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Comment by Bryan Altman on October 4, 2010 at 6:33pm

Flashover is a transition stage between growth and fully developed. Backdraft can happen any time a fire is in the decay stage, which is cause by being ventilation controlled. The fire tetrahedron consists of heat, fuel, oxygen and a chemical chain reaction. When the heat, fuel and oxygen are in sufficient amounts then you can have a fire. Any of those that are reduce will cause the fire to die down and go out. In a backdraft they oxygen side is reduce, thus the fire dies down. the fuel is still present and so is the heat. All it takes is a introduction of oxygen for the fire to pick up where it left off. You can tell here that it is not flashover because the compartment doesnt become fully involved once the violent ignition takes place.

Comment by Lee on December 6, 2009 at 6:14pm

This is a training rig that is used to simulate a backdraft, by creating a fire burning in a poorly ventilated compartment. As I understand it, in principle a backdraft doesn't have to use up all the oxygen just enough for the mix of fire gases (unburnt products of combustion) too be too rich and oxygen levels too low. This rig enables the operators to get above the UEL (upper explosive limit) quickly, and then induce a backdraft type explosion, but in a controlled manner. The room does not in fact burst into flames but there is a massive deflagration through the fire gases as the oxygen levels rise in the compartment bringing the mixture of smoke gases and oxygen within the UFL (upper flammable limit). The flames travel through the smoke layer, at subsonic speed giving the impression of an explosion.

A cold smoke explosion, different to a backdraft, can also happen and is in some ways the same except that the fire is practically out and nothing is actually burning in the compartment. There would be heavy smoke logging, and as smoke consists of flammable particals, when oxygen in entrailed into the compartment can become within its flammability limits. Any turning over and damping down can obviously uncover embers which within the worst case scenario can ignite the cold smoke gases, again causing deflagration throughout the smoke layer, hence the explosive appearence.

A flashover as I understand it happens when a well ventilated fire is left to develope, with massive heat increase. The primary fire creates a hot smoke layer spreading across the room radiating heat downwards. The remaining items in the compartment start to pyrolise giving off flammable gases as they decompose. Once the heat is adequate the flammable gases that are created by the items, not involved in the primary fire, ignite. The point in which practically every flammable item in the compartment is involved in fire is the point of flashover.

This is, dare I say it, some knowledge I gathered during my initial training period and may be out of date or possibly ill remembered. Still, Flashover or Backdraft, education of the risks of each is a life saver.

Comment by Kathy Williams on November 2, 2009 at 12:53pm

Isn't this a flashover? My understanding is that a backdraft fire is caused when a fire uses up all available oxygen in a closed room and then sits in a dormant state waiting for a door or window to be opened or forced open and introduce new oxygen, whereupon the room bursts into flame.