I would like to show you a very illustrative video where you can watch clearly the quick evolution of a fire from its initial phase until fire is totally developed, becoming the called flashover.
The flashover can de defined as a sudden rising of the speed of propagation of a confined fire caused by the sudden combustion of accumulated gases under the roof and by the general ignition of combustible materials in the room caused by the released radiation by warm gases.
The flashover can be given every time we have these conditions: first, the ignition of fire in a closed space, because the accumulation of gases plays a main role. The second requirement is a presence of air enough to be feeding the fire.
Taking as an example the room shown in the video, where the fire starts by a wrong put out cigarette in the sofa, the evolution of the fire until the birth of the flashover will be the following:
- First, the flame is little and the combustion has oxygen enough in the room.
- The fire grows slowly, being in this stage the sofa the main combustible. The sofa produces flame and gas emissions, irradiating heat at the same time that other combustibles do (table, curtains).
- While the time passes by, the fire diameter is growing, flames are getting higher and fire velocity increases.
- The combustion smokes and gases density, formed mainly by CO2, CO and water vapour, will be increasing under the roof. The accumulated layer of gases temperature and density becomes higher.
- The flames, the warm gases and the roof itself, make increase the combustible area temperature and then begin to throw into the air inflammable gases.
- When a distilled gases concentration is produced in the furniture and cladding area and reaches the lower ignition limit of these, it takes place the general fire of all combustible materials in the room. This acceleration stage of propagation is known as flashover.
As you can see in the video, it takes less than 3 minutes from the appearance of the first flame to the development of the mentioned flashover, so impressive:
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