Thread: CAF Vs. FOG

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    Default CAF Vs. FOG

    With the hype over CAF in the last few years, it has me thinking....

    If CAF is a water flow of anywhere from about 25-100 GPM, with some foam and alot of air mixed in, doesnt CAF seem strangely similar to indirect application of water fog? We will take a 25 GPM line into a structural fire now, with air and some foam mixed in and its innovative technology, but if you take 25 GPM of water in without air and foam its suicide, according to some.

    It is said that CAF will extend your water "life" and give you more bang for your buck. If you used water fog flows as low as CAF water flows, you'd do the same thing, assuming you were able to acheive the steam conversion and other required variables to effect extinguishment.

    I have never been through an actual CAFS class, so I may be missing some important points. I am looking for some information to help understand the principles here. It almost seems that we have taken water fog firefighting principles and added some foam to make the water work a little better.

    I understand the effect of class A foam in making water more efficient, but I seem to be understanding that the actual bubbles are important for heat absorbtion, moreso than the foam agent. The idea of more water surface to heat (bubbles in CAF) seems pretty similar to the use of water droplets (fog).

    I need some help understanding this.
    Last edited by MG3610; 12-23-2007 at 09:55 AM.

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    The foam doesnt break down like untreated water, thats why you are required to use so much less. The foam requires a lot more energy from the fire to break it down. If you try the same thing without foam you will be killed or severely injured.

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    A CAFS department worth its weight doesn't point to water conservation as a primary advantage of CAFS. The quick knockdown is the selling point. Crews are exposed to a hostile enviorment for less time. And because proper application of CAFS knocks down fire quicker I suppose that "will extend your water 'life' and give you more bang for your buck," but that is not the goal. The goal is using a direct attack to put the fire out faster.

    A great diffrence between a low volume indirect fog/steam attack and CAFS application is that for the fog to work you need a very compartmentaly contained fire to trap the water fog and let the steam do its work. A CAFS attack works well on both ventilated fires and compartmental fires.

    Both methods need crews that are well trained on their selected method. Most people that have had bad experiences with CAFS are due to improper implementation, either at the pump panel or the nozzle.
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    I don't think you can compare the two as easily as you think. The processes are very different in CAFS suppression vs. Fog use.

    With CAFS, the film formation causes the water to coat surfaces and resists evaporation. This results primarily in fuel/oxygen separation, and some surface cooling much more than the environment cooling effect of Fog. CAFS also lasts longer which maintains those effects while the environment and fuel are further ventilated and cooled.

    Water Fog cools the environment and reduces suspended gas temperatures below flashpoint. It often has much less of a direct effective on surface temperature, but as long as the pyrolized gases are kept cool, the end result is usually the same; suppression. In an open environment however, application rates may never overcome heat production with low flows.

    The benefit of CAFS is reduced steam production, and the coating properties result in less re-application of water to burning material (and therefore) less water use and damage. There is debate whether that can also result in a safety hazard due to a potential inability of CAFS to prevent or suppress a flashover, but that one is still out with the jury.

    Fog is great for steam production, but not fuel penetration. In a larger fire, it may require much more water application to cool the fuel, and therefore the secondary negative effects of water damage, increased structure stress due to weight, and heavy/reactive hoselines is a tradeoff.
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    Quote Originally Posted by mcaldwell View Post
    I don't think you can compare the two as easily as you think. The processes are very different in CAFS suppression vs. Fog use.

    With CAFS, the film formation causes the water to coat surfaces and resists evaporation. This results primarily in fuel/oxygen separation, and some surface cooling much more than the environment cooling effect of Fog. CAFS also lasts longer which maintains those effects while the environment and fuel are further ventilated and cooled.

    Water Fog cools the environment and reduces suspended gas temperatures below flashpoint. It often has much less of a direct effective on surface temperature, but as long as the pyrolized gases are kept cool, the end result is usually the same; suppression. In an open environment however, application rates may never overcome heat production with low flows.

    The benefit of CAFS is reduced steam production, and the coating properties result in less re-application of water to burning material (and therefore) less water use and damage. There is debate whether that can also result in a safety hazard due to a potential inability of CAFS to prevent or suppress a flashover, but that one is still out with the jury.

    Fog is great for steam production, but not fuel penetration. In a larger fire, it may require much more water application to cool the fuel, and therefore the secondary negative effects of water damage, increased structure stress due to weight, and heavy/reactive hoselines is a tradeoff.
    Thank you, quite helpful to better understand.

    So if I understand correctly, CAF cools the surfaces faster, whereas fog cools the atmosphere. Obviously this would be the reason for dramatic temperature reductions with CAF vs. fog, true?

    Can anyone point me in the direction of good research data explaining these principles?
    Last edited by MG3610; 12-23-2007 at 05:30 PM.

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    Quote Originally Posted by mcaldwell View Post
    There is debate whether that can also result in a safety hazard due to a potential inability of CAFS to prevent or suppress a flashover, but that one is still out with the jury.
    This is one thing I have also heard, that troubles me. Is there any ongoing research or field expierences that are doing anything to deal with this possibility? A recent LODD in Germany with a CAF line was discussed in an issue of Fire Chief Magazine, and I believe it cited CAF as a possible contributing factor.

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    Quote Originally Posted by MG3610 View Post

    Can anyone point me in the direction of good research data explaining these principles?
    http://www.firetactics.com/CAFS.htm

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    Quote Originally Posted by Batt18 View Post
    Beat me to it. Pauls site has some good info.
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    Hi,

    The problem with the comparison, is that it's made with "fog" without any details.
    I can't agree with the fact that fog cant' tackle solid phase of fire.
    In order to understand the problem, just take your Akron (eg) nozzle.
    Set is to low flow rate, with a pattern just between protection and attack. Then sit on your knees, nozzle at 45 from the ground, and open and close quickly. You'll see a kind of cloud of dropplets "flying" for a long time. Now, do the same with a high flow rate. You'll see dropplets are bigger, and fly for less time.
    If you want to cool the gases, use low flow rate to let the dropplets stay in the smoke, without touching the wall. By using short burst, you'll be able to cool the gazes and go to the fire. Then you have to tackle the fire. For that if there are some vent on the room, use fog at high flow rate. Big dropplets will go through the heat, to the fire. If there is no vent, use small burst of smoth bore directly to the solid phase.
    Two fuels (solid and gas) so two way of doing.

    The main problem with CAF is that it's not possible to change the concentration "on the fly" and not possible to use fog pattern. So you can attack directly the fire, but if you have to run 10 m throught the smoke layer, it's not very "secure".

    Maybe a system which allow water fog, and on the fly, foam application then back on water fog and so on, would be the best. Dream?

    Regards to you all
    Pierre-Louis

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    Quote Originally Posted by PlLAMBALLAIS View Post
    Hi,


    Set is to low flow rate, with a pattern just between protection and attack.
    "Protection pattern"? Steam, high flow air and less punch are not what I'd call protective. Longer reach and more water on the burning material, with some heavy drops made by swirling the nozzle or bouncing the stream off the ceiling is more protection in my book. I'm not saying fog doesn't work or but the "protective pattern" is a dangerous misnomer.

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    Default Surface Cooling and Gas Cooling

    As a starting point, I will concede that my experience with CAFS is limited, but have followed its development and applications with considerable interest.

    Most of the CAFS-Structural Firefighting demonstrations I have seen (video and in person) have shown the effectiveness of CAFS in controlling an unshielded, post-flashover fire. In this situation it is quite effective. However, in my limited use of this tool, it appears to have quite limited effectiveness in cooling the hot gas layer while working in to access a shielded fire. The stream punches through the hot gas layer and simply cools the ceiling of the compartment. Most CAFS systems are not designed for pulsed application (as used in gas cooling). However, I have heard that there is a German system that can be used in this manner (no info as yet on exactly how this is accomplished).

    At present, I don't think that there is enough research to answer the questions raised about the effectiveness of CAFS across the board in interior fire attack. Like many other things in the fire service, lots of opinions (likely some of them right) but not a great deal of evidence in support (evidence from the lab, full scale test, and field experience). While the lab and full scale tests are not identical to conditions encountered in the field, they provide a solid basis for understanding how and why things work the way the do.

    The incident in Germany mentioned in an earlier post involved failure of a CAFS hoseline due to the effects of heat exposure. In that a CAFS line contains mostly air, it is less resistant to the effects of heat than a line containing water. In addition, the hose in question was of lightweight, single jacket design (likely a factor).

    Tests are scheduled in France later this year to examine some of the issues surrounding the use of CAFS in a structural environment. Check on www.cfbt-eu.com for additional information.

    Cheers,
    Ed Hartin, MS, EFO, MIFireE

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    The main principle in CAFS is to break the surface tension of material and allow the water to penetrate. Faster water penetration equals more energy the fire has to consume to burn the material. CAFS flow the same gallons per minute just do the job faster, hence less water. The incident in Germany in my opinion was totally bad firefighting. Parts of floors were left unsearched for fire while the hose teams went to higher floors. Then the floors completely lit up. Firefighting is the same with Cafs as regular water with the exception of cellar fires or compartment fires. Imagine a hardware store basement filled with HAZMAT, with cafs you just pump it full of foam and your done. No risk to ff to save paint, fertilizers or other chemicals. CAFS is also not the shaving cream that most people associate it with. The shaving cream mix is reserved for exposure protection. It does an amazing job. Those of you that have row houses only a few feet apart would love it.

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    Quote Originally Posted by RFDACM02 View Post
    "Protection pattern"? Steam, high flow air and less punch are not what I'd call protective. Longer reach and more water on the burning material, with some heavy drops made by swirling the nozzle or bouncing the stream off the ceiling is more protection in my book. I'm not saying fog doesn't work or but the "protective pattern" is a dangerous misnomer.
    Please, read again my post: I'm not talking of "protection" but of the pattern you must use for progression. The right angle is when you turn your nozzle's head such as the pattern is between the "protection" one and the attack one. This mean a pattern of about 60. With such an angle, you can put small dropplets in the smoke layer.
    You say that putting directly water on the fire is better. I agree at 100%. But take a glance at many NIOSH reports on LODD. You'll see that firefighters don't die in front of the fire. They die on the way to the fire: not in the bedroom in fire, but on the corridor from the main entrance to the door of this bedroom. And during this way, i'ts not possible to put water directly on the "solid" fire, as you can't see it.

    Best regards
    Pierre-Louis

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    The Oct.2007 Fire Chief magazine has the complete story on the German fire.

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    Having been able to play with CAF's for some time now I LIKE IT.

    Reasonably well involved SFD knocked down from the outside with 2 CAF lines through the windows, and done fast.

    Good blazing hedge row in an orchard on fire, stand back about 30 feet with the solid tip on and knock it down in no time, change to the fog nozzle, and set up solution and water mix for clean up.

    Beware though that the cooling effect of CAF is not as rapid as straight water, so while it provides a quick knockdown, there is a point where changing to a solution water mix, or straight water should be used, heavily burnt material will retain enough heat to reignite if it isn't completely cooled.

    Other advantage to true CAF systems, only the first length of hose produces friction loss due to the mixture scuffing up and mixing, after that it is so small per length you may as well ignore it.

    500 meter CAF line still flowing strong, try that with water.
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    You dont play with CAFS either use it or dont. Learn to use it and you'll understand it. You fight the fire the same way as you always have. It just takes alot less time to put it out. People who say its for depts. that dont go interior havent seen it used. You can use use it from the exterior such as basement fires or compartment fires and I think thats where the mistake is made. Remember you control the mix you can make the mixture anything you want. Hence you can cool burning material.

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    Quote Originally Posted by rescuedawg View Post
    You dont play with CAFS either use it or dont. Learn to use it and you'll understand it. You fight the fire the same way as you always have. It just takes alot less time to put it out. People who say its for depts. that dont go interior havent seen it used. You can use use it from the exterior such as basement fires or compartment fires and I think thats where the mistake is made. Remember you control the mix you can make the mixture anything you want. Hence you can cool burning material.

    In our part of the world to "play with" something is to use it. I think the rest of the Kiwi's post showed that.

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