Thread: Class B for CAFS???
09-09-2004, 07:28 PM #1
- Join Date
- Nov 2003
Class B for CAFS???
Anyone using class b foam with CAFS on flammable liquids. Does it work as well as class a does on normal combustibles? And how are your flow rates etc. Any help is appreciated
09-10-2004, 12:36 AM #2
- Join Date
- May 2001
That is a good question?
09-10-2004, 04:42 AM #3
I question what the benefit would be of doing so, other than stretching a limited water supply on an initial attack from tank water.
I also wonder: would adding more "depth" to the foam blanket then decrease the actual surface area the AFFF would be able to cover, compared to a thinner layer of aspirated AFFF?
Hmmmmmmm I've read that some places use Class B foam with CAFS. Since you're going for vapor suppression and "healing" foam, I'm not sure how CAFS would enhance this. It might...
09-10-2004, 04:48 AM #4
Gleaned from an article on fire suppression in aircraft hangars... haha, kind of applicable? Like our experience has shown, you can extinguish small Class B fires with Class A CAF, so I guess it depends on the hazard you have in mind. The tests here show it will work, but definetly not as well as Class B.
Preliminary testing had demonstrated that, to control and extinguish spill and pan fires, a density (on the floor) of 1.6 L/min/m2 for the low-level nozzle, and 1.0 L/min/m2 for the overhead nozzle, was required for 2% AFFF or 0.3% Class A foam, at an expansion ratio of
10 to 1. These densities were used in all fire tests with both the overhead and low-level nozzles.
To determine extinguishing capability and effectiveness, the following tests were conducted:
Small Pan Tests – In these tests, 8 L of heptane was placed over 80 mm of water in the 1.22m by 1.22 m pan, and the fuel ignited and permitted to burn for 30 s before commencing fire suppression. The nozzle (either overhead or low-level) was activated manually and allowed to operate until the fire in the pan was extinguished.
Fire test results showed that overhead nozzle CAF system with 0.3% Class A foam controlled (90% fire size reduction) the small pan fire in less than 35 s and extinguished the fire in less than 141 s. The same system with 2% AFFF controlled the fire in less than 55 s
and extinguished it in 70 s. Low-level nozzle CAF system with 0.3% Class A foam controlled the small pan fire in less than 28 s and extinguished the fire in less than 56 s. The same system with 2% AFFF controlled the fire in 20 s and extinguished it in less than 53 s.
Large Pan Tests – Fire tests were also conducted using a circular pan, 2.44 m in diameter, with a 127 mm lip height. The total quantity of fuel in the large pan (either gasoline or JP5) was 40 L floating above a base of 100 mm of water. The pre-burn times for the gasoline fires were 20 to 30 s while, for the JP5 fires, the pre-burns were from 15 to 20 s from the time the flames reached the walls of the pan. Fire test results showed that overhead nozzle CAF system with 0.3% Class A foam controlled the large JP5 pan fire in 180 s and extinguished the fire in 247 s. The same system with 2% AFFF controlled the JP5 fire in 48 s and gasoline fire in 62 s, and extinguished the JP5 fire in 65 s and gasoline fire in 118 s. Low-level nozzle CAF system with 0.3% Class A foam controlled the large JP5 pan fire in 35 s and gasoline fire in 120 s, and extinguished the
JP5 fire in 137 s and gasoline fire in 220 s. The same system with 2% AFFF controlled the JP5 fire in 18 s and gasoline fire in 25 s, and extinguished the JP5 fire in 29 s and gasoline fire in 39 s.
Spill Fire Tests – For the spill fire tests, 0.9 L/min of heptane was fed through a 12.7 mm diameter pipe and allowed to flow across a sheet of 12.7 mm thick gypsum wallboard placed on the floor. The heptane was ignited and permitted to burn for 15 s before commencing fire suppression. Fire test results showed that the overhead nozzle CAF system with 0.3% Class A foam controlled the spill fire in less than 40 s and extinguished the fire in less than 132 s. Using
2% AFFF, the fire was controlled in 25 s and extinguished in less than 48 s. Low-level nozzle CAF system with 0.3% Class A foam controlled the spill fire in less than 20 s and extinguished the fire in less than 56 s. The same system with 2% AFFF controlled the fire in less than 20 s and extinguished it in less than 53 s.
The overall test results show that the newly-developed CAF system with its overhead and low-level nozzles performed well in extinguishing the test fires, that simulate possible fire scenarios in an aircraft hangar. Using 2% AFFF in the CAF system performed better than using 0.3% Class A foam, in both the control and extinguishment of the three test fires. Overhead nozzle alone had difficulty in meeting the control and extinguishment criteria (30 s control and 60 s extinguishment) of the hangar protection, however, low-level nozzle performed much better and met the control and extinguishment criteria in most of the fire scenarios.
The technical feasibility of using CAF fire suppression for Group II aircraft hangars is predicated on the system being able to meet the design parameters for suppression implied in NFPA 409 with the added caveat of aircraft protection. This means that the prototype system
must achieve fire control in 30 s and extinguishment in 60 s. As can be seen from the fire test results, the prototype CAF system with overhead and lowlevel nozzles together was capable of meeting the required objectives with 2% AFFF foam for the large pan test and was close to meeting the objective with Class A foam. Both Class A and AFFF foam met the objective in the small pan and spill fire tests.
With these results, it can be concluded that it is technically feasible to use CAF fire suppression with AFFF to meet the design parameters for fire suppression in Group II aircraft hangars.
09-10-2004, 04:51 AM #5
Another test by the same group I think:
"Comparison of the Fire Suppression Performance of Compressed-Air Foam with Air Aspirated and Unexpanded Foam Water Solution
Institute for Research in Construction, Jan. 2004, 25 pp.
Crampton, G.; Kim, A.
Using aspirated Class B vs. Class B CAF
This one seems to support superior extinguishing power, along with using less product (water and foam). Makes sense I guess.
""4.0 Conclusions and Discussions
This test series has shown the superior fire extinguishing properties of compressed-air foam over air-aspirated foam and foam-water spray. This was true for both Class A and B foams on heptane and gasoline fires. Extinguishment density (Table 2) is a calculation determined by the applied flow rate multiplied by the time to extinguishment 18 and divided by the area of the pan. These values reveal that CAF extinguishes the heptane fire with at least 30% less material than good quality air-aspirated foam and 87% less material than foam-water solution using Class B foam. These numbers are further improved when CAF is delivered through the CAF rotary nozzle. CAF also had the ability to extinguish the fire using Class A foam while air-aspirated foam could not. This is due to the fact that the delivered foam is uniform in consistency, has smaller more rugged bubbles, and longer drain times. As the quality of the air-aspirated foam improves, its performance improves, but it only approaches the quality of CAF and, as more energy is used to generate the foam, less power is available to the stream for transporting it. Unexpanded AFFF solution alone cannot match the performance of CAF or air-aspirated foam when delivered into the base of the fire. The flow rate had to be increased threefold before it could extinguish the fire, showing that the film-forming layer must remain on top of the fuel to be effective. This is difficult when the density of the solution is greater than the fuel.
The extinguishment densities for the gasoline tests demonstrated that CAF could extinguish the fire with at least 60% less material than the air-aspirated foam using Class B solution.
The reduced solution concentration tests showed that CAF extinguishment density increased 67% when the concentration was cut in half. The air-aspirated foam extinguishment density increased 150% when its concentration was halved. Reductions in solution concentrations affect foam quality and performance to a much greater extent in air-aspirated systems than CAF systems. This is a result of the foam being generated in the pipe rather than in the short expansion zone of an air-aspirated nozzle. Even when the concentration was reduced by a third to 2%, the CAF system only suffered a 13% performance reduction while the air-aspirated performance dropped 27%."
Last edited by Resq14; 09-10-2004 at 04:57 AM.
09-10-2004, 12:06 PM #6
- Join Date
- Nov 2003
Thank you guys, so far. Yes water can be an issue here and we are looking at CAFS. So, if I follow, the extended drain time and "ruggedness" of the CAFS bubble structure should be a good thing right? I was on the Pierce website, and they said their system can reduce the application rate by 33% if I'm not mistaken. We have lots of highway traffic, trucks etc near here and no dedicated foam apparatus as well as all volunteer. Not being a math genius when it comes to firefighting what would you need to flow from a CAFS unit for a class b fire, say, 1000 sq ft hydrocarb ? Also, knowing Capt Lou is the big CAFS guy, if your out there, any opinions?
09-18-2004, 09:51 PM #7
- Join Date
- Jan 2001
- Madison, NJ USA
I understand your question to be; Does class B foam applied with a CAF system work as well on flammable liquid fires as class A foam applied with a CAF system on normal combustibles?
The answer is YES! There is no better “bubble” delivery system than CAFS. Class "B" foams are designed to impede the release of water in order to maintain a good bubble structure (blanket) and not mix with what it is applied on, hydro-carbons or polar solvents. The applied percentage would still be as what is dictated by the type of "B" foam being applied and what it is being to. For example if you are using a 3 x 6 "B" foam you would still have to apply the foam at 3% for hydro-carbons (gasoline) and 6% for polar solvents (alcohol). The issue or question that must be asked is can your foam concentrate pump, pump the higher % of foam and keep up with the necessary water flow rate? To answer this question you must know the GPM flow rate of your foam pump. Most foam pumps that come with a larger CAF system have a maximum gpm flow rate of 5 gpm. Also one must take into account the viscosity of the "B" concentrates, which are thick like molasses. A 5 gpm foam pump can only keep up with a water flow of 166 GPM using a 3% concentrate and 83 GPM using a 6% concentrate. Not a whole lot of water flow for a "B" foam operation. Most "B" foam operations require a larger sustained flow rate. Some smaller foam pumps can not pump the thicker "B" concentrates. This being said, I am not suggesting that you spec out a "LARGE" gpm foam pump for "B" foam with your CAF system. I say this because the larger foam pumps are TOO big for the lower % injection rate of class “A” foam. Also the larger foam pumps are designed to be used in conjunction with larger water flows associated with BIG “B” foam operations. I would highly recommend NOT having a “B” foam as part of your CAF system. I would only use “B” foam by way of an “auxiliary pick up” tube and utilizing a 1% “B” foam. This is because I can easily flush my system of “B” foam before going back to “A” foam and my 5 gpm foam pump will be able to keep up with a water flow rate of 500 gpm.
I would also not recommend installing or utilizing a dual tank set up unless you plan on putting “A” foam in each tank. I don’t recommend having “A” and “B” foam in each tank, as the possibility of having a major failure occur of the foam system due to the two very different concentrates mixing together. “A” and “B” foams do not like each other. If they do mix, even a small amount, it will start turning the mixture onto a solid “plug” in your foam line. This will prevent any concentrate from flowing to or thru your pump.
With regards to the use of class “A” foam applied with a CAF system on “B” type fires, it would work for knockdown and extinguishment of small “B” fires. This is possible because of the small, tight uniform bubble structure of CAFS. You will not get a film forming barrier and the water will drop out of the foam blanket faster because it is designed to, but on smaller “B” fires it will work.
Hope this helps.
09-19-2004, 10:03 AM #8
- Join Date
- Nov 2003
As always Capt Lou, great post. Thank you for the info. So, now knowing I have to keep the same percentage, can the actual application rate be dropped? I am going by what I read on the Pierce web site. And from your experience how big of a class b fire can you handle with a cafs (class a) unit? Rough estimate please.
09-22-2004, 03:01 PM #9
- Join Date
- Jul 2002
I just attened a Foam Technology class at the State Fire School. The instructors, who do delivery service for Pneumax on CAFS units, said there are new Class A foams that are within 3 seconds of meeting the standards for class B foam. When these are on the market, they will solve the A/B problem. They even suggested that Class B may become a thing of the past, other than at oil refineries and other concentrated sites.
We were considering putting some Class B on our trucks, but not any more.
09-21-2011, 04:08 PM #10
- Join Date
- May 2011
CAFS Class A on Class B Fires
Yesterday we took our CAFS Engine to a training class at a local oil refinery we cover in our first due area. The burn site we used for a test of the Class A CAFS on a petroleum product (in this case the product was naptha) is a 60 foot tank about 3 foot high with a 20 foot back splash left from a 1/4 of the original tank. There were numerous factors involved such as we conducted about 10 fires with water only prior to our test burn and we were only trying to knock down the fire with an 1 3/4" CAfs line. The end result was we failed to knock down the fire with class a only and had to assist exstinguishment with normal class b. We were only flowing 60GPM thru the line which was not near enough flow for the extent of fire. We did however notice some effect it was doing on the fire and if our application may have been wetter as in 90 gpm we would have knocked it down enough to be manageable until a class b application could have been established on an emergency. We may next week try to use the same tactic but use our 2 1/2" blitz attack line at 90 gpm and see how that effects the knock down.
We did this only to see if we could have good knock down on a class b fire such as a tank truck accident until we can get our portable eductor in service for class b. We are not planning to use class a on class b fire that are large. However we have used it on smaller fires where about 100 gallons of diesel fuel were burning at a triaxle fire with great success.
We are looking at trying Class b with CAFS in an alternative way but are waiting on more feed back first.
09-21-2011, 10:14 PM #11
- Join Date
- Jan 2008
As a rural fire department we us caf's for class b fires in our industrial area which amount's to one pharmaceutical company,and two ethonal plant and possible a third coming down the road. we use thunder-storm 1-3 arr-aff and 1 thunderstorm class a. We have had zero issues in using it
09-22-2011, 06:26 AM #12
- Join Date
- May 2011
I missed the one question of why we would want to use class b with CAFS. Our theory of wanting to do this is to gain the thicker blanket, use less foam and water, and have the lighter manuverable line like we do in the class a CAFS line. The only concern I have is do we loose the Film Forming capability by adding the compressed air which in turn would shorten the burn back time before needing to apply more to the blanket?
09-22-2011, 10:01 PM #13
- Join Date
- Oct 2010
My thought would be, would the high energy CAFS stream be detrimental in a pooled fuel fire, vs the gentler application from an aspirated nozzle?
One of the draws I always hear about is the reach you gain by adding compressed air to the stream. This, of course, means a higher velocity stream. I can easily imagine problems when blasting a pool of fuel with this... ie spraying fuel everywhere, drilling the stream into the pool, vs floating the foam on top, etc.
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