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Important Factors and Probability of Fire
Fires in Automobiles Involve Random Factors
While the mechanisms of fire are clear, and in extreme conditions, easily predictable, the occurrence of fire is probabilistic in nature. Particularly in vehicle fires, there are numerous factors, many of which (e.g. wind, speed of travel, operating conditions) that occur in unpredictable ways. The probability of the occurrence of a sustained fire is dependent on four major and commonly considered factors (or elements):
Probability of a sustained fire is determined by:
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Fuel Ignition |
Mixture Propagation |
The actual number of underlying factors is much higher. Each of the additional factors results in a probability distribution of its own related to conditions that will and will not support fire. The following is a partial list:
Probability of ignition is determined by:
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Fuel type Fuel volume Fuel temperature Droplet size Air flow Space geometry Oxygen presence (volume) |
Ambient temperature Hot surface temperature Hot surface texture Residence time of vapors around hot surface Location of spark or flame Energy of spark or flame |
While tables may list the autoignition temperature of motor oil to be 500-700 degrees F, there are some circumstances in which it will not ignite at 800 degrees F. However, given similar conditions, the probability of autoignition of motor oil is greater at 800 degrees F than it would be at 500 degrees F.
Similarly, many factors influence the probability of fire propagation.
Probability of fire propagation is determined by factors including:
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Initial energy of fire Fuel type Fuel volume Fuel temperature Adjacent fuel type Adjacent fuel distance |
Droplet size Air flow Geometry of space Ambient temperature Thermal responses of container surfaces |
Consequently, there is a high probability that fire will not occur or propagate the first time some of the conditions are present. Therefore, it is likely that some remaining general evidence may help define the cause of the fire. For example, if there is an allegation of leaking fluid in the engine compartment that fueled a non-collision fire, it would be likely that such fluid had leaked for some time before conditions aligned to cause fire. Examination of the garage floor where the vehicle was parked may support or refute this possibility. Or if a fire was caused by an electrical fault, it would be possible that prior to a fire, the electrical circuit in question may have malfunctioned in some observable way. It is also true that fires can occur even in the absence of predictive evidence.
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