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The use of fans to augment or implement the ventilation effort con be very useful. Modern fans can move tremendous amounts of air and also smoke, heat and fire! The greatest air movement from these devices can most often be obtained by using them in the positive pressure mode, blowing fresh air in while providing an ex-haust opening for smoke, heat, and fire on the opposite side of the fire. Before beginning positive pressure ventilation efforts, the incident commander must have a very good idea of what will happen when that inrush of fresh air hits the fire. He or she must know the answers to these questions: 1. Where is the fire? 2. Where are the occupants? 3. Is the fire traveling in any void spaces? 4. Can the fan entry point fire location exhaust opening be configured to properly direct the products of combustion?
The effect of blowing fresh air on a fire from a fan is the same as when it is directed out of a bellows onto a blacksmith's hearth. The fire intensifies. The fan must not be allowed to blow the fire at any victims who are on the opposite side of the fire or at any firefighters who are attempting to rescue these occupants. For that reason, positive pressure ventilation (PPV) must not be used if firefighters are entering the building from any points other than the fan's entry opening, such as when performing vent, enter and search operations.
Similarly, PPV should not be used if it is suspected that fire is traveling in void spaces such as a cockloft or pipechase. The fan will blow the fire at a faster rate through these concealed spaces than firefighters can open them up. Finally, if the fire is already venting out of several openings, it may not be possible to direct the air movement out of any other channels. In this case, the fan can be used as a supplement to the existing ventilation, putting "the wind" at the firefighters' backs. Be sure to prepare for the initially intensified fire when the fresh air hits the fire. Have a charged hoseline ready to immediately hit the flames as entry is made.
Remember, ventilation at the right time, place and fashion is critical to structural firefighting. Vent and ye shall live!
John Norman, a Firehouse® contributing editor, is a captain with the FDNY, assigned to Rescue Company 1 in Manhattan. He is also an instructor at the Nassau County, NY, Fire Service Academy and lectures nationally on fire and rescue topics. Norman is the author of Fire Officer's Handbook of Tactics, which may be ordered by calling 800-752-9768.