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A burn test was conducted to evaluate the propagation of a fire from burning vegetation underneath a vehicle. A 2013 four-door sedan was instrumented with thermocouples throughout the engine compartment, interior, underbody, and trunk as well as a heat flux sensor underneath the vehicle. The vehicle was placed on a bed of straw to simulate a wildland fuel load. The fire was ignited in the vegetation under the engine compartment near the driver-side front wheel. Initially the fire spread outward from the point of origin under the vehicle. As the fire grew, it spread to the engine compartment and travelled through the vegetation outside of the footprint of the vehicle. The fire progressed rearward along the outside of the vehicle while the fire under the engine compartment continued to grow. During the test, the front and rear driver-side doors were opened at t=1.00 min. and t=1.15 min., respectively.

Two full-scale burn tests were conducted to evaluate the propagation of an engine compartment fire into the passenger compartment of consumer vehicles. In particular, the effect of penetrations in the bulkhead separating the engine compartment from the passenger compartment was examined. The first burn test involved two vehicles of the same year, make, and model. One of the vehicles was left in the original equipment manufacturer (OEM) configuration. The other vehicle was modified by welding steel plates over the pass-through locations in the bulkhead between the engine and passenger compartments. After the fire was initiated in the engine compartment and had reached the onset of flashover, the heat and flames from this fire began to effect the passenger compartment. At about this same time, flames extending from the engine compartment around the hood began impinging directly on the outer face of the windshield.

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.

Two full-scale burn tests involving identical side-by-side all-terrain vehicles were conducted to evaluate fire spread, changes in temperature distributions over time, and how burn patterns correlated to the known point of origin of the fires. The fires were initiated by igniting body panels at opposite corners of the vehicles such that in one test the fire propagated downwind and, in the other, it propagated upwind. In both tests, drop-down from the body panels onto the tires resulted in ignition of the tires. This was an important feature of the mechanism of fire spread. Once the tires began to burn, a transition occurred and the rate of fire spread to the remaining portion of the vehicle increased. Although the time between fire initiation and this transition was significantly different in the two tests, the time to spread and to consume the remaining combustibles within each vehicle was relatively consistent, independent of wind direction.

Hot surface ignition of combustible material is a known cause of vehicle fires. Although the detailed mechanisms of hot surface ignition are highly complex, the surface temperature is known to play a crucial role in this process. There has been limited previous work in the literature on this topic, much of which has focused on engine or exhaust system surface temperatures of the most common types of passenger vehicles. Also, much of this work was done in an unrepeatable manner and suffered from measurement technique induced errors. The focus of the present work is on repeatable and low measurement technique induced error temperature measurements of exhaust system surface temperatures of rear- and mid-engine sports cars. Temperature measurements were made at several points along the exhaust systems of vehicles both with and without turbo chargers on a 5-mile oval track.

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.

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.

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.

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.

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.

One of the known causes of motor vehicle fires is hot surface ignition of combustible material that contacts engine exhaust system components. While ignition is a complicated phenomenon, the temperature of the surface is known to be an important parameter. However, little data is available in the literature concerning exhaust system temperatures, and much of this data is confounded by thermocouple attachment techniques and undocumented variations in driving conditions. In the present study, engine exhaust system temperature measurements were conducted using six test vehicles on a level, 2-mile oval test track at constant vehicle speeds ranging from 0 (idle) to 70 mph. By normalizing transient temperature curves with these steady-state temperatures along with ambient temperature, the rates at which the exhaust system components warm up and cool down are also compared.

Techniques for soil-tripped and curb-tripped rollover testing have been developed and reported in earlier papers. The tests reported in these earlier publications were conducted with a variety of vehicles launched at speeds close to 30 mph. Several additional soil-tripped rollover tests were conducted using a single model of mid-sized sedan launched at speeds ranging from 13 mph to 42 mph. This test series provided information about the minimum trip speed and the influence of trip speed on the characteristics of vehicle rollover. The results of this test series as well as the previously reported tests have been studied to obtain insights about minimum trip speeds, furrow characteristics, angular velocities, rollover distances, trip and post-trip decelerations and the influence of speed on rollover mechanics.