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Results from a full-scale vehicle burn test involving a sport utility vehicle illustrated how fire spread throughout the vehicle, how temperature distributions changed over time, and how arcing-through-char does not always occur in a vehicle fire. The fire was initiated on a grommet on the rear portion of the passenger’s side of the engine compartment. Once the temperature near the origin reached approximately 600°C, the rate of fire spread rapidly increased. Over the next 3.5 minutes, the fire spread to all locations within the engine compartment and both front tires. Although certain circuits within the vehicle’s electrical system were energized for the duration of the fire, with the battery located at the rear of the passenger compartment and the ignition switch in the “off” position, no evidence of beaded copper was observed on any of the conductors located in the engine compartment for this test. However, numerous fuses were found to have activated after the fire.

A full-scale burn test of a 1992 compact pick-up truck was conducted to evaluate how temperature distributions changed over time, the manner in which the fire spread, and how burn patterns produced during the fire correlated with important characteristics of the fire such as the area of origin. After the fire was initiated on the lower portion of the dashboard of the test vehicle, it spread locally to nearby dashboard material and, at the same time, developed a strong temperature gradient from the ceiling to the floor. Once the ceiling temperature reached about 600°C, the rate of fire spread increased and, within 1 minute, the passenger compartment was fully involved. Initiation of the engine compartment fire, which occurred about 4 minutes after the passenger compartment was fully involved, was consistent with fire spread through the heating, ventilation, and air conditioning (HVAC) duct that passed through the passenger's side of the bulkhead.

Data from a full-scale vehicle burn test involving a cargo van illustrated how temperature distributions changed over time, the manner in which fire spread, and how patterns produced correlated to the origin of the fire. The fire was initiated on the driver’s side of the engine compartment and initially grew slowly with the high-temperature zone near the area of origin. Once the peak temperature reached about 540°C, the rate of flame spread increased such that over the next 4 minutes the fire spread across the entire engine compartment. In the next stage of the fire, which occurred shortly after full involvement of the engine compartment, the fire spread into the passenger compartment. A strong vertical temperature gradient developed from the ceiling to the floor and as the passenger compartment became fully involved, the passenger compartment temperatures both increased and became more uniform.

Results from a full-scale vehicle burn test involving a 1998 compact passenger car were used to evaluate vehicle fire dynamics and how burn patterns produced during the fire correlated with important characteristics of the fire, such as the area of origin. After the fire was initiated at the air filter in the engine compartment, the fire spread locally and, once the temperature near the origin reached about 750°C, the temperature at all but one location within the engine compartment began to increase. These temperatures continued to increase for the next 6 minutes and then a temperature gradient began to develop in the passenger compartment between the ceiling and the floor. About 5 minutes after the engine compartment became fully involved, the ceiling temperature reached about 590°C and flame spread within the passenger compartment increased. Over the next 4 minutes, the passenger compartment also became fully involved.

During the course of a fire and subsequent exposure to the environment, iron and low-carbon steels oxidize by two mechanisms: high temperature oxidation and atmospheric corrosion. Of particular interest to fire investigators are oxide properties and distribution that could be of use to better understand important characteristics of the fire such as the location the fire originated, the direction the fire traveled or even temperature versus time characteristics. This could be particularly valuable in cases where burn damage to combustible material, which is known to be an important indicator of fire origin, is so extensive that little if any material remains after the fire. However, there is little data in the literature that specifically addresses the utility of oxide properties in the context of fire investigations.

Temperature measurements during a full-scale burn test of a 2001 full-size pickup truck showed that the fire progressed in distinct stages in both the engine and passenger compartments. Although the fire started in the engine compartment and had a relatively long growth period, when a localized area reached about 700°C, a distinct transition occurred where the rate of fire spread increased, leading to full involvement of all engine compartment combustibles. As the engine compartment became fully involved, a hot gas layer then accumulated at the ceiling of the passenger compartment, producing a strong vertical temperature gradient. When the temperature at the ceiling reached about 600°C, another distinct transition occurred where the rate of fire spread increased, leading to full involvement of the passenger compartment. The highest temperature during the test occurred within the engine compartment in an area that had the greatest fuel load, and not the area of origin.

This paper summarizes hot surface ignition data for automotive fluids in the literature, as well as the ignition data for vegetation, paper and cotton, and compares it to measured motor vehicle exhaust system temperatures. While hot surface ignition is a complex phenomena and the temperatures attained by motor vehicle exhaust systems depend on many factors, these comparisons can be useful in evaluating motor vehicle fire causation scenarios. Comparing hot surface ignition data in the literature is complicated by limitations in the statistical analysis used to address the underlying probabilistic nature of the ignition data. Because the statistical uncertainty of measured ignition probability can be significant, this paper reviews the three methods that have been used to address this probabilistic nature in the literature and illustrates statistical techniques that can be used to make statistically significant comparisons between different sets of ignition data.