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MFA #8: Timing is Everything - Delivering the correct one-two punch of water and air

I used the term “Vertical Vandalism” as the title of my most recent post 

(http://community.fireengineering.com/profiles/blog/show?xg_source=a...), leading some to believe that I was suggesting we abandon that tactic.  In fact, my specific wording was that we could stop “routinely” creating damage in the pursuit of increased airflow to the fire compartment, and that even “reducing” such actions would be an improvement.  While I further suggested that, all things considered, vertical ventilation may be the worst method for removing products of combustion, unless there is a handy hatch or door to open as in the NIST/UL live fire experiments, I did not say it should never be performed. 

As with most blog titles, I was just trying to inspire interest and discussion regarding an idea, in this case the following: Fire dynamics research has demonstrated that any airflow to and from a ventilation limited fire causes more heat to be created than can be released, so it should be minimized until after water has been applied to the fire.  With combustion then controlled (a.k.a. cooled, extinguished, knocked down), is cutting a h*** in a roof, with all of its related difficulties, dangers, and damage, necessary, especially when there are better (i.e., easier, safer, faster, less destructive) methods?  What some of the readers' responses showed me was that there are not only fervent advocates for vertical ventilation in general, but that many have persistent and strong beliefs in its value prior to fire control.  

Let’s put my radical views on cutting roofs aside for now, and take a look instead at the ideal timing of this tactic.  Now, even the most ardent ventilation advocates should agree with the need to perform it in close coordination with extinguishment efforts.  We wouldn’t open a roof before the Engine crew is also ready to go to work, and shouldn’t do so long after the fire is out.  It is also a given that the products of combustion ought to be removed from the interior as soon as possible, though creating more in the process than can be released is a losing battle.  So, when, in relation to the process of stretching and operating interior hoselines, will ventilation actually improve interior conditions? 

Research using live burns has repeatedly shown that opening up a building containing a ventilation limited fire does only bad things until after water is applied to the burning fuel.  Many prestigious organizations, such as NIST, UL, FDNY, ISFSI, LACoFD, and NFPA (and these are just the ones that can be listed by their initials), have recommendations and/or policies and procedures that recognize that ventilation of a compartment on fire is harmful if performed before water application.  This includes attic fires, to which vertical ventilation caused such increased heat production that the products of combustion were not only exhausted upward, but forced downward through any openings into the rooms below.  

Even in the controlled setting of a staged fire in a laboratory, there were many factors that impacted the effects, good or bad, of ventilation, including vent location vs. fire location, fire intensity, and horizontal vs. vertical.  Of note, while creating a vent opening remote from the fire, such as by leaving the front door open upon entry, may not cause a fire to progress to flashover for a minute or so, a vertical vent path created directly over a fire was shown to increase fire intensity to that deadly stage within 10-15 seconds.  I have read various misinterpretations of the ideal point at which the fire should be vented, including “when the hoseline is in position” or “when the Engine crew has water”, but it is the actual cooling of the fuel that changes the conditions in favor of allowing for the safe addition of airflow to the fire compartment.  Quite simply, the direction provided by the fire dynamics research is to wait for the water to do its job before opening up. 

Despite these experimental findings, others in the fire service promote ventilating prior to the application of water to the fire as they still believe it will improve conditions for advancing interior firefighting crews and other occupants.  Ok.  I know better than to get in the way of someone with a chainsaw or an axe.  Their passionate defense and promotion of early vertical ventilation, though, ignores the substantial evidence that such actions create more difficult, and even deadly, conditions for the very persons they are intended to protect - firefighters and civilians.  Yes, removing the smoke, steam, and heat remaining after a fire is knocked down is a vital tactic that improves conditions for everyone inside, and we must remain adept at its timely and efficient performance.  We can argue another day about the best method for accomplishing ventilation, but it must be delayed until water is applied to the burning fuel.

My goal with this series is to spread information on modern fire attack principles and practices.  This is a conversation, and you all have the opportunity to challenge or support my positions and interpretations, and thereby add to our collective understanding.  As I mentioned in my initial posting, even cutting down (no pun intended) on harm in the name of ventilation would be an improvement.

MJC

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