CAFS – Back to the future

Published:  28 May, 2013

Mark Cummins developed what is now known as CAFS in the 1970s while working with the Texas Forest Service.  in an exclusive interview with Ann-Marie Knegt he explains why he is committed to promoting this technology to the international firefighting community, while clearing up some common misunderstandings about these systems.

What was your role in the development of CAFS?

David Cummins, my brother, had several pick-up trucks that he used to patrol lumberyards and other industrial sites for security contracts. He asked me if I knew of any fire fighting equipment that he could fit onto his trucks which would be able to extinguish both class A and class B type fires. I used a concept my father had designed for the Mad Dog crash truck. This consisted of an old chemical fire extinguisher that had two pressure tanks that were filled with an A and a B solution. When the two chemicals were mixed in the fire hose the chemical reaction created a very durable foam blanket. The unit worked so well that I built several more and sold them to fire departments in our local area. I also provided a maintenance service to refill the tanks after the fire departments used them. It was during one of my service calls that I discovered by accident how to create CAFS foam. The B product in the tank was bicarbonate of soda and dish detergent. When I opened the valve to drain off the left over pressure, the small drain tube belched out the most beautiful, well-formed shaving cream foam that I had ever seen. I quickly went back to the shop to start investigating how the foam was created in the small tube, and discovered that the friction inside the tube created turbulence that mixed the soapy water and leftover air into very dense and tiny foam bubbles. These foam bubbles coated the inside of the tube and caused a fast flowing centre core of bubbles to pass on top of these slick bubbles. There was practically no friction loss in the tube and there was no obstruction needed to mix the water and air.

This was the invention that I was awarded the US, UK, and Australian patents for, now called compressed air foam systems.

How did the initial systems work compared to modern CAFS?

I made the first units with pressure vessels because it was less expensive and much less complicated than using water pumps. Commercial air compressors were very dependable and low priced, and it was simple to premix dish detergent in the tank and start the automatic compressor. High quality garden hoses worked really well as a fire hose. Later on I created larger units, which were installed on fire trucks.

The Texas Forest Service then hired me to develop the foam system to improve their wildland fire fighting capability and to use water more efficiently. I added a water pump to a standard 250 gallon water tank and combined the air compressor to mix with the water in a simple plumbing T fitting. These units outperformed the larger 750 gallon trucks and could even extinguish structural (house) fires. There was some initial resistance within the US Forest Service at first to accept my invention. I renamed it Water Expansion System, and when the US Forest Service managers saw the first demonstration and how fast it extinguished fires with such a small amount of water they were impressed, and they told my boss what a great thing it was, but it sure did look like foam. 

Next was a demonstration for the Bureau of Land Management, and I was sent with my Texas Blizzard (a large military 6x6) all over the USA showing and fighting fires of all types. This truck was the first to use a large air compressor and eventually we rigged it with water pumps and screw-type air compressors. We ran into an old problem with one of the US Forest Service research centers saying that we could not use this truck to fight house fires because we were not trained or equipped to meet NFPA recommendations. We protested and the BLM agency stood firmly behind us saying that we were well-trained firefighters and that this foam system could do more than 10 of the US Forest trucks. We set up comparison demonstrations all over the country and eventually convinced them that the Water Expansion System was able to extinguish all types of fires. Later I renamed it Compressed Air Foam Systems (CAFS).

Although this technology is not new, why is its acceptance taking so long?

I believe there are many reasons why the technology is so slow to become the standard in firefighting. The main reason lies in a lack of knowledge about how to use it and comparing it to how we were trained to use water. Water is used to absorb heat.

We have designed equipment, we have designed fire hydrants and fire trucks to pump water and we have taught how to get the water on the fire in the most practical way. That worked pretty well when houses were made of wood but the changing building materials make it hard for water to do its job. When you heat wood and synthetic materials above 300 degrees F they begin to break down into their elements and compounds and if they come into contact with oxygen and an ignition source they will combust or burn. Most of these products of combustion are hydrocarbons that repel water so it is difficult for water to cool them and normally it just pushes these gases around into other areas. Foam is made with surfactants that actually attract the hydrocarbon products of combustion, and this allows the foam to cling to the gases and scrub the toxic molecules out of the air. This can save a great many lives by removing the cancer-causing smoke and extinguish the fires much faster than water.

 All these new applications for foam have caused the fire service to consider major changes about how it trains and how it is equipped. I believe there is a resistance to having to relearn how to use the foam. 

What are the most common misunderstandings about CAFS?

CAFS engines are very complex these days. I can use a standard, unmodified, commercial air compressor and a simple manifold to connect a water hose from any engine that can pump 100 gpm or more of water at 120 psi then turn that water into 20 times the volume for the discharge. I never use a reducing tip. The bigger the discharge, the better.

 The placard settings on the CAFS units are the result of people that are drawing information from NFPA recommendations about water requirements and they believe CAFS should be used like water. And then there are the pump manufacturers that are getting their information from people that don't have any real experience using foam. There are serious issues with the complexity of matching and controlling a big water pump with an air compressor attached to it. The bigger the water pump the more cooling it needs. Air compressors need RPM to make high volumes of air and to circulate the cooling oil in them. When I need 3 cubic feet of air for each gallon of water to produce a 20 to 1 expansion of the water, it creates a lot of mechanical problems for engineers of big high-priced water pumps.

I was asked to teach a department that had a CAFS system and when they turned it on it almost blew me down because it was set up with so much water and very little air. I would hate to even try to use that set up in a structure. The basic CAFS set up should be very easy to handle with the exception of the initial opening of the nozzle that gives you an amplified burst of power. The foam is adjusted by adding water and agent to a flowing stream of high volume air. I don't like the ‘wet’ and ‘dry’ terms to describe the foam, I prefer wetter or dryer, meaning you have introduced more or less water into the hose. The pressure needs to be set at 100 to 120 psi or you will be stripping the bubbles because of high velocity on exiting the nozzle. Adjust the water valve as needed by the nozzleman, and the hose tender keeps the kinks out of the hose. A whip line is a great help to keep from kinking the hose at the nozzle when interior firefighting. Put a finger in the CAFS straight stream to make a fan pattern for wide angle sweeping to absorb smoke and heat. It really should be very simple, but it is hard to understand for some people. The concentrate setting controls how durable the foam is and how fast or how long the drain time is. A fixed setting is a waste of good foam because if it is too lean you run the risk of not making any foam at all or causing excessive run-off. And setting the concentrate too rich might be at the wrong time in the fire application for a slow draining blanket of foam. Adjust the concentrate as needed by the nozzleman for long lasting foam or fast draining foam. Changing the setting of the concentrate does not make wet or dry foam it only makes the foam more or less durable.

Critics doubt the operational safety of CAFS in regards to the reliability of the technology. What is the reason for this and what would you say to them?

There is a legitimate concern, when risking your life, that your tools should be dependable. There are problems with some of the chemical injectors being used with CAFS. If the injector does not sense water movement then it does not add agent to the mixing manifold. When the pump operator starts the flow of water there is a short delay in concentrate injection. This causes a slug of water that does not turn into foam and is flowing to the nozzle man. This slug of water is not what the nozzle man is expecting and he normally shuts the nozzle, which stops the water flow so the chemical injector stops injecting chemical which causes another slug of water to flow to the nozzle and the nozzle man does not get a usable stream of water or foam. There are ways to overcome this problem, but if the nozzle man has had a bad experience with the system he will be hard to convince that it is all it is said to be. 

 Another problem is interior firefighting with a straight stream of foam. The velocity is difficult to control for close-up fire fighting, so I teach the nozzle man to put a gloved finger in the foam stream to create a fan pattern to sweep the area. This pattern is also best for clearing the room of toxic smoke and heat. With interior firefighting with CAFS it is difficult to avoid kinks in the hose while manoeuvring the nozzle. This breaks the bubbles and reduces the ability of the foam to do its job. I use a short non-collapsible hose extension on the end of the standard hose for all of my CAFS applications. It makes it much easier and more reliable to handle the CAFS discharge.

Any remarks in conclusion?

Even though CAFS have been around for more than 40 years now, the technology offers immense room for further development and for firefighters to become experts in the use and implementation of CAFS foam for many new applications such as for coal mine fire fighting and bio-remediation foam for hazmat and warfare defence. On my part I will continue to strive for an increased understanding and better acceptance of the technology, because I believe it will help save people’s lives, and create more efficient and safer firefighting operations, now and in the future.

  • Operation Florian

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