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  1. #1
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    Default PPV fans as NPV?

    Quick question.....

    I always thought (and can only find information to support what I was taught) that PPV fans should not be used as "smoke ejectors" or for negative pressure ventilation.

    Does anyone out there know anything to the contrary?

    Thanks.


  2. #2
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    Default Would you get Combustion?

    Are your PPV blowers Gas/Electric? Wouldn't your gas blowers choke out without adequate oxygen to achieve combustion?

  3. #3
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    Just a thought about using them for NPV. If the smoke conditions are too bad the motor will shut down (won't it?) I imagine that they can be used if it is necessary. What are you trying to accomplish by doing this? Are you trying to remove the CO that you have already pumped into the building during PPV? We are now carrying both gas and electric fans on the apparatus. Both have advantages and disadvantages. As far as any concrete evidence one way or another I have none.
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  4. #4
    Forum Member nmfire's Avatar
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    Default

    This is easy. Is it electric? You can stick it anywhere you want if you can get electricity there. If it is gas, you can't really put that inside without filling the structure with more CO than there was to begin with.
    Even the burger-flippers at McDonald's probably have some McWackers.

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    55 Years & Still Rolling hwoods's Avatar
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    Lightbulb And.............

    LT32, Good Points. The one thing that bugs me, however, is the fact that there is no such thing as a Positive Pressure Fan. I know, I know, it's heard on the radio every day, "Get a positive pressure fan up here......" BUT the truth is that there is no such thing. POSITIVE PRESSURE VENTILATION IS A METHOD, NOT A MACHINE.
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  6. #6
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    Default

    So.......so far, everyone agrees with me that a (gas) fan should NOT be used for negative pressure ventilation.

    Well, I am being told from the "higher ups" on my department that it CAN be used for NPV.

    Not only is there the CO argument, but NPV needs to be at the highest point in the opening with little opening around the smoke ejector, and I don't see a gas fan hanging high up in a doorway or window :-)

    Any other info to the contrary will be welcomed.....I'm trying to understand my leadership's view on this.

  7. #7
    Forum Member Bones42's Avatar
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    Default

    Ok, we have a gas fan that is designed to be used in a PPV operation (ok Hwoods ) and we have used it inside to clear a room in a NPV operation. We have a hose that attaches to the exhaust pipe and placed the end of the hose downwind. That brings the exhaust out of the building along with the rest of the bad air. Simple solution to a small problem. CO meters were used to monitor the room and had good success.

    I'd rather the electric fan for the operation, but other problems caused us to not be able to run the electric fan.

    We also use the exhaust hose for PPV operations for the same reason, to keep the CO levels down, just run the hose off to the side so it's not in the air path.
    "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?

  8. #8
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    Default PPV and NPV Unit project

    Hi, I am from Perú and I want your advice because I am presenting a project to my cityhall for buying a ventilation equipment (PPVand NPV, and equipment to do vertical ventilation); And I want to be sure that its the rigth desition.
    Its important to know that here in Peru our houses and buildings are made of brik and concret, so doing vertical ventilation can be very dificult if there ar no windows...
    I also have read in tihs forum that some departments use PPV after they control the fire and other since the beging of the operations. If you have some standarized information about it, like magazine articules, books, web pages I would be very glad.

    "A few years ago there was a fire in a discoteque it had not windows, and more than 15 persons die, it was very dificult for rescue team to find the victims becasue of the hume "

  9. #9
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    Default

    I don't see why the NPV has to be at the highest point of the opening if using a PPV fan. I would think if it was placed to direct the blowing air just inside the door frame then a venturi effect would occur and it would work quite well. Same principle as hydraulic ventilation with a combination nozzle.

  10. #10
    MembersZone Subscriber Edward Hartin's Avatar
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    Default PPV/NPV Ventilation Equipment

    topicob134,

    Drop me an e-mail at hartin@ci.gresham.or.us and I will forward the information that I have on the topic.

    Cheers
    Ed Hartin, MS, EFO, MIFireE

  11. #11
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    We found that not only do you have all the issues mentioned, but a fan running in clean air does not get covered with the products of combustion. Most fans (gas or electric) used for NPV need to be cleaned after use to get them to work properly and not get everything close to them all gunk.

    You just about have to decontaminate the fan used in bad air. If you don't you have all the bad stuff we wear SCBA and other PPE on the outside of the fan. You touch it you are now contaminated.

    A light smoke condition for burnt toast is one thing, smoke from a working fire is another...

  12. #12
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    Exclamation Fan of PPV

    Here's another question - if you have a natural gas leak inside a structure what method do you use?

    My basic FF 1 training had this question on the exam, I did well on that exam, and I thought I understood the reasoning involved until I was instructed by a Chief to loose the gas PPV fan I had set up outside the front door and bring two electric powered smoke ejectors inside and connect them !

    He didn't like the CO being pumped in which I understand. Does anyone know where you can purchase the exhaust hoses or did you just make your own?

  13. #13
    Forum Member Bones42's Avatar
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    Default

    We purchased our exhaust hose from www.allhandsfire.com I think you can also get them directly from your fan manufacturer.
    "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?

  14. #14
    Forum Member MemphisE34a's Avatar
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    Default

    Quote Originally Posted by nmfire
    This is easy. Is it electric? You can stick it anywhere you want if you can get electricity there. If it is gas, you can't really put that inside without filling the structure with more CO than there was to begin with.
    I don't think so. Even with the fan outside blowing in, exhaust from the fan is blowing into the structure. Think about it. The exhaust is right behind the fan. Even outside the building, it is pulled right into the fan and blown into the building. The same would happen when inside the building, blowing the exhaust out.

    I am not going to go break the CO monitors out and find out for sure, but if I were in Vegas I would bet that the difference would be miniscule.

    My guess is that we do it the way we do because that is the way it was taught. You know kinda like all the other fire service things we do because we always have, but no one knows why.
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  15. #15
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    Default

    Ran into this yesterday. Ran an auto alarm for a gas detector in a single family residence. Upon arrival there were alarms sounding inside, no homeowners around, and everything was locked up tight. While waiting for a LEO (our policy before gaining entry unless something is visible from the outside) the alarm company found a code to the garage. This is the homeowners third residence and they are there very rarely. We made entry through the garage and detected higher than normal readings of gas inside the structure. Gas and power were shut off at the meters. IC ordered positive pressure ventilation set up through the garage. Realizing he was pumping exhaust into the structure, that was shut off and natural ventilation techniques were employed. A well-intentioned captain decided that he was going to just turn the fan around. Not only is this basically ineffective with a gas powered fan of this type (without a valance, the air is mostly sucked in from the sides) but should you succeed in drawing the gas out of the structure, there's a chance (however slight) that the gas engine has now become your ignition source for a big boom.

  16. #16
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    1) Why would you need NPV over PPV? The situations I can think of...I'd probably just punt with natural ventilation.

    2) The reason you want them high is you're presumably venting hot smoke. Heat rises. You want that out first.

    3) I've seen PPVs brought inside more than once to go down a hallway or otherwise operate from a relatively clear area and speed the clearing of a smokier area. Not as NPV, just PPV.

    4) My bigger beef and more common observation is people who'll walk by a perfectly fine smoke ejector trying to get a "PPV Fan" rather than use the smoke ejector backwards. Bit less common today as new trucks come with PPV fans and the ol' smoke ejectors become rarer.

    5) I suspect an awful lot of people now have never seen a smoke ejector used during a fire attack and the incredible amount of crud and crap that does happen. If your very, very lucky you could even see a smoke ejector dragon when the superheated products of combustion it's ejecting meet fresh air.

    6) And point 5 brings up point 6 -- was your PPV fan engineered with NPV in mind? Smoke ejectors are ruggedized expecting to be working in a hot environment. PPV fans aren't necessarily.

  17. #17
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    Default

    [QUOTE=Dalmatian190] If your very, very lucky you could even see a smoke ejector dragon when the superheated products of combustion it's ejecting meet fresh air.


    This is extremely cool, saw it one time. Froze everyone on the scene for a few seconds.

  18. #18
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    Thumbs up PPV fan works equally well in Negative mode.

    Thje U.S. military did testing in the negative pressure mode to see if they could remove contamenates(bilogical and chemical)from a building. The results showed that a PPV fan removes just as well in the neg. mode as it did in the positive. I have tried it and used cardboard over a remote window. The cardboard sucked into the window when the fan was turned on. The fan should be inside the door just the opposite of how you would use it form the outside. You want to create a seal. The CO gas is not much of aproblem since it is being sucked out of the building with the air movement. If there is heavy smoke PPV is a better option as the smoke will be drawn through the blades and gum them up as well as possibly choke out the motor in the neg. mode. You also need to be aware that in a fire situation you would draw fire to the fan opening. However, in minor smoke situations sometimes the negative mode gives a better point of vantage and is a viable option.

  19. #19
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    In the 80s,when I was in the Navy,we'd use the installed ventilation after checking it out.High speed supply and high speed exhaust would clear a compartment quicker than you'd think.I forget the exact CFM rates but the ship I was in was scrapped back in 98 so I doubt it matters now.
    For higher volumes,we'd use an air powered fan for both negative and positive pressure ventilation to avoid sparks in explosive atmospheres,and because usually the installed vent system was wasted after a fire anyway.

  20. #20
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    PPV and NPV both have their uses. Either can be used (barring any time constraints) interchangably. There ARE some subtle differences in tactics, however...

    In my experience, PPV is much easier to deploy in a hurry. It removes huge volumes of heat and smoke quickly, and leaves your means of egress unobstructed. All of these traits are favorable during a combined attack. CO isnt going to be an issue during this timeframe; your fire crews should still be breathing SCBA air and fighting fire. The Key feature here is a rapid removal of heat and smoke.

    I prefer NPV fans for overhaul operations. The fire is knocked down, visibility is improved, and heat is of limited issue. The use of a PPV at this point would severly hamper any effort in reducing CO levels (unless electric, of course). NPV also can be slightly more time consuming when setting up. (Hangers if no windows available, tarps to prevent recirculation, power cords, etc..) This is definately not a trait one would want during a fire attack.

    There are ALWAYS special situational events that would benifit more from one machine or another. Just remember, you can drive a nail with a halagan, but wouldnt a hammer do better? Point being, you can DO the job with either fan, but in certain situations, one will shine more than the other....

    Be safe

    REW.

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