Methods
Mechanical fans can be used to provide positive pressure ventilation when used in tandem with either existing openings such as windows, skylights or heat/smoke vents on the roof; or by cutting new exhaust vents in the building. If there is no suitable existing hole, firefighters may use their equipment to make one, such as specialised saws for cutting a large hole in the roof. A conical hose-stream aimed around an opening -of a window or door, etc.- entrains smoke and thus increases the exhaust rate of smoke from the space. This is a process called "hydraulic ventilation". This strategy might be used when the fire is small and protecting property from smoke damage can be achieved safely. It can also be used more aggressively when a structure is "fully involved" and the smoke is obstructing the nozzlemans view of the hotspots.
High-rise buildings sometimes also incorporate fans to produce a positive pressure in stairwells and elevator shafts to reduce smoke infiltration into those spaces.
When glass windows in a burning structure burst from internal pressure and heat, or the fire burns through the roof, it may be said to have "auto-ventilated" or "self-ventilated."
Read more about this topic: Ventilation (firefighting)
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