FR Myths & Dirty Laundry: Our Official Blog

Arc vs Flash

Posted by John O'Sullivan on


Flash fire is a common threat where chemicals (oil, gas, coal, dust, etc.) can ignite in the air. Under perfect ratios of fuel-to-air, the slowest a flame front can move through a meter of air is 3 seconds. There is no coincidence that it is also what determines the upper threshold for exposure industrial personnel to flash fire in NFPA 2112.

By Comparison, Arc Flash (an electrical threat) is typically only a fraction of a second in duration. However, the energy released is multiple times greater. (Note: the claim that electrical arc flash reaches 35,000 degrees is incorrect, it is closer to 17,000 degrees Fahrenheit).

This graph compares the temperature of an Arc Flash and Flash Fire. The width of each bar represents the duration which heat is released.

You will notice that the duration of an electrical Arc Flash is shorter, but the temperature is much greater when compared to a Flash Fire. This difference between temperature and seconds is also why there are different codes which address each particular threat.

You will be more comfortable, and likely safer if you match your arc and flame resistant clothing to the threat. We suggest not using arc level or "HRC" categories found in NFPA 70E if your threat is an industrial Flash Fire from oil, gas or dust. Conversely, it does not necessarily help you to require a certified NFPA 2112 piece of clothing if your workplace threat is an electrical Arc Flash.  

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