Respuesta :
Positive-pressure attack is only effective if the location of the fire is known and the appropriate exhaust-to-intake ratio (greater than 1 to 1) can be achieved.
Positive Pressure Attack (PPA) is a coordinated fire attack where fans are used to assist in controlling the fire. Positive Pressure Ventilation (PPV) is the use of fans to remove the products of combustion after fire control.
For interior crews, successful and safe fire attack is much less about fighting fire than it is about fighting smoke. With Positive Pressure Attack (PPA) not only are firefighters not in obscured, flammable, carcinogenic environments but victims who may be in areas that are survivable on our arrival are also benefited.
While many different variables (fan size, setback distance, angle, intake, exhaust, etc.) can affect the pressures created by a fan, the exhaust is the most critical to PPA success. Again, the fan needs to produce more pressure than the fire, and having an exhaust to inlet ratio of 2:1 is more effective than 1:1 or <1:1. It needs to be clarified that the inlet is not necessarily the attack entrance door but rather the door/opening to the fire room. While this 2:1 ratio was possible in the experiments, many buildings make this exhaust: inlet ratio difficult or even impossible to recreate. If the building isn’t cooperating, just add water. Applying water to the fire will reduce the pressure (and the temperature, energy, and power) inside the fire room, which will allow PPA to be more effective.
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