Ventilation—the Overlooked Basic

Ventilation—the Overlooked Basic


Volunteers Corner

“Ventilate!” The often given command after the fire has been knocked down. Why delay when removing the heat and smoke will assist the attack team in reaching the fire? Ventilation also reduces the buildup of convection gases, limiting the spread of fire throughout the structure.

Ventilation, the second most important aspect of fire fighting, is the creation of controlled drafts in a burning building to aid fire extinguishment by the planned and systematic removal of heated air, smoke and fire gases, followed by the replacement of a supply of cooler air.

There are three types of ventilation: vertical, horizontal and forced, which is accomplished by mechanical fans or fog streams.

The reasons to ventilate are numerous. Foremost of these is the safety of occupants and fire fighters. Proper ventilation to clear rooms, halls or stairwells is needed in conjunction with rescue operations.

Another important reason to ventilate is to avoid losing the building. Since ventilation removes toxic and flammable gases, improves visibility and exhausts the heat buildup, fire extinguishment time will be lessened, reducing heat, smoke and water damage. Further, the speed of the attack is increased and both horizontal and vertical fire spread are curtailed by venting.

Ventilation also alleviates the possibility of a back draft. In tact, vertical ventilation must be performed if there are back draft indications. Ventilation makes the area safer to work in with the removal of carbon monoxide and other combustible gases. Ventilation can also remove the danger of fire spread to both internal and external exposures.

An easy rule of thumb for when to ventilate is simply when dense smoke, intense heat or dangerous gases prohibit access to the seat of the fire. Many factors have a bearing on where to ventilate, but generally, venting is done as directly over the seat of the fire as possible.

Common sense and experience will also indicate when to ventilate. When size-up reveals a pressure buildup due to smoke, heat and gases forcing out smoke between bricks, weatherboards and shingles, or from around windows, doors anci eaves, venting is necessary.

The timing of ventilating is critical, and there must be coordination between those performing engine and truck duties. Normally, venting is not done until a charged hose line is ready; however, this only means the window should not be broken or the ceiling punched through. The preparation work, such as making the roof cuts, should be initiated while hose lines are being stretched.

Where not to ventilate is as important as where to ventilate. In most instances, ventilation should not be carried out until the location of the fire is established, otherwise there is the danger of venting into an uninvolved area and pulling the fire through the building or toward advancing fire fighters.

Vertical ventilation should be at the highest point over the fire for single-story buildings, attics and top floors. In multistory buildings, vertically ventilate elevator shafts, skylights, scuttle holes and stairwells when it does not pull smoke and heat toward people attempting to escape.

Power saws are generally used to make vertical openings, being faster than the reliable ax, which can also be used. The blunt end of a pike pole, Clemens hook or stripping ladder will be needed to remove the ceiling.

For a standard dwelling or taxpayer, a 4 x 4-foot hole is necessary. For structures with larger areas, these dimensions will have to be increased or multiple holes cut. On peaked roofs, work down from the ridge as far as can be reached; or for plywood roofs, work to the end of the first sheet that could be as much as 4 x 8 feet. On lightweight flat roofs, take out the entire 4 x 8-foot plywood panel. Be sure to cut along rafters, bar joists and purlins, not through them. For arched roofs, a long narrow cut can be made to open into several rooms or a large area. This cut should be between the rafters (32 inches wide), leaving only one nailing point on each roof sheathing board to be pulled, that at the center rafter. The ceiling below would then have to be removed.

Horizontal ventilation must be done on the fire floor and the floor immediately above it first. Then check for fire extension through the interior wall, starting at the upper floors of the building and working down to the fire tloor. Only experienced fire fighters should be sent above the fire. Windows, transoms, louvers, gables, and attic or dormer windows can all be opened or removed to horizontally ventilate.

Air currents play an important role in ventilation. Opening a door or window on the wrong side of a building may reverse air currents, driving heat and smoke back upon fire fighters, or drawing it into other areas. Ventilation openings on the leeward (downwind) side are made at the top of the windows first, followed by lower openings on the windward side. Be sure that all obstacles like shades, curtains, drapes and screens are removed. Remember that glass is the cheapest thing to replace. If a window is stained or cracked, remove it. Use the flat of an ax or a forcible entry tool from a parallel or higher position and clean out the glass completely, since one window opened correctly is much better than several merely broken.

Horizontal or cross ventilation is accomplished by opening or breaking windows or by removing the end of a gable roof. If fire fighters are inside, windows either can be opened as for cross venting or they can be opened from both the top and bottom equally. When the ventilation team is outside, windows must be broken from a point aside or above the window (the upper floor or roof can be used). When possible, always check the area below for fire fighters before starting to break glass.

Mechanical or forced ventilation can improve the output of horizontal openings. Smoke ejectors can be placed high in windows or doors to pull out smoke and gases. A second ejector can be used to blow fresh air in at the opposide side of the room, hall or building.

Fog streams can be used to create a venturi pulling the products of combustion with the stream as it is directed out an opening. The nozzle should be placed on a 60° angle and directed out an opening from about 2 feet inside the structure with the stream covering about 85 percent of the opening. This is a very effective method of venting, especially immediately after knockdown.

At no time should a fire fighting stream be directed into a ventilation opening. This only places a cap over the opening and, in fact, generally drives the smoke and gases further into the structure. Streams should be operated just above ventilated openings and projected slightly above the horizontal plane. In this position, the streams help cool the thermal column and extinguish sparks.

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