Utgivningsår/Year of issue: 1994.
Sidantal/Number of pages: 41.
Rapportnummer/ Report!number: Räddningsverket, rapport!P21-092/94.
Keywords fire ventilation, positive pressure ventilation, PPV
Summary This report!presents a survey of positive pressure ventilation, (övertrycksventilering). Calculations have been performed of the flows and pressures created. Some American tests and actions have been evaluated and simulated in a computer. Tactics, techniques and safety precautions necessary using positive pressure ventilation are briefly reviewed. The following conclusions were drawn.
Positive pressure ventilation employed before fire control is effective for small fires, where smoke is the main problem rather than flames. Used after fire control, it is also an effective way of reducing damage caused by smoke.
When positive pressure ventilation is used during a ventilation-controlled fire, the intensity of the fire increases. If it is used at a fuel-controlled fire, the fire may increase or decrease depending on the fire load in the direction the flames are driven. However, the change is not as large as in the case of the ventilation-controlled fire.
Knowledge concerning the air inlet and outlet, as well as the way in which the air travels through the building, is essential. The space between the fire and all outlets must be completely evacuated before considering the use of positive pressure ventilation.Under certain circumstances, the safety increases with positive pressure ventilation. Visibility increases, and with it the efficiency of actions. The heat load decreases, giving less strain on the fire fighters. However, education and training is necessary, as well as a standard operating procedure. Even fire pre-planning work is affected.
Additional research is needed, and should be carried out in four steps:
1) Computer simulations,
2) Full-scale fire tests,
3) Development of guidelines,
4) Education and training. The best results would be obtained if a comprehensive view of the whole area of fire and smoke ventilation was taken.
'When the inlet and outlet vents are first opened, the buoyancy of the hot smoke and gases may be sufficient to overcome the PPV fan for a short period. The hot gases will flow out of both vents. This appears to occur because the PPV fan does not seal the whole of the door opening equally. The majority of the air flow is along the axis of the fan. A simple test with a piece of foil or tell-tales fixed to a ventilation opening will show a flow in through the top of the doorway when there is no fire. However, the smoke and hot gases from a fire can overcome this and flow outwards'.
Fire Experimental Unit - UK - 1996.