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  • Trench cut

    I have been researching trench cut practices and I have come across some differing (surprise there) opinions. It boils down to:
    Are trench cuts only viable at "necks" in/between roofs. Necks are defined as places where the roof size is pinched down to a smaller size than rest of roof?
    Any thoughts? Also, if the above is true, then what is best tactic to stop fire spread in common roof of "non-necked" buildings?

  • #2
    Trenches are made the quickest in the "neck" of a building. However it may not always be the best spot and certianly is not the only spot.
    In order to be effective they should be in the area of at least 3 foot wide, they should also be made well ahead of the fire so as to allow time to be completed before the fire gets to the hole. You should not open the hole until the fire is at the hole, this keeps it from advancing towards the vent. It is also a good idea to place a second trench after the first, this allows for a secondary stopping point.
    Placement will be dictated by wind direction and fire travel, the same as any other vent point. It makes no sense to place the hole in an area so far away that the fire may not reach it, just because it is the narrowest point of a building.

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    • #3
      I just read this the other day, written by member NDemarse, and hosted at Brotherhood Instructors:

      http://brotherhoodinstructors.com/wordpress/?p=82
      www.iaff2625.org
      http://twitter.com/Local_2625
      http://www.facebook.com/IAFF2625

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      • #4
        Originally posted by MEck51 View Post
        Trenches are made the quickest in the "neck" of a building. However it may not always be the best spot and certianly is not the only spot.
        In order to be effective they should be in the area of at least 3 foot wide, they should also be made well ahead of the fire so as to allow time to be completed before the fire gets to the hole. You should not open the hole until the fire is at the hole, this keeps it from advancing towards the vent. It is also a good idea to place a second trench after the first, this allows for a secondary stopping point.
        Placement will be dictated by wind direction and fire travel, the same as any other vent point. It makes no sense to place the hole in an area so far away that the fire may not reach it, just because it is the narrowest point of a building.
        I would have to disagree with two points that you are making regarding a trench cut.

        First, if you wait until the fire is "at the hole", it is too late and you will never be able to open this cut fast enough to prevent the fire from advancing beyond the trench. It is incredibly manpower intensive to open one of these and can be very time consuming. I agree that you should not open it prematurely, but waiting until the fire is at the opening is defeating the purpose.

        And secondly, do you have any idea how long it actually takes and how many firefighters you must commit to cut and pull a trench cut? Making a SECOND trench is impractical in the real world and should not be at all necessary if the first one was done correctly and in the proper location.

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        • #5
          The ability to recognize the need for and to execute a trench cut can mean the difference between saving the structure or burning it down.

          You have to make the cut where you need it. If the fire has gone past the "neck", you may have to cut the full width of the roof. Been there, done that!
          ‎"The education of a firefighter and the continued education of a firefighter is what makes "real" firefighters. Continuous skill development is the core of progressive firefighting. We learn by doing and doing it again and again, both on the training ground and the fireground."
          Lt. Ray McCormack, FDNY

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          • #6
            Dont forget the charged line!!!!!!

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            • #7
              Originally posted by JaySNJFF View Post
              I have been researching trench cut practices and I have come across some differing (surprise there) opinions. It boils down to:
              Are trench cuts only viable at "necks" in/between roofs. Necks are defined as places where the roof size is pinched down to a smaller size than rest of roof?
              Any thoughts? Also, if the above is true, then what is best tactic to stop fire spread in common roof of "non-necked" buildings?
              Here is an article on La county website. It may help you. We changed the terminology of trench cuts to strip cuts back in the early 80's....of course, west coast...

              http://www.lacountyfire.com/article78.html

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              • #8
                Before a trench is cut a vent hole must be done. If not the trench acts as a vent and pulls heat and fire towards it, making it extremely difficult or impossible to finish the trench. You'll cut a building or two ahead of the fire,depending on speed of fire spread, allowing sufficient time to complete cutting before the fire's up your *** chasing you. There are many areas in my city that have 2 and 3 story row frame homes 5-8-12 in a row, all attached with an approximately 3 foot high common cockloft (some places call it an attic). In some of these there are NO firewalls. Trenching is common at these top floor fires to stop it from running the block. These have no "neck" or narrow section. The two main cuts are made the entire depth of the roof at least 3ft wide, as was mentioned, and sectioned about 4-5 feet long for ease of pulling. If the fire is in the middle of the block you may have to cut two trenches, one on each side, if there are several buildings in harms way on both sides of the fire building. This is alot of cutting, so you need to make sure your saw is full of gas all the time, before the crap hits the fan.
                Attached Files

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                • #9
                  Originally posted by JaySNJFF View Post
                  Also, if the above is true, then what is best tactic to stop fire spread in common roof of "non-necked" buildings?
                  try a big vent hole with alot of guys underneath with hooks and hoselines!

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                  • #10
                    Here is the most important thing you need to know abou trenching.

                    Don't try it at a fire scene if your only training has been reading reading a book or an Internet forum.
                    PROUD, HONORED AND HUMBLED RECIPIENT OF THE PURPLE HYDRANT AWARD - 10/2007.

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                    • #11
                      Some good points on this. I think The Brotherhood website by DeMarse would be the place to go on this, it pretty much sums it up.

                      Just remember.....-it is a defensive tactic.
                      -Cut up the sections so you can pull them fairly easily.
                      -Make the cut at a location where you'll have time pull it
                      -Make inspection cuts between your main hole over the fire and the trench, lets you know when the fire is approaching the trench.
                      -If you can use the narrow parts of the roof to your advantage, then use them...less cutting. Work smarter, not harder.

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                      • #12
                        Originally posted by LeatherHed4Life View Post
                        try a big vent hole with alot of guys underneath with hooks and hoselines!
                        Exactly! Get ahead of where the fire is, aggressivly pull ceilings and get water up there....it really is that simple.

                        Comment


                        • #13
                          Originally posted by GeorgeWendtCFI View Post
                          Here is the most important thing you need to know abou trenching.

                          Don't try it at a fire scene if your only training has been reading reading a book or an Internet forum.
                          This is true. Remember most training is done in three phases.

                          Now if you complete the triangle and see the associated YouTube video...then by all means have at it
                          Co 11
                          Virginia Beach FD

                          Amateurs practice until they get it right; professionals practice until they cannot get it wrong. Which one are you?

                          'The fire went out and nobody got hurt' is a poor excuse for a fireground critique.

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                          • #14
                            jakesdad, you are right about the timing of opening the trench. You should not wait until it is right under to open, I was taken a little too literal on that one, although that is how I typed it.

                            As far as the second trench, yes you should not need it, if done correctly the first time. And more than likely you won't get a second shot on most buildings. But if you do have a building that big to need it, you should prepare.

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                            • #15
                              The Jersey Capt. speaks of the truth..a heat hole must be cut above/nearest the seat of the fire as possible to buy you time for your strips. And with well trained companies you should have no problem dropping in 2 strips in a timely matter. Good working saws, fuel and good chains + training = a successful strip evolution. Like MattyJ said, as you progress on the roof make smoke indicator cuts off the purlins and beams you are working off of to determine conditions within the attic/cockloft.
                              Last edited by MattyS; 06-24-2008, 08:47 PM.
                              The good thing about this job is that we have done so much, with so little, for so long that we can do everything with nothing...... which is what is wrong with this job.
                              KTF | DTRT

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