Fire ventilation

esults in quicker and more simple extinguishing. Thespread of the fire can be more easily prevented and thereforethe damage caused by the fire can be better contained.Fire ventilation at a later stage, when the fire is ventilationcontrolled, often means that it is more difficult toimplement internal suppression. In closed areas the firescenario can accelerate violently when air gains access tothe fire as a result of fire ventilation, in particular if the firehas been underway for a prolonged period in the closedarea. The intensity of the fire can increase, the fire spreadsmore quickly, more fire gases is formed, and the fire becomesmore unpredictable. If the fire rapidly becomes fullydeveloped it can be more difficult to penetrate into the fireroom. The impact of the heat increases both on the enclosingstructures and on the fire fighters. There is also anincrease in the production of fire gases, which can spreadthe fire. Fire ventilation of areas with fully developed fireshas a limited effect. It can therefore be wise to vent adjacentrooms where the damage is not so serious.Fire ventilation should be implemented as soon as possibleduring the fire and rescue operation. If the fire is fullydeveloped in one or more rooms, it is very often better tofocus on fire ventilation of the adjacent rooms where thefire has not yet spread.Extreme caution is required in the case of ventilationcontrolledfires in very large or inaccessible rooms. Aboveall it is necessary to coordinate with other measures beingtaken at the scene of accident, in particular the suppressionmeasures. In all probability the fire will increase in intensityafter implementing fire ventilation. If air is supplied to aventilation-controlled fire the worst scenario can be a firegas explosion, or a backdraft.Fire gas explosionWhen unburnt gasesfrom an underventilatedfire flowthrough leakages intoa closed spaceconnected to the fireroom, the gases therecan mix very wellwith air to form acombustible gasmixture. If these gasesare ignited, a fire gasexplosion may occur.BackdraftBackdraft is theburning of heatedgaseous products ofcombustion whenoxygen is introducedinto an environmentthat has a depletedsupply of oxygen dueto fire. This burningoften occurs withexplosive force.15