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  • #31
    Originally posted by J.Beck View Post
    I probably did misunderstand the OP, although, the point remains the same - pressurizing an exposure, attached or not, is VERY effective.
    For a detached exposure, effective at doing what?
    "Nemo Plus Voluptatis Quam Nos Habant"
    sigpic
    The Code is more what you'd call "guidelines" than actual rules.

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    • #32
      Originally posted by DeputyMarshal View Post
      For a detached exposure, effective at doing what?
      Eliminating fire spread to the given exposure.
      Cognition before Ignition

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      • #33
        Originally posted by J.Beck View Post
        Eliminating fire spread to the given exposure.
        How do you propose that pressurizing a detached exposure will prevent fire spread given that fires typically spread to detached exposures either by radiant heat or direct flame contact; neither of which is effected by pressurization?
        "Nemo Plus Voluptatis Quam Nos Habant"
        sigpic
        The Code is more what you'd call "guidelines" than actual rules.

        Comment


        • #34
          Originally posted by DeputyMarshal View Post
          How do you propose that pressurizing a detached exposure will prevent fire spread given that fires typically spread to detached exposures either by radiant heat or direct flame contact; neither of which is effected by pressurization?
          Pressurization has everything to do with keeping out direct flame contact and radiant heat.

          As fire spreads it seeks to go to a neutral or negative pressure (outside air, non-pressurized buildings, etc). Fire will not spread where there is a positive pressure, thus the reason for pressurizing exposures.
          Cognition before Ignition

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          • #35
            Originally posted by J.Beck View Post
            Pressurization has everything to do with keeping out direct flame contact and radiant heat.
            Pressurization has zero effect on both of those modes.

            As fire spreads it seeks to go to a neutral or negative pressure (outside air, non-pressurized buildings, etc). Fire will not spread where there is a positive pressure, thus the reason for pressurizing exposures.
            Pressurizng a detached exposure does nothing to prevent either radiant heat or direct flame contact from igniting its exterior. If you want to keep a detached exposure from igniting, keeping heat/fire off of its exposed surfaces is typically going to be a far superior strategy to pressurizing it.
            "Nemo Plus Voluptatis Quam Nos Habant"
            sigpic
            The Code is more what you'd call "guidelines" than actual rules.

            Comment


            • #36
              Originally posted by DeputyMarshal View Post
              Pressurization has zero effect on both of those modes.
              Pressurizng a detached exposure does nothing to prevent either radiant heat or direct flame contact from igniting its exterior. If you want to keep a detached exposure from igniting, keeping heat/fire off of its exposed surfaces is typically going to be a far superior strategy to pressurizing it.
              Of course traditional exposure protection via. charged handlines must by utilized for proper exterior exposure protection. But, to protect the entire(interior/exterior) structure, pressurization must also be utlized.
              Cognition before Ignition

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              • #37
                Originally posted by J.Beck View Post
                Of course traditional exposure protection via. charged handlines must by utilized for proper exterior exposure protection. But, to protect the entire(interior/exterior) structure, pressurization must also be utlized.
                If you protect the exterior the interior isn't a primary exposure.

                Of course, if you have the luxury of excess manpower standing around with nothing better to do, go for it...
                "Nemo Plus Voluptatis Quam Nos Habant"
                sigpic
                The Code is more what you'd call "guidelines" than actual rules.

                Comment


                • #38
                  Originally posted by J.Beck View Post
                  Fire will not spread where there is a positive pressure, thus the reason for pressurizing exposures.
                  Good lord, do you understand basic fire behavior or heat transfer? How does PP affect radiant heat transfer or conductive transfer?

                  It's amazing that more of us haven't burned down blocks ignoring the use of positive pressure on exposures. Where I live, if the positive pressure can protect a house, they probably would rather have it burn then pay the heating bill.

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                  • #39
                    Originally posted by DeputyMarshal View Post
                    If you protect the exterior the interior isn't a primary exposure.

                    Of course, if you have the luxury of excess manpower standing around with nothing better to do, go for it...
                    Capiche.

                    Cognition before Ignition

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                    • #40
                      Originally posted by J.Beck View Post
                      Of course traditional exposure protection via. charged handlines must by utilized for proper exterior exposure protection. But, to protect the entire(interior/exterior) structure, pressurization must also be utlized.
                      You could also use land use/fire codes to ensure exposures were not an issue in the first place. This in fact would actually be more complete protection, though likely slightly less realistic than your inflatable fire protection bubble?

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                      • #41
                        Originally posted by RFDACM02 View Post
                        Good lord, do you understand basic fire behavior or heat transfer? How does PP affect radiant heat transfer or conductive transfer?

                        It's amazing that more of us haven't burned down blocks ignoring the use of positive pressure on exposures. Where I live, if the positive pressure can protect a house, they probably would rather have it burn then pay the heating bill.
                        I have no idea what you are talking about in your second paragraph. So I will address the first one only.

                        Talking specifically about fire spread and fire behavior; fire will move to an area of lower pressure, it is simple science and is backed up by NIST. I am not sure how else to explain this concept to you. "Radiant heat transfer" and "conductive transfer" are severely limited by PPA due to decreases in compartment temperature. For every 18 degrees dropped in temperature, combustibility is decreased by 50%. Thus, disrupting a portion of the fire tetrahedron and decreasing the potential for fire spread.
                        Last edited by J.Beck; 12-29-2010, 06:14 PM.
                        Cognition before Ignition

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                        • #42
                          Originally posted by RFDACM02 View Post
                          You could also use land use/fire codes to ensure exposures were not an issue in the first place. This in fact would actually be more complete protection, though likely slightly less realistic than your inflatable fire protection bubble?
                          It is not my concept. It is something that initially I severely disagreed with and set out to prove wrong...well, here I am 50+ burns later and I am the biggest PPA advocate there is.

                          Don't believe it?

                          Prove it wrong.
                          Last edited by J.Beck; 12-29-2010, 06:17 PM.
                          Cognition before Ignition

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                          • #43
                            Originally posted by J.Beck View Post
                            I am not sure how else to explain this concept to you.
                            Seriously? You might want to start by gaining a better understanding yourself.

                            "Radiant heat transfer" and "conductive transfer" are severely limited by PPA due to decreases in compartment temperature.
                            1) Positive pressure won't significantly lower compartment temperature in an exposure unless it's because it's cold outside and you have the door open for PPV.

                            2) Radiant heat transfer is unaffected by ambient air pressure or temperature.

                            3) Conductive heat transfer isn't greatly affected by the minor variations in temperature you might get pressurizing an exposure.

                            4) Direct flame contact to a wall is unaffected by the pressure on the other side of the wall.

                            For every 18 degrees dropped in temperature, combustibility is decreased by 50%.
                            I have no idea where you're getting this information. A material's ignition temperature is unaffected buy the temperature of its surroundings. (Not that PPV is going to significantly alter the ambient temperature of an exposure building.)

                            Thus, disrupting a portion of the fire tetrahedron and decreasing fire spread.
                            Even assuming PPV in this scenario has any useful effect on the inteior of the exposure building, it has no effect whatsoever on the part of the exposure building actually in danger of ignition; the exterior of the building exposed to the fire in the neighboring structure.

                            PPV and PPA certainly have tactical benefits -- in the fire building. In a detached exposure? Not so much.
                            "Nemo Plus Voluptatis Quam Nos Habant"
                            sigpic
                            The Code is more what you'd call "guidelines" than actual rules.

                            Comment


                            • #44
                              Originally posted by DeputyMarshal View Post
                              Seriously? You might want to start by gaining a better understanding yourself.



                              1) Positive pressure won't significantly lower compartment temperature in an exposure unless it's because it's cold outside and you have the door open for PPV.

                              2) Radiant heat transfer is unaffected by ambient air pressure or temperature.

                              3) Conductive heat transfer isn't greatly affected by the minor variations in temperature you might get pressurizing an exposure.

                              4) Direct flame contact to a wall is unaffected by the pressure on the other side of the wall.



                              I have no idea where you're getting this information. A material's ignition temperature is unaffected buy the temperature of its surroundings. (Not that PPV is going to significantly alter the ambient temperature of an exposure building.)



                              Even assuming PPV in this scenario has any useful effect on the inteior of the exposure building, it has no effect whatsoever on the part of the exposure building actually in danger of ignition; the exterior of the building exposed to the fire in the neighboring structure.

                              PPV and PPA certainly have tactical benefits -- in the fire building. In a detached exposure? Not so much.
                              PPA and PPV are not the same and we both (mostly me), seem to be bleeding over both concepts. Much of my later responses (responder to another poster) deal specifically with PPA concepts; i.e. temperature decrease, etc. While yours seem to be focusing more on PPV and exposure protection (The OP).

                              Unfortunately, I am out of time to give you back a response that your post deserves. I will get back with you tomorrow.

                              Thanks.
                              Cognition before Ignition

                              Comment


                              • #45
                                Originally posted by J.Beck View Post
                                While yours seem to be focusing more on PPV and exposure protection (The OP).
                                Which would seem appropriate since it is, after all, the subject under discussion.

                                Unfortunately, I am out of time to give you back a response that your post deserves. I will get back with you tomorrow.
                                Stay safe, Cap'!
                                "Nemo Plus Voluptatis Quam Nos Habant"
                                sigpic
                                The Code is more what you'd call "guidelines" than actual rules.

                                Comment

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