1. #51
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    "So in this case, if as stated in earlier posts there were no firewalls, the trench method would be ineffective, and would at best only slow the extension slightly?"

    No. If there were no fire walls, and in this case there are not, then the trench cut would be effective in cutting of the fire extension in the cockloft, if there was rapidly extending fire there. Just because you may have extension into the cockloft does not mean you must perform a trench cut. The amount of fire, reports on extension from interior units, the coordination fire attack itself, all contribute. Remember a fire wall is a true fire wall if it separates, completly, the adjoining buildings. Some construction styles in garden apartments, townhouses and townhomes give an appearance of having a fire wall, but do not completely separate the buildings.

    "Or were you referring to the fact that it does not appear to go from the edge of the exterior wall to the edge of the other exterior wall?"

    I believe that he is referring to the fact that the cut does not extend, or was not completely opened up the whole length, from roof edge to peak and opposite roof edge.

    "Also, would the trench normally be done "downstream" or down nozzle from where the fire is, in anticipation of the fire being pushed that direction by prevailing winds, forced ventilation, or water attack?"
    Would you like the text book answer or the real world answer? The trench cut must be done in cooperation with the fire attack, or the fire will be "pushed". In my experience of doing trench cuts, the primary consideration was what part do we want to save?

    In the photo below, a truck crew went to the adjoining apartment building and performed a trench cut slightly past the area of extension in that unit.


    Backstep, remember, A.269 made department history by calling it in and requesting Communications dispatch the box and second alarm at the same time.
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    Last edited by bcarey; 01-28-2007 at 08:13 PM.
    "If you put the fire out right in the first place, you won't have to jump out the window."
    Andy Fredericks,
    FDNY E.48, SQ.18
    Alexandria, VA F.D.

    Rest in Peace

  2. #52
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    OK....I think I understand it a little better now. The trenching will "pull" the fire to its direction, but hopefully protect the other side by venting flame and hot gases out the roof, essentially stopping the extension through the attic or cockloft voids. It does not necessarily have to be done in the current direction of fire travel.

    And I understand about the communication with interior crews and further size-up before just blindly initiating a trench.

    Thanks!!

  3. #53
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    "The trenching will "pull" the fire to its direction, but hopefully protect the other side by venting flame and hot gases out the roof, essentially stopping the extension through the attic or cockloft voids. It does not necessarily have to be done in the current direction of fire travel."

    It can pull the fire, and you most likely would do it in the direction of fire travel, but the principle is to cut off the fire from traveling the whole building. What you do when you trench a roof is create an actual trench, a moat for example, a break in the building from the burning portion and the nonburning portion. It is unlikely you would do a trench cut as part of roof ventilation for a top floor apartment room on fire. An advanced fire involving two or more units on a top floor, maybe. It depends on the indications of extension when you arrive and your knowledge of that building's construction.
    Last edited by bcarey; 01-28-2007 at 09:50 PM.
    "If you put the fire out right in the first place, you won't have to jump out the window."
    Andy Fredericks,
    FDNY E.48, SQ.18
    Alexandria, VA F.D.

    Rest in Peace

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    OK...its getting clearer...thanks for the clarification. Give me another 20 years and I'll know twice as much of a 1/4 of what I should.........

    Instead of a 2/20, I'll probably be the 20/2........

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    SWLA,
    Here is a link to a good article about flat roof ventilation here on Firehouse http://cms.firehouse.com/content/art...r.jsp?id=49753
    I agree, this trench cut is incomplete for whatever reason. It should extend completely from one exterior wall to the other. There may be a time when high wind, for example, would affect the placement of the trench but it is more common to place the trench cut as a defensive measure between the fire and the part of the building you intend to save.

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    GREAT article..... and not as simple an operation as what I thought it might be. Quite a big decision.

    We are a rural area, and offhand the only large building I can think of is the school........maybe a warehouse.

    I don't think I'll ever see this one done, but it is good to understand it. Okay, thanks guys!

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    Default Trench, Dampen, And Pray

    Not in the essentials manual but it works... If the fire is spreading rapidly we have had success by getting one unit (or apartment) ahead of the fire in the direction of fire travel. Then cutting a trench in the roof, pulling ceiling on the second / top floor, then applying water to the unburned area between the trench and the fire.

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