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    Default Positive Pressure Ventilation

    I have been looking for a good website or training material that covers PPV. I am trying to train some new members in my department and am looking for some training material. Does anyone have anything or any ideas ??

    Nick Ragucci
    NickRagucci@msn.com

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    I started a thread about a year ago on this subject after I sat through a class on PPV. The class was offered through the National Fire Academy so you can maybe ask them for material? They sent us an instructor, so I do not know if they gave him his material or if he made up his own.

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    Actually it was a class on fireground resource management, but PPV was covered in the class.

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    “Positive-Pressure Ventilation

    When portable fans operated by gasoline engines were introduced it was soon discovered that their usefulness as smoke ejectors was limited by the smoke. If the smoke was too rich, the smoke would stall the engine and stop the fan. Then it was learned that, when the fan was placed outside the building and directed “push instead of pull,” clean outside air would displace the contaminated air inside the fire building. This practice became known as “positive-pressure ventilation” and was widely used in Los Angeles and some other parts of the Far West for a few years before the idea spread to other parts of the country.

    In some areas, it was greeted skeptically as another example of grasping for the mechanical “quick fix,” but many who have used it say that it is a valuable tactic. There is a notable lack of hard data from scientific study to confirm or deny the carious arguments for and against it, yet no doubt exists that the fan will push large volumes of air. The question is what benefit or harm will it bring; the answer depends on how and where it is used. Like many other concepts, its benefit is in proportion to the knowledge of the user.

    A researcher who has conducted considerable testing of it is Homer Robertson of the Fort Worth, Texas, fire department. His findings are well expressed in some of his writing.

    Robertson suggests using this method to clear smoke out of a residential structure quickly after the fire has been extinguished. For most effective use, he lists these requirements.

    1.The cone of air from the fan must cover the intake opening to form a seal around the opening.
    2.The discharge opening should be at the highest and farthest point, if possible.
    3.The size of the discharge opening should be three-fourths to one and one-half times the area of the intake.
    4.The path of air movement should be controlled by opening and closing doors, windows, scuttle holes, and so on.

    He suggests that a two-story structure be ventilated by the first clearing the first story and then closing the first story discharge and so the air will move upward. He also found that the system can control air flow in high-rise structures and limit smoke spread in strip shopping centers after the fire has been extinguished.

    This technique raises questions about the advisability of using forced ventilation when the fire is still burning. Some advocate it and others are appalled at the very thought of pushing all that oxygen into a fire. Furthermore, the velocity of the air movement may force the fire into uninvolved areas. Robertson offers several warnings, including caution in ascertaining the exact location of the fire and placing hose lines in proper positions before starting the fan. He claims that benefits during fire attack may include better visibility, lower temperature, and less steam build-up.”

    Firefighting Principles & Practices
    2nd Edition
    William E. Clark
    Fire Engineering Books and Videos
    Pages 128-129

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    I seem to remember that the National Institute of Standards and Technology, (NIST) or some other similar group did a study on PPV. I just can't remember the details...(Yes CRS )

    Can someone else remember??

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    If one was inclined to study PPV/PPA, there are some decent resources on the web.
    www.vententersearch.com (see Adding Fuel to the Fire and the comments)
    www.fire.gov/PPV/index.htm(Maybe what ChiefDog is referring to?)
    www.fireventstudy.com

    We tried to make a go of it here and failed. I'm of the opinion that while it can work there are significant factors that pertain to your location in the country. No, really! Not fire burns differently sh*t, but how homes and buildings are built and how daily occupants use them affects how you control PPV outlets, etc. These factor into the indications and contraindications for PPV/PPA and failure to recognize them, is asking for trouble.

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    Quote Originally Posted by KevinFFVFD View Post
    Robertson suggests using this method to clear smoke out of a residential structure quickly after the fire has been extinguished. For most effective use, he lists these requirements.

    1.The cone of air from the fan must cover the intake opening to form a seal around the opening.
    2.The discharge opening should be at the highest and farthest point, if possible.
    3.The size of the discharge opening should be three-fourths to one and one-half times the area of the intake.
    4.The path of air movement should be controlled by opening and closing doors, windows, scuttle holes, and so on.
    Is that worded correctly? My training and experience says that the discharge opening must be three quarters to half the size of the intake opening, not times which would make the outlet larger than the inlet thus not allowing any pressure to build up. Maybe that says the same thing, but to be clear, the outlet opening should be smaller than the inlet.

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    Quote Originally Posted by RFDACM02 View Post
    Is that worded correctly? My training and experience says that the discharge opening must be three quarters to half the size of the intake opening, not times which would make the outlet larger than the inlet thus not allowing any pressure to build up. Maybe that says the same thing, but to be clear, the outlet opening should be smaller than the inlet.
    Not that we have done PPV a lot, but I would say that you are both in the ballpark. Controlling the output to be the same or just slightly larger is the key. ( Output In the 0.5 to 1.5 of the input opening) Who has a measuring tape... Guess-ti-mate and go for it.

    You see it go down hill quickly if you have multiple doors and windows opened up. Like RFDACM02 says you can't pressurize the building if it is a sieve.

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    Quote Originally Posted by RFDACM02 View Post
    Is that worded correctly? My training and experience says that the discharge opening must be three quarters to half the size of the intake opening, not times which would make the outlet larger than the inlet thus not allowing any pressure to build up. Maybe that says the same thing, but to be clear, the outlet opening should be smaller than the inlet.
    That's what the book says. IDK if it is a typo or what. Need to check on that.

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    Or for those pesky, hard to find fires,just fire up the fan. It'll show up quick enough,hehe T.C.

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    We have had a lot of success with positive pressure in our area I would say we use PPV on 90% of our fires and 99% of our house fires. Especially in light weight construction houses there is no need to ever get on the roof and vent them if you train and use PPV properly. We use both methods mentioned sometimes we pressurize the building for 30 seconds then enter the building with the fan going. (Always from the door you have the fan in) And sometimes we knock the fire check for extension then fire up the fan. It just depends on the size up and conditions. This is not something you can take one class on and be good at you can very easily burn a structure to the ground or even worse burn firefighters. But you can also make a firefighter’s job a lot safer and put the fire out faster. Now just because it works for us does not mean it will work for you. We have been training and using it for at least ten years b/c they have been on the trucks and used as long as I have been on the job. As with every tool we use Train, Train, and train some more. And if it is not for you don't use it.

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    Quote Originally Posted by giweff View Post
    Especially in light weight construction houses there is no need to ever get on the roof and vent them if you train and use PPV properly.
    Wouldn't say never. There are times when PPV can work well in one situation and times vertical ventilation works better. Such as a fire in the cockloft.

    You can't be fixed on one way of doing something, then caught with your pants down when it don't work.
    Last edited by tnff320; 02-25-2009 at 01:41 AM.
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    Quote Originally Posted by RFDACM02 View Post
    Is that worded correctly? My training and experience says that the discharge opening must be three quarters to half the size of the intake opening, not times which would make the outlet larger than the inlet thus not allowing any pressure to build up. Maybe that says the same thing, but to be clear, the outlet opening should be smaller than the inlet.
    Yes it is worded correctly. 3/4 of something is the same as 3/4 times something. A fraction less than one multiplied by another number results in a smaller number than the original.

    Say you have an 8 square foot opening, 3/4 of this would be 6 square feet, correct? As far as the math goes
    Code:
    3/4 X 8 = 3/4 X 8/1
    = (3 X 8)/(4 X 1)
    = 24/4 = 12/2 = 6
    So the book agrees with your training and experience.

    Yeah for fractions!

    Quote Originally Posted by tnff320
    You can't be fixed on one way of doing something, then caught with your pants down when it don't work.
    You couldn't be more right, at least in my humble opinion.
    Last edited by Gnufsh; 02-25-2009 at 03:31 AM.

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    Quote Originally Posted by Gnufsh View Post
    Yes it is worded correctly. 3/4 of something is the same as 3/4 times something. A fraction less than one multiplied by another number results in a smaller number than the original.
    Thanks for the math refresher, as you can read I got it by the time I finished typing, I merely left it in because in it's cited form it is a common mistake.

    But none the less, can anyone who is using PPV/PPA regularly, confirm the outlet size as a fraction of the inlet? I've not heard of anyone using an outlet equal to or larger than the inlet side. In fact it would seem to not allow any pressurization, merely just pushing air, which will remove smoke in path of air travel but not necessarily in other spaces as true PPV might.

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    Fire Engineering has a webcast on their site for PPA. Just type "positive pressure attack" in the search box on their site and it should take you to it.

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    We have used it with a larger exit than inlet. Key was to control the exit opening initially, to allow the pressure to build, then expand the exit. If/when you see reduced effectiveness, you can then reduce the exit point again if needed to allow pressure to rebuild.

    Having too small of an exit can also allow pressure to "back up" and reduce it's effectiveness as well, basically the PP fan trying to blow into a solid wall.
    "This thread is being closed as it is off-topic and not related to the fire industry." - Isn't that what the Off Duty forum was for?

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    Default Thanks guys

    Well first of all thanks to everyone that has gotten back to me on this subject. I am from upstate NY and PPV isn't used very much at all around here so it is something I personally want to learn and mast and something i would love to train guys with.

    Can i ask a ? if you have a typical 2 story balloon frame construction with a fire on the first floor rear say in a kitchen and you wanted to use PPV your inlet would obviously be a at the front door but where would the outlet be ? The first floor or the 2nd floor rear ?

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    a typical 2 story balloon frame construction
    Those few words right there tend to negate the use of PPV. Balloon frame construction and positive pressure tend to not mix well.

    IF conditions were actually optimal for PPV in your situation above...exit would be the kitchen window.
    "This thread is being closed as it is off-topic and not related to the fire industry." - Isn't that what the Off Duty forum was for?

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    Quote Originally Posted by nragucci33 View Post
    Can i ask a ? if you have a typical 2 story balloon frame construction with a fire on the first floor rear say in a kitchen and you wanted to use PPV your inlet would obviously be a at the front door but where would the outlet be ? The first floor or the 2nd floor rear ?
    A lot of the time with balloon frame, by the time the fire is reported, your dispatched, and make scene the fire is going to be running up the walls. Definately vertical ventilation will have to be used. Especially in a kitchen where there is more open spaces running straight up for utilities, along with the vertical space in the walls. Gives the fire easier access to an open vertical space.

    And for the sake of answering the question, I am with Bones in saying it's going to be the kitchen window.
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    Quote Originally Posted by giweff View Post
    We have had a lot of success with positive pressure in our area I would say we use PPV on 90% of our fires and 99% of our house fires. Especially in light weight construction houses there is no need to ever get on the roof and vent them if you train and use PPV properly. We use both methods mentioned sometimes we pressurize the building for 30 seconds then enter the building with the fan going. (Always from the door you have the fan in) And sometimes we knock the fire check for extension then fire up the fan. It just depends on the size up and conditions. This is not something you can take one class on and be good at you can very easily burn a structure to the ground or even worse burn firefighters. But you can also make a firefighter’s job a lot safer and put the fire out faster. Now just because it works for us does not mean it will work for you. We have been training and using it for at least ten years b/c they have been on the trucks and used as long as I have been on the job. As with every tool we use Train, Train, and train some more. And if it is not for you don't use it.

    We use PPV here a lot as well. However, we use it to clear homes after the fires are extinguished to expedite removal of gases and smoke if needed. We also clear homes filled with smoke from small fires, etc. We vertically vent 90% of every one of our fires. I don't see the logic of turning a fan on and sticking into a open door where fire is burning inside. No matter how much you are trained the fact is the fire is going to intensify, spread to areas that were not initially involved, and you really are not controlling the fire at all. All you’re doing is creating increased fire damage, and putting everyone in the structure at more risk for flashover.

    Pressurize the building for 30 seconds then enter!

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    Ok thanks for your help with this. Does anyone have a general rule of thumb for when and when not to use PPV. I take it balloon frame is out and has anyone worked with it in large area warehouses at all.

    Nick

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    Does anyone have a general rule of thumb for when and when not to use PPV.
    When you are able to control where the fire is going to spread to, use it.
    "This thread is being closed as it is off-topic and not related to the fire industry." - Isn't that what the Off Duty forum was for?

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