Compressed-air foam systems are included in 4% of all pumping apparatus being delivered today. Still, several common misconceptions about the application's overall versatility remain.

Much like the fire tetrahedron, there is also a finished foam tetrahedron. Each side, or component, must be present in the appropriate proportion to effectively deliver a finished foam. Once combined in measured amounts, water, foam concentrate, air and mechanical agitation will produce some quality (measured by drain time), and quantity (measured by expansion ratio) of finished foam.

Testing done by the National Fire Protection Association, Underwriters Laboratories, and the National Institute for Standards and Technology show that the foam application method has no affect on the necessary critical application rate. Fire requires a minimum application rate of water to absorb the BTUs being generated. Foam either from a CAFS or a standard nozzle must be applied in sufficient quantity for successful suppression to take place. Class A foam is an enhancement to, not a replacement for, water.

Like most things, the quality of what goes into the foam mix affects the quality of what comes out. Cheap foam concentrate has to be used at a higher injection ration (up to 1%) to make good foam, eating away at any perceived cost savings. Also, very hard water with high pH or mineral content limits the amount of bubbles a system can generate.

Water and air temperature also are factors. The colder it is, the harder it is to make bubbles. Often injection percentages have to be increased dramatically in cold weather to produce an acceptable quality and quantity of finished foam.

Hose-handling characteristics of high-energy CAF lines require additional training and understanding for crews to be safe and effective. Though lightweight and easy to maneuver, these lines store the energy of the air compressor's pressurization. When opened, the stored energy is released, and crews need to be prepared for this force. Additionally, kinking a CAFS line certainly will change both foam quality and flow rate and ultimately could cause slug flow, an inconsistent mixture of air, water and foam concentrate in the hose that causes the line to uncontrollably react. Too short or too long of a preconnect length may hinder proper bubble creation in the hose line. Rougher interior hose linings produce more consistent bubble structure, while smoother linings produce less consistent structures.

The operator is as important as the equipment. Though many of the commercially available integrated CAF systems provide automatic air and water pressure flow balancing and control, operator error easily can generate unsafe slug flow, poor foam quality or foam concentrate waste.

Many firefighters who have seen finished CAFS streams are surprised by the bubble structure of the highly expanded shaving cream-consistency foam. This dry foam is good for exposure pretreatment, but often lacks the necessary water to drain into fuels and stop them from burning. The limited water drain can lead to rekindling and overhaul challenges. Wet foam may be preferable for deep-seated fires.

NFPA 1145, Guide of the Use of Class A Foams in Manual Structural Firefighting, offers suggested nozzle choices for different manual firefighting challenges. For instance, when using a high-energy foam system for direct attack, the system should be adjusted to provide a wet foam. A conventional nozzle can be used to provide a protective fog pattern, though reach and foam quality may be diminished.

The more a nozzle shapes a CAF stream, the more it will strip out the bubble structure, creating a wetter-finish foam. A fog-pattern nozzle is necessary, however, for firefighter protection or to apply foam to a wide area quickly. For exposure protection, the appropriate foam can be produced by varying the mix ratio, and/or changing the discharge device. Smooth-bore nozzles, automatic CAF nozzles, or open ball valves should be used to deliver drier foam.

Typically a break-apart combination nozzle will provide maximum performance for all CAFS applications. The smooth bore can be customized for dry foam applications and an automatic tip designed specifically for foam applications can provide a protective fog pattern or wetter foam for penetration.

But CAFS isn't the only foam delivery system available to fire departments. Low- and medium-expansion foam tubes that easily attach to firefighting nozzles offer operational flexibility and finished Class A foam performance for a fraction of the cost.

CAFS is a high-energy delivery system for Class A foam. Class A foam is nothing more than the soap agent that makes the water foam up as it is agitated. Often, departments don't realize that common pumping systems and regular nozzles and attachments will work fine with Class A foam. Foam attachments, typically only costing several hundred dollars and requiring no special maintenance or training, are a cost effective solution for nearly any foam application challenge.

CAFS and foam attachments are both a method and manner of delivery of a tactically desired finished foam. While the foam attachment is a low-energy delivery system using the energy of fire stream (flow and pressure from the fire pump) to create mechanical agitation at the nozzle tip, CAFS takes advantage of the energy of both the fire pump and an on-board air compressor, or tanks of compressed air, to create a finished foam.

Adding a foam attachment to existing handline nozzles requires few other changes. No special hose handling is required, the same nozzle used for water only applications is used for foam applications, and the attachment can be quickly removed if the fireground conditions change.

Though ideally suited for use with Class A foams, medium and multi-expansion attachments are the recommended equipment for AFFF-AR (alcohol-resistant) foam applications on flammable liquids. Providing typically up to a 25-to-1 expansion ratio and often lengthy drain times, medium-expansion attachments are an effective tool when using Class A foam for pre-treatment or exposure protection applications. One down side to low-energy foam delivery when foam blanket longevity is necessary is that the injection ratio of the foam concentrate may need to be increased to 0.5% or 0.75% to get the performance required.

Unlike CAFS, nozzle-aspirated foam uses the energy of the fire stream's flow and pressure to generate mechanical agitation at the nozzle tip. But creating more highly expanded foam reduces its reach. The same amount of energy will provide long reach with minimal foam expansion, great expansion with limited reach or somewhere in the middle.

A handline combination nozzle and foam attachment does nothing to enhance the application of CAF. Quite the opposite, the addition of this equipment will turn highly expanded foam back to a wet solution. The best choice for CAF applications is a smooth-bore tip or an automatic nozzle designed specifically for high-energy delivery applications.

A handline combination nozzle using a multi-expansion foam attachment will provide the nozzle operator several finished foam choices depending on the tactical fireground need. Maximum reach and penetration with little expansion, wetter foam for soaking fuels, or a drier foam for pre-treatment and exposure protection are all choices the initial attack crew can make as needed.

There are several benefits with CAF applications, but the low cost, tactical flexibility and simplicity of low- and multi-expansion foam attachments make them a viable alternative. Commercially, most fixed, selectable and automatic nozzles have corresponding low- and medium-expansion foam attachments designed specifically to optimize foam performance. If you don't have big bucks for bubbles, consider the potential a simple foam attachment will add to your operations.

Read the sidebar article, Old Foam Could Contaminate Groundwater, to learn how an older foam is affecting Minnesota residents today.

---

Rod Carringer is the vice president for sales and marketing for Task Force Tips.

Related Stories

• High Aspirations
• Triple Wash
• Understanding CAFS Performance