Coordination is arguably the most influential and critical of the Four Tenets. There are three elements of ventilation that determine its impact on the fireground: timing; location; and amount. While there is a set of fundamental parameters for which they follow, each of these variables is inherently unique to every incident. Communication with the interior crews is essential to properly addressing those factors and ensuring that any action taken will facilitate a specific objective, providing a tactical advantage, and is aligned with the mission – preserving life and property (Grimwood, 2008). As Lt. Rob Brown, FDNY (2016) states, “We must make decisions based on the operational needs, not the individual needs. Doing so, he explains, requires the utmost “positional discipline.” The decision to ventilate, therefore, must be based upon the progress of the engine company, the ventilation profile and how additional ventilation will affect conditions and operations.
The most prominent misconception, regarding ventilation, is its thermal impact. The belief, within the fire service, has been that ventilation reduces temperatures within the area of involvement. That assumption was derived from the distinctive relief felt when vertical ventilation takes place. By creating a dedicated, low-pressure outlet, vertical ventilation alters the neutral plane and causes it to rise. The sudden lift and redirection of heat is responsible for the perceived drop in temperature. If an opening exists below the neutral plane (open door or window), it will then become an inlet. The uni-directional flow (upwards of 20mph) will proportionately draw fresh air into the space as the contaminated air is discharged. While the evacuation of smoke and fire gases provides an initial benefit, the additional supply of oxygen will begin to accelerate the combustion process; increasing the heat release rates and causing the temperatures to rise.
As the fire continues to develop, its (by)products can overwhelm the vertical opening, no matter how large it may be. The capacity of modern combustibles (btu and hrr) is nearly insurmountable – two to three times that of the Legacy Era. Because fires have become so overly fuel-rich, ventilation alone cannot transition them to a fuel-limited state (Kerber, 2011). This fact exposes another misconception, regarding its ability to prevent the spread of fire by localizing its growth. Vertical ventilation, on its own, does not adequately possess the sustainability to contend with the fire’s energy output and should not be employed as a long-term means of containment. If water is not promptly applied to the area of involvement, cooling the fuel packages and absorbing the heat being generated, the benefits of vertical ventilation will be short-lived.
Ventilation has a finite window of effectiveness, as the fire will not immediately react to the change. The time frame is dictated by the fire conditions, the ventilation profile and the opening(s) created. The higher the interior temperatures and the ventilation point, the greater the air flow and the closer it is to the fire, the faster it will respond. As the environment continues to evolve, fires are reacting to ventilation at an accelerated pace; diminishing that “grace” period (>75% reduction from the Legacy Era). Once it expires (approximately two to three minutes), conditions within the flow path will abruptly deteriorate. The area will become untenable, potentially with little to no warning, and a (ventilation-induced) flashover will be imminent – as little as ten seconds (Kerber, 2011).
In the UL report, The Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction, Steve Kerber (2011) simply explains that if air is added to the fire and water is not applied, in the appropriate time frame, the fire gets larger and the hazards to firefighters (and victims) increase. As the old saying goes, “If you put the fire out, everything else gets better” (Norman, 2012). As a basic, guiding principle, ventilation should not occur until fire attack is underway or the flow path can be effectively managed until that time, unless there is a known life hazard (VES scenario). The success of ventilation, consequently, is contingent upon the ability to synchronize its execution with confinement and extinguishment efforts.
To be continued…
Grimwood, Paul. (2008). Euro Firefighter. United Kingdom: Jeremy Mills Publishing.
Brown, Robert, Smart 4 Life Lecture, April 16, 2016.
Norman, John. (2008). Fire Officer’s Handbook of Tactics, 4th Ed. Tulsa, OK: PennWell.
Kerber, Steve. (2011). The Impact of Ventilation of Fire Behavior in Legacy and Contemporary Residential Construction. Retrieved from http://www.ul.com/global/documents/offerings/industries/buildingmaterials/fireservice/ventilation/DHS%202008%20Grant%20Report%20Final.pdf