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Permalink Reply by Chris on August 7, 2009 at 4:33pm

Hello Aussie fireman,

I will try and help with this question the best that I can. As you must know, heat and smokes natural progression is to rise, so, basically by cutting a hole in the top side( roof ) directly above the fire, it allows for heat and smoke to take it's natural progression (up), inessance keeping the fire contained to that area, and not having it spread horizontally across the ceiling and or roof space as it would if it had no other place to vent to. We try to only employ this tactic when the fire is a top floor fire, on in single story structures, we would not employ this tactic on a first floor fire, in a 2 story structure for that would aid in the fire spreading up to the upper floors.

As for the trench cut, that is employed in longer buildings, with fire traveling horizontally to the unburned section, you would bascially cut a large long hole from peak to the bottom, so when the heat and fire got to this location, the theory is that it would go up and out, and not continue horizontally to more of the unburned section.

You see most pics and video with a good top side vent with a lot of smoke and or fire coming out under pressure, that is a good hole, so now instead of all of that being held inside, it is not venting out the hole. Also, after we cut the hole we always try (pending conditions after the hole is cut) to reach down in with a hook or pike pole to push the ceiling down to allow those products of combustion to escape from that location.

Hope this helps.

Permalink Reply by Chris on August 7, 2009 at 5:08pm

Hey, there is a great place to get some information on this that I just remembered. Vententersearch.com, and under articles July 2007 "why we do what we do" There is a great picture sequence with explanation about verticle vent, I would recommend it.