Passenger Cars and Light Trucks
Donan Engineering’s fire investigators and mechanical engineers combine to totally assess vehicle fire investigations. As is true with any origin and cause investigation, complete and concise background information pertaining to the vehicle and its use prior to the fire is of paramount importance. As with other investigations, many times the owner of the vehicle will not be completely forthcoming with all pertinent information. The insured may feel the circumstances surrounding the fire event might preclude their coverage.
Today’s passenger vehicles have nearly all of the comforts of home. With the addition of sophisticated audio/video systems, navigation systems, multi-zone heating and cooling capabilities, and the hybridization of vehicles, the demand on and design of the electrical systems of our cars and trucks is increasingly sophisticated.
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Origin and cause investigation of vehicle fires is similar in many ways to structural fire origin and cause. The investigation begins with an exterior survey of the vehicle to determine if the fire originated inside or outside of the vehicle. A survey of this area is then conducted to determine the direction of fire extension.
Most passenger vehicles can be segmented into three separate function areas: the engine compartment, the passenger compartment, and the cargo (trunk, truck bed) compartment. In most sport utility vehicles (SUVs) any cargo-carrying area is common with the passenger compartment.
Fire damage resulting from a fire inside of the passenger compartment can be severe. The ratio of combustible items to area inside of a vehicle is much greater than is found in a normal structure. Therefore, if sufficient oxygen is available, the resulting damage is significant.
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Many of the components used to manufacture today’s vehicles are combustible. Plastic and resin-based materials have replaced steel in various areas of today’s vehicles. This creates a much greater fuel load than in older vehicles.
Ignition sources to be considered in the passenger compartment of vehicles include the electrical system and any modifications or additions made to the system after delivery to the consumer: radio/stereo and audio changes, amplifiers, speed warning devices, navigation devices, and aftermarket remote starting systems. Often the installations or modifications are not properly fitted with a suitable over-current protection device. The lack of current protection along with improper protection of wiring from physical damage can be disastrous. Another common ignition source inside the passenger compartment is discarded smoking materials.
Engine compartment fires result from many potential ignition sources coupled with the availability of combustible or flammable liquids normally present in the engine compartment. Nearly all of the liquids found in the engine compartment of a passenger vehicle will burn. This includes, but is not limited to: gasoline, diesel fuel, engine oil, transmission fluid, windshield washer fluid, antifreeze, brake fluid, power steering fluid, and air conditioner compressor oils. With the abundance of available fuels, careful consideration must be given to the first ignited fuel.
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Ignition sources inside the engine compartment are also numerous. A gasoline engine relies on a high-voltage spark to ignite the compressed fuel/air mixture. This high voltage spark is over 40,000 volts, which is capable of causing an arc with sufficient temperature to ignite flammable or combustible vapors.
Hot surface ignition of fuels will most likely occur in the engine compartment of a vehicle or at the catalytic converter. The exhaust system of a normally operating engine can easily reach over 900 degrees F. This is sufficient heat to auto-ignite most liquid fuels found in the engine compartment. An improperly maintained or operating engine can produce exhaust temperatures even higher than those of a properly operating engine.
A very viable ignition source in the engine compartment of a passenger vehicle is the 12-volt electrical system and storage battery. Numerous positively charged cables and wires are present in the engine compartment. By design, many of these conductors are not overload-protected. If these cables are not maintained or kept properly secured, an unprotected short circuit can occur and will most likely result in a fire.
Donan Engineering’s staff of fire investigators includes professionals who possess in-depth knowledge of passenger vehicle components and systems. Mechanical engineers and vehicle experts are available to assist in specific component studies of suspected failure modes.