What Is a Flash Fire?

Mary McMahon

A flash fire is a rapidly moving and very hot fire that can develop when oxygen interacts with flammable substances suspended in the air. It can potentially be very dangerous and may be unexpected in nature. Some measures to address flash fires can include using filtration systems to keep flammable materials out of the air, installing sprinklers to quickly douse such fires, and ordering personnel to follow safety procedures when working in environments with a risk of fire.

Flash fires are sometimes seen in operating rooms.
Flash fires are sometimes seen in operating rooms.

One example of a flash fire can be seen in operating rooms, where flammable anesthetic gases may interact with lasers, cautery equipment, and other electric devices. Spontaneous ignition can occur. Sometimes this results in an alarming bright flash and nothing more, and in other cases patients may experience serious burns or even death. If fire reaches the airways, it can cause significant health complications for the patient. Operating room staff take a variety of steps to reduce the risk of fires of this nature, as they can be especially dangerous for patients with serious illnesses or injuries.

A flashover is a cataclysmic escalation of a fire in a contained space.
A flashover is a cataclysmic escalation of a fire in a contained space.

Flammable suspended particles can include metals and materials like flour. Flash fires can also develop in environments where liquids evaporate and create flammable vapors, or when flammable liquids are aerosolized, as may occur when gasoline squirts out of a container because it is under pressure. A spark can ignite the material, and it will burn very hot and spread until it runs out of fuel. The duration is typically short because the flash fire consumes the flammable material so quickly.

Flash fires can combine with other phenomena to create considerable safety problems. One risk is flashover, where all the flammable material in an area ignites at once because conditions reach a critical point. This can create an explosive release of energy, as the air will expand rapidly and may run out of room, breaking down walls and ceilings. In the trench effect, flames in a flash fire jump up a barrier, with the potential to spread into another area.

Industrial environments are a common location for flash fires, as personnel work with flammable materials and may generate sparks in the course of their work. Filtration systems and ventilation hoods can be helpful, as can techniques like periodically spraying down an area to remove suspended particles, and shielding devices that generate sparks to prevent ignition. Sprinkler systems and other options like inert gas fire suppression systems can also be useful tools for fire safety, kicking in when a flash fire erupts to minimize damage.

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Discussion Comments


@KoiwiGal; - Sawdust is a fire risk, of course and needs to be managed, but it is often too big to cause a real flash fire. For a flash fire you really need a lot of very small particles suspended in air like a cloud of dust. Sawdust is usually large and heavy enough that it falls to the ground fairly quickly. It would burn quickly, like kindling, but not explosively.


@browncoat - I guess what happens is that the individual particles all catch fire from each other so quickly that the fire just explodes until they are all burned up. Honestly, it kind of makes me want to try it (in safe conditions of course) but I wouldn't know how much would be a safe amount to use.

They probably have the same problem with a lot of flammable substances, like sawdust, when it becomes airborne. In fact, I'm surprised there aren't more flash fires involving sawdust, since it seems like the kind of substance that would be constantly around workshops where sparks from electric tools would be common.


I never realized that flour could be so flammable until I read about an incident in a factory a few years ago when a flash fire caused by loose flour created an explosion.

And I read an email on Snopes a while ago that recommended using flour to douse fires, which is actually the exact worst thing you could possibly do, aside from pouring oil on a fire to put it out.

I actually think this is something that should be explicitly taught in schools, because throwing baking soda on flames is a method of putting them out and I could see people making the leap that flour would do just as well.

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