Continuing my theme of rebutting the new reasons traditionalists are coming up with to avoid changing their approach to firefighting, given that many of its original justifications have been effectively disproven, this post will focus on the air flow component of the “How to Control Combustion” equation, commonly referred to as tactical ventilation. I addressed the resistance to the use of exterior hose streams in MFA #32: Changing the Rules – New excuses for old habits (athttp://community.fireengineering.com/profiles/blog/show?xg_source=a…), and already did a five-part series on the modern view of tactical ventilation (beginning at http://community.fireengineering.com/profiles/blog/show?id=1219672%…). This post will therefore focus less on its lack of scientific basis, and instead on the attempts to justify the persistence of this practice beyond its proven usefulness.
Ventilation has been a tactic that, for decades now, we were repeatedly encouraged to perform more often, and many a firefight that went poorly was blamed on its delay. Even at fires that were put out fairly directly, the timing of ventilation was usually a topic of discussion and concern, resulting in efforts to ensure its more rapid performance and closer coordination with other activities. The focus on this intervention was due to the belief that it could direct the products of combustion out of the structure, clearing out smoke and heat ahead of firefighters searching and advancing hoselines, and generally improving interior conditions. With the combination of such promised benefits and ease of performance, at least for horizontal ventilation, it was understandable that this would be a standard and favored technique.
We now know that increasing the air flow to a fire produces more heat and smoke than can be released, unless it is propelled outward by the use of a fan or coincidentally opportune wind direction. With passive ventilation, whether horizontal or vertical, the smoke and heat being exhausted outward is matched by that spreading inward. While the propensity for ventilation to increase fire intensity had long been acknowledged, even amongst its most fervent advocates, the significance of the worsening of interior conditions was not previously appreciated. Fire dynamics researchers have not so much informed us of something we didn’t already know, but instead demonstrated that the magnitude of the resulting deterioration was far beyond that which had been recognized. The evidence is irrefutable of the remarkable increase in the production of heat and smoke that follows any increase in air supply to a fire, and can no longer be dismissed as the minor side effect of an otherwise useful technique. Even when properly performed, traditional ventilation maneuvers will make things worse. When poorly performed, such as without immediate water application to the fire, it can kill everyone within a burning building.
(Positive Pressure Attack [PPA], a technique that utilizes fans to direct air flow through a burning structure and out of an exhaust route near the seat of the fire in order to augment the release of products of combustion, can be the exception to the “ventilation makes things worse” rule. Though it still results in the increase of the rate of combustion, the products of that reaction – smoke and heat – are pushed out of the building, instead of being allowed to spread back within, and it actually accomplishes the results we had been intending with passive ventilation. That is, it improves conditions for entering firefighters, who are essentially provided with a flow path to follow to the seat of the fire. When used after fire knockdown, this same process is called Positive Pressure Ventilation [PPV]. Both of these versions of active ventilation are much more effective than passive ventilation, while at the same time more complicated and, at least for now, controversial. For more information on these approaches to enhancing and controlling the exhaust of products of combustion, those interested can find a training program based on the latest research at http://ulfirefightersafety.com/projects_blog/ul-fsri-launches-posit….)
So, faced with the knowledge that a technique is not only ineffective for the purposes for which it was intended, but is actually harmful, how do those who still hold this tactic in high regard respond? Apparently, they attach a warning label. Demonstrating verbal hedging any federal agency would be proud of, the typical cautionary statement regarding performing ventilation now goes something like this:
“Ventilation can make conditions worse, so be careful.”
Of course, the newly proven dangers of this tactic are only incompletely conveyed by this advisory, or similar statements that it must be “closely coordinated with extinguishment”, or to “make sure the line is ready before taking a window or opening a roof”. While in no way inaccurate, they are so vaguely worded as to suggest the need for less caution than the research showed was necessary. In fact, increasing the air flow to a fire should not be allowed until the fire is extinguished. We can certainly debate the definition of that end point, such as whether it is sufficient to merely knock down the visible flames, and it likely does not require the complete elimination of combustion to the point of accomplishing overhaul, but the key and unarguable principle here is that the fire must no longer be in a state that would react to increased ventilation.
In addition to failing to impart the danger inherent in this maneuver, these tepid advisories misleadingly imply that it should be performed immediately. I would suggest instead that the demonstrated risks of performing this action prior to fire control (i.e., death by flashover) combined with the benefits of water application (immediate reduction in interior temperatures) render it a tactic that can safely be delayed for the short time it takes to confirm fire knockdown. Though the exhaust of heat and smoke remaining after extinguishment is certainly an important process, it’s not one that requires split second timing, especially given the risks of any error in that timing. Keep in mind, too, that while ventilating a still-burning room might result in an impressive discharge of smoke and/or flames (which, unfortunately, is matched by the heat and toxins that are spreading back into the structure), merely breaking windows of an extinguished fire allows for a lazier release of smoke, then consisting of less heat and more water vapor. Cutting holes in roofs is a lot of effort for not much better effects. Those who wish to rapidly clear out the remaining products of combustion would be more efficient spending their efforts setting up for PPV, let the interior crew break out the windows when ready, and turn on the fan at the sound of glass breaking or when so directed.
There are many other examples of traditionalists attempting to fit the square peg of habit into the round h*** of facts. I once heard a respected (by me and everybody else) fire service instructor, while arguing for interior instead of exterior attacks, suggest that flow paths might be avoided by moving to the side of a room between the fire and the exhaust site. Unfortunately, the products of combustion moving from the fire room to the outdoors would first completely fill the intervening room where firefighters were located, leaving nowhere to hide. I also recently attended a presentation by a seasoned and capable truck officer from a medium-sized midwest city who rationalized that, since smoke is actually unburned fuel, then this justifies its immediate removal to protect entering firefighters and civilians. Unfortunately, passive ventilation does not accomplish this, and instead just causes the production of more “fuel”.
We have been presented with compelling evidence of the need to change our tactics, but remain embroiled in discussions about the necessity of doing so. Misguided dogma continues to be professed, and disproven beliefs are being replaced with alternative rationalizations, all in an attempt to avoid the abandonment of the familiar. Like it or not, the new approach not only has a strong scientific basis, but the resulting changes are logical, practical, and actually easier than the methods being replaced. The time will come when not using an exterior stream when the opportunity presents, or increasing air flow to a fire before applying water, will be recognized as the mistakes they are.
We can keep trying to come up with new excuses, but change will eventually no longer be optional.
The author can be reached at firstname.lastname@example.org