It is being said that the fatal explosion that killed a 35-year-old battalion chief while operating at a tractor-trailer fire was a “smoke explosion.” The investigation continues, looking at other fuel sources, such as the foam insulation in the trailer. They have ruled out a BLEVE. A sample of rigid foam insulation from the trailer was provided for testing to identify the foam type and its potential as a fuel source for the smoke explosion. The refrigerated intermodal container had a portable generator, or genset, affixed to the bulkhead of the container. The genset in this incident ran on diesel fuel and included a self-contained diesel fuel tank on the lower portion of the genset device. Based on the information provided by the UL Research Institutes team, a visual inspection of the diesel tank did not reveal any evidence of bulging or rupture. The container was loaded with frozen chicken.
The fire service is not taught to recognize Type 111 trailers as a pressure vessel. When impinged by fire, these trailers can become pressurized. The same fire dynamics principles that apply to structure fires apply here as well. As the temperatures inside a closed compartment increase, the pressure inside the compartment also increases. The pressure continues to build without a sufficient pressure relief vent(s). The Type 111 trailers, when configured for refrigerated applications, have void spaces between the inner and outer floor, walls, and roof that are filled with combustible foam plastic insulation. This means that even an empty trailer has a significant fuel load.
Additionally, on this unit, there was an integrated refrigeration unit that consisted of pressurized cooling lines and a compressor system much like in a typical refrigerated trailer. The various containers integrated into the refrigeration system could suffer a catastrophic failure as the refrigerant becomes heated when exposed to fire. This could eventually lead to a boiling liquid expanding vapor explosion (BLEVE). In this incident, the refrigeration overpressure appeared to ventilate and maintain safer pressures. This incident is NOT believed to be the result of a BLEVE.
The fire service at large is aware of the potential surrounding a catastrophic failure of tank trailers or fuel tanks, such as a BLEVE or a burn through, that contributes to significant fire growth and potential. However, the same care is not taught for type 111 trailer responses, which may support more complacent responses. Like this case, a smoke explosion can happen in any fire in a compartment. This could be a structure fire, or something different, such as the trailer in this instance. The key indicators are that the compartment is filled with combustion products, and oxygen is consumed or limited. All it takes is the introduction of oxygen to the mixture to support a violent reaction. The fire service should be taught that even though explosion hazards are less prevalent than fire hazards, there is a risk associated with explosion hazards at heavy vehicle incidents [IFSTA 2023].
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