commentary LightRock on 27 Sep 2007 09:47 am
Today’s Pumper Design
LightRock checks in:
In a column a few weeks ago, we addressed the amount of growth in areas beyond the traditional suburbs. It is now estimated that about 25% of the U.S. population lives in these areas, often without benefit of municipal water systems and, as such, no fire hydrants. In that column we promised to address what fire departments in these areas are doing in response to this trend. This week, I’d like to talk about some of the ways pumper design for departments in these areas is evolving.
One very straightforward change is that water tank capacity on pumpers continues to get larger. In days gone by, the water tanks on pumpers were often 500-gallon capacity, sometimes larger and in some cases even smaller. Today, while 500-gallon tanks are still used in some urban areas, 750-gallon tanks have become the norm and 1,000 gallon tanks are also quite common. 1,250-gallon and even larger tanks are not unheard of. Larger capacity water tanks can extend initial attack time and/or allow initial attacks with higher flow lines.
Class A foam and Compressed Air Foam Systems (CAFS) are becoming more popular. These technologies have been around now for the better part of 3 decades, but over the last 5-10 years more reliable and easier to use systems have helped make these firefighting technologies much more mainstream. When used for structural firefighting, Class A foam is injected into water at a rate of .3-.5% and serves to enhance the extinguishing effectiveness of “plain” water, contributing to faster knockdowns, less post-knockdown burnback and less time consuming overhaul. At injection rates in the .5 to 1% range, fire streams with Class A foam can also be used for enhanced exposure protection. No special nozzles are needed when using Class A foam. I often tell people to think of Class A as water on steroids.
CAFS takes this concept to an even higher level. In addition to water and Class A foam, compressed air is injected into the fire stream. This creates an emulsion that offers even greater knockdown power with a number of other benefits, including lighter charged hoselines and the ability to project streams greater distances. CAF also sticks to whatever it hits. Effective use of CAFS typically involves some special hardware and some additional training, but for those who have seen CAFS in action, this added level of complexity is well worth it. CAFS can also be effectively applied as part of an exterior based attack. (Yes, I know the term “exterior attack” makes many of you cringe, but given the current state of affairs in building construction, it is a reality of modern firefighting life.) If Class A is water on steroids, think of CAF as “water squared.”
The enhanced extinguishing effectiveness of Class A and CAFS have been described and documented in a number of studies, including a landmark study conducted by the Los Angeles County Fire Department about 7 years ago. In referring to CAF, one magazine article about the LACoFD study put it well: Bubbles beat water.
Think of the enhanced capability of a pumper with a 750-1,000 gallon tank and Class A foam or, even better, CAFS. Initial attack effectiveness grows significantly. A 1-3/4″ handline flowing 150 GPM with Class A foam is going to perform more like a 200+ GPM handline. What is knocked down stays down. Another way to express this lift in effectiveness is to think of water tank capacity. A pumper with a 1,000 gallon tank and Class A foam “acts” like it is a pumper with 1,500 gallons onboard. Use of CAFS takes these numbers and blows them away.
Another change in pumper design involves water intake and discharge plumbing that is oriented to quickly developing and maintaining higher flows. Many of today’s pumpers have multiple large diameter (4″ or greater) intakes and multiple discharges for high flow handlines and the increasingly popular lightweight, portable/quickly deployable master stream appliances.
For fire departments in the areas beyond the ‘burbs, a pumper like the one we’ve described gives the officer and crew the ability to hit hard, hit fast and hit safely.
This brief video demonstrates the quick knock-down and residual smothering properties of a CAFS-charged hose line.
See you next week…
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