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Thread: CAFs Pressures.

  1. #1
    SBrooks
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    Default CAFs Pressures.

    I have a question for you guys from the unenlightened east coast...

    How do you you do pump calculations once CAFs enters the equation? Specifically for those of you who would use CAFs for interior firefighting...what size/length line, what water pressure, what vol. of air?

    If one of you knows how, please make this line into an appropriate CAFs line:

    150' x 1.5" x 150 gpm + Automatic Nozzle=
    1.50 x 24.0 x 1.5^2 + 100 = 181 psi engine pressure

    Before you ask, yes, an automatic nozzle, and no, nothing less thatn 1.5" line.

    Just curious, it seems to me (who's never acutally seen a CAFs line in operation) that calculations would be extremely difficult, considering the compressable nature of the foam, you know, PV = nRT, differential equations and all.

    Thanks



  2. #2
    ka
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    <<How do you you do pump calculations once CAFs enters the equation? Specifically for those of you who would use CAFs for interior firefighting...what size/length line, what water pressure, what vol. of air? >>

    Flip on switch the system automatically ballances the water and air 50/50. 60 to 90 gpm 60 to 90 cu fm with 1 3/4" hose. 50 to 400 foot lines work well all at the same EP they flow the same gpm.

    <150' x 1.5" x 150 gpm + Automatic Nozzle=>

    90 to 100 psi. = 50 to 75 gpm 50 to 75 cufm

    <Just curious, it seems to me (who's never acutally seen a CAFs line in operation) that calculations would be extremely difficult, >

    You're right lots of folks have trouble remembering one psi for all lines and guns. Normally 100 psi.


  3. #3
    SBrooks
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    What then would happen if you increased the throttle to make it 150 or even 180 psi? Would it still work? What kind of foam / stream would you get? Nozzle rxn? Perhaps a better question would be what kind of flows can you expect from various handlines. Also, I understand that foam can smother fire, but for interior firefighting, through an automatic nozzle, is the foam effective enough to make up for the 50% loss in cooling flow? Seems that in a really hot fire, using an automatic, the foam might break down and leave you with little more than some suds and amended water. Why couldn't you get the best of both worlds and have more water with your foam?


    ka, thanks for your reply

    [This message has been edited by SBrooks (edited March 19, 1999).]

  4. #4
    ka
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    <What then would happen if you increased the throttle to make it 150 or even 180 psi? >

    You'd get an over pressuried stream just like over powering a water stream

    <Would it still work?>

    Yes

    < What kind of foam / stream would you get? >

    A got powerful one

    <Nozzle rxn? <

    Sure

    <Perhaps a better question would be what kind of flows can you expect from various handlines. >

    20 gpm 1" 60 gpm 1 1/2" 90 gpm 1 3/4" 110 gpm 2" 240 gpm 2 1/2"

    <Also, I understand that foam can smother fire, but for interior firefighting, through an automatic nozzle, is the foam effective enough to make up for the 50% loss in cooling flow? >

    There aere four sides to chose from. Cooling...it does that, remove fuel does that...chain reaction does that, oxygen does that. Why go just for one side? A dry chem extinguisher will take out most rooms.

    <Seems that in a really hot fire, using an automatic, the foam might break down and leave you with little more than some suds and amended water.>

    I've never experienced that. Water will leave you hanging when 95% is on the floor or burnig you in the form of steam

    > Why couldn't you get the best of both worlds and have more water with your foam?>

    I guess I don't have a clue what is being asked?



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    Let me preface this by saying I have never worked with a CAFS on a structure engine. I have only worked with CAFS on a wildland engine.

    Ka seems like he knows what he is talking about so if ka would like to correct my on anything I would not feel hurt. So first a quick overview of plumbing, at least on our wildland rig.

    The foam and water mix like any other rig. Then at some point before it enters the hose the air is injected into the mix. The pressure on the water/foam mix had to be extremely close to the pressure on the air for it to mix properly. If the water pressure was to high it would hold back the air where it came into the plumbing and if the air was too high it would hold back the water. Or we had the auto switch that we didn't like to use for some apparatus specific mechanical reasons.

    That being said, our compressor was not connected to the pump. So you could run the water pressure up and not the air and as noted above it wouldn't work. You would get a chopping machine gun effect that was very ineffective.

    From our wildland rig we were producing effective streams at 8-9 GPM where the same hose and pressure without CAFS we would be using 50-60 GPM. So I could only imagine that a structure engine with CAFS would also use 7-8 times less water.

    One of the philosophies that we lived by with CAFS is that that while you are using way less water it is water that is being applied to where it needs to be. ie. foam will stick to a surface that needs cooled where water will hit the surface and bounce or run off. I don't know how accurate these numbers are but we were taught that with straight water 80% ended up on the ground and 20% did some good. When you introduce foam those numbers moved to about 70/30 and when you introduced CAFS those numbers almost flopped to 20% on the ground and 80% ended up doing good. And thats how you could end up using so much less water and still do the same amount of work.

    OH, and friction loss and all that stuff you worked so hard to memorize... that all went out the window. Because essentially you were pumping mostly air down the pipe and air has virtually no friction loss. We had basically a two cylinder, two stroke snowmobile engine running the water pump on our wildland engine and we could push foam straight up for a long ways with no problems as long as we didn't stop. Once you stopped you started building slugs in the line that the pump couldn't push out.
    Last edited by RJAbbott; 10-17-2008 at 01:44 AM.

  6. #6
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    I've been engineer on a CAFS Rescue-Pumper for 8 years now and been through the Waterous CAFS class twice.

    KA appears to have it right, one note: Most current CAFS systems are limited to 150psi, so that it the max usefull pressure you can run at.

    Fog nozzles remove a large part of the effectiveness of CAFS, you should run smoothbore, personally I like 15/16" or 1" (1" is too large for straight water or foam from a 1.75" hose though).

    Fire flows in 1 3/4" line are 90GPM for 1:2 CAFS, and 135GPM for 1:3 (my personal choice for interior attack). Pump and nozzle pressure are always 100psi, any higher and the stream starts to disassociate too quickly and you loose your reach (that's using smoothbore).

    There is no friction loss with CAFS, I've personally pumped lays over 1000' and had the nozzle crew ask for less pressure even though I was at idle.

    There is elevation loss/gain, which is why the crews had too much pressure in the previous line.

    Even though you are using less water the water is much more efficient at cooling the fire and breaking the triangle, it is not however a magic bullet. If your fire load is more than 135gpm CAFS will not work, period.
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    Is nozzle reaction for 100psi CAFS similar to 100psi water???

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    Quote Originally Posted by neiowa View Post
    Is nozzle reaction for 100psi CAFS similar to 100psi water???
    No, there is quite a bit more reaction than straight water due to the expansion of the air coming out the nozzle (exact numbers escape me, but its like 50% more). It takes some getting used to, I'm a big guy and can solo a CAFS noz, but I don't dare do it while moving and I usually prefer to take a knee before opening the nozzle. Some of our smaller women had a hard time getting used to it, but they did (just requires a little more help from the backup person and a little technique).

    One other note, CAFS is very loud, again due to the air escaping, the nozzle man will not hear his radio, I even clip mine to my SCBA shoulder strap and put it right near my ear. Again the backup person needs to help the noz, relay things to them.
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    2 caveats. One, if you insist on using an automatic nozzle for CAFS, find out as much as you can about it. A nozzle not made w/ CAFS in mind will require higher nozzle pressure simply due to how some of the proprietary baffle designs work. Ie- your stream will not be as effective. I believe TFT has one out that is designed to work well with CAFS. Also, why does it have to be an automatic nozzle? CAFS was intended to be optimized with a smoothbore nozzle. It's also MUCH easier to pump a CAFS line with a smoothbore as far as achieving proper flow, nozzle rxn etc. Unfortunately, many around here are too unfamiliar with smoothbores and can't effectively pump them when using CAFS.

    I'm no CAFS "expert" but I have used it extensively and found out what works the best with our equipment. YMMV.
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    Quote Originally Posted by Fire304 View Post
    Even though you are using less water the water is much more efficient at cooling the fire and breaking the triangle, it is not however a magic bullet. If your fire load is more than 135gpm CAFS will not work, period.
    I haven't heard of this issue with CAFS, can you expound please. What if instead of the 15/16ths we used a 1 3.8" ball valve with out a tip? is there a direct corralation to quantity and hit power? or isn't there?








    Kudos to RJAbbott for resurrecting a dead thread 9 years into it's passing. Not a record but deserves an honorable mention

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    As I previously mentioned, most of us use either 2:1 or 3:1 CAFS, which is 95 and 135ish GPM respectively. This ratio is set at the pump panel based on how wide open your air and water valves are. Unlike in water pumping CAFS nozzles do not necessarily control the volume of water you get. Nozzle size will effect the "dryness" of the CAFS you put out at the tip plus it will affect your ability to loft the foam any distance. Using a wide open ball valve you'll get very dry shaving cream like foam, but it will be so light that it won't carry very far. While I have not experimented with limiting water flow so as to generate a table of numbers, smaller nozzles will at some point limit your flow.

    My FD has chosen to use 15/16 because it produces pretty good CAFS. Though the 1" tip performed better if you were to loose the compressor (which has happened to us) you get a very poor stream from straight water of Class A. The 15/16 is just about the limit of what our hose can flow and produce a good stream.

    If you troll around in these threads you'll occasionally run into a comment like "CAFS is ok for overhaul, but its no good for knock down." Usually if you dig into the comments you'll find one of 2 things has happened. Either the user was trying to use it like water (which basically completely ruins the whole purpose of putting the bubbles in the water and gives you booster reel performance), or they were dealing with way too much fire for the 95GPM they were getting.
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    Fire 304, about the 135 gpm limit, have you ever used CAFS through a 2.5" hose? We run a Blitzfire with a 2" smooth bore tip off of 2.5" hose, 1 person can put out a whole lot of fire. My guys were amazed at a fully blown 2 story house how much fire this combination put out.
    Our regular attack lines use 1.5" hose with 1 3/8" shutoffs with no tip pumped at 110 psi. We have had very good success with this combination, but that came after many hours of training, trial & error, and using various combinations with a whole bunch of white stuff all over the place.

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    We have a 2.5" CAFS preconnect, but honestly we've never really played with it. I have no idea what sort of flows it is capable of. I think of it more as a feeder line which we can wye 2 hand lines off of if needed. I'm sure it'll flow more, but have no idea how much, or if the air plumbing can inject enough into the flow to make effective CAFS. The one time I've pumped that discharge it was into a nearly 2000ft long feeder for a brush fire, and that was very low flow.

    BTW, you can get more water than 135GPM from a 1 3/4, but you'll be cutting the air back to the point that it's not really CAFS anymore.
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    A 21/2" CAF's line is a very effective tool we flow about 200gpm 70 cfm at 100psi and can get 240gpm 80cfm @140 psi
    We have seen impressive Knock downs on large fires with the 21/2" CAF's line
    Those who say CAF's is not effective on large fires need to leave the 11/2" on the Truck and start off pulling 21/2" lines.
    With the 21/2" line you can deploy and flow with less manpower and still be able to reposition and advance.

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    Capt., whats the recoil like on that 2.5? Can 2 men handle it? Or does it become more of a fixed line once its flowing?
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    Yes, there is a recoil that you need to be aware of, but with two TRAINED firefighters they should be able to handle it, but you can wear them out if you have an extended operation and they are advancing.
    Unlike a normal water filled 21/2" a CAF's line has the air mix that makes it much lighter and easier to move with fewer people. once the water 21/2 is charged it takes a small army to move it.
    Our last commercial we advanced 700' of 21/2 to an interior position and were able to move as we needed and again no pressure loss, lighter line, and excellent knockdown.
    We are using both an Akron blitz nozzle and a blitzfire portable monitor on our 2/12" lines just remember to pull the stream shaper off the blitzfire or it will mess up your bubbles

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    Fire 304, our blitzfire is a one man operation, if needed, gun is light and stable, hose is light and movable by one person. Usually, on an exterior attack, the gun is set, flows CAFS for 1-2 minutes, knocks the fire, shuts down, moves to next position, opens, knocks, moves, repeat as needed. Very successful in this role. Unfortunately, or thankfully, we have not had the opportunity to use this setup on an interior attack, but it is in our playbook.

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    We used CAFS for knockdown just the other day. It worked just fine for a two room fire. Some of the people that were there were amazed at how clean the attack crew was when they came out!

    I think it's fine for knockdown, just as long as you remember to base it one the conditions. I think if I had heavy heat/pre-flashover conditions I'd stick with water for the gas-cooling ability but if you have the right conditions, with a good coordinated vent, and you don't have to hunt or go deep for the seat of the fire, there's nothing wrong with CAFS for initial attack.

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    Hi All,

    We use a 2.5" pre-connect with both a hand nozzle and/or a Blitz nozzle. The fire knockdown capabilities of a 2.5" CAFS line are far greater than any equal size water only line flowing the same gpm.

    Remember the basic “Rule of Thumb”. “Small fire, small water, Large Fire, large water”. Use the same for a CAFS attack. The difference will be in the total amount of water used to extinguish the fire.

    In a heavy fire condition CAFS will work far better then plain water. Remember that "plain water" is very inefficient as an extinguishing agent, small or large fire. To compensate for water’s inefficiency you have to flow it for a longer period of time, hence using more water overall. CAFS makes the water 3 to 7 times more efficient. You are still flowing water, but instead of 80-90% of it converting to steam and/or beading up and running away during a plain water attack, the tiny little "air" bubbles that are carrying and protecting the water will allow the water to reach what is burning and to POP as they fly thru the air to absorb the heat. The bubbles POP at about 140 degrees. And there are millions of them. The bubbles are the key. That is why a straight bore nozzle is best with CAFS as it does not pop bubbles.

    My experience has been that with CAFS the tables are turned. 80-90% of the water now stays and fights the fire with you while 10-20% of the water runs away. I like the CAFS odds better. It has also been my experience that CAFS elongates your booster tank by as much as 3 times its amount compared to plain water attacks. So if you are caring 500 like I do on my engines it is equivalent to 1500 gallons of water. Provided the pump operator does their job correctly and the nozzleman does theirs.

    The fire attack is little different too. Nozzleman are “painting” all surfaces in the fire room or area with CAFS bubbles until they feel the temperature drop. As apposed to an indirect stream to the ceiling with plain water. This attack technique works well for an interior CAFS attack.

    Hope this helps,

    Be safe,

    Captain Lou
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    Last edited by CaptLou; 12-31-2008 at 01:43 PM.
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    As Lou Said Big fire Big Water and if its a big fire leave the 11/2" on the truck and go big, theres always time to get the smaller line there never seams like you can get a bigger line once you start.
    After Using CAF's on Larger Fires, with a properly pumped and sized line I feel Much more comfortable with A line flowing CAF's then plain water on NAF's.
    The only time I have had a problem with An unvented attack we "tried" to use CAF's through a Fog nozzle.
    We will cool as we go quick shot as we advance so you are not ignoring the fire gases, the One thing that you should remember is that you can extinguish so quickly that unless you paint your surfaces you have a chance of rekindle.
    Its the Abilities of the CAF's line that I wan in high heat because not only are you going to extinguish the fire faster you are going to dramatically drop the room temptress with less water and less chance of inverting.
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