Fire ventilation

increases the risk of explosion. When venting toxic gases itis important to take into consideration where the gases areto be transported, and that the outlet of the large diametertube is placed so as to prevent further damage occurring.Experience has also shown that what might functionextremely well during one operation, might not function atall the next time in similar situations. This could, forexample, be because negative pressure ventilation is sensitiveto how the fan is positioned, or to where the outlets andinlets are placed in relation to each other and the fire.A special situation where negative pressure ventilation isused is during the use of high expansion foam in buildings.To dispel the air quickly from a room that is to be filled withfoam, a suction fan is placed at the outlet. This has provedto be a very useful solution to more quickly fill a room withhigh expansion foam.Pressurising of adjacent roomsThe pressurising of adjacent rooms involves using a fan tocreate a higher pressure in adjacent rooms, i.e. outside thefire room. The purpose of this is to prevent the spread offire and fire gases to adjacent rooms. This can be an appropriatemeasure when the fire is a large one or is difficult toget at, when it is difficult to implement fire ventilation ofthe fire room, or if the fire is otherwise difficult to suppress.However, it is necessary for the walls or other separations tohave a certain fire resistance, i.e. that the walls or separationscan withstand flames, high temperature or fire gasesfor a certain period, without the fire or fire gases spreadingthrough them.When an area ora fire cell is consideredto be lost it can often bebetter to focus onprotecting adjacentrooms, for exampleby pressurising theadjacent room withthe help of fans.63