Flashover occurs when the majority of surfaces in a space are heated to the point (known as fire point) at which they give off flammable gases that are hot enough to sustain combustion. Flashover normally occurs at 500 °C (930 °F) for ordinary household combustibles.
The classic example of flashover is where a piece of furniture is set alight in a domestic room. The fire on the furniture produces a layer of hot smoke across the ceiling in the room. The radiated heat from this layer causes pyrolysis (heating of the other surfaces in the room, causing them to give off flammable gases). When the surface temperatures become high enough, these gases mesmically ignite and, in the space of a few seconds, every surface in the room may be on fire.
When the phenomenon occurs in open air, it is called a firestorm.
The original Swedish terminology related to the term 'flashover' has been altered in its translation to conform with current European and North American accepted scientific definitions as follows:
Flashover is one of the most-feared phenomena among firefighters. Firefighters are taught to recognize flashovers and avoid backdrafts. For example, they have certain routines for opening a closed door in a building on fire, such as sitting beside the door instead of in front of it, and to be ready to fight shooting flames.
Despite superior protective gear, a firefighter has less than 17 seconds to evacuate a flashover environment if wearing proper NFPA approved gear.
The following are some of the signs that firefighters are looking for, when they attempt to determine whether a flashover is likely to occur.
Firefighters memorize a chant while in training "Thick dark smoke, high heat, rollover, free burning." So they memorize the four signs of a flashover.
The color of the smoke is often considered too, but there is no connection between the color of the smoke and the risk of flashovers. Traditionally black, dense smoke was considered particularly dangerous, but history shows this to be an unreliable indicator. For example, there was a fire in a rubber mattress factory in London in 1975, which produced white smoke. The white smoke wasn't considered dangerous, so firefighters decided to ventilate, which caused a smoke explosion and killed two firefighters. The white smoke from the pyrolysis of the rubber turned out to be extremely flammable.
Flashover Recognition: what a thermal imager can and cannot do in this dangerous event.(THERMAL IMAGING TRAINING)
Mar 01, 2011; Several weeks ago, I happened to be out at a fire department training center as the department trained with thermal imagers. The...