Table of Contents

Check out our Pin Map Showing where questions originate!!


  1. Class A CAF Effectiveness on Class B or C Fires?
  2. Can a CAF smooth bore nozzle be used intermittent on electrical fires?
  3. Good home defense CAF System?
  4. CAF hose length requirements?
  5. Retrofit Feasibility?
  6. CAF for Interior Fires?
  7. CAF on Grease Fires?
  8. CAF on Polar Solvent Fires
  9. Question on Method of Interior Attack?
  10. What is the source of the Compressed Air?
  11. Air Valve Operation & Special CAF Hose?
  12. Can you use Class B Foam on a Class A fire?
  13. Limited or inadequate Air Flow Problems?
  14. Using CAF on a Vacuum Tanker (Tender)?
  15. ISO and Compressed Air Foam?
  16. Pumping CAF through a water engine?

If we have an engine operating at a scene that is not CAF equipped, Can we supply that engine with CAF and will the first engine have good product at their nozzle??

Pumping CAF through another non-CAF engine is possible, but here is what will happen - if the non-CAF engine is still pumping, its pump will be ineffective as you will be pushing bubbles and air through the pump (cavitation). 2nd - pumping CAF through the pump (whether running or not) places a lot of obstruction in the CAF stream, thus popping many of the bubbles and making the CAF less effective. Grant it, the foam will continue scrubbing through the final hose, which might increase its bubble capacity again.

CAF can be pumped long distances without any reduction in the stream. The most effective scenario would be to supply the final attack hose lines directly from the CAF engine, by passing the non-CAF engine. In other words, if the CAF engine is some distance away, connect the CAF supply line via a wye directly to the hose lines attacking the fire. If the CAF engine is sitting right next to the 1st engine, you can also break the non CAF lines at the truck and attach directly to the ball valves of the Charged CAF lines off the second due truck, 1.75" to 1.75". No Wye needed.

An alternative would be to not use the CAF at all and just pump water from the CAF engine to the original non-CAF engine but this would be very ineffective as we all know that CAF is superior to water in fire extinguishment.

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I noticed that you had a Mr. James Bradley from ISO as one of the speakers at the last symposium. (SW CAF Symposium) Do you have the text or any printed materials that he developed for his portion of the presentation? We utilize CAFS in our department and we just completed field testing by ISO. The Field Representative indicated a slight interest in CAFS and I was curious if Mr. Brady’s knowledge would benefit our rating if we could get him and our Field Rep together. Thanks for any help you can provide.

I am sure that your field rep showed a "Polite" interest instead of a slight interest. Texas passed legislation called the Texas Addendum to the Fire Suppression Rating Schedule. The schedule dictates additional information be included in the rating. 30% of the Texas Addendum credit is based on CAF.

So far, ISO refuses to recognize CAF any where else and will probably not do so unless forced to do so by individual state legislation.

Our people did not see any hand out information at the symposium. I have spent some time researching Texas Legislature. I recently received information from the Texas Department of Insurance (attached). This information is now posted on this web site. In the meantime, here is the speaker's information if you wish to speak to him directly:

Phillip Bradley
Community Mitigation Services
Insurance Services Office
430 W. Braker Lane Suite 350
Austin, TX. 78759

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Howdy, I don't know muck about CAFS, no one in our area uses it, but the guys on our dept love our class A foam and I think CAFS shows great promise. Now the question, we just signed a set of specs for a vacuum tanker to be delivered early in 2008, ever seen anyone use the vac/pressure compressor for these systems for CAFS? We already have a 1000gpm pump and a 500 gpm Robwen bladder type class A proportioner. Why can't we just include the valving to add air into the preconnects? Am I nuts? There are lots of these vac tankers out there with fire pumps on them, why aren't they using CAFS? If this sounds feasible, please help me save our specs while there's still time! I'm sure you probably expected me to say we don't have much extra money to deal with, guess what, we don't, we're already over budget, but isn't the compressor the most expensive part? I guess I need to see one of these systems to see how they work...Thanks for any input!

I spoke with a vacuum tanker builder at FDIC in reference to your question. He indicated that the vacuum system is relatively small cfm and operates at a low negative pressure. The system could flow neither the volume nor the pressure (up to 150 psi) required of a CAF system.

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We have a Hercules CAF System. When we flow an 1-3/4" line at 100 gpm (80-100 psi) we cannot get any more than 22-25 cfm. When we gated the water down to 50 gpm, there was no change in the air flow. We have electric air valves that cannot be adjusted for volume. Could this be a compressor problem or are the air lines designed for a maximum of 25 cfm?

There could be several possibilities here:

Generally, a 1-3/4" line cannot handle 100 gpm and 50 cfm simultaneously. That is too much volume for the hose. Cutting back to 90 gpm usually allows 45 cfm to flow through the hose. But since you did gate back the water, the air flow should have increased simultaneously.

You did not state if you were flowing water from a hydrant? When flowing from a high pressure hydrant or other pressurized water source, there is no need to throttle up the engine RPM to get the needed water pressure. Without the increased RPM, the compressor may not spin fast enough to generate adequate volume. If the water source is high pressure, gate down the intake flow and increase engine RPM.

Most of the CAF systems on the market are designed for high CFM flow through each line. While it is possible that the system was designed to hold CFM to 25, it is doubtful. There is also a possibility that maybe the air flow hose to you discharge line could be kinked, damaged or partially plugged. Try another discharge and see if the situation is the same.

Another cause could be a partially blocked or stuck air inlet valve on the compressor. The valve adjusts to increase the air volume. If it is stuck, it might limit the air volume. Also, the air inlet valve is controlled by the air control circuit. There could be either a problem or mis-adjustment in the air control circuit. One way to check this is to see if the air and water pressures are balancing.

And finally, it is possible that the air flow meter might not be reading correctly and the air might be flowing adequately. Some of the meters can be calibrated. Check your manufacturers documentation.

If none of these options corrects the flow, contact the manufacturer for advice.

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Looking at the FAQ section of your web site, regarding the question of the difference between class a and b foams, can a person surmise that class b foam can be used (AFFF 3/6) for a class a fire with results similar to that with a class A foam? If so, what would the proportioning ration be? Just wondering if we could be doing that. Thanks

Class A Foam can extinguish a Class B fire, but Class A foam cannot be used as a protective blanket. It will not work. Class B foam is designed (manufacturer's instruction) to be used at 3/6% for Class B fuels. Class B foam is designed to form a vapor barrier. Class B foam is not designed to be used on Class A fuels at any concentration. Class B foam contains reportable contents (contents not proven to be non-hazardous). Class B Foam also does not have an affinity to carbon (Class A) fuels. It most likely will not stick to the fuels like Class A Foam. It will require clean-up. It also will not reduce the black smoke emmissions. If anything did go wrong and the fire didn't go out, or if the clean-up was costly, there would be no liability defense.

Two different fire problems require two very different agents. Our job is to assess the fire problem and decide if it requires a carbon loving (Class A) agent or a product that is chemically opposed to carbon (Class B).

Our recommendation would be to never consider using Class B Foam on a Class A fire.

One additional question. We are in the early stages of specing out a possible truck to be financed by a hopefully successful FEMA grant application. The truck we desire is quite large and we are concerned about total costs. Adding CAFS seems to add 40K+ to the cost. Can a smaller system be used to just power 1 1-1/2" line with CAFS, and make it dual purpose for A and B foams? I have read somewhere that this can be done for a fraction of the cost. Do you have any knowledge of these systems?

You can build an engine to do just about anything, with or without dual purpose foams. There are smaller compressors that can be installed. I recommend nothing smaller than an 80 cfm if you are planning to fight structure fires. It is critical to have a back up CAF line just incase anything goes wrong. 80 cfm will supply two lines.

Waterous offers a lower cost line of PTO powered CAFS systems called the Silver series. The 80 cfm model is the 80SP. Training is not included and
should be considered as an option when purchasing the system.

A proportioner to do class B will be expensive as it must be capable of high volume (10 to 12 gpm). It would be more cost effective to use a Foam Pro 1600 proportioner for class A CAFS. An eductor and an aspirating nozzle will work for class B in the rare occasions that it will be needed.

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Can you please explain the effectiveness of Class A foam through a CAF system when it is used on Class B or C Fires?

The reason CAF is effective (ability to absorb heat faster) on Class "A" fire is due to the expanded surface to mass ratio of each water droplet in the form of a bubble. It is the heat absorbing ability of the water, that in a bubble form, absorbs the heat faster. 

Using a good quality Class "A" CAF on a Class "B" fire would give you the same result. The expanded water droplets in bubble form would absorb the heat faster, thus making the CAF more effective. One thing to remember, however, is that Class "B" foam is designed to form a vapor barrier over a contained spill of a liquid. A Class "B" fire can be extinguished using good quality Class "A" CAF, however, the Class "A" Foam will not form an adequate vapor barrier to prevent possible flash re-ignition. "Vapor suppression is not provided and use for that purpose is not recommended."

Class "B" Concentrate CAF, will also expand water droplets into high surface to mass ratio bubbles. These bubbles will again absorb the heat faster, thus making Class "B" CAF more effective than solution. This foam will then produce the vapor barrier on a contained liquid. 

The key here is understanding what is happening. CAF, whether Class "A" or "B", absorbs heat faster by changing the water droplets into a high surface to mass ratio bubble. It does not matter which concentrate is used, it is the expanded surface to mass ratio of the water that absorbs the heat. 

Class "B" Foam in a blanket, has the ability to create a vapor barrier on a contained spill liquid. What does Class "B" Foam do on a non-contained spill? The liquid can flow out from under and beyond the vapor barrier. If the spill is not contained, Class "B" and Class "A" CAF are both effective for fire extinguishment, but neither will provide an adequate vapor barrier. Again, in this case, vapor re-ignition is a possibility. 

Keep in mind that a good quality Class "A" concentrate will be UL Tested as a "Wetting Agent" and that testing looks specifically at the Class "B" extinguishment abilities of the Class "A" product. The testing process to receive UL listing can be found in the specifics of The UL 162 Test and NFPA 18 Test documents. Several Class "A" products are UL Listed. Since the Class "A" product listing is based on Class "B" fire tests specifically, the statement can be made that some Class "A" concentrates will work on Class "B" fires with scientific tests to validate the statement. 

Suffice it to say that a good quality Class "A" CAF will be more than adequate for most simple hydrocarbon fire problems many fire departments routinely encounter. Polar solvents and commercial quantity spills and fires will require Class "B" foam in large quantities and Universal / ATC / ARC type concentrates in many cases. Many small to medium departments may not be equipped to properly handle large scale Class "B" events.

As far as Class "C" energized fires go - keep in mind that the stream of Class "A" CAF bubbles is 99.7% water and being a continuous column of water will conduct electricity quite well. There are no known scientific tests on this matter, however, we at do know a few "test subjects" we could volunteer (just kidding)!

Additional information on this subject may be found in  a recent Fire Chief's Magazine Article - No Size Fits All!

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I was wondering weather you knew if there was any evidence to suggest that a cafs straight stream or smooth bore could be effective on electrical fires if applied in bursts (impulses), I mean intermittently?

As far as Class "C" energized fires go - keep in mind that the stream of Class "A" CAF bubbles is 99.7% water and being a continuous column of water will conduct electricity quite well. Since the CAF stream contains water, it should be considered with the same caution as a regular straight stream of water. It would be safe to assume that the water drops in expanded bubble form are all in contact with one another and could thus conduct the electricity with potentially disastrous results.

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Is there a good CAF system available to home owners for home defense?

I am sure there are several good home defense CAF units available on the market. Most will come in the variety of a fixed or portable stored energy type system. Stored energy meaning that there is a stored amount of water and compressed air. These systems can come in many sizes and designs. The duration will depend on the amount of stored contents and operator control. does not recommend nor endorse any specific type system. However, we occasionally get advertisement from system manufacturers. Continue your on-line search with the best of luck and periodically check our page "CAF Systems & Related Equipment" to see if any such systems are listed there.

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I am thinking of getting a 30 gal stored energy system for a small truck for quick response. What length hose is recommended? They're not sure if 50 feet or 75 feet comes with the unit. I don't want to give up pressure because the unit is so small.

There are specified hose lengths for CAFS. The mix of solution and air must be scrubbed to form the bubbles. The fire hose does the scrubbing. It takes a minimum of 50 feet of 1" hose (100' of 1-1/2" and 1-3/4") to adequately scrub the bubbles. As far as pressure loss between 50 and 75 feet, the loss would be negligible. In CAF, the hose does the scrubbing which is good. Water has the problem of dealing with friction loss from fire hose. CAF does not. One additional item, some of the stored energy units come with a preconnected reel line. Some fire departments have experienced inconsistant or poor CAF with 3/4" hose lines. Consider using 1" lines. 

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We have a 1995 E-One and a 1989 Mack that I would like to retrofit with CAFS. Yes I am totally committed to CAFS fire fighting and we will be purchasing two new engines in 2007 that will have CAFS, but still want to explore the possibility of the retrofit. Is it possible for one or both?

Check our section on CAF Systems in reference to retrofits. It will depend on the space available for the compressor, the cost and complication to add the system, and the expected remaining life of the truck.

Just about any truck with a centrifugal pump cab have a CAF system added, it just depends on the specific situation. Most seem to use the PTO method of compressor power, if PTO ports are available.

Another consideration is what NFPA "Annex D" will have on the 1989 Mack (bringing the unit up to 1991 Standards).

We at recommed contacting several engine building companies to get estimates for a conversion. This will give you an indication if it is worth the conversion. Many older trucks have been successfully converted. I one converted a 1981 E-One, adding a 60 cfm auxiliary engine driven compressor, porportioner and foam concentrate tank. The unit is still in service.

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I'm a firefighter in the UK. There is a big emphasis in European fire departments on understanding fire behavior, the formation of superheated gases and un-burnt products of combustion etc. We work with water fog sprays to cool these gases and reduce the risks and improve the conditions in compartments for us. We are looking at acquiring some CAF system fire appliances, I wondered what your experiences of using CAFS were inside property fires? I'm well aware of the advantages of using CAFS on external fires. Any advice is much appreciated. Good site, keep up the good work !!

CAF works great in structure fires. The increased surface to mass ratio of the bubbles (compared to water drops) results in immediate heat absorption. CAF is applied in a straight stream using smooth bore nozzles (or shut off butts with tips). With the proper CAF, the stream does not interfere with the thermal layers. Having an affinity for carbon, CAF also attaches it self to the un-burnt products (carbon) eliminating ignition. The application of the correct CAF, absorbs the heat so quickly that almost no steam is generated, therefore, there is no steam expansion to push the thermal layer down as occurs using water spray.

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I was wondering does cafs have value for grease (fat fryer fires?) and would it be less likely to spread the fire if applied as a spray( fine mist)???? Would it also have value as a straight tip or smooth bore & or a reducer that had a straight tip???? I found some one who said they modified their water extinguisher to run as a CAF system.  They said that they effectively made a cafs formulation by drilling holes 3 inches from the top of the pick-up tube and filled with 1.5 gallons plus foam. The person said they filled this to 100 psi and effectively used it as cafs system (the reason I ask the ? is) I was wondering would you think this could have value for a grease fire?

First, CAF has the ability to rapidly absorb heat which could have value on grease fires, based on the application of the CAF. CAF is very high energy. A normal CAF stream has a 60 foot reach. Shooting a CAF stream directly into a grease fire could easily blow the grease every where with potentially disastrous results. Depending on the size of a grease fire and the location of the grease, a CAF stream might be aimed just above the fire thus absorbing the heat. CAF might also be bounced off a wall at a grease fire, however, the high energy might still cause a negative effect. 

The only way to make a fine mist from CAF is at the far end of the 60 foot stream. This might work only if the nozzle operator can stand 60 feet from the grease. Using any fog nozzle with CAF strips the bubbles away from the foam resulting in the application of foam solution (foam and water only). Foam solution, while much more effective than water, does not have the expanded surface to mass ratio that CAF has, and thus cannot absorb heat as rapidly. 

Placing a reducer on a straight or smooth bore nozzle strips some of the bubbles from the foam making a wetter CAF, but the stream still has the same high energy. 

An alternative on a grease fire might be to use a dry chemical fire extinguisher (Sodium Bi-Carb type hood system) or to use a foam in a medium expansion, low energy aspirated stream. This way the foam can be lightly applied to flow over the grease.

Well if discharged into heat above the fire is it possible it could rain down gently and be effective?

CAF will always be more effective than water, however, water is not always the solution. 

One of our instructors also made a CAF extinguisher using 1 liter of solution. While it does make CAF, it is difficult to regulate the outcome. If CAF is applied too wet, it causes steam conversion that might have a negative effect on a grease fire. If it comes out too dry, it will not absorb the heat. There is no way to insure or regulate the proper ratio when some of the air in the extinguisher is moving the water, and some of the air is mixing with the water. In our instructor's tests of the extinguisher, only a portion of the solution was exhausted. This results in a very short duration exposing the operator to potential hazardous consequences. 

Our recommendation is to stay with the current NFPA and UFC standards for extinguishment of grease fires. 

If your experimentation continues and you solve any of the above concerns, please let us know

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We are about to start up an ethanol plant in our jurisdiction and I need some help. I have been researching using our CAFS pumper with a foam pro 3012 proportioning system to apply National Gold AR-AFFF foam. What I can find it is good to do. Tonight I see NFPA 11 that says CAFS is not to be used on polar solvent fires. I'm confused. Why would this not be allowed to use CAFS on polar fires? Any help you can give me would be appreciated. Class A I am familiar with but the AR-AFFF I don't know that much about. Thanks for any suggestions you can provide.

Many responders forget that CAFS produces high velocity streams. These streams certainly increase our reach, stand off distance and thus safety at Class B incidents. But, that high velocity stream can severely disrupt the protection of the Class B blanket that is being produced. When producing a blanket on polar solvents the higher percentage rate being provided actually produces more of a membrane then a film such as is the result at lower percentages on simple hydrocarbons. This membrane helps isolate the polar fuel from the water that composes the majority of the foam. That same membrane can be breached from a variety of sources such as turnout boots, high velocity streams and etc. It's been noted that the membrane doesn't reseal as quickly as does the film in straight AFFF. During a training evolution note the sticky membrane that attaches it self to your personnel's gear.
Another safety point to consider is the need to never allow a stream to be plunged into a pool or tank fire due to the thermal dynamics that may exist subsurface. A high velocity CAFS stream certainly can have a penetrating effect from a misdirected smooth bore nozzle. Many agencies require there personnel to use fog nozzles during Class B application in order to have a wide pattern available for protection from radiant heat in the event of a flare up.
These are just a few thoughts on this in depth subject for you to consider. Many facts, scenario's and unfortunate events are studied and taken into consideration in the formation of NFPA standards. We commend you on starting your research prior to committing your forces.

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I'm a French FF studying rapid fire progress for years. Actually, we are just discovering CAF and we have some questions.
On your web site, you say that the use of CAF is possible inside structure, but that's you can't attack directly smoke at ceiling level as this will made a thermal inversion. Of course, it's also true if you use a too important flow rate or a narrow fog directly to the ceiling.
With a fog nozzle, we cool the smoke using a 60° wide fog, at low flow rate. But how can we do with a CAF? e.g. I'm in a corridor, with a smoke layer at 1,50m from the ground. I have to travel about 10m to the bedroom door to attack. For that, I've to cool this smoke layer (assuming the bedroom door is not completely open, so attacking from this distance is not possible).
Do I have to "paint" the wall just under the smoke layer, wait, go forward 1 or 2 meters, paint again the wall and so on? Or do I have to paint the wall from my location up to 10 meters then wait and go directly to the bedroom?

CAF is very effective in structure fires. Compressed Air Foam is applied in straight stream form using a smooth bore nozzle. The straight stream does not interfere with the heat layers. The heat will not drop to the floor level. CAF will instantly take the carbon out of the smoke increasing visibility and will simultaneously reduce the heat.
Compressed Air Foam is applied wet (using a 1" smooth bore tip) by painting all the surfaces around a door and especially the ceiling to overwhelm BTU production and reduce the heat and smoke. It is the bubbles that reduce the heat. The bubbles must be applied at the ceiling level as well as at all levels. If the door is partially open (as in your example) some of the CAF bubbles will float into the room reducing the heat as you make your way down the corridor.

This is interesting, but seems to be strange as on your web site I can read:
#1 CAFS causes the temperature to rise within a structure as fire control is initiated. 
FALSE ! This myth is perpetuated by firefighters with little or incorrect training. A brief application of dry foam into a super heated atmosphere will cause extreme thermal disruption at ceiling level thus forcing high temperature gases to floor level driving fire fighting forces out of the building and worsening conditions for trapped occupants. 

And for me, that's the truth, because even with a water spray, if you attack at ceiling level, you have thermal inversion. So, if I've a smoke layer at 1 meter from the floor, what do you suggest? Paint inside the smoke with the potential problem of thermal inversion or paint the wall just under the smoke?

You are partially correct in what you read. It does say a brief application of DRY foam will cause extreme thermal disruption. The key word here being DRY FOAM. Dry foam has a higher air than water ratio. The high air volume can not only disrupt the thermal layer, but there is inadequate water in the foam to absorb the heat. The water will turn to steam, expanding and cause thermal layer disruption.
In a structure fire, CAF MUST be applied WET, with a higher water than air ratio. There will be no disruption of the thermal layers and there is adequate water to absorb the heat. The heat absorption is so fast that almost no steam conversion occurs. WET CAF is applied by directing the straight stream in an inverted U shaped pattern across the ceiling and up and down the walls, painting all the surfaces with the WET bubbles.
In early CAF use in the 1990's, many firefighters were attacking structure fires with too DRY CAF. Statement #1 is a MYTH based on these DRY attacks.

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I would like to know from where you are getting the compressed air? Is it from air compressor or any other source? What is the pressure and cfm of the compressed air which you require for this application?

It depends on the system. There are stored energy systems that get the air from stored pressure tanks. Some systems use tanks as small as SCBA tanks. Others use larger compressed air tanks.
On the constant flow systems, a compressor is used. Cfm ranges from 35 to 200. The small units use piston compressors, the larger units use screw type compressors.
The amount of air required depends on the application. A 35 cfm compressor can supply a 1" hose line. A 200 cfm compressor can supply 4 hose outlets, a deck gun and an auxiliary outlet.
The ratio of water to air that is applied will depend on the specific application, usually either for direct flame extinguishment or for application of a protective foam blanket.
Compressed air foam systems are generally operated between 80-140 psi, again depending on the specific application.

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We have recently purchased a new truck with a Waterous 80-SP CAFS system on it. During our delivery instruction, we were shown a video about a Phoenix FD truck on operation of the CAFS. During the video, they had stated and demonstrated how to achieve "wet" foam. They had the discharge completely open and the air control valve partially opened. Then when they went to a "dry" foam, they completely opened the air control valve and partially closed the discharge valve to achieve 40gpm. After reading the operation manual that came with the truck, it stated to fully open the air control valve and control the desired foam consistency by the discharge valve. So I am wondering which way is the correct way or are both usable?
Also, in the manual it states, "Utilize fire hose that is rated by the hose manufacturer for use with CAFS." Is this something that we should be concerned about? We are unsure about the history of the hose manufacturers.

1st, congratulations on the purchase of your new CAF system. Proper operation and application of CAF will provide tremendous benefit to your community.
With the manual air valve, adjusting both valves will provide an infinite number of Solution: Air ratios. The goal is to provide the optimum ratio for the finished foam needed - a wet foam for extinguishment (higher solution ratio) and a dryer fluid foam (higher air ratio) for the protection blanket. Many environmental factors can effect both the optimum ratio and finished foam. The optimum ratio in Phoenix might be slightly different than the optimum ratio in Maine. The recommendation is to follow the manufacturer's direction, continue practicing with the CAF, and adjust as you see fit for your particular needs and environment.
As far as the hose goes, there are special CAF hoses available on the market and for a price. However, using the appropriate length of standard fire hose will provide adequate scrubbing to form the needed finished foam. No special hose is necessary.
In order to have a long and happy relationship with your CAF System, detailed class-room with hands-on instruction is highly recommended. See this site's section on INSTRUCTION. Waterous offers a full day in-house DELIVERY INSTRUCTION CLASS  utilizing a cadre of instructors located around the country. Also check out their CLASS SCHEDULE SITE   to see if one is already scheduled in your area. inFOAMation associates  also offers quality in-house instruction tailored to meet your specific needs.

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Compressed Air
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Revised: May 31, 2007 .