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A number of changes have had an impact on the fire service in recent years: reduced manning, energy conservation measures producing "tight building syndrome," increased awareness of property conservation, improved fans and heavier fuel loads of plastic producing toxic smoke. All of these factors affect one of our primary firefighting tactics...ventilation.
Ventilation can be defined as the process of removing toxic products of combustion and replacing them with fresh air. It can be...but I like my definition better. It keeps me focused on the critical nature of the process. To me, ventilation is an ongoing battle between the fire and the firefighters for control of the building. The fire is constantly pumping the building full of toxic and flammable gases. Fire-fighters must wage war against the fire, using the right weapons at the right time to succeed. Remember, this is war, "The War That Never Ends," and if you win, you save the building and avoid casualties. If you lose, you will be driven out of the building and can suffer many casualties.
Reasons For Ventilation
There are two main reasons for performing ventilation: venting to let attack teams enter and operate for attack within the structure, often called venting for fire, and venting a specific area to provide fresh air for breathing and to improve visibility while searching, known as venting for life. Unfortunately, the distinctions are lost on many, as is even the need for ventilation in the first place. You see, the universal use of self-contained breathing apparatus (SCBA) has some people thinking that ventilation is less important than in the past just because they can breathe. There are problems with this thinking. First, it totally ignores any victims still in the building. They don't have masks! Second, it assumes that the firefighters' masks will always protect them. This is not always so.
Photo courtesy of Photos Unique/Beth Cagle-Webster
Firefighters operate on the roof during a blaze that eventually destroyed a school administration building in Lake Orion, MI, on Feb. 8, 1997. Ventilation is an ongoing battle between the fire and the firefighters for control of the building.
Several firefighters have been killed in recent years when they experienced mask problems in contaminated areas running out of air, becoming entangled or having the facepieces pulled from their faces. At the scene of one such firefighter fatality, the process of "ventilation" had been undertaken, with many windows on the upper floors opened by the interior forces from top and bottom, textbook style. The glass damage was minimal...the firefighter is dead! The third problem with ineffective ventilation is the buildup of heat which results when venting is not prompt and effective. The mask protects you against smoke but not from heat.
Firefighters determining the proper amount, type and timing of ventilation must evaluate many factors before beginning their tasks. Should the ventilation be vertical (roof), horizontal (window) or a combination of both? Will natural air currents suffice or should the process of ventilation be expedited using mechanical ventilation? If mechanical ventilation is used, should it be positive or negative pressure? Should the venting be started immediately or be delayed until the hoseline has water on the fire? The answers depend on the circumstances determined during the size-up, as well as equipment and manpower constraints, and building features and the intended purpose of the ventilation: venting for fire or venting for life. The most important concept to remember, however, is that the ventilation must be of sufficient volume to win the battle with the fire.
The damage that results from our efforts should be commensurate with the amount of damage the fire is causing and the extent of the life hazard. If the fire is a low-intensity mattress or other smoky, low-heat fire like food on the stove windows should be opened, not broken. Mechanical ventilation is often beneficial in moving this cool smoke and poses few of the dangers possible when using fans during working structural fires. Window venting is the most suitable type of ventilation for most fires in houses and similar-size structures which have high window-to-room-size ratios. Window venting is very quick and relatively easily performed, and can be targeted to specific rooms. When interior forces are able to operate in the building, they can evaluate the conditions to decide to vent the windows. In the past, a guide I used stated, "If you can stand up long enough to manipulate the locks, raise the windows. If you can't stand up that high or for that long because of heat conditions, it's time to take the glass." While this is still a good rule of thumb, a few additional points should be made.
First, you must have an idea of what progress fire control and search efforts are having. For example, if the fire seems to be under control and the primary search is complete and negative (no victims found), you may want to raise the windows instead of breaking glass, even though the area is moderately warm or even hot. Con-versely, very dense smoke conditions present when there is a strong potential for either locating a victim or fire extension justify breaking glass even in the absence of extreme heat.
The second factor to consider when deciding whether to break glass or not is that conditions are likely to worsen before they get better. Venting not only provides fresh air to trapped victims, it improves conditions for firefighting, leading to earlier control and less likelihood of firefighters getting disoriented or trapped if hoselines are operating on the fire. Breaking glass provides double the window-opening area that raising double-hung windows does. Since these are the predominant windows present in the majority of residential buildings, firefighters must be prepared to break glass if conditions require. The lives of occupants, as well as firefighters, hang in the balance.
Breaking glass, of course, is not something that can be reversed once it has taken place. Firefighters must properly time their ventilation efforts. Venting too early will allow the fire to extend, while delaying ventilation will subject firefighters to unnecessary punishment from heat. Generally, venting for fire should take place just as the hoseline begins its attack. This is best coordinated via radio. A member of the attack team should give the word to "take the windows" just prior to the nozzle team opening the nozzle. If radios are not available, the person doing the vent should wait until the sights and sounds of hose stream operation steam, and fire knockdown confirm the line has indeed begun operating. One exception to this sequence is made in the case of tightly sealed areas, typically glazed with double- or triple-pane energy-efficient windows. In this case, the sudden admission of oxygen as the attack crew enters can have catastrophic results; sudden rapid fire development or even backdraft are possible. When energy-efficient windows are encountered, window venting should be undertaken as soon as possible, while the attack team is in a safe area, preferably behind a closed door. If this is not possible, it may be desirable to delay venting until after the hose stream has thoroughly cooled the fire area.
One type of ventilation that should never be delayed is vertical ventilation. Vertical ventilation is critical in larger, multi-story buildings, such as apartment houses, schools and office buildings, which have stairways that serve as the occupants' primary escape route. At house fires, vertical ventilation is not a primary tactic because of the time and effort required to reach and cut through the roof material and the limited benefit to be gained if the fire is on a lower floor. In houses, the windows usually are sufficient vent points, given the relatively small areas and fire loads involved. Larger buildings have relatively larger floor- area-to-window-size ratios, higher life hazards and often heavier fire loading. In addition, they typically have stairways that go all the way up through the roof, ending in a small stairwell structure called a bulkhead, or are provided with glass skylights over the stairs to let sunlight in. These features make vertical ventilation at these structures far simpler and faster than cutting the roof at a house fire. Firefighters merely have to force open the door on the bulkhead or break or remove the glass in the skylights to accomplish the job of vertical ventilation at these structures. This critical task must begin immediately since the stairway, which dozens of occupants may be using for escape, also is the fire's chimney, resulting in rapid spread of smoke, heat and fire to upper floors. Vertical ventilation prevents mushrooming on upper floors.
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.