66 show the two batteries located in the cargo box. Note how one battery has suffered a fire where the other battery is unscathed. Also note in Figure 7.56 that one end of one of the battery cables was not damaged. Figure 7.67, Figure 7.68, and Figure 7.69 depict the burn pattern inside the cargo box. All the switches and other components were chopped off the cargo box wall by the fire department. Note that the burn pattern is concentrated on the left side. It angles up the back wall of the cargo box.

Figure 7.70 AC condenser above batteries.

Figure 7.71 Heavy-duty electrical fire.

Figure 7.72 Heavy-duty electrical fire.

The configuration of the cargo box had the two batteries located to the right as viewed from the cargo box door. The inverter unit was located to the left of the batteries. The battery B+

switches and other components were mounted on the cargo box wall. All do not present signs of high internal heat. Note that the burn pattern originates below the switches and other components on the cargo box wall. The burn pattern supports the conclusion that the inverter unit was the primary failed part. Figure 7.70, Figure 7.71, and Figure 7.72 depict the upper portion of the cargo box that caught fire. This is the AC condenser and AC blower motor located directly at the roof of the cargo box, but below the bus floor. Note that some damage has occurred to the aluminum fins. However, the vast majority of both assemblies are intact. This example proves the following: the heat was from an electrical source; the primary fuel was from the outgassing volatile organic compounds (VOCs) from the affected plastic and wire insulation; and the 1200°F heat did not entrain throughout the box with sufficient intensity to even burn the paint off the outside of the cargo box door or melt the aluminum of the cargo box. This fire example was purely electrical in nature, with a low transfer temperature. Note that the entire vehicle body and cargo compartments are constructed of aluminum. The most common alloy is AISI 6160. This will have a melting point of approximately 1100° to 1200°F. Inspect the copper of the battery cables. Distinct de-bundling and fraying of the strands and braids of the affected ends has occurred. Both ruddy-red and black-oxide discoloration of the cables show electrical activity. Also of note is that the vehicle is configured with two Group 8D batteries. One was destroyed by fire, while the other was not damaged, although it was physically located just inches from the one that was involved in the fire. The copper strands of the cables were heated to the point of melting/breaking. This means that the copper of the strands was heated to minimally 1900°F to make the copper lose its tempering and become brittle. However, the surrounding aluminum components did not suffer nearly as much heat damage. This is proof that localized electrical heat, not convective heat, caused the damage. Figure 7.73 shows the results of a fire in a heavy-duty application of a farm tractor. This model is a universal tractor with hydraulic hook-ups to allow the main tractor to pull several different farming trailers. Thus, the same powerplant can be used as a disc, seeder, thatcher, harvester, etc. This tractor had only harvested three fields of corn when the fire occurred as it was being operated. The view in Figure 7.73 depicts the right side of the tractor. The box above the remains of the diesel fuel tank is the battery box.

Figure 7.73 Electrical fire in harvester.

Figure 7.74 Area of original electrical fire in harvester.

Figure 7.75 B+ junction box.

Figure 7.76 End of the remains cable that routes from the junction box.

Figure 7.77 End of the remains cable that routes from the junction box.

Figure 7.78 Battery B+ cable at the battery box.

Figure 7.79 Battery B+ cable at the battery box.

Figure 7.74 reveals the area of origin. This is the battery B+ cable that routes to the B+ terminal on the back of the alternator. The tractor left the factory with insufficient cable holddowns. The corn stalks pushed the battery B+ cable over on top of the neighboring AC hose. After sufficient chafing occurred, the battery B+ cable shorted against the AC hose. Remnants of the AC tubing are stuck to the B+ cable at the site where the hose has parted. The fire mechanism was the breach in the AC hose that caused the polyalkalyene glycol (PAG) oil to spew out over the left side of the front fiberglass hood. The ignition mechanism was the arcing of the B+ cable on the AC tube. The hood caught fire and spread to the cabin area, causing the resultant damage. This particular fire was not touched or extinguished by the fire department. The tractor merely exhausted the fuel for the fire and snuffed out. The tractor was dragged back to the barn area, where it was inspected. Figure 7.75 depicts the B+ junction box formerly located on the left front cabin pillar. Clearly, this junction has melted away in the fire. Note the familiar ruddy-red discoloration on the surrounding cables, and the brittle nature of the copper strands. This obviously was an area of high electrical heat. Figure 7.76 and Figure 7.77 show the end of the remains cable that routes from the junction box in Figure 7.75. Note the signs of high electrical heat.

Figure 7.80 Another tractor of the same model.

Figure 7.81 Another tractor of the same model.

Figure 7.78 and Figure 7.79 reveal the battery B+ cable at the battery box. Note the debundling of the cable strands, the brittle cable strands, and discoloration of the copper. Also note that surrounding plastic structures were not damaged. This is proof that the localized heat damage to the cables is electrical in nature. Figure 7.80 and Figure 7.81 show another tractor that is of the same model, only a few VIN numbers away from the first one that caught fire. This one had harvested only one field of corn. Note that the battery cable is resting on top of the AC hose. Figure 7.81 depicts what the junction located on the left front cabin pillar looked like before the fire. From these two examples, it can be realized that the effects and signs of electrical fire are the same regardless if the fire was automotive electrical, heavy-duty truck/bus, or a tractor fire. The principal difference is that the larger the battery capacity, the greater the potential for destruction. However, the failure mode signs are the same.

7.8.6 Electrical Circuit Shorting into Another Circuit Sometimes, the vehicle fire event is due to a circuit overheating into another circuit instead of finding a path to ground. The shorting into another circuit may present at a positive circuit into one or more positive circuits. This will cause unwanted feedback and energizing of a secondary circuit which, in turn, can cause wiring to overheat and possibly cause an electrical fire. The facts of loss regarding the next example include that the subject vehicle was parked for the night in the garage. Approximately two hours after parking the vehicle, the owner noticed a smoke smell. He investigated the garage but was unable to find the source. Approximately 45 minutes after the owner first detected the smoke smell, the smell became worse. The owner again investigated inside the garage. This time, the interior of the subject vehicle had started to catch fire. The owner could only identify that flaming combustion was coming from the driver side area. The fire department had been summoned. Unfortunately, the vehicle fire had damaged both the vehicle and the residence. The first two fire investigations were undertaken by a number of outside and factory engineers. All the investigations resulted in a “cause undetermined” finding. Although the subject vehicle was still under factory warranty, the cause had not been determined at that point in time. As a result, the factory declined to pay for the damages. The attorneys assigned to subrogate the case for the insurance carrier continued attempting to locate the expert that could resolve their Gordian Knot. A determination of the primary failed part was discovered after about two hours of investigation by this author using the principles outlined in this publication.

In keeping with the purpose of Battery Fires: Why They Happen and How They Happen, the identity of the vehicle is not revealed. The point is to inspect the burn pattern that appears on the driver door. This is depicted in Figure 7.82, Figure 7.83, Figure 7.84, and Figure 7.85.

Figure 7.82 Crimped gooseneck fire. Burn pattern is shown on driver door.

Figure 7.83 Crimped gooseneck fire. Burn pattern is shown on driver door.

Figure 7.84 Crimped gooseneck fire. Burn pattern is shown on driver door.

Figure 7.85 Remains of dashboard and interior following crimped gooseneck fire.

Figure 7.86 Battery and power distribution module following crimped gooseneck fire.

Figure 7.87 Battery and power distribution module following crimped gooseneck fire.

Figure 7.88 Inside fuse panel formerly mounted on the dashboard.

Observe that most of the paint is still remaining on the outside of the driver door. Some burn pattern is present, but the paint is mostly intact. The white tape is part of the weatherproofing service that the storage yard provided to protect the fire evidence. The point here is that the paint is burned off the door panel side; the door suffered very little exterior damage by comparison, and the area at the A-pillar and door threshold received minimal heat damage. By comparison, the interior was nearly consumed. Figure 7.85 depicts the remains of the dashboard and interior. Note the heat pattern damage appearing on the heater core and the AC evaporator. The damage pattern moves distinctly from the left to the right. Note how the sides of both assemblies are more damaged on the left side than on the right. This indicates that the fire burned longest and, therefore, communicated the most heat on the left side of the assemblies first. Because the fire facts indicate that the fire had to be electrical in nature, the investigating engineer should know the basic layout of the dashboard and power distribution module before attending the first inspection. The investigating engineers should familiarize themselves with the wiring layout for that model in advance. Figure 7.86 and Figure 7.87 show the battery and power distribution module for the subject vehicle. Note the lack of high electrical heat on either component. Figure 7.88 depicts the inside fuse panel formerly mounted on the dashboard. Note the lack of signs of high electrical heat on the main power wire to the fuse panel.



Figure 7.89 Door wiring harness following crimped gooseneck fire.

Figure 7.90 Wiring harness for left door following crimped gooseneck fire.

Figure 7.91 Wiring harness for left door following crimped gooseneck fire.

Figure 7.92 Wiring harness pinch point.

Figure 7.93 Wiring harness pinch point.

Figure 7.94 Rubber gooseneck removed and cut open.

Figure 7.95 Rubber gooseneck removed and cut open.

Figure 7.96 Rubber gooseneck removed and cut open.

Figure 7.97 Inspection of wiring harness.

Figure 7.89 shows the door wiring harness with the rubber gooseneck protective boot removed from the A-pillar area. Note the signs of high electrical heat on the wiring protruding from the

gooseneck. Also note the remains of what used to be a connector appearing in the background. The male and female ends are still stuck together on the remains of the connector. The male ends are ripped loose from the wiring bundle. Although the fire evidence was disturbed from two prior investigations, the information as relayed states this was how the other investigators found this wiring bundle and connector. This connector and wiring bundle are normally located behind the left kick panel. This was the area of origin. Note that the left kick panel is destroyed, yet the paint on the A-pillar is not. Another point to note is that this connector is the one that supplies the current to accessories located in the left door. Figure 7.90 and Figure 7.91 reveal the wiring harness for the left door after it was separated from the rubber gooseneck and is being pulled out through the speaker hole in the door. Note the signs of high electrical heat on the ends; the signs of high electrical heat diminish as they reach the interior area of the door. Finally, the colored insulation of the wiring is seen. Note that the exposed wiring has a kink in it. This may be from handling during prior investigations. The wiring harness was not in a bind when discovered by this author. Figure 7.92 and Figure 7.93 depict the wiring harness pinch point where the insulation on the wiring bundle has been compromised from opening and closing the door. This melted section of wiring was physically located inside the rubber gooseneck that connects from the driver door to the left A-pillar. Figure 7.94, Figure 7.95, and Figure 7.96 depict the rubber gooseneck removed from the door, placed on a table, and cut open. Note the slight drip of melted rubber. This is an indication of high electrical heat that had to occur before the vehicle caught fire. There is no possible mechanism for convective heat to transfer inside the rubber gooseneck to damage the wiring as observed. This damage is from compromised insulation that back-fed into other circuits, causing the harness to overheat and the vehicle to catch fire. Figure 7.97 shows the wiring harness as removed from the vehicle and set out for inspection and photography. This type of failure can occur to any vehicle. Most modern vehicles with electric windows and door locks will have a similar wiring loom inside a similar rubber gooseneck. It is a design issue for the electrical engineer to specify that the wire used in this application have sufficient flexibility to allow for the anticipated number of cycles for the door. One area for the investigating engineer is to examine any repair work performed on or near the suspected damage area. In the example, the driver door had been worked on for two different service issues prior to the date the fire started. If the exemplar wiring harness in Figure 7.97 is inspected, two plastic hold-downs are used to

locate the wiring loom as it enters the door. These are of particular importance in preventing a wiring loom pinch from the window mechanism. The service procedures performed should be reviewed to determine if the original positioning of the harness was not returned to OEM state. These types of wiring harness guide and hold-down are common to every door that has electric features. The investigating engineer should make sure any fasteners are affixed into their holes as part of the investigation.

7.8.7 Signs of Electrical Heat on Fusible Links and Fuses Caused by High Circuit Draw All vehicles vibrate as a matter of normal use. If the vehicle is used in off-road application, the vibratory cycling and amplitude will be greatly enhanced. This may have the effect of causing push connectors to loosen. However, whenever this issue occurs, it is not possible to determine if the loose connector came from the factory in that fashion, or if the looseness developed from vibration over time. Regardless of how the looseness comes to be in a connector, this merely lends credence to the old adage of “loose wires cause fires.” Although simplistic, the adage has a great deal of truth.

Figure 7.98 Fusible link overheat.

Figure 7.99 Fusible link overheat.

Figure 7.100 Fusible link overheat.

Figure 7.98 depicts the fusible links that were removed from the power distribution module, and then laid flat for photographing. Note the discoloration in the fusible link spades. These are signs of varying degrees of high electrical heat caused by too much current draw in the affected circuits. No short circuit has occurred. The circuits were overheating. This can cause

the loosening of the female portions of the connector, adding to the overheating circuit issue. Figure 7.99 and Figure 7.100 show the power distribution module battery B+ terminal and the battery positive terminal. Note that there is little sign of high electrical heat at the power distribution module B+ input lug. Yet, the battery positive lug has melted out of the battery. The battery melting the positive terminal was due to the numerous circuits drawing too much current as the vehicle was operated.

Figure 7.101 Overheated fuse.

Figure 7.102 Blown fuse.

Figure 7.101 and Figure 7.102 show a fuse subjected to high heat draw and a blown fuse, respectively. Both fuses protect different parts of the evaporative emissions system and the fuel pump. The wiring for both systems runs through the same conduit located near the service hatch under the rear seat.

The blown fuse depicted in Figure 7.101 was due to a worn fuel pump. The circuit was operating, but the bushing or pump on the motor were creating too much friction in the pump motor. In turn, this caused the circuit to begin overheating because the electric motor for the pump was dragging and moving toward “locked rotor amperage.” This presented as a meltdown in the circuit wiring, and yet the fuse did not blow its link. There are signs of high electrical heat on the fuse spades. It should be noted that all electric motors are nothing more than a dead-short until they begin to revolve their armature. The more friction that is present to drag on the armature, the greater the electrical heat that will be required to keep that motor rotating. Many times, the electric motor will be the actual primary failed part. The wiring is the part that caught fire. Figure 7.102 shows the fuse that was blown as the result of a short-to-ground caused by the melting fuel pump circuit. The fuse link has broken, but there are no signs of high electrical heat on the fuse spades. The discoloration on the fuse spades indicates high electrical heat either due to a bad connection or other high current draw through that part of the circuit. Other possibilities could be that the female portion of the fuse panel that the fuse spade plugs into is not gripping the fuse spade with sufficient interference fit. In simpler terms, the push-fit of the male-to-female connection is not tight enough. As a general rule, fuses will blow their element at a draw of approximately 20% greater than their printed rating. This is not a legal requirement or in response to any recommended industry practice. It is simply a figure common to most fuse designs. The investigating engineer should rig up a testing jig with a carbon-pile battery load tester to cause various fuses to blow their elements and to melt automotive wire samples. This testing is to familiarize the engineer with lab samples of known current levels that caused the destruction of the sample. One precaution is to perform any such experiments in a well-ventilated area. Hydrogen cyanide gas is formed when plastic is burned.

7.8.8 Cratering on Connectors If the site of electrical heat draw is greatest at the connectors that supply that failing circuit, many times the individual connector will melt a hole or crater in the connector slot it is located within. The rest of the connector may or may not present electrical heat. The electrical heat may present to varying degrees. As a general finding, the individual connector slot that was the hottest due to electrical heat draw will present as a portion of the connector body melting.

Figure 7.103 Electrical connector cratering.

Figure 7.104 Electrical connector cratering.

Figure 7.105 Electrical connector cratering.

Figure 7.106 Electrical connector cratering.

Figure 7.107 Electrical connector cratering.

Figure 7.108 Electrical connector cratering.

Figure 7.103, Figure 7.104, Figure 7.105, Figure 7.106, and Figure 7.107 depict different connectors that present cratering. Examine each connector housing carefully. There will be

parts of the connector plastic that have melted away where other parts of the same connector still have plastic remaining. The degradation and consumption of the plastic indicates that this particular wire was overheating for a longer timeframe than the others. It had more time to damage the plastic. Note in Figure 7.103 that the connector body is melted from right to left as viewed. The two wires on the right have melted their blue rubber weather boots away where the next to adjacent wires still have their weather boots intact. Note the condition of the weather boot on the wire just to the left of the two intact blue weather boots. This weather boot is partially protected by the remaining piece of connector body. If the heat that damaged this weather boot were convective then the other two blue weather boots would be as damaged as the wires on either side of the blue weather boots. Convective heat attacks in waves, not pinpoints. This is evidence of electrical heat. The loose wire from another circuit is not related to the connector that melted. Figure 7.104 shows that the paint has scorched next to the connector, yet there is no sign of flaming combustion. Had flaming combustion occurred, smoke would be emanating from the burning plastic at the site. However, there is only the scorched paint and melted connector to indicate the area of origin. The burn pattern moved away from this area. The damage to the connector and the scorched paint are both indicators of high electrical heat. Note in Figure 7.105, Figure 7.106, and Figure 7.107 that the consumption is different on the different connectors. In Figure 7.105, note how some of the wire connectors are showing their metal connectors, and how the plastic body of the connector has melted unevenly. The uneven melting and exposing of the metal elements indicates high electrical heat in these wires. Also note the signs of high electrical heat on the wires for that connector. Figure 7.106 and Figure 7.107 reveal that the consumption of the plastic connector housing is also uneven. Some of the wires are showing their metal connector ends because the housing is completely melted away. Figure 7.108 depicts the analog portion of a control module. Note the smaller pins located along the upper row. The analog portion of the circuit is on the lower row with the larger pins. Obviously, this module has suffered an internal failure, causing the unit to overheat and melt the connector. Also note that the electrical heat has begun to ingress onto the analog connector on the right side. Some of the pins of the connector have begun to misalign. These connectors and module depicted are further evidence that electrical heat will present at the site of the failure, and then begin melting or heating toward the source. The fuse or fusible link will not always blow, preventing an electrical fire. The investigating engineer should procure and review the circuit schematics when an electrical

failure is present. The data will be required for the report. Should the issue ever become a court case, the investigating engineer will be required to explain precisely how the circuit operates. Moreover, a review of the schematic for a given circuit may reveal potential design flaws.

7.8.9 Formation of Copper Chloride This is a subject of debate. The fire science community, comprised mainly of ex-fire department personnel, completely rejects any theory or data regarding this subject. The NFPA 921 Guide flatly states the greenish discoloration is meaningless. Herein lies the debate: automotive engineers have long known this discoloration is commonly formed in electrical fires on automobiles. As noted previously, house wiring has different characteristics and, therefore, will react differently in a fire event. Moreover, the vast majority of house wiring is solid core copper. There is very little stranded wire, whereas an automobile is wired exclusively with stranded wire. Notably, recreational vehicles are wired with solid core wire as an exception. For example, house wiring will commonly have an extra layer over the insulation. One example is the thermoplastic high heat-resistant nylon (THHN) coating. This is a clear, high heat-resistant covering over the top of the wire insulation. There are no automotive wiring harnesses that have a THHN coating. However, this phenomenon typically presents only in stranded copper wiring that has polyvinyl chloride insulation () with no extra layered insulation. The phenomenon is not associated with wiring insulation comprised of polyethylene (). This phenomenon appears as the greenish accumulation on the wiring. It is caused by the conversion of the chloride in the polyvinyl chloride into hydrochloric acid. It is also most common to a circuit that had an electrical overheat condition occur. This formation is far less common on circuits that were destroyed by convective or another type of heat. Figure 7.109 depicts a battery cable with the characteristic green discoloration of the formation of copper chloride. This is the result of the formation of copper chloride on the cable bundle strands after the fire converted the chloride from the PVC insulation. The copper chloride formed either by the water used to extinguish the fire or moisture from the evening dew after the fire event. This example was tested along its length. No copper sulfate was present. This conversion of the PVC insulation into hydrochloric acid that attacks the copper strands causing them to turn green is also most commonly associated with electrical heat, not convective heat. There is one caveat: An incendiary fire is sometimes capable of achieving the

BTU transfer temperatures required to form copper chloride.

Figure 7.109 Copper chloride formation.

Figure 7.110 Condo with a high-line car fire.

Figure 7.111 Details of a high-line car fire.

Figure 7.112 Details of a high-line car fire.

Figure 7.113 Details of a high-line car fire.

Figure 7.114 Details of a high-line car fire.

Figure 7.115 Details of a high-line car fire.

Figure 7.110 shows the damage caused by a fire from a parked car. In this example, the vehicle depicted had been parked approximately three days before the fire event. A fireman was walking down the alley next to the garage where the vehicle was located. As is common with garage fires, the garage door began to open because the fire inside was attacking the switch wires that activated the electric garage door opener. The fireman was able to observe flames beginning to issue from the trunk area. Unfortunately, the fire propagated out of hand. The fire department was unable to extinguish the blaze before it destroyed five condominiums. Also note that each of the condominiums has a detached garage. The fire was able to cross the patio to begin attacking the residential structures. Figure 7.111, Figure 7.112, Figure 7.113, Figure 7.114, and Figure 7.115 depict the battery B+ cable as it routed from the right side of the trunk, over the right side wheelhouse, down the right edge of the seat, and under the carpet and door threshold plate. Note that the B+ cable has formed copper chloride on the affected portion of the wire as it routes from the battery to the side of the rear passenger seat. There, the B+ cable resumes its original convolute conduit form. The signs of high electrical heat stop at this area. What is believed to have occurred is that the B+ cable insulation was compromised over time with the sliding in and out of passengers, and a baby seat that was commonly mounted in the right rear seat area.

The B+ cable insulation developed a high resistance short-to-ground at the far right side of the seat. This caused high electrical heat to attack the B+ cable from the site of the compromise back to the battery. The battery subsequently set the trunk on fire. The fire was able to propagate due to the presence of papers in the trunk along with some combustible fluids (oils). This allowed the fire to become a high-order fire with sufficient BTU transfer temperatures to attack the garage structure.

7.8.10 Electrical Fire Is Not Always a Large-Order Fire Event Figure 7.116 depicts the headlamp assembly of a truck. Note how the plastic of this assembly reacts to heat. Most of the headlamp assembly housing is still intact. The portion that suffered the electrical fire was the turn signal / marker light circuit contained in the same housing. Figure 7.117 and Figure 7.118 show the wiring that routes to the marker light and the turn signal light inside the headlamp assembly. Figure 7.119 depicts the turn signal / marker light wires and the headlamp wiring as the wires enter the housing through the weatherproof rubber boot. The blue, yellow, and white wires that show no high electrical heat are the ones to power the headlamp. The orange, black, and white wires that all reveal signs of heat damage are the wires for the turn signal and marker light. The white wire is the common for the two bulbs. Note the lack of damage on all of the wires as they route through the rubber weather boot.

Figure 7.116 Headlamp fire.

Figure 7.117 Wiring that routes to marker light and turn signal light inside headlamp assembly.

Figure 7.118 Wiring that routes to marker light and turn signal light inside headlamp assembly.

Figure 7.119 Turn signal / marker light wires and headlamp wiring as wires enter housing through the weatherproof rubber boot.

Figure 7.120 Connectors that started the headlamp fire.

Figure 7.120 and Figure 7.121 depict the culprit connectors that started the fire. Note how the clip-on connector with a label of #18 has its spades spread apart, where the other two labeled

#16 and #17 have normally spaced connector spades. High electrical heat caused the #18 spade to loosen and distort. The bad connection developed into a low-order electrical fire. Had this damage been the result of convective heat then the other connectors should show the same distortion. However, they do not. All were exposed to the same amount of convective heat.

Figure 7.121 Connectors that started the headlamp fire.

7.8.11 Aftermarket Accessories Not Properly Installed Many times, the aftermarket accessories can be the source of electrical fire. Figure 7.122 depicts the vehicle that caught fire due to an overheated power amplifier affixed to a subwoofer located in the rear cargo area. These installations are commonly called a “boom box.” These units tend to generate a great deal of heat when used at high volumes.

Figure 7.122 Aftermarket accessory (boom box) fire.

Figure 7.123 Fuse installed on the amplifier.

Figure 7.124 Fuse installed on the amplifier.

Figure 7.125 Aftermarket accessory fire. Electrolysis has begun to form.

Figure 7.126 Aftermarket accessory fire. Electrolysis has begun to form.

In this particular example, the owner of the vehicle was operating the “boom-box” while sitting in the vehicle. The engine was not running. The owner smelled smoke, investigated, and saw that the amplifier and nearby combustibles had begun to catch fire. Obviously, the owner's efforts at stopping the fire were not successful. The hydrogen cyanide in the smoke forced the owner to flee for fresher air. Note that the burn pattern is at mid-level across the length of the vehicle, with slightly higher BTU load in the rear area where the fire started. This was a witnessed fire. Figure 7.123 and Figure 7.124 depict the fuse installed on this amplifier. The fuse is most commonly located next to the positive terminal of the vehicle battery. Sometimes, these installations will locate a battery in the rear of the vehicle near the power amplifier. On full volume, some of these power amplifiers can drain a vehicle's battery in less than a half-hour of use. Thus, a separate battery is needed. One point to note when high-draw aftermarket electronics are installed on a given vehicle is the propensity for the owner to also change out the alternator for a unit that has a higher output. The investigating engineer should inspect the alternator to determine if it is OEM or has been modified for a higher-output model. Many high-output “will fit” alternator designs that are available on the aftermarket will bolt into the OEM bracket, or have their own bracket that uses the OEM alternator mount holes. It may be helpful for the investigating engineer to procure a mechanical drawing or photograph of what the OEM alternator should look like to determine if the system has been modified. Compare the drawing to the fire evidence at the inspection.

Note that the fuse in Figure 7.124 is rated at 200 A. If the average figure of 20% redundancy is factored in on this fuse, then the fuse link will not blow short of 240 A being drawn through the fuse. As has become obvious to the reader, an electrical fire is possible when the circuit is protected with a 15-A fuse. As has been discussed, when a battery's voltage begins decreasing under load, the current increases to meet the power requirements of the circuit. The circuit rapidly begins to overheat. In short, as the voltage drops in a given circuit, the amperage present begins to rise. Figure 7.125 and Figure 7.126 show electrolysis that has begun to form at the B+ connectors and “ring” terminal that affixes the B+ cable to the battery positive cable clamp. Note that the ring terminal has melted through, yet the link on the fuse shows no signs of electrical heat. Note how the top edge of the ring clamp has a shrunken edge, and the inside portion of the ring loop has a portion of the melted metal protruding into the inner circle of the ring. Clearly, the ring connector has melted from electrical heat; this is evident because the fire did not extend into the engine compartment. Aftermarket accessory fires do not always result in total destruction of the vehicle. Figure 7.127 and Figure 7.128 show the damage caused to the front hood by a fire resulting from incorrect installation of an aftermarket alarm system. Note that the resulting heat from the burning insulation barely scorched the paint on the hood. The information label on the underside of the hood is largely intact.

Figure 7.127 Aftermarket alarm fire.

Figure 7.128 Aftermarket alarm fire.

Figure 7.129 Area of wiring that overheated and caught fire.

Figure 7.130 In-line fuse that protects the aftermarket B+ wire.

Figure 7.131 Area where overheated circuit becomes non-overheated section.

Figure 7.132 Power wire draped over fuel filter.

Figure 7.133 Aftermarket alarm fire.

Figure 7.134 Aftermarket alarm fire.

Figure 7.129 depicts the area of wiring that overheated and caught fire. Note that the damage is limited to the wiring insulation and convolute conduit. Figure 7.130 shows the 15-A in-line fuse that protects the aftermarket B+ wire. The fuse is installed near the battery. Figure 7.131 depicts the area where the overheated circuit becomes the non-overheated section of the circuit. Clearly, the insulation on the wire had overheated to the point of combustion. The circuit was pulling too much current through the wire for the rating of the insulation and wire. Figure 7.132 reveals the power wire draped over the fuel filter. This electrical failure could easily have become a large-order fire had the flaming combustion or electrical heat been able to achieve a breech in the fuel filter or line. Figure 7.133 and Figure 7.134 do not show why this circuit failed. Note in the photograph that the gap on the ring terminal affixed to the B+ power lug in the power distribution module is loose. The gap in the ring terminal is on one side in Figure 7.133. When the wire was pulled, the gap in the ring terminal shifted, as shown in Figure 7.134. Although the connector in Figure 7.133 and Figure 7.134 is not the cause of the fire, it is a loose connection that had the potential for causing non-operational issues. The point is that the investigating engineer should check all connections for looseness, even if no signs of high electrical heat are present.

Clearly, this is a case of improper installation of an aftermarket option. One issue that did not present is the cable underneath the loose connection of the aftermarket ring terminal on the power distribution module. If the screw was loose-fitting on the ring terminal, then the OEM cable underneath the aftermarket ring terminal was also loose. The way the circuit failed and melted is also further proof as to the erratic nature of electrical failures leading to fire. If the investigating engineer is an employee of the vehicle manufacturer for the vehicle involved in the fire, and the investigation indicates that an aftermarket installation is the causal factor, the investigation ends there. If the investigating engineer is not representing the vehicle manufacturer, then the investigation must press on until the primary failed part is determined or, in the contrary, a “cause undetermined” finding is made because the fire evidence remaining is insufficient to support a conclusion with any reasonable certainty. In the case of the second example, where the investigating engineer is representing the owner or insurance carrier for the owner, then a successful subrogation action depends 100% on the accuracy of the investigating engineer to troubleshoot the circuit for the primary failed part, and establish solid proof as to why the failure occurred. Thus, for the subrogation action to be successful in this case requires that the investigating engineer take a step back and get the “big picture” of the failure. Note that the wiring close to the aftermarket module located at the left side of the dash did not suffer any wiring overheat issues. All of the heat is located from the middle of the wires at the firewall to the power supply side of the affected circuit. The fuse is not blown. The investigating engineer needs to recognize and add up all the factors. The question, “Why did the circuit overheat?” must be answered. The possibility of loose connections should never be overlooked. If the investigating engineer demonstrates solid knowledge of failure modes and why a circuit failed, the subrogation action will settle sooner. Again, this relates back to the analogy of “Rock of Gibraltar evidence.” If the investigating engineer has discovered evidence that places the investigation solidly upon The Rock, then no obfuscating argument will dislodge the case. The engineer has solid proof.

7.8.12 Failure of an Electromechanical Device The most common electromechanical devices to suffer failure with a potential of fire are switches and relays. Most of the time, a technician will diagnose one that has simply failed and will recommend replacement. Many times, this failure mode will lead to a “cascading thermal event.” This is the case in which the failing circuit causes a secondary fire event before fire is

extinguished. Sometimes, when the switch assembly has a ground wire included in the bundle of wires, a resistive short-to-ground occurs. This will induce circuit overheating, leading to fire. In this particular example, the vehicle was parked at the owner's residence for approximately two hours. The neighbor ran over to the owner's house to inform him that his truck was smoking and starting to catch fire. The fire was observed by the two men to originate in the area of the left door or left side of the dashboard. The fire department arrived to extinguish the fire.

Figure 7.135 Window switch fire with cascading thermal event, showing two burn patterns on driver door.

Figure 7.136 Window switch fire with cascading thermal event, showing two burn patterns on driver door.

Figure 7.137 Basic burn pattern on inside of truck.

Figure 7.138 Basic burn pattern on inside of truck.

Figure 7.139 Basic burn pattern on inside of truck.

Figure 7.140 Basic burn pattern on inside of truck.

Figure 7.141 Basic burn pattern on inside of truck.

Figure 7.142 Wiring harness inside door.

Figure 7.143 Crimp in the armrest combination switch after door slammed on the wiring.

Figure 7.144 Failed armrest combination switch.

Figure 7.145 Connector that supplies current to the door wiring.

Figure 7.146 Armrest assembly sitting facedown on the ground.

This particular example had two electrical events occur. Note the burn pattern on the driver's door. There is a distinct burn pattern at armrest level and a rounded one below. Figure 7.135 and Figure 7.136 depict the two burn patterns on the driver door.

What has occurred to cause this particular burn pattern is that the electric window, lock, and mirror combination switch on the armrest had suffered an internal failure, leading to fire. This created the upper burn pattern on the outside of the driver door. The secondary burn pattern that appears as the rounded burn pattern below and separate from the upper one was caused when the fire department arrived, broke the driver window for access to the fire, and unlocked and opened the driver door after the flaming combustion was over. The armrest combination switch fell out onto the ground. The fire department personnel closed the door, pinching the wiring harness for the combination switch between the door and door jamb. The battery had not yet given up all its electrons. The pinched wiring shorted against the door and door jamb, creating the secondary burn pattern. In this case, this was the cascading thermal event. Figure 7.137, Figure 7.138, Figure 7.139, Figure 7.140, and Figure 7.141 depict the basic burn pattern on the inside of the truck. Note the burn pattern on the driver door, which shows that most of the armrest has melted. The burn pattern propagated across the dashboard, and front and rear seats. Note that the burn pattern diminishes in destruction of the polymeric composites at the cab rear wall and passenger door. Clearly, the burn pattern indicates that the failure occurred at the driver armrest area. Figure 7.142 depicts the wiring harness inside the door. Note that most of the convolute conduit is still intact along with much of the wiring insulation. The damage to the wiring is closer to the window switch. Figure 7.143 shows the crimp that was put in the armrest combination switch after the unit fell out onto the ground, and the fire department personnel slammed the door on the wiring. This created the crimp in the wiring and also created the burn pattern on the wiring. Note the familiar ruddy-red discoloration of the wires that indicates high electrical heat. This is what created the lower burn pattern on the driver door. Clearly, the battery had not given up all of its charge for this secondary burn pattern to occur. Figure 7.144 depicts the actual failed armrest combination switch. Note that the connector at the bottom of the switch is not cratered. Some damage has occurred to the wiring, but the connector itself did not burn through. Also note that the switch top is beginning to separate from the rest of the switch. Figure 7.145 depicts the connector that supplies current to the door wiring. Note that the connector is not melted. The burn pattern clearly indicates that fire occurred from within the door wiring on the driver side. Additionally, a secondary thermal event occurred when the fire department personnel slammed the door on the wiring harness without first disconnecting the battery.

The fact that there is a secondary burn pattern is proof positive there were wires that were energized at all times, even with the ignition key in the “off” position. If these wires were not energized, then the secondary pattern would not have formed. Figure 7.146 shows the armrest assembly sitting facedown on the ground. This is how it would have landed when the fire department opened the driver door. In this example, the combination switch overheated because the switch developed an internal resistive short-to-ground. The emphasis here is that the switch overheated and caught the armrest on fire. However, the battery had not exhausted all of its energy. Had the resistive short been a direct short, this would have caused the fuse for that circuit to blow its link. The resistive short has the capacity to cause electrical heat leading to fire, yet not exhaust the capacity of the battery in the process. A secondary issue was that the connector that supplied current to the combination switch and lock for the driver door is not melted and does not show signs of high electrical heat. This is an indicator of the low level of current being pulled through the connector. The current was sufficient to cause a fire but not sufficient to cause the connector to melt. The fact that the second thermal event occurred after the armrest combination switch event occurred is proof that not all electrical fires drain the battery. In this example, the flaming combustion was completely extinguished before the door was slammed on the wiring harness. The fire department mistakenly believed the battery had given up its full charge during the fire event. In conclusion, a final point to note is that the vast majority of manufacturers of the components that go into the making of a vehicle or product, as well as the manufacturer of the vehicle itself, will universally have an internal policy to the effect of: “The failure is never the fault of our product.” The investigating engineer will be subjected to the most ludicrous of opinions and fire theories as to why the fire occurred from the other engineers or fire-cause and origin experts. The basic logic behind this policy is when one cannot win by logical technical argument, then obfuscate. Muddy the waters a bit to confuse the judge or jury. This technique works more often than it does not. The investigating engineer must be able to demonstrate why his/her fire theory is the most logical reason the failure occurred. All evidence must be examined carefully. No stone can be left unturned. All possible theories or failure scenarios must be examined. The Scientific Method must be employed as fully as possible. The basic laws of electricity should be memorized such that the investigating engineer can discuss them at length should questions of such a nature be raised at a deposition. The rules of evidence and conduct of the investigation as described in the latest edition of NFPA 921 must be observed. All testing must be conducted using proper methodology. Any deviation or failure will likely be exploited to the

disadvantage of the investigating engineer. The interpretation of fire evidence is subjective. It is a combination of both an art and a science.

References 7-1. SAE International. Technical Standard SAE J369—Flammability of Polymeric Interior Materials - Horizontal Test Method and SAE J1344—Marking of Plastic Parts. 7-2. Gregory J. Barnett, Automotive Fire Analysis: An Engineering Approach, Third Edition, Lawyers and Judges Publishing Company, 2013, p. 49. 7-3. Exhaust temperature measurements taken by this expert in testing of various vehicles, 2012, Costa Mesa, CA. 7-4. John E. Bringas and Michael L. Wayman, Casti Metals Red Book (Non-Ferrous Metals), Third Edition, Casti Publishing, 2000, pp. 463-546. ISBN 1-894038-42-8 (bound).

Vehicle Battery Fires: Why They Happen and How They Happen Back Matter Print ISBN: 978-0-7680-8143-5 eISBN: 978-0-7680-8361-3 DOI: 10.4271/R-443

Glossary

The following list contains terms concerning fire science. Fire science is generally not studied in most engineering programs at the university level. Thus, the investigating engineers should familiarize themselves with the terms, and study fire science at it relates to automotive fires. It should also be noted that a great deal of misinformation circulates among fire investigators relating to automotive fire. This is because most fire investigators did not work at an automobile manufacturer for their career or have the technical expertise as an automotive engineer. For example, NHTSA defines a vehicle “fire” as any thermal event that was sufficient to melt the insulation from a single wire. The vast majority of vehicle fires as defined by the NHTSA are small-order fires. Fire department personnel are never called out on these fire events because the part merely melted the insulation from a wire, caused a small fire that snuffed itself out, or was easily extinguished. The affected vehicle is simply driven or towed to a dealer or repair shop and repaired. One of the reasons that electrical failures tend to be less destructive is that fuel must be in very close proximity to the electrical failure or there is no fuel to create the large-order fire. When polymeric composites burn, the flaming combustion will cause the polymeric composite to outgas oxide of nitrogen (NOx). This is an inert gas. The gas surrounds the flaming combustion, choking off the oxygen, and thereby snuffing out the flames. This skews fire department personnel's viewpoint of what automotive fire should look like. In turn, it causes the misinformation to circulate among fire investigators. The following are some selected terms and explanations of the terms with which the average engineer would not be familiar. The investigating engineer must be absolutely familiar with all of the terms. Many of these selected terms and explanations are more common to the fire science community than the engineering community.

Air Entrainment Sometimes this term is simply referred to as “entrainment.” It is defined as “the air being drawn through an aperture into a fire.” This creates a “chimney effect.” As the heat rises

in a high-order fire, air will be pulled into the combustion process from any available duct or opening. An example of this would be that a seat is on fire and the window on the other side of the vehicle is open, with all the others closed. Air necessary to feed the flaming combustion on the seat will be drawn through the open window to feed the combustion.

Ampacity This is the maximum current that a given wire size and alloy is designed to conduct. Most automotive wire is ordered from wire manufacturers per the automobile manufacturer's specifications. The amount of over-current protection from the alloy will differ. There is no FMVSS code that pertains to the type of wiring alloy to be used in vehicles sold in the U.S. market.

Ampere This is defined as the unit of electric current that is equivalent to a flow of one coulomb per second. One coulomb is defined as 6.24 × 1018 electrons [G-1].

Arc or Arc Bead This is the arc of electricity that can ignite flammable vapors. Or, in an electrical failure, an arc bead can form where a wire with sufficient current capacity will melt the copper wiring strands, forming them into a melted pool at the end of the wire or site of deadshort.

Area of Origin This is defined as the portion of the vehicle where the fire started.

Arson This is the crime of maliciously and intentionally pouring a flammable liquid or placing highly combustible material in a vehicle, then deliberately igniting it. This type of fire is generally referred to as “incendiary” in reports. Note: The term “arson” is a legal conclusion. This finding requires a judge or jury to reach. The

investigator will list signs of an incendiary fire but cannot reach that conclusion logically in his or her report.

Auto ignition Sometimes, this term is referred to as “spontaneous combustion.” The terms are not interchangeable. Auto ignition is the temperature as exerted from an outside influence that creates an environment hot enough for the material to initiate combustion. Spontaneous combustion is more associated with ignition from two materials combining to create the heat from within. Spontaneous combustion generally refers to a chemical or biological reaction to create the heat.

BLEVE Acronym for “Boiling Liquid Expanding Vapor Explosion”. This type of explosion is associated with a boiling liquid inside a sealed container. When the heat becomes great enough, the container will breech (explode). If liquid inside the container is flammable, then quantities of flaming material will be spewed around the area of explosion. An example of a BLEVE would be if an empty paint can containing a small amount of water and a sealed tight lid is placed in a campfire. Eventually, the water will convert to steam, pressure builds, then the paint can will explode.

British Thermal Unit (BTU) The quantity of heat required to raise the temperature of one pound of water one degree of temperature as measured in Fahrenheit at an atmospheric pressure of 1 and ambient air temperature of 60°F. One BTU equals 1055 joules, 1.055 kilojoules, and approximately 252 calories.

Burn Rate or Heat Release Rate This is the rate of heat generated by material consumption from burning. All materials located within ½-in of the airspace on a motor vehicle sold in the U.S. Market after 1971 must be compliant with FMVSS 302—Interior Flammability.

Cause Also referred to as “Cause and Origin” of a fire event. On automobiles, this is defined as

the primary failed part that caused the heat leading to fire. Note that the primary failed part is not necessarily the first part that caught fire. An example of the primary failed part not being the first to catch fire is a blower motor for a heating, ventilation, and air conditioning (HVAC) system that has bad armature bushings. The additional friction created by the worn bushings will cause the electrical portion of that circuit to heat. As the friction from the worn bushings increases, the heat in the circuit increases. This can lead to the insulation on the affected wiring heating to the point of ignition.

Combustible This is defined as a material of or having a low rate of combustion. This differs from flammable in automotive fire analysis. An example would be that gasoline is flammable. It has a very high rate of combustion that places it into the definition of “flammable”. Trunk trim or the Masonite board that covers the spare tire are examples of combustible material normally found on an automobile.

Competent Ignition Source This is defined as a source of ignition that has sufficient energy and intensity that is capable of transferring energy or heat to the fuel for a long enough timeframe to raise the fuel to its point of ignition. An example of a competent ignition source would be if a fuel rail were leaking on any given engine. The leak is of sufficient quantity to generate volatile vapors. The alternator has a fan to blow cooling air over the interior of the alternator. The brushes at the back of the alternator will typically spark as the alternator operates. As the vapors are drawn through the alternator, the brush spark will ignite the vapors. The spark would be considered a competent ignition source.

Conduction The definition is limited to heat. This is heat being transferred to another area via direct contact with the heat source. In automotive application of this definition, some type of heat on one side of the metal causes a structure on the other side of the metal to catch fire, despite no opening for direct contact with the flame.

Convection Sometimes called “heat convection.” This is heat that expands as it circulates in an enclosed environment. The heat of the continuing combustion will create an expansion effect, causing the heat in that environment to circulate around and damaging the surrounding structures.

Deduction This is the logical process whereby a conclusion is drawn from logical inference from the given premise. It includes “deductive reasoning.”

Drop Down Generally, this definition is used in terms of flaming combustion dropping from the area of flame onto another surface. In automotive fire applications, the drop-down flaming bits of plastic have very little chance of igniting another part of the upholstery the flaming bits land upon. Sometimes referred to as “fall down” fire.

Failure Analysis A logical, systematic examination of an item, component, or assembly for determination of the reason that component failed. Analysis should include an assessment of all possible causes for this type of failure to occur.

Flammable Limit The upper or lower concentration limit at a specific temperature and/or pressure whereby the liquid or material will reach the point where combustion is possible. This term differs from the term “Flash Point.” Flash Point refers to the lowest temperature at which the liquid begins to vaporize at a sufficient rate to support a momentary flame across the surface of the liquid.

High-Order Fire A high-order fire on an automobile is defined as one involving one of the flammable or combustible fluids that are normally found on-board. The amount of BTU load generated by a high-order fire is considerably greater than what is generated by an electrical failure

leading to fire. Electrical fire is generally considered a “low-order” fire.

High-Resistance Fire This refers to the electrical overheating of a given circuit that allows that circuit to heat to the point that the insulation begins outgassing combustible vapors. It can also apply to an electrical module. See Figure 3.6 as an example of a high-resistance fire.

Inductive Reasoning This is the logical process of working from a conclusion to the premise for any given problem.

Low-Order Fire This is the opposite of high-order fire. This refers to a fire that has little potential for expansion or propagation. Combustion is limited. Many times, the fire merely snuffs itself out for lack of fuel or air.

Overhaul This term is common to fire-fighting personnel. It generally refers to the removal of all the burned fire remains from a structure. The burned parts and contents of a building are hauled outside and separated. Any and all “hot spots” or areas of smoldering combustion are snuffed out or otherwise extinguished by the fire personnel.

National Fire Protection Association (NFPA) This is an organization located in Quincy, MA that is comprised of scientists, engineers, and fire experts. This group publishes national “codes” in a similar manner to SAE International. Some codes become adopted verbatim by local fire authority or governments. One publication that is of particular interest to this book is the NFPA 921 Guide to Investigating Fires and Explosions. This publication is regarded as the general guideline to be adhered to for fire investigations that will eventually be headed to court or other legal action.

Nanocomposite

Definition as applies to automotive applications: A group of composites where the main part of the volume is occupied by a compound from the group of oxides, nitrides, boridies, silicides, and natural substances. A nanocomposite is a multiphase solid material where one of the phases has one, two, or three dimensions of less than 100 nanometers across, or structures having nano-scale repeat distances between the two different phases that comprise the material. In automotive plastics, the nanocomposite particles or fibers are finely dispersed in each other in order to elicit the particular nanoscopic properties. In the simplest case involving automotive polymers, adding nanoparticles to a polymer matrix can enhance the performance of the polymer dramatically. This is achieved by simply capitalizing on the nature and properties of the nanoscale filler. This approach can create a polymer that is highly resistant to combustion. The nanocomposite polymer is very effective in providing performance that is substantially different or better than those of the polymer matrix. For example, rock talcum ground up into nano-sized particles is embedded into the polymer mix before casting the polymer into shape. The adulteration of the polymer will be up to 40% rock talcum. This combination of polymer and rock talcum creates a nanocomposite that resists or severely limits the majority of accidental combustion events that occur in an automotive fire. This example of nanocomposite material will also resist accelerated combustion (i.e., arson-related fires).

Piloted Ignition This term refers to an ignition source or flame that is used or can cause ignition of a fire. An example would be the pilot light on older gas stoves.

Polymeric A type of plastic substance that is formed by linking together molecules of similar or different monomers to form substances of high molecular weight and differing characteristics [G-2].

Protocol When used in a fire investigation context, the protocol document is generally prepared by

the party that has organized the inspection. The protocol sets forth all the agreed upon activities that are anticipated to occur during the inspection. It will also set forth the agreed upon method to store any evidence discovered. A copy is distributed to all parties and agreed upon before inspection or re-inspection occurs. All parties sign and return a copy. NFPA 921 Guidelines call for a copy of the entire signatures page be distributed to all parties.

Pyrolysis A process in which material is decomposed, or broken down, into simpler molecular compounds by the effects of heat alone. Pyrolysis may precede combustion. Pyrolysis generally occurs over a long timeframe. This process of oxidation will dehydrate plastics over time into a state that may ignite more readily than when the plastic was new.

Radiant Heat This is heat energy that is carried via electromagnetic waves that are longer than light waves and shorter than radio waves. Radiant heat will increase the surface temperature of any substance capable of absorbing heat. Radiant heat upon the right material can lead to combustion.

Scientific Method The systematic pursuit of knowledge involving the recognition and formulation of a problem, the collection of data through observation and experiment, and the formulation and testing of a hypothesis.

Spoliation of Evidence The loss, destruction, or material alteration of an object or document that is evidence or potential evidence in a legal proceeding by one who has the responsibility for its preservation. If this occurs, the investigating engineer will likely be accused of, or see other parties to the investigation get accused of, “spoiling the evidence.” This may or may not be a valid accusation depending on the person's viewpoint. The proper methodology at a fire investigation is to allow all parties to inspect and photograph the evidence believed to have caused the fire or any important pieces of evidence discovered during the investigation. If that evidence is to be taken into

possession for future testing or safe keeping, the box or container used should be sealed in front of all parties. The parties present at the sealing of the evidence should use a marker pen to sign across the tape sealing the box. The investigating engineer should photograph the box in the sealed state. When the box is retrieved at a future date for testing or reinspection, the signatures across the sealing tape should be intact, thereby proving the evidence has not been disturbed.

Statute of Repose “A statute that bars a lawsuit a fixed number of years after the defendant acts in some way (as by designing or manufacturing a product) even if this period ends before the plaintiff has suffered an injury.” “A statute of repose limits the time within which an action may be brought and is not related to the accrual of any cause of action; the injury need not have occurred, much less have been discovered. Unlike an ordinary statute of limitations which begins running upon accrual of the claim, the period contained in a statute of repose begins when a specific event occurs, regardless of whether a cause of action has accrued or whether any injury has resulted.” [G-3]. The term “statute of repose” is not meant to constitute legal advice. It is merely a common law term for which the investigating engineer should know the definition. A statute of repose will vary from state to state in the United States. The point is, the period of time that statute applies to a given product is not the same as a warranty period. For example, a vehicle may have a 3-year/36,000 mile general powertrain warranty. The statute of repose for a given state may be up to 12 years. Obviously, the vehicle is far out of warranty, yet the statute of repose still applies should a failure occur that leads to fire.

References G-1. Thomas Reddy, Linden’s Handbook of Batteries, 4th Edition, McGraw-Hill Education, 2010, Sections 1.1, 16.8, 16.9, 16.67, 16.74, 22.20, 26.2, 26.3-13, and 33.6. G-2. Don Goodsell, Dictionary of Automotive Engineering, Second Edition, Oxford, England, Butterworth-Heinemenn, Linacre House, 2002. G-3. Black’s Law Dictionary, Seventh Edition, Bryan A. Garner, Editor in Chief, West Group Publishers, 1999, p. 1423

Index

NOTE: Page numbers followed by ‘f’ and ‘t’ refer to figures and tables respectively. 2-Ethylhexanoic (2-EHA) acids, 107 2015 Toyota Prius, 63

A AA batteries, 78 AAA batteries, 78 Absorbent (absorptive) glass mat (AGM), 18, 24-26, 25f batteries, 39 AC electrical fire, 64 AC electricity, 63 AC evaporator, 167 Advanced lead-acid battery designs, 27-28 Aftermarket accessory fire, 191f, 192f, 193, 193f Aftermarket alarm fire, 194, 196f, 197f Agastya Samhita, 3 AISI 6160, 157 Alternator(s) generators and, 57-61 intact after house fire, 60f melted, housing, 59f mount bracket, 58 Amalgamation, 5 American wire gauge (AWG-SAE) size, 39 Ammonium chloride, 7 Ampere, 9, 10, 12 Ampere-Hour, 62 Anode/negative electrode, 17 Arc bead, 144

Arcing B+ cable, 48 Area of Origin, 85, 103, 105, 158f, 161, 172 Armrest combination switch, 204f Atraverda battery, 28 Atraverda Bipolar, 28 Auto ignition, 64, 65, 106, 107 Automotive electrical fire science, 97 electrical fire analysis, 109-112 fire analysis of vehicle, 101-102 compartmentalization, 102-105 engine compartment, 106-108 FMVSS 302, interior flammability, 99 SAE J369, 100 SAE J1344, 100-101 safety, 97-98 signs of electrical heat, 112-113 aftermarket accessories, 189-199 battery explosion caused by outside influence, 121-127 battery plates, 113-116 copper chloride, formation, 181-186 cratering on connectors, 176-181 discoloration, bundle de-stranding, and fraying of cables, 127-144 electrical circuit shorting into another circuit, 163-173 electrical heat on fusible links, 173-176 failure of electromechanical device, 199-207 heavy-duty applications, 144-163 no Large-Order Fire Event, 186-189 shrunken or exploded remnants of battery lugs, 116-121 Axion Power E3 Supercell®, 28

B “Bad contact” issues, 44 Baghdad Batteries, 1, 2f Barium sulfate, 20 Battery(ies) B+ cable, 115 defined, 3

explosion caused by outside influence, 121-127 history, 1-8 on/off switches, 147f tender, 71 B+ cable, 40, 51, 115, 122f at battery box, 160f, 161f resting on AC pipe, 48f routing to PDM, 47f Bendix Corporation, 37 Bendix® starter drive, 37 B+ junction box, 159f Blown fuse, 175f, 176 Boom box, 189, 192 fire, 190f Brake fluid, 106 Brine, 3 Brine beneath salt lakes, 75 British Thermal Unit (BTU), 39, 99, 109 Bromine chloride, 77 Brown, Joe, 10-11 Bundle de-stranding, 127-144 Burn pattern on inside of truck, 200f, 201f, 202f on wall of electrical box, 153f, 154f Burn Rate, 100, 105

C Cable clamps, battery, 121 Camaro model, 40 Camaro trunk, 40 Carbon brushes, 57 Carbon-pile battery load, 176 Cargo box, 148 Casing design considerations for forklifts and heavy equipment, 29-31 Cathode/positive electrode, 17 Cause and origin, 39, 102 Charge-depletion, 94

Charge-sustained modes, 94, 95 Charging of lead-acid battery, 68-73 Chemistry of lead-acid plate design, 31-35 Chinese super-capacitor electric bus, 84, 84f Chloride Accumulator Battery, 12 Circuit failure, 64 Circuit over-current protective devices, 40 Claw-pole alternators, 57 Cold cranking amps, 62 Combat battery degradation, 38 Combustibility resistance standards, 98 Combustible, 39, 88, 102, 108 Combustible fluids (oils), 186 Compact liquid cooled alternators, 57 Compartmentalization, 102 Competent ignition source, 88 Condo with a high-line car fire, 182f Constant-current charge, 69, 70 Constant-potential charging, 33 Contact tension, 3, 5 Convective heat, 128 Convective heat attacks, 180 Conventional Flow Notation theory, 62 Coolant, 107 Copious bubbling, 32 Copper, 127-129 strands, 157 Copper chloride, 181-186 form, 182f Corporate Average Fuel Economy (CAFE) standards, 35 Corrosion degradation, 53 Coulomb’s law, 15 Cranking performance, 62 Cratering on connectors, 176-181 Crimped gooseneck fire, 164f, 165f, 166f, 167f Crinkle tube, 48 Cruickshank, William, 5 Cruise control switch mount, 111f

Current overload fuses, 43f

D Daniell cell, 5, 6f, 7f Dashboard, melted, 65f, 67 Davidson, Robert, 12 DC electrical fire, 64 DC electricity, 37, 63 DC to AC inverter, fire, 146f, 147f De-bundling, 157, 163 Deep-cycle battery designs, 26 Deep-cycle industrial flooded-cell battery, 30f Defective same-model radiator, 133 Degree of fire, 102 Designs, battery absorbent (absorptive) glass mat, 24-26 advanced lead-acid battery designs, 27-28 casing design considerations for forklifts and heavy equipment, 29-31 chemistry of lead-acid plate design, 31-35 concept, 15-17 deep-cycle battery designs, 26 dual battery technology, 29 elements of battery, 17-19 gelled electrolyte lead-acid designs, 23-24 insulator and separator design, 20-21 lead-acid plate designs, 19-20 valve regulated lead-acid designs, 21-23 Desulfation, 33 Detroit electric 60985 Brougham, 11f Dimethoxyethane, 78 Diode bridge, 58 Dioxolane, 78 Direct and alternating current battery ratings, 62-63 charging of lead-acid battery, 68-73 electron flow, 61-62 failure mode differences, 63-68

generators and alternators, 57-61 Discharge-charge cycling, 33 Discharge-recharge cycles, 20 Discoloration, bundle de-stranding, and fraying of cables, 127-144 Does not ignite (DNI) materials, 100 Door wiring harness, 168f, 169f Doping, 89 Dry battery designs primary, 8 secondary, 8 Dual battery technology, 29

E Ebonex®, 28 Edison, Thomas, 9 EEStor®, 28 Electrical box, 154f Electrical circuit shorting into another circuit, 163-173 Electrical connector cratering, 177f, 178f, 179f Electrical fire analysis, 109-112 from failed radiator fan, 131f, 132 in harvester, 158f with melted fusible link, 129f, 130f Electrical heat, 112-113 on fusible links, 173-176 leading, 112 signs of aftermarket accessories, 189-199 battery explosion caused by outside influence, 121-127 battery plates, 113-116 copper chloride, formation, 181-186 cratering on connectors, 176-181 discoloration, bundle de-stranding, and fraying of cables, 127-144 electrical circuit shorting into another circuit, 163-173 electrical heat on fusible links, 173-176 failure of electromechanical device, 199-207

heavy-duty applications, 144-163 no Large-Order Fire Event, 186-189 shrunken or exploded remnants of battery lugs, 116-121 Electric forklifts, 29 battery, 30 design, 30 Electric motors, 176 Electric Storage Battery Company, 12 Electric vehicle (EV), 63, 91 Electrocution, 98 Electrolysis, 30, 69, 193 Electrolytes, 11, 38, 18, 77 accumulation on a PDM casing, 46f Electromotive force, 6 Electron flow, 61-62, 61f Electron Flow Notation theory, 62 Elemental sulfur, 77 Engine compartment, 121f Engine control module (ECM), 26 Engine oil, 107 Ethylene glycol blends, 107 Exide Technologies, 12 Exploded lead-acid battery, 116f, 117f, 118f, 122f-125f Explosion, battery, 37

F Failed armrest combination switch, 204f Failed radiator fan motor, 132f Failure mode differences, 63-68 Failure of electromechanical device, 199-207 Faraday’s first law of electrolysis, 68-69 Faraday’s second law of electrolysis, 68-69 Faure, Camille, 9 Federal Code of Regulations, 98, 109 Fiber mats, 25 Fire analysis of vehicle, 101-102 compartmentalization, 102-105

engine compartment, 106-108 examples, 128 Firefly Energy, 27-28 Flashback prevention safety subsystem, 22 Float charging, 33 Flooded-cell battery, 18f design, 25 FMVSS 302, interior flammability, 39, 98-99 Forklift battery, 30 Formation, 19 Franklin, Benjamin, 3, 62 Fraying, 157 Fraying of cables, 127-144 FreedomCAR and Vehicle Technologies (FCVT), 92 Full hybrid vehicles, 94 Full-synthetic motor oil, 108 Fuse installed on the amplifier, 190f, 191f Fusible link overheat, 173f, 174f Fusible links, 40

G Galvani, 12 Galvanic cells, 5 Garage fires, 185 Gasoline, 106 Gauntlet Motive Battery, 10 Gell-cell, 18 battery, 24 Gelled electrolyte lead-acid designs, 18, 23-24 Gel polymer electrolyte, 79 Generators and alternators, 57-61 Gibbs, W. W., 12 Graphene, 79-81, 79-85, 81f matrix, 82f nanotubes, 81

H Headlamp fire, 186f, 187f, 188f Heat damaged battery terminal protector, 55f Heat soak, 44, 108 Heavy-duty applications, 144-163 Heavy-duty electrical fire, 145, 156f Heavy-truck application, 63 HEV. See Hybrid-electric vehicle (HEV) High electrical heat, 149f, 151f Highly crosslinked polypropylene (HCPP), 105 High-order fire, 39, 99, 106, 186 High-resistance failure, 68 High-voltage battery pack, 98 High-voltage cables, 98 House fire, car after, 60f Human vernacular, 62 Hybrid-electric vehicle (HEV), 91 beginnings, 92 configurations, 95 types, 93-95 Hybrid organic acid technology (H-OAT), 107 Hydrogen cyanide gas, 176 Hydrogen gas, 19

I In-line fuse that protects the aftermarket B+ wire, 195f Insulator and separator design, 20-21 Internal combustion engine (ICE), 93 International Conference of Electricians, 6 Iron disulfide, 78

J “Jelly roll” electrolyte, 88 Johnson Controls, 29 Joule heating, 17

Joule’s first law, 17 Jumper lug, 130 “Jumper” lug arrangement, 38-39 Jumping, dead battery, 39

K Khujut Rabu, Baghdad, 1 Konig, Wilhelm, 1

L Lead-acid battery, 8-10, 34, 37 advantages, 9 charging, guidelines, 72-73 cutaway view, 119f designs, 10-12, 10t exploded, 73f historical advancements, 10t Lead-acid charging, 69 Lead-acid plate designs, 19-20 Lead-antimony-tin alloys, 19 Lead-calcium-tin alloys, 19 Li-ion cell fire, 85f, 86f, 87f Liquid cathode, 76 Lithium-air battery, 78-79 Lithium batteries, 75-76 characteristics and issues, 85-89 future battery and super-capacitor designs, 79-85 lithium-air battery, 78-79 lithium-ion perchlorate manganese oxide cell, 77 lithium-ion thionyl chloride cell, 76-77 lithium-iron disulfide, 78 lithium tetrafluoroborate with carbon monofluoride cathode, 78 primary, 76 Lithium-ion batteries, 69 Lithium-ion perchlorate manganese oxide cell, 77

Lithium-ion thionyl chloride cell, 76-77 Lithium-iron disulfide, 78 Lithium tetrachloraluminate, 76 Lithium tetrafluoroborate with carbon monofluoride cathode, 78 Lithium-thionyl chloride batteries, 76 Lithium-titanate battery, 29 Localization, 5 Location, designs components surrounding the battery, 44-56 importance in early designs, 37-38 in model vehicles, 38-43 Low-order fire, 106 Low-voltage circuit, 63 Lugs, battery, 49

M Maintenance-free batteries. See Sealed batteries Manganese dioxide, 76 Matsushita Electric Works, 78 Melted alternator B+ cable, 141f, 142f, 143f Melted battery from over-cranking, 55f Melted headlamp driver module, 134f, 135f Melted high-discharge headlamp, 136f-138f Melted PDM cable with red discoloration, 141f Melting fuel pump circuit, 176 Metal-air battery chemistry, 78 Micro-corrosion in circuit, 63 Micro hybrid, 93 Micro-hybrid vehicles, 93 Mild hybrid vehicles, 94 Minimum flammability, 98 Modified-constant charging, 33-34 Molten copper droplets, 30 Multiple-layer capacitors, 85 Multi-walled carbon nanotubes, 80

N Nanocomposite plastics, 97, 100, 101, 105 Nanorods, 81 Nano-scale sheets, 81 Nanoscrolls, 81 National Fire Protection Association (NFPA), 181, 207 National Highway Traffic and Safety Administration (NHTSA), 56, 98, 109 Negative cable on battery, 52f NFPA 921, 207 Nickel-metal hydride (NiMH) battery, 28, 91 HEV, 92 beginnings, 92 types, 93-95 Nine-cell lead-acid battery, 9 No Large-Order Fire Event, 186-189 Normal failure mode, 67

O Off-roading, 67 Ohmic heating, 17 Ohm’s law, 16, 62, 65 Organic acid technology (OAT), 107 Organic solvent, 76 Outgassing, 69 Overhaul, 148 Overheated fuse, 175f Overheated lead-acid battery grid, 113f, 114f, 115f Overheated PDM cable, 139f, 140f Overheated wiring, caught fire, 194f

P Park, Menlo, 9 Passivation, 77 PDM at cigar fuse holder, melted, 66f PDM lid, 66f

Pedestal, 118 Planté, Gaston, 8 Plates of automotive (cranking) batteries, 34-35 battery, 113-116 corrosion, 69 Plug-in hybrid electric vehicle (PHEV), 91 Plug-in hybrid vehicles, 94 Polarization, 5 Polyalkalene glycol (PAG) oil, 48 Polyalkalyene glycol (PAG) oil, 161 Polyamide, 105 Polyamide 66, 101 Polyethylene (PE), 181 Polymeric carbon, 81, 100 Polymer matrix bipolar substrate, 28 Polypropylene, 101 Polyvinyl chloride insulation (PVC), 181 Porous carbon electrode, 79 Positive terminal next to PDM, 45f Power distribution module, 175 Power relays next to battery, 45f Powertrain control module (PCM), 26 Power wire draped over fuel filter, 196f “Pre-fuse” module, 51, 53f failure, 51f, 52f, 103f, 104f Primary lithium batteries, 76 Production methodology, 81 Propylene carbonate, 78 glycol, 107 Protective shields, 40 Protocols, 100 Pulse charging, 33, 69 Pulse conditioning, 33 Push-on connector, 139

R Ratings, 62-63 Ampere-Hour, 62 cold cranking amps, 62 reserve capacity, 62 Watts, 62 Recharging, 5 Reserve capacity, 62 Resistive heat, 65 Revolutions per minute (RPM), 57 RIN 2127-0068, 110 Ripple voltage, 72 Rock of Gibraltar, 112 Rolled graphene, 80f Rubber gooseneck, 170f, 171f, 172 Rubber separators, 21 Ruddy-red discoloration, 119

S SAE J369, 100 SAE J1344, 100-101 Safety switch, 98 Salient-pole alternators, 57 Scientific method, 3, 105, 207 Sealed batteries, 21 Sebacate, 107 Self-extinguishing (SE) materials, 100 Self-extinguishing/no burn rate (SE/NBR), 100, 105 Separators (positive and negative plates), 21 Series-parallel HEV, 95 Shelf life, 78 Shrunken battery terminal, 120f Shrunken or exploded remnants of battery lugs, 116-121 Society of Automotive Engineers Standard J369, 100 Society of Automotive Engineers Standard J1344, 100-101 Solenoid, 37

“Sponge” lead, 31 Stand-alone control voltage regular sensor, 42f Stationary battery installations, 72 Sturgeon, William, 5 Subrogation, 67 Sulfation, 32-33, 72 Sulfuric acid vapors, 44 Sulfuryl chloride, 77 Super-capacitors, 82, 83 bus, 84 Surface charge, 77

T Terminal voltage, 62 Terracotta jars, 1 Tesla, Nikola, 9 Thermal inertia, 103 Thermal runaway, 88, 89 Thermoplastic high heat-resistant nylon (THHN), 181 Thionyl chloride, 77 Topping charge, 71 and float charge, 70-71 Toshiba, 29 Transmission and power steering fluid, 106 Trickle charge approach, 34 Trough battery, 5 Trunk battery fire, 39 inner cover, 41f outer cover, 41f

U UltraBattery®, 27 United States Council for Automotive Research (USCAR), 92

V Valve regulated lead-acid (VRLA) designs, 18, 21-23 batteries, 22f Varma, Brajendra P., 24 Vehicle fire investigation, 97 Vibratory-caused thermal runaway, 79 Vibratory cycling and amplitude, 173 Volatile organic compounds (VOCs), 157 vapors, 88 Volta, Alessandro, 3 Volta pile battery, 4f, 5

W Watts, 62 Weatherproofing service, 167 Wet cells, 7 Wide-open throttle (WOT) mode, 95 Windingless rotor alternators, 57 Window switch fire with cascading thermal event, 199f, 200f Wiring harness, 48 chafing on AC pipe, 49f inside door, 203f inspection, 171f pinch, 172 pinch point, 169f

X Xenon headlamp, 134

Y Yai, Sakizou, 7 Yai Dry Battery, 7, 8

Z Zinc, 7 Zinc powder, 3

About the Author

Greg Barnett is an automotive engineer and technical expert, with a career spanning over 45 years in the automotive, heavy truck, and equipment industry. He was last employed by Land Rover of North America as a field service engineer and instructor of automotive technology. He achieved the level of factory Certified Master and accredited instructor. Currently, he works as a consultant assisting attorneys, insurance carriers, and automobile manufacturers on legal actions that require technical expertise. His casework revolves around large losses caused by vehicle fire, product failure, product refinement, professional negligence, personal injury, vehicle arson, and fraud. Mr. Barnett is a four-level Certified Master by the National Institute for Automotive Service Excellence (ASE) and was listed in the Automotive Hall of Fame as a World Class Technician in 1994. The author began collecting data on vehicle fires starting in the early 1990s. His experience with actual vehicle fires began in the 1970s. As vehicle plastics evolved into modern polymerics, Mr. Barnett began documenting the lack of combustibility of the materials selected by manufacturers in various fire cases. Identifying and understanding the combustibility of compounded polymerics and nanocomposites is critical to any vehicle fire investigation. These observations and the data collected on vehicle fire analysis became the subject of his Master's thesis and eventually morphed into his first book, Automotive Fire Analysis: An Engineering Approach, published in 2003.