Over the past two decades, there have been some reasonable debates and some less reasonable marketing on the duration and energy of hydrocarbon flash fires, despite the fact that existing North American standards were quite clear on the subject. NFPA (National Fire Protection Association and CGSB (Canadian General Standards Board) both defined flash fire with identical technical language: the main factors being diffuse fuel in air, an ignition source, a rapidly moving flame front, and a consequent duration of 3 seconds or less. The NFPA 2112 standard requires a manikin test duration of 3 seconds precisely because it is viewed as the practical upper limit of a flash fire. Groundbreaking research was recently conducted to answer the debate and vet the standards. The key differentiator between a fire and a flash fire is the fuel. In a fire, the fuel is concentrated (pool fires, jet fires, etc) and thus is not a significant limiting factor in duration; it will burn for minutes or hours or even days if not actively extinguished. Conversely, in a flash fire the fuel is diffused in air (gas leak, vapor cloud, combustible dust, etc.), meaning it will be consumed very quickly once ignited, as the flame front moves very rapidly from the ignition point to the source and/or to the limit of the cloud and goes out. Thus, the duration of heat levels sufficient to ignite flammable clothing or cause 2nd degree burns to exposed skin is very brief in any single location within the flash. This short duration is what makes these events survivable without respiratory protection, and with a single layer of FR clothing, as opposed to SCBAs and turnout gear worn by firefighters (FR clothing will not ignite and continue to burn, but single layer, breathable FR does not provide sufficient insulation against protracted fire exposures).
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