Backdraft or Smoke Explosion
I read with great interest the photostory on the front page of Firehouse.com this morning. It is the one where several brothers in PA narrowly escaped inury from a Backdraft explosion. I'm starting this thread because it appears from the pictures and from what everyone was doing that "everything was being done correctly." I can't say that I would've done anything different...however, I have a couple of questions. This is not a critique...I'm trying to learn from these guys so that nobody on my crew gets hurt.
First of all...was the explosion a true backdraft, or was it a "smoke explosion," where the smoke fell within it's explosive ranges down in the basement? How do we keep ourselves from getting into the same position? Would it have helped to ventilate more prior to the first hoseline entering? From the description, it seemed like it would have appeared to be a fire on the second floor? What other size-up cues can be looked for?
Again...this is not a critique. It is intended to figure things out from a size-up and tactics point of view to prevent injuries and deaths.
Stay safe, everyone.
Backdraft or Smoke Explosion Reply to Thread
Vincent Dunn has documented the difference; Check on his web site I believe he has it posted their.
Backdraft and Smoke Explosion
Sorry for my late entry into the discussion but I have been on the road.
First to address the issue of definitions, there are a number of different definitions for fire behavior phenomena. However, I would agree that Karlsson and Quintiere provide a good starting point.
Flashover: The transition from a fire in the growth state to fully developed stage. Adequate oxygen is required for this to occur (either as part of initial development in the compartment or subsequent to increased ventilation)
Backdraft: Ignition of flammable products of combustion and unburned pyrolysis products from a underventilated fire. This may occur as autoignition or piloted ignition. However, conditions for a backdraft typically involve high temperature and limited air supply prior to occurance.
Smoke Explosion: Piloted ignition of flammable products of combustion or pyrolysis products that are premixed with air and within their flammable range (not a common event).
For a more detailed discussion and case studies, see my series of articles on extreme fire behavior on this web site.
The difference between a ventilation induced flashover (flashover following an increase in ventilation when the fire is ventilation controlled) and backdraft is the rate of increase in energy release (backdraft generally has a more rapid increase in heat release rate and subsequently is often more violent, particularly when confined). However, a vent induced flashover is also quick and can result in a considerable "push" of hot gases. It is difficult to differentiate between these phenomena on the fireground (and it may not be that important as the initating factor and mitigation tactics are essentially the same).
Looking at the photos in this incident, I would guess (based on the limited information available) that this was in the what the Swedes would call the "gray area" between vent induced flashover and backdraft. In either case, cooling the gases (i.e. indirect attack) and ventilation (a bit tougher given the fire location) provide two tactics to mitigate the hazards presented.
The first photos do not show smoke from the basement, but smoke, air track, and heat indicators may have been visible on closer examination (limited smoke under pressure, stained and/or cracked windows, air track into the basement, etc.). It is always difficult to read the fire from a still photo, but looking for critical cues provides good practice and a starting point for discussion.