Can you really PUSH fire through a structure?

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Permalink Reply by Larry Lasich on August 1, 2011 at 11:44pm

There is no science that shows that applying a hose stream to to the fire compartment will push it.  Hot gases and steam WILL migrate from the fire compartment to other uninvolved parts of the structure (areas of higher pressure moving to areas of lower pressure).  The heat, pyrotoxins and CO of uncontrolled fire growth are (IMO) more dangerous to potential patients than steam and soot moving away from the fire compartment, so making a transitional attack will improve the victim profile.

Also, the last info that I had heard/read was that the attack crew had about 100 seconds (for a first floor fire) to put a overwhelming amount of water on the fire after venting the entry door before the extra air being carried in causes rapid fire development.  Making the exterior to interior (transitional) attack gives the first crew that much more time.  

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Remember:  we are getting better at fighting fire, but buildings are getting better at burning.  Stay ahead of the curve!

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Permalink Reply by Brian Jones on August 2, 2011 at 7:23am

Think of it this way...When you fan a camp fire or use a bellows to fan a fire in a forge, what happens?  The air causes the flames to blow and intensify.  When you open a fog stream into a fire, the fog stream itself is actually a mix of water and air, mixed turbulently together to make a fog type stream which evaporates faster into steam, and the steam absorbs more heat.  When you apply this air/water mix at pressures of up to 120 PSI you can very well fan the flames and cause them to intensify and spread faster, causing the illusion that they are being "Pushed" into the structure.

I have always believed that using a fog stream to attack a fire from the outside is bad news, it just spreads the fire into the house.  In basic you are taught to attack the fire from the unburned to the burned, "Pushing" the fire outside.  If you think a quick exterior attack can be made it should be with a smoothe bore nozzle which will help limit the amount of air and the "pushing" effect.  Studies are being made everywhere in regards to the use of different types of nozzles and the effects their patterns have on the fire in an enclosed space, and the disruption of the Thermal Layer, and the creation of steam and its effects.  If you google this I am sure you will find tons of stuff on these studies and its great reading.

Good topic for discussion and I hope some of the respected speakers chime in here as well.

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Permalink Reply by Larry Lasich on August 2, 2011 at 11:21am

I should have qualified this by saying that we don't want to hydraulicly ventilate the compartment from the out side in, so yes, a solid stream or a fog nozzle cranked to straight stream is the only way to go.

The reason that I always go to the science is because there is a lot of myth and legend that is being taught.  Any time I have a thought about something like this, I look at what NIST is doing.

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Permalink Reply by Tom Burger on August 3, 2011 at 7:16pm

I am not a science guy. I can see the argument from both sides. However! I will tell you about a call I was on. We had a call for a house fire. I was on the first arriving engine. We had fire venting out the window of a single story house. D/A corner From that window there was a carport exposure about three feet away. As we arrived, the fire had ignited the underside of the carport.I deployed a 1 3/4 line and started attacking the carport. This took about 30 seconds or so to put out. I then turned towards the window and started attacking the fire from the exterior of the house through the window the fire was coming out of. Long story short, I knocked down all the fire I could from the window. About the same time this was taking place a second 1 3/4 line was deployed from the same engine to the window next to me. D-side. This window had to be broken out. Nobody was inside while this was going on. When we thought we had all the fire out we went around to the A-side B-corner to enter the house. We had not pushed any fire through the house. The only room damaged by fire was the fire room and closet. The rest of the house sustained smoke damaged except one room that had its door closed.

Hope that helps you out?

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Permalink Reply by Dan Rice on August 3, 2011 at 7:21pm

Craig,

I think you are most likely correct in saying that the fire spreads unchecked throughout the building where we have not yet made it. I do not agree in most cases with making an exterior knock on a fire that you plan on going interior on anyhow. With the exterior knock I feel that in most cases that immediately instills the thought that, “Now we got it knocked, lets take our time” and that my friend is dangerous. I feel that if we are going to make a knock then lets go get it and then we can assure where it is going, what it has done, and not be blindsided by finding out its already advanced beyond where we thought it was. But pushing fire through a building, in most cases no, however you must take into consideration that you are doing reverse hydraulic ventilation and that in some cases might intensify your fire in places you are unaware it has traveled. My opinion is, though you might not “Push Fire” you might as well go in and get it as long as the environment allows it! Also keep in mind that if there are victims in that structure, you will be pushing the heat and steam onto them possibly. Just a thought. Great topic though!

Be Safe and Aggressive!

Dan  

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Permalink Reply by Michael Dombroski on August 4, 2011 at 10:57pm

Hi Craig

This is a very interesting topic and is frequently debated here down under as well.  After having been led to believe that we could "push" a fire through a structure for a number of years I have observed rapid exterior "knock downs" on a number of occasions and have not seen any evidence of the fire being "pushed". 

Having said that I have seen, as you describe, the fire continue to develop from the room of origin into the hall way via open doors while an exterior attack was commenced.  As pointed out by others, use of fog can do two things as well; i) hydraulically ventilate causing fire intensity to increase, and ii) it may prevent the fire from ventilating through that window which may alter the airtrack and promote fire travel away from that opening. 

If the room is isolated, i.e. door closed, an exterior attack is very effective and I have seen training videos of the Sweedish fire fighters extinguish room fires externally with a fog attack extremely effectively.

Given that it's not often we are able to determine whether the door is open or closed I prefer the interior attack.  This assures that we are preventing fire spread and is putting fire fighters immediately at the point where a search for victims should commence.  It is also placing a hose line near the room of origin ensuring that fire fighters deployed for primary search have some protection between them and the fire right from the outset.

The thing that will have the greatest effect of moving a fire through a building is ventilation, and its unplanned and unco-ordinated  use will be far more dangerous than having a crack at the fire from the outside on the way past.  Of course it goes without saying, that its either interior OR exterior.  When we have guys on the inside, we should not be poking a hose through the window, no matter how great the temptation.  I have seen fire fighters burnt a number of times due to this.

Great topic and I will be reading the replies with a great deal of interest.  Thanks.

 

MD - New Zealand

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Permalink Reply by Craig Hicks on August 4, 2011 at 11:22pm

Thanks for all of the replies so far. At a department I worked at a few years ago, we had 7 firefighters on duty divided between three stations. Three at the main station, and two at each substation. It was not uncommon (but also not the norm) for us to make a quick knockdown from the outside with a hoseline while waiting for the next company to arrive as backup before going in and finishing the job.

 

Next point. A fire when in the free burning phase puts out X number of BTU's per minute that it burns. If you did happen to have the opportunity to make a quick knockdown from the outside, lets just say you cut 100,000 BTU's from the fire. That's a 100,000 BTU's that aren't heating up anymore material and stopping that much fire.

 

That being said, if there was a victim in the vicinity of the room of fire, you just pushed several hundred gallons of steam right down on top of them. Reminds me of the Houston video that shows several minutes of a house burning and the firefighters seemingly not doing anything, when all of a sudden two firefighters pop out the front door with a victim. The victim survived and recovered. An exterior attack in that case would have been bad. Venting the fire TO the victim may have claimed their life.

 

Really enjoying all the replies so far. Not disagreeing with anyone either. Just like to hear the discussion.
Thanks

Craig

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