Firefighting 101                                                         by:  Dan Howell

Ventilation - What, When, Where and Why?

Ventilation is one of the most important fireground operations. Proper ventilation aids firefighters in all aspects of interior operations, including rescue, fire attack and overhaul. Yet, ventilation is one of the most neglected and misunderstood operations on the fireground, often being delayed or ignored completely. As a result, important advantages that ventilation could provide are lost as the scene develops. It should instead be the goal of firefighters to make use of these advantages with proper and timely ventilation. This article begins a series of articles that will discuss many aspects of ventilation and answers the questions of what, why, when and where.

Ventilation is the systematic removal of smoke and heated fire gases from a burning structure. Some of the forms ventilation takes are cutting the roof, breaking glass, and setting up ventilation fans. Ventilation makes use of a tendency of fire to follow the path of least resistance and takes advantage of the behavior of heated gases, which will rise until inhibited by the confines of the structure. When heated gases are released to the atmosphere by ventilation, conditions inside the structure improve as heat levels are reduced, fire spread is decreased and visibility is increased. There are four basic situations in which ventilation is performed: fire control, fire attack, rescue and overhaul. Each situation has individual objectives and will be examined separately to answer the remaining questions of why, when and where.

Fire control represents the necessary operations to reduce fire spread or the elimination of conditions that could lead to dangerous fire events such as flashover or backdraft. Three examples of using ventilation to aid fire control are found during backdraft and flashover situations as well as when attempting to slow down the horizontal spread of fire and fire gases. When backdraft conditions are present, the structure must be vented before entry at the highest and safest point above the fire. This will allow the heated gases to escape and the flammable atmosphere to ignite in a more controlled manner. Entry should be delayed until there is an adequate amount of visible fire to indicate that backdraft conditions have been removed. Flashover conditions requiring ventilation are equally dangerous and may be performed before or after entry. If firefighters operating on the interior suddenly find themselves operating in increasing levels of heat, they should consider breaking windows to reduce the amount of heat that mushrooms to the floor. If conditions continue to deteriorate, the firefighters should move to a safer location. If exterior firefighters recognize high heat conditions on the interior, they should initiate ventilation on the burning side of the structure. This will provide additional ventilation for the fire and reduce fire spread in the direction of entering firefighters.

When attempting to reduce horizontal fire spread, ventilation is an invaluable tool. By venting as close as safely possible to the fire, the mushrooming of flames and heated gases can be reduced. This will reduce the horizontal spread of the fire. It will also reduce the build-up of gases in lower portions of the structure. The advantages of this ventilation are especially evident in attic fires and older balloon construction where the fire has penetrated into the walls and is spreading rapidly into the attic. Therefore, when faced with these situations, firefighters should make every attempt to provide the necessary ventilation.

Providing ventilation for fire attack is also referred to as “venting for fire”. When firefighters enter a structure to attack a fire, they are faced with zero visibility and high heat conditions. Furthermore, when they attack the fire, steam produced from their attack displaces the higher heated gases and conditions at the floor will worsen. By providing ventilation that is coordinated with fire attack, interior conditions can be greatly improved for the firefighters. This ventilation should be provided by the time that the attack crew reaches the fire and if possible, should be established before entry. The structure should be vented on the burning side so that the fire will not be spread to other portions of the structure. These openings will also allow the fire attack to push the steam and heated gases away from firefighters. Venting for fire attack will normally involve the breaking of windows and opening exterior doors near the fire. Any windows with hot, pressurized smoke behind them should be vented. Windows that have already vented should have any remaining glass fully removed to improve their venting performance.

Ventilation provided to assist rescue operations is also referred to as “venting for life”. While performing search and rescue, the lack of visibility and operations in close proximity to the fire, again, challenge firefighters. As a result, firefighters will find themselves in need of good ventilation. Venting for rescue differs from venting for fire attack because the priority does not rest on saving the structure. The search and rescue crews should break any windows and make any openings necessary to complete their search. These vents will help improve visibility, reduce the build-up of heat, give the firefighters a chance to orientate themselves and provide for additional escape routes. If the structure is ultimately lost, the incident will still be a success if firefighters complete their search and save any trapped victims. For these reasons, firefighters should not be afraid to ventilate as they perform search and rescue if interior conditions make it necessary.

During overhaul, large volumes of smoke and heat will remain in the structure requiring adequate ventilation. Ventilation during overhaul is performed after knock down has occurred and will be less destructive than ventilation to support rescue and fire attack. During those operations, large open vents are mandatory. Often, during overhaul, simply raising windows will provide sufficient ventilation. During overhaul, ventilation fans are good tools to supplement any natural air currents in the building since the fire is no longer creating its on currents. Effective ventilation during overhaul improves visibility, allows firefighters to more efficiently locate any remaining hotspots and reduces the temperature of the interior.