Fire ventilation

The pressurising of adjacent rooms can be achieved bymaking only one inlet, and by placing a fan in it. If thespread of fire gases to the pressurised room is not extensive,this measure is often sufficient. If hotter gases has alreadymanaged to spread to the adjacent room, the pressurisingshould be supplemented with an outlet.One alternative is to connect a large diameter tube to thefan, which leads fresh air into the adjacent room. In suchcases it is possible to use disposable polythene large diametertubes, since there will only be a low temperature in thelarge diameter tube. This can be an appropriate measure ifthe room is deep inside the building, or if rooms have aspecial value (archives, computer rooms, museums etc.). Itis then important that other openings, apart from the openingfor the large diameter tube, are blocked so as to achievethe greatest possible positive pressure in the room.Positive pressure ventilation(pressurising of rooms exposed to fire)Positive pressure ventilation involves supplying a lot of airto the fire room, or the fire compartment where the fire is,by means of powerful fans. This measure is often combinedwith internal fire fighting.The purpose of positive pressure ventilation is to quicklylocalise the fire and to remove the heat so that furtherspreading of the fire is dampened, and so that the fire fighterscan quickly start saving lives and extinguish the fire.The working conditions for the fire fighters is considerablyimproved, since temperatures drop and visibility becomesmuch better. Evacuating persons also have a greater opportunityto escape the effect of toxic gases, while it is easier forthe fire fighters to find trapped persons more quickly. Positivepressure ventilation often makes it possible to implementrapid internal fire fighting in a safe way.The method is based on placing one or more fans closeto openings to push out and vent fire gases through outlets.A normal strategy would be to:64