After dispelling the falsehoods, fire departments can improve their efficiency with foam.
Despite its gaining notoriety and acceptance, several myths about CAFS exist. First is the misconception that CAFS is primarily for volunteer fire departments. The inference is that CAFS aids fire departments with limited personnel, limited water supply and a requirement for more effective fire suppression. Yet these requirements fit all types of fire departments.
There is a belief that a CAFS fire stream will not project as far as a water stream. However, the CAFS stream will far outreach the water stream when using the same size orifice and delivery rate due to the pneumatic action of the hose line. CAF can be delivered at many varied delivery rates, which in essence creates a dry foam (low rate of foam solution flow) to a very wet or fluid foam (higher rate of foam solution flow). Because the water in CAF does the cooling, it is the mass or weight of the foam solution that will determine distance and ability to reach the target.
Another, and probably the most controversial, aspect of CAFS applications is the myth that there is not enough water in the CAFS stream to cool the fire effectively. The traditional use of plain water fire streams has jaded the fire service's view of how much water is needed. But using only plain, untreated water only attacks one side of the fire triangle — heat. To overcome the fire's BTUs, plain-water attacks must use more and more water until the fire diminishes. This is the critical application rate.
The efficiency of the water is improved chemically by the Class A foam, and mechanically by the compressor. The National Interagency Fire Center in Boise, Idaho conducted several tests on this that revealed a disturbing finding: Untreated water in fire streams is approximately 10% effective. There were many factors that led to this conclusion, but the biggest efficiency thief in plain-water attacks is the negative effect surface tension has on the ability of the water to adhere to surfaces and cool. The water simply rolled off or did not penetrate the fuel source. NIFC found the simple addition of Class A foam helped overcome the effects of surface tension and actually increased cooling ability 300% and ability to soak in by over 1,000 times. In addition, Class A foam is highly attracted to carbon. By adding air, it can be stuck to ceilings and areas to which water simply cannot adhere.
For example, consider a fire involving a couple standard-size bedrooms and associated furnishings. An indirect attack at the highest point of heat output, or the ceiling, using a straight-bore nozzle is begun. The 1I-inch hand line flowing 150 gpm is not effective but a 2H-inch hand line flowing 250 gpm puts the fire out. The 1I-inch hand line was resulting in about 15 gallons (10% of 150 gpm). The 250-gpm hand line had a positive effect because the critical application rate was actually about 10% of that number, or 25 gpm. As mentioned, CAF can be stuck to ceilings and walls. This is important because heat always rises and always gravitates towards a cooler atmosphere.
Using this same scenario, a CAFS stream at 50 gpm (nearly 100% efficient), direct it to the ceiling would put the fire out twice as fast (50 gpm CAFS at high efficiency versus 25 gpm net effective water application) and use only one-fifth of the water.
Another myth is that of the universal foam. There are various types of foam available and different scenarios for their use. About 95% of the time, Class A foam will be used in CAFS. Protein foams and the various AFFF for hydrocarbon-based fires also are important. The growing popularity of ethanol-based fuels is a bona fide reason to consider A/B foam systems.
The fact is there is no such animal as universal foam. Class A and Class B foams are as different as black and white. Universal foams are either emulsifiers or Class B-based foams that have wetting abilities when proportioned in ranges typically less than 1%. Universal foams will disturb the smoke generated by the fire and make it increasingly more difficult to see when conducting interior operations. In addition, the chance of mixing Class A foams and the universal foams increases, and the result could be disastrous to equipment and the fire suppression crew.
With the myths busted, it is important to consider how to select the proper terminal hardware to effectively generate CAFS streams. A good deal of the foam generated at the tip of the nozzle actually is created by the scrubbing action of the foam solution and air introduced into the hose line. The goal is to create a blanket consisting of tightly packed mini bubbles with water held in suspension during the creation of the finished foam exiting the nozzle. The best way to minimize the disturbance to the finished foam would be to eliminate the nozzle all together. That is not practical, therefore the next best selection would be the smoothbore nozzle and ball valve with the largest orifice available (typically 1K inches for 1H- and 1I-inch hand lines).
Actually, many experienced CAFS users discard the smooth-bore tip that comes with the ball valve and opt to use the ball valve itself. The problem with that scenario is that there is no thermal protection as is commonly found with fog or combination nozzles. Many departments have tried using combination or fog nozzles, but those are not made for CAFS. All the effort to produce tightly packed CAF bubbles will have been destroyed when the air in the bubble is stripped by the spinning teeth of the nozzle. This reduces the finished foam to nothing more than what could have been accomplished by a much less expensive Class A foam proportioning system.
There is much debate about proper CAFS flow rates and the amount of foam solution ratio to the air generated by the compressor. For each 1 scfm of air when combined with 1 gpm of foam solution, the result will be a sticky foam with great cooling effect and about a 7-1 expansion ratio at the tip. Therefore, the largest, balanced flow from a typical 1I-inch hand line is 75 gpm at 75 cfm. Beyond that range of foam solution flow, the weight and mass of the solution will far outstrip the air allowed in the line. Kicking the flow rate up on a CAFS line that is delivering a constant output of 75 cfm of air more than 75-gpm rate of delivery will produce a wet foam. For example, 100 gpm of solution typically only allows for 25 to 30 cfm of air to fit in the hose line.
Proper application and use of terminal hardware is best taught on live-burn props. Teach the suppression crew to paint the ceiling and the upper third of the adjoining walls with CAF. This results in less disturbance to the thermal balance and crews experience less heat hitting them in the face when proper application allows the conversion to take place in a controlled manner over their heads.
There are some of the anomalies regarding CAFS applications, as well as common problems encountered by those unfamiliar with using CAFS. One of the biggest complaints is hose line kinking. This can be due to a number of problems, but typically the attack line was deployed improperly. The line may also kink if the solution flow is too low. It is the weight and mass of the water suspended in the CAF bubble that prevents the hand line from kinking, when used at proper operating pressures (100 to 125 psi in rated-compressor output).
Other differences occur when departments using high-rise or apartment packs use CAFS in a larger supply line and distribute that flow rate through two or more smaller lines. Only so much foam and air can be mixed into a given diameter. With a 2H-inch supply line that distributes two smaller 1I-inch hand lines, it is possible to flow approximately 125 to 150 gpm at 125 to 150 cfm of air through the larger line. This creates no problems when both the smaller hand lines are being used simultaneously.
Should one of the hand lines be shut down, however, the compressed-air foam coming out of the other hand line would be wet and the loss of pneumatic pressure could diminish the stream reach. Elevated streams, such as aerial devices or hand lines that go up in elevation, will not have a negative effect on engine pressure as long as the CAFS is flowing. Should the CAFS line be shut down, the water in the foam bubbles begins to leach out and returns towards the lowest point in the water column. This would result in either severely diminished stream reach should the CAFS flow be redeployed or in the need to increase engine pressure to overcome the hydraulic effect of what is now water in the hose line until it exits the tip and returns to a lighter, pneumatic CAFS stream.
It is also important to understand how to specify and maintain a CAFS properly. CAFS is a combination of compressor, foam delivery system and a water pump. For a CAFS to work properly, all three components must work together harmoniously and reliably.
One of the most common mistakes is selecting a foam-delivery system. High-quality CAFS components are not cheap. Department should spend a great deal of time asking for references, researching blogs, and talking to neighboring departments to find out what is working and what is not. There is a wealth of information available in articles and on the Internet to serve as a basis for investigation.
Do not buy any CAF system that adds significant complication to regular pump operations, excessive weight, costly pump compartment manipulation or unnecessary increased horsepower requirements. Always ask if it is possible for the system to be demonstrated at the department. Compare systems side by side if possible; several of the CAFS academies allow this. Look at component accessibility and how the pump operator's panel is laid out. These systems have become increasingly robust, so look for safety interlocks that prevent damage to the machinery and possible injury to the user. Make sure that the system is installed to the pump manufacturer's specifications.
Once fire departments move past the misconceptions surrounding CAFS, they can begin increasing their effectiveness and efficiency.
Neal Brooks is an apparatus division national sales manager with& Co.
The 2008 Focus on Foam is sponsored by: