VENTILATION AT FIRES
WILLIAM E. CLARK
Wisconsin Fire Service Training
When should it be used . . . How to achieve it . . . What it can do
IF A SUITE of living room furniture, consisting of a davenport and two overstuffed chairs, were in an open field and ignited, the resulting fire would not be difficult to extinguish with a small amount of water. In fact, firemen could walk up close and extinguish the fire with a pump tank.
*Adapted from “Fire Service Training” Volume 1—No. 3, published by the Wisconsin State Board of Vocational and Adult Education, C. L. Greiber, director.
If the same furniture were burning in its ordinary location, a living room, the job of extinguishing the fire might not be so easy. In many cases, firemen might be incapacitated by the smoke and large amounts of water would be necessary. In other instances, the failure of the firemen to get in close and quickly extinguish the fire could result in extreme damage to the building.
What causes the difference?—The amount of ventilation! The furniture burning outside is no problem because heat and smoke rapidly dissipate into the atmosphere. The same furniture burning in a building will cause large amounts of heat and smoke to build up within a structure because heat and smoke can’t escape to the outside atmosphere fast enough. Consequently, firemen have to advance to the fire under very unpleasant conditions. Even if they are protected by masks, the heat may be punishing and lack of visibility a problem.
Difficulties posed by an interior fire can be greatly reduced by making the conditions as similar as possible to those of the outdoor fire; that is, to thoroughly ventilate the building. However, ventilation should not be performed in a haphazard manner. It is a subject in fire fighting second in importance only to the application of water—and in many cases is essential to permit proper application of water. Every fireman should be thoroughly acquainted with it.
What is ventilation?
Ventilation, applied to fire fighting, means the planned and systematic removal of smoke, gases and heat from a structure and is performed for any of several reasons:
- To save life by removing smoke and gases endangering occupants of the building who are trapped or unconscious.
- To discover exact location of fire by allowing smoke to lift.
- To permit firemen to enter and remain in the building to extinguish the fire and search for helpless occupants, as well as prevent extension of the fire. At most fires, the purpose of ventilation is to permit the firemen to advance close to the blaze and extinguish it quickly with a minimum of damage. The danger of asphyxiation is reduced, discomfort lessened and visibility improved to make operations safer and more efficient.
- To prevent backdraft or smoke explosions. The so-called “backdraft” or “smoke explosion” is actually an explosion of carbon monoxide mixed with air. Carbon monoxide is given off at fires where there is insufficient ventilation for complete combustion. If a door is opened, sufficient air may enter and mix with the carbon monoxide, forming an explosive mixture. If there is sufficient heat present to ignite this mixture, an explosion may result. This is a rare occurrence, but a dangerous one responsible for many deaths and injuries. Therefore, the possibilities must be considered. Proper ventilation may prevent it or lessen its harmful effects.
- To control spread of fire. Heat rises until it meets an obstruction such as a roof or ceiling. It then travels horizontally, seeking an opening where it may rise again. An opening made in a roof will “pull the fire” to that opening and allow it to vent upward into the atmosphere through that opening. Air currents are set up which cause the fire to move in that direction and tend to keep it from spreading elsewhere. Such an opening made directly over the fire will help to localize it, but an opening made at another spot will draw the fire to that location.
When should ventilation start?
Ventilation should be performed at fires in buildings, ships or other enclosures where smoke is present; also where gases or fumes have accumulated from causes other than fire.
Ventilation should begin as soon as water is up to the nozzle, not before. Opening up a building permits more air to get to a fire and accelerates burning. A charged hose line must therefore be ready for action as soon as ventilation begins. There is an exception to this rule: A skylight, scuttle cover or door at the top of a stairway in a multistoried building may be opened to prevent “mushrooming” or heat and smoke banking up on the top floor, when this would endanger human life. This can be done without waiting for water.
- At the roof: Heat and smoke rise, accumulate at the topmost point, then start banking down. An opening in the roof will permit smoke and heat to escape rapidly. When there are no natural openings in the roof such as skylights, scuttle holes, etc., and conditions are not severe enough to warrant cutting a hole, ventilation of the attic or top floor must suffice. Roof ventilation is often valuable even though the fire is in the lower part of the building, or in the basement. A hole may be cut in the roof when fire is in the cockloft or top floor and sometimes when fire is elsewhere in the building and a heavy smoke condition prevails on the top floor that cannot be removed sufficiently by other means.
- At windows: Windows should be opened on the floor where the fire is located and on all floors above that where the smoke has accumulated. Usually there is no advantage to opening windows on floors below the fire.
- At doorways: Doors should be opened to permit air circulation to remove smoke.
- Any other covered or partly covered opening on a level with or higher than the fire should be opened.
Philadelphia F. D. photo by Kennedy
West Milwaukee F. D. photo
How is ventilation performed?
When an entire building is to be ventilated, such work should begin at the top of the structure and proceed downward, floor by floor. If the lower part of the building is opened first, fire may break through the window openings there and make ventilation of upper floors impossible or endanger men who may be ventilating or performing other duties above the fire.
Opening roof: Firemen go to the roof and remove scuttle covers, skylights, etc. and sometimes cut holes in the roof surface. One large hole is better than several small ones. It should be cut directly over the fire, if possible, but not at a point that would endanger an adjacent building.
Skylights may be removed by prying loose the coaming and lifting the skylight or by loosening the coaming on three sides, leaving the fourth for a hinge and folding the skylight back onto the roof. When removal is not feasible, individual glass panes may be removed without damage by prying up the metal divider strips and sliding the glass out. If no other means will work, the glass may be knocked out with an axe or any other tool.
Opening windows: If conditions permit, this should be done by firemen working from the inside. Blinds and shades should be raised or removed and drapes and curtains pushed back or removed to permit smoke to escape. Screens should be removed and storm windows removed or broken out. Some fire officers believe that double-hung windows should be opened two-thirds of the way from the top and one-third from the bottom, but this is of little consequence. The main point is to get the window open at the top to let the smoke escape. Fresh air will find its way in to replace it. Good cross-ventilation can be accomplished by opening windows on the leeward (away from wind) side of the building at the top, and those on the windward side from the bottom.
Casement and factory-type pivoting windows have to be opened according to their design. Many windows are difficult or impossible to open in the allotted time. If smoke conditions warrant it, they should be broken. Glass is the cheapest part of most buildings and much valuable property has been destroyed by flames because firemen hesitated to break windows that couldn’t be opened.
A quick way to break glass above the ground floor is to raise a ladder and let the top of it fall against the window. It can be moved from window to window, doing the job much quicker and more safely than could be done by a man working from a ladder.
Plate glass show windows in most stores usually have a lighter glass transom located above the heavier glass. This is easily broken and often affords adequate ventilation, permitting the show window to remain intact. In extreme cases the plate glass may be removed. In either situation, if there is a partition between the store and show window, it must be removed.
Basement fires: Basement or cellar fires present special ventilating problems. Windows, where present, and doors should be opened. Sometimes windows are recessed in enclosures covered with an iron grating at street level. This grating may be removed by breaking the concrete at the corners, or the bars may be spread and a pike pole is inserted to break glass.
When deadlights are present in the sidewalk over a basement, they may be knocked out with the back of an axe, a hammer head pick, or a maul. The removal of coal chute covers may also assist ventilation. In some stores, the removal of panels under the front of the show window gives direct access to the basement, affording good ventilation.
Where no other means is effective a hole may be cut in the floor above the basement. This should be guarded by a charged hose line. Hot air heating registers in floors can be utilized by removing the grille and pushing down the hot air duct. This will have the same effect as cutting a hole in the floor and is quicker and less damaging.
Ship fires: Some fire departments may be called upon to fight fires aboard sea-going cargo ships. Ventilation aboard ships calls for “trimming” ventilators, that is, turning the ventilating funnels away from the wind, removing hatch covers (it should be remembered that there may be additional hatch covers at the “tweendeck” level), and opening lazaret hatch doors. Engine rooms are often equipped with skylights similar to those on the roofs of buildings which may be treated in the same manner to effect ventilation.
—West Milwaukee F. D. photo
Mechanical ventilation: In addition to ventilation by natural means, movement of smoke, gases and air can be forced by mechanical devices. Fans of varying size are employed by many fire departments; these usually range from 5,000 to 15,000 cfm capacity.
Since the use of fans has become popular, there is a noticeable tendency in small fire departments to neglect natural ventilation. In fact, many poorly trained fire departments depend almost entirely on mechanical ventilation and overlook the advantage of opening windows, etc., as previously described. Smoke ejectors are valuable when properly used, but they are best used as an adjunct to natural ventilation, or in cases where natural ventilation is ineffective.
If the results of natural ventilation are not satisfactory, a smoke ejector should be used. It must be remembered that if not properly employed, they can do more harm than good. An exhaust fan will draw the smoke and fire toward the fan; therefore, the location must be carefully selected.
This problem was exemplified at a recent fire in the attic of a one-story dwelling. The firemen were able to enter the ground floor with ease, only a slight amount of smoke was present there. They placed a blower fan in the front doorway and an exhaust fan in the rear dorway. In a moment a large volume of smoke was drawn from the attic into the first floor and the firemen were driven out of the building.
Fog nozzles have been used for ventilation for more than 80 years, yet today we find many fire departments using them only for extinguishing the fire. Common fog nozzles induce a great amount of air to follow the fog stream and can move from 10,000 to 30,000 cubic feet per minute depending upon size, type, fog pattern and location of nozzle.
To remove smoke with a fog nozzle, the nozzle is held inside a window or doorway and aimed toward the outer air. Experiments in Wisconsin show that the wider the fog pattern, the greater the air movement, but the pattern should not cover the entire opening. Better results were obtained when the nozzle was a few feet from the opening than when it was close to it. The same precautions mentioned for the use of fans apply also to the use of fog nozzles for ventilation.
It should be remembered that a hose stream aimed into a window, doorway, skylight, hole or other opening has tile same effect of nullifying ventilation as if the opening had a cover placed over it. At the same time openings should not be made where they may jeopardize nearby structures by extending the fire unless adequate protection in the form of hose streams is at hand.
When holes for ventilation are cut in a floor, they should be near a window if possible. The relieved smoke will then go through the open window. If men with a protecting hose line are driven out of the building, upward extension of fire through the hole can be prevented by directing a stream from the outside through the window. It is not desirable to cut holes in the path of travel because firemen may step into them.
Whenever a hole is cut in a roof or floor, or a skylight or scuttle cover is removed, the opening should be probed with a tool or pike pole to find if there is any obstruction, such as a ceiling, below the hole. When such obstruction is found, it should be opened or pushed down.
When breaking glass, make sure no one below will be struck by the falling debris. Warning should be given in ample time.
-Photos courtesy West Milwaukee F. D.