CAFS on the fireground, how did we get here?
By: Neal Brooks (As Published in Fire Chief Magazine - Focus On Foam - May 2007)
Perhaps the danger of structural collapse will change the old guard’s minds when comparing the suppression benefits of untreated water with compressed-air foam. By Neal Brooks
Who remembers the old 3-D paper glasses with a red plastic lens on one side and a blue plastic lens on the other? When worn at the movies, they gave objects filmed with a special process a more realistic depth and quality. If removed for an instant, the view became fuzzy and distorted, perhaps even unrecognizable. Most would agree that the 3-D view was clearer and placed things in perspective. The same analogy can be used to describe the traditional fire service view when the debate begins about the best fire suppression system or method of delivery. Many traditionalists would argue that water — often in huge volumes — is the only thing needed to suppress a fire. But that’s single-dimensional thinking. The goal should be to suppress fire in a safe and effective manner, and water may not always be the preferred method.
Statistics compiled by the National Institute of Occupational Safety and Health reveal that more water can create structural collapse problems. From 1979 to 2002, there were more than 180 firefighter fatalities due to structural collapse, not including those firefighters who died in the collapse of the World Trade Center. A majority of collapse fatalities, over 65%, occurred during fire attack. The rapid addition of extra water weight during large-volume or blitz attacks creates the potential for catastrophic loss. A hand-line attack of 250gpm is adding one ton of additional weight per minute. Consider another related potential problem. In 1990, the National Interagency Fire Center in Boise, Idaho, found that 75 cents out of each dollar paid out by Oregon insurance companies was spent on water damage, not direct fire damage.
Apparatus and delivery systems have vastly improved over the last three decades, and many hybrid systems have evolved. For example, the Class A foam system and its hybrid derivative, compressed-air foam, have gained popularity. Even so, traditionalists still will grumble about revolutionary new developments were all the rage but quickly fizzled out, such as high-pressure fog systems.
Early in the fire service, the debate over the best or most versatile nozzle application was limited because there was only one choice: the straight-bore, or smoothbore, nozzle. It was a simple, user-friendly design that did the job. But the nozzle didn’t afford much protection to the user in close combat situations with a lot of heat and visible fire. To address such situations, the fog nozzle and its hybrid derivative, the combination nozzle, were developed. Firefighters could generate a protective fog pattern when necessary, adjust the nozzle to straight stream for additional reach or concentrated attack, or use a modified combination of both to expand the suppression diameter of the water exiting the hose line. In addition, breaking up that straight stream of water into the small droplets of the fog pattern dramatically increased the amount of heat absorbed. Changes in nozzles were accompanied by modifications to the traditional centrifugal pump to make it smaller and lighter while increasing the volume of water delivered. The need to reduce friction loss brought the two-stage pump, a centrifugal pump with two impellers and a method of diverting the internal flow to build additional pressure when necessary.
With all of these benefits, why not boost the pressure even more? Enter the high-pressure fog system. With it came the advent of new pumping systems, new nozzles and the promise to revolutionize the industry. While high-pressure fog systems have their following in many European markets and New Zealand, their popularity in the United States soon fizzled. Traditionalists would agree in theory that the high-pressure fog system should have been a great idea. It provided lighter, more maneuverable hand lines; a highly atomized fog pattern that absorbed tremendous amounts of heat; and low water usage. Great concepts, great benefits, yet the idea failed. Why?
To start, there were a limited number of manufacturers. And to achieve these extremely high discharge pressures, the pump had to have a third- and even fourth-stage pump added, which meant more cost. Maintenance was more expensive, too. But the root cause of failure was really quite simple. The application stream was very limited in its reach and was dangerous when used close to heavily involved structure fires emitting high volumes of heat. So, the theory was great — high energy, more surface area of the fire stream to absorb the heat of combustion, and conservation of water. The fire service needed to take the positives from this system while overcoming its glaring negatives.
Then came the compressed-air foam system, which employs the same traditional water pump and water source while adding two components: a foam delivery system and a high-quality, industrial air compressor. CAFS has been around since at least the 1940s, when a similar system was employed by the British Navy in ship holds housing the engine room and fuel supplies. CAF systems also were seen in the U.S. Forest Service, especially in Texas during the early 1970s.
Despite this history, tradition is the main roadblock to CAFS in many departments. “We have been putting fires out for 100 years with plain water. Why complicate the system?” asks the traditionalist.
Here’s why. Most of what we encounter everyday is carbon-based, including many if not most of the materials used in commercial and residential buildings. This fact has a tremendous bearing on the effectiveness of water relative to burning material. There’s a phenomenon that takes place at water’s molecular level called surface tension. To see an example of what surface tension does, place a glass under a dripping faucet. As the volume of water approaches the top of the glass, a dome forms above the rim. Water’s closely bonded molecular structure allows this to happen. If it did not bond tightly through surface tension, water exiting a hose line would go in every direction, much as it would in zero-gravity. While this would be a positive result, the negative effect plays out when water encounters its target because water tends to repel rather than bond readily with a carbon-based item. It instead finds the lowest point of elevation and puddles. Of course, just using more water can contribute to structural collapse.
Firefighters must overcome the negative effects of surface tension without compromising the delivery of the extinguishing agent. Enter soap. Without soap in the dishwasher or laundry machine, water could not penetrate the soil or the grease. It works the same way when using plain water on the fireground. Applying untreated water results in highly inefficient runoff, a point brought home by NIFC, which discovered that nearly 90% of the water it used on test fires had no effect because it couldn’t penetrate. A better option is a detergent foam or a surfactant, which readily mixes with water and breaks down surface tension. Many of the foam suppliers that manufacture Class B or A foams had to develop a low-cost foam concentrate that didn’t adversely affect the environment while still improving water’s firefighting capability. The industry responded slowly at first, but today many suppliers manufacture environmentally friendly foams. The net effects are quicker knockdown, less damage and less water used.
We now have an inexpensive way to treat water and increase its efficiency and ability to penetrate carbon-based items by the addition of Class A foam. However, another problem arises when the foam solution is applied from traditional nozzles. In a highly fluid state, it continues to run off vertical surfaces and areas of high heat concentration, such as ceilings. The answer is to alter the form or substance of that foam solution to make it stick to those surfaces. CAFS can do that. Also, injecting air creates a substantially greater number of smaller bubbles from a single droplet of foam solution, thereby increasing the cooling effect by exposing a greater surface area. Tests have shown that compounding is typically 7:1 and as high as 30:1 in certain delivery rates. The suppression medium continues to be water, but water that has been improved both chemically and mechanically.
Consider the fire triangle. The three essential elements of combustion are heat, fuel and oxygen. CAF attacks all three sides by removing the heat and blanketing the fuel source, thereby removing the fuel from its source of oxygen. Tests have shown that method uses less water and causes a more rapid drop in temperature, which results in more rapid suppression. The lessened amount of water reduces potential for related structural collapse, improving overall firefighter safety. In addition, property owners may not suffer economically as much as they have in the past with plain water attack. An analysis of several fires in Idaho and Wyoming by insurance adjusters indicated that CAF operations resulted in only 10% to 20% of the water damage considered normal.
Traditionalists may ask, “If CAFS is so good and so effective, why doesn’t the Insurance Services Office recognize its use?” It does in Texas, where the state fire marshal’s office studied the net effect of CAFS versus the traditional suppression. The results were so convincing that legislation was passed to give 1.5 ISO credit points to those adhering to minimum requirements and using a CAFS Class A pumper in their community. Why just in Texas? Someone should be asking the question, don’t you think?
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