As we continue to discuss and explore modern fire attack (MFA) methods, I thought it was time to start talking about what may be the greatest tactical change: we can stop routinely cutting holes in roofs and breaking windows of burning buildings! (And by "greatest" I mean the one offering the most benefits and challenges.) Now, you can read all of the recent fire dynamics research reports and analyses yourself and never find that recommendation, but I see it as a logical and practical progression of the structure fire fighting improvements already being implemented based on those experiments. I believe that eliminating, or even just reducing, the performance of vertical ventilation will significantly reduce risk, free up resources, and improve our efficiency on the fireground.
Here’s my reasoning: Live fire tests demonstrated that creating a ventilation opening above or beside a fire in a compartment increases the heat output of a fire, without improving conditions. The more ventilation, the hotter the fire becomes. Water application, on the other hand, has been shown to quickly and extensively cool the interior environment, even if initiated before entry (See MFA #4: The New Rules at http://community.fireengineering.com/profiles/blog/show?id=1219672%...). These findings lead to the recommendation that ventilation not be performed until after the burning fuel has been extinguished, so it will not react to increased air flow, and then only for the purpose of removing smoke and steam. Therefore, ventilation is no longer intended for fire control, but is an overhaul tactic, and should be considered as such when we make risk/benefit calculations regarding the best method for its accomplishment.
It was previously taught that ventilating a fire improved conditions for occupants and firefighters. In addition, it was emphasized that any fire that had “darkened down” due to having consumed the available oxygen within the structure - what we would now call “ventilation limited”, and which describes the stage of many fires upon our arrival - must be opened at the highest possible point in order release the pent-up products of combustion and prevent a backdraft explosion. With these motivations, it seemed reasonable to use whatever means necessary to quickly create openings in burning buildings, including destroying windows and damaging rooftops in the process. Immediately sending two or more firefighters above a fire and having them cut a h*** in the roof(s), and then the ceiling(s) below, at the time was thought to be an appropriate and necessary utilization of fireground resources (in this case, personnel, time, and luck). Based on the knowledge at the time, it was calculated that the harm inflicted to the building by this aspect of the firefighting process was justified by the harm prevented by more rapid fire control. Indeed, many of us have developed impressive skills in the performance of this difficult and hazardous process, and are rightly proud of those abilities.
With recent live-fire experiments instead demonstrating the necessity of limiting, to the extent possible, the amount of air flow to a fire involving today's contents, the previous ventilation mandate has been repealed, and we must re-evaluate our approach. No longer is there an urgent reason to commit personnel to the time-consuming, dangerous, and, as we now know, unproductive process of opening rooftops, or even the extensive removal of windows. Certainly the increase in visibility and decrease in temperature that result from post-extinguishment ventilation are beneficial, but with the fire at that point already controlled, we no longer have the justification of causing damage to prevent damage. Many of us veteran firefighters have found it necessary at times to step in to prevent over-eager rookies from breaking windows long after a fire is extinguished, and this new insight should inspire the entire fire service to undertake a similar reconsideration of what have become our routine actions.
My personal misgivings about vertical ventilation are a recent development, arrived at only after repeated exposure, over several years, to the findings of the fire dynamics research that consistently contradicted any claims of its benefit. In fact, I fought hard, for many years, to increase the use of ventilation. For some departments with whom I served, a h*** in the roof was usually there only because a fire had burned through, and we struggled to improve our ability to perform vertical ventilation in a more timely manner. Training, equipment improvements (specifically, motorized cutting tools), SOPs, critiques, and more training eventually brought us to the point of integrating this step into our fire suppression efforts, though we were often holding back on entry and water application as we focused on that tactic. Now I work with firefighters who can vent a roof almost as quickly as we can stretch hoselines, and our challenge is to restrain them until water flow begins. For example, I was once on the first-in Engine with my current Department at a 3rd floor garden apartment fire when, as we searched the unit, the smoke cleared and a shaft of light from the ceiling – or, at least, from where the ceiling had been before the truck crew cut a vent h*** in it - illuminated the site of where a small fire had self-extinguished. And we on the Engine had arrived on-scene first!
Considerations about which method to utilize for smoke removal need to include firefighter safety, ease and speed of performance, collateral damage, and effectiveness. Vertical ventilation is, in fact, the most efficient natural method, but only in the narrow context of comparing the passive movement of smoke between either vertical or horizontal openings. In other words, if you have ready-to-open exhaust paths to the side of or above a fire, as the live fire experiments had built into the structures they were using, the rooftop route removes the products of combustion better. But, while hot gases will self-exhaust upward more quickly than laterally, and will do so even without the assistance of fans or hose streams, actually creating an opening in a roof and ceiling(s) of sufficient size to allow for this natural movement, in the best location, and in a timely manner is, as we all know, no easy task, and not without significant drawbacks. Furthermore, with a charged hoseline already in hand, and likely a portable fan on the rig, why should we limit ourselves to natural ventilation when we can augment and direct the exhaust of products of combustion? Certainly, any existing rooftop openings that allow the passage of smoke (e.g., bulkhead doors, hinged skylights) should be utilized, but, lacking the presence of such vents, I would argue that the risk, effort, time, and destruction entailed in performing vertical ventilation renders it far from the most efficient method.
Obviously, getting to and operating upon any roof is dangerous, designed as they are for shedding the elements rather than supporting groups of heavily-equipped and vigorously working firefighters. Such factors as pitch, darkness, smoke, and precipitation, frozen or otherwise, commonly add to the hazards, while fire burning below multiplies them. Once the roof is successfully mounted and footing is secured, actually penetrating the multiple layers of roofing material, and avoiding structural (supporting) members, all the while coordinating theses actions so that they are completed immediately after the application of water, requires yet another feat of skill, daring, and, sorry to say, luck (that there was not a rain roof, collapse, miscommunication, or any other mishap).
The preventable damage issue is significant. A friend who makes his living as a remediation contractor, making repairs necessitated by fires and firefighting, informed me about the downstream costs associated with our line of work. Boarding up a broken window at about $50.00, or a roof vent at $100.00, is just the beginning. When damaged, modern windows need to be replaced in their entirety, with a unit cost in the $200.00 to $300.00 range, and installation easily doubling that price, accompanied as it often is by the need to replace/repair trim, siding, etc. On the roof, closing the h*** we make is relatively straightforward, especially if we keep to our textbook 4-foot by 8-foot size, unless rafters or, God forbid, trusses are also cut, necessitating their repair. The real money is typically spent to replace the shingles on the entire surrounding slope, or “field”, if not the whole roof, in order to restore a uniform appearance. This can easily run into several thousands of dollars. All of these costs, of course, assume we were successful in checking the fire damage before it rendered the structure unsalvageable, a condition reached quite rapidly in many cases.
The alternative approach to ventilation after fire control is to choose an exhaust opening, which the fire has often already done by causing a nearby window to fail, or by opening a window if all remain intact, and then directing a water stream out of the window to pull, or placing a fan at the entry to the fire area to push, the smoke out. In this manner, the products of combustion are removed from the structure in a rapid and controlled manner, and via a more efficient and safe utilization of personnel. (The subject of Positive Pressure Ventilation [PPV] will be the topic of a future MFA post, but keep in mind this point: if conditions worsen after ventilation is performed, a fan can be turned off, but a cut roof cannot be closed.)
Our newfound knowledge of fire behavior has allowed us to revise our approach, in the process making firefighting a little safer, easier, and faster, though it remains, admittedly, far from safe, easy, or fast.
PS: I appreciate the support and interest from the hundreds who have been following this series on Modern Fire Attack, and would encourage anyone who notices anything I may have left out or misinterpreted to utilize the handy Comment box that follows this post to add their voice to this discussion.