Fire ventilation

tion: for example, when implementing positive pressureventilation in the case of an apartment fire it is also possibleto achieve the effect of pressurising the stairwell. It is alsopossible to implement various types of positive pressureventilation. Mechanical ventilation must be combined withcreating openings, so as to achieve horizontal or vertical ventilation(i.e. so that both inlets and outlets are achieved).Note that mechanical fire ventilation can have asignificant effect on the fire scenario. For this reasonextreme caution should be observed when using fans,regardless of how the ventilation is implemented.Negative pressure ventilationNegative pressure ventilation is based on creating a negativepressure in an opening to the fire room, or to the roomexposed to fire, by means of a fan. Alternatively the negativepressure can be created by means of a fan in the middle ofthe room or in the building. This fan is then interconnectedwith the surroundings, for example by using a large diametertube. There are also instances where the fan is placedoutside the building, with a large diameter suction tubethat is led into the building.Negative pressure ventilation can be used as a tacticalmeasure during a fire and rescue operation, but is preferablyused during mopping up and salvage and overhaul. Themethod requires several preparations. If the fan is placedfor example in an opening, the rest of the opening must becovered. It may also be necessary to use a large diametertube to remove hot gases.Situations where negative pressure ventilation can besuitable include fires in basements or other fire rooms thatare not in direct connection with the outside, and wherefire gases must be transported through rooms that have notyet been affected, for example via a stairwell. Negative pres-59