Back in the early 1990s, a lot of fire departments didn't specify foam systems, because they were concerned about the reliability of the proportioning devices, the complexity of the system operation and the effectiveness of foam. For those who took a wait-and-see position back then, it's time to take a second look.

Modern foam systems are reliable, accurate and increasingly user-friendly. In many systems, the pump operator simply has to flip a switch and twist a knob to be flowing the correct proportion of foam. Some are even simpler. As for the effectiveness of foam, many experienced operators say, "Show me someone who doesn't believe in the effectiveness of foam, and I'll show you someone who hasn't tried it."

Even the concentrates themselves have improved significantly. For example, Class A foams used to be applied at 1%, but are now so effective at suppressing fires that they're regularly applied at 0.5% or less, producing two or three times as much finished foam per gallon of concentrate. Class B foams that were applied at 6%, the only available option, are now also applied at lower concentrate percentages. In addition, environmentally safe foams have replaced older foams whose chemical makeup would classify them as hazardous materials under current regulations.

Foam proportioners nfpa 1901, Automotive Fire Apparatus, establishes requirements for seven types of foam-proportioning systems, including simple eductor, pressurized bladder, dual piston and automatic direct injection. Other systems that won't be examined here are either variations of these or used primarily by large industrial fire apparatus at oil refineries and other plants.

Each type has its advantages and disadvantages, depending on the application. For example, a system that's completely unsuitable for one application may be the most cost-effective solution for another. In general, more-expensive systems have more advantages and fewer disadvantages than less-expensive systems, but departments should consider the specific application before they buy any system.

Simple eductor. At the low end of the price range, a simple eductor foam system can provide a real value for certain applications. Akron Brass, Elkhart Brass and several other companies make eductors. In this type of system, water from the pump passes through a narrow passage in the eductor, called a venturi, where it creates an area of low pressure. This low pressure draws the foam concentrate through a metering hole and into the water stream. By varying the size of the metering hole, Class A and Class B foams can be proportioned between 0.5% and 6%.

The advantages of this type of system are cost, ease of operation and extreme simplicity: There are no power requirements, no controls and no moving parts. Unfortunately, there are also several disadvantages, including a fixed water flowrate, high pressure drop and short hose lays. Plus, the nozzle can't be elevated above the eductor, and the eductor must be thoroughly cleaned after each use to prevent clogging.

Despite these limitations, there are many applications where an eductor foam system would be an economical choice, such as on a pumper that occasionally responds to vehicle accidents or other incidents where there's the possibility of a flammable liquid fire.

In a typical application, a 100-foot length of 1H-inch hose is preconnected to an eductor mounted behind the pump panel and is used to apply 3% Class B foam through a fixed flowrate nozzle. Eductors for this kind of application are generally available in 60-,95- and 125gpm ratings. The nozzle flow rating has to be matched to the eductor rating for the system to work properly.

Pressurized bladder. As you move toward the middle of the price range, a variety of foam systems offer enhanced performance. One of the best known is the Robwen Flow-Mix pressurized bladder proportioner. In this design, water from the pump flows through a differential pressure valve. A small portion of water is bled off upstream of the valve to press against a flexible foam-filled bladder inside a metal tank, forcing the foam through a metering hole and into the water downstream of the valve.

The advantages of this type are simplicity, ease of operation and the ability to proportion foam over a wide range of flowrates. For example, the Flow-Mix has a variable proportioning range of 0.1% to 1.0% for Class A foam, operates from 2gpm to 550gpm and can also be used with Class B foam. There are no hose length or nozzle elevation restrictions. The system's disadvantages include the lack of a foam-level visual indicator and the inability to refill the foam tank while the system is operating. An optional dual-tank system with a selector valve eliminates the latter problem.

Dual piston. This design, also in the middle price range, uses water pressure to operate a dual-piston foam injector that pumps the foam into the water stream. It has all the advantages of the pressurized bladder design, but it can be used with a standard foam tank or cell to eliminate the disadvantages of those units.

Robwen's Hydro-Flo 100 has a variable delivery rate of 0.1% to 1.0% for Class A foam, operates from 5gpm to 100gpm and can also handle Class B foam. The company will be introducing its new Hydro-Flo 600 model at Fire-Rescue International. This larger model can proportion Class A foam up to 600gpm and is expected to proportion Class B foam in the 300gpm range.

Both the Flow-Mix and Hydro-Flo series offer a moderately priced foam system that can be used on many structural, flammable liquid and wildland-urban interface fires where maximum delivery rates are in the 300gpm to 600gpm range.

Automatic direct injection. At the upper end of the price range, automatic direct-injection foam systems like the FoamPro from Hypro are the most common configuration. In this type of system, the water flowrate is measured by a flowmeter. An electrical signal from the flowmeter controls a foam-proportioning pump, which automatically varies the amount of foam being injected as the water flowrate varies.

One of the greatest advantages of these systems is their ability to accurately proportion foam over a higher range of flowrates than other systems. For example, most direct-injection systems can handle water flowrates from about 30gpm up to about 1,000gpm for 0.5% Class A foam.

Other advantages include their very low pressure drop and their ability to monitor and display information about flowrates, foam proportioning percentage and foam levels. One of the disadvantages of these systems, besides their cost, is their electrical power requirement, which can consume up to 50 amps for the foam-injection pump.

Automatic direct-injection foam systems are usually specified by departments that use foam frequently. For these departments, the cost of foam concentrate is a significant factor, so they need a system that will accurately control the amount used under varying flow conditions to minimize operating expenses.

Direct-injection foam systems are often integrated into the main centrifugal pump installation. Waterous, for example, has developed the FoamManager system, which plumbs a separate foam proportioner into a manifold on the centrifugal pump. The manifold includes a flowmeter, an nfpa-required check valve to prevent foam solution from backflowing through the pump and multiple flanged ports to allow foam to be plumbed to several outlets.

Also in this category, Hale offers the FoamMaster 5.0 system with proprietary components and controls for use on their pumps. The system includes a rotary gear foam pump, one or more flowmeters, check valves, and an electronic control unit with a microprocessor to display information, monitor and adjust flowrates, and send appropriate warnings. The system can be plumbed to multiple outlets.

The facts about CAFS Compressed-air foam systems are rapidly moving out of the forests and into the cities. Anyone who has seen a cafs demonstration on a structure fire has become a believer. In addition to its superior firefighting capabilities, compressed-air foam can reduce stress on firefighters, and reduce damage to equipment, property and the environment. (See sidebar below.)

In operation, a foam-proportioning system first generates the appropriate foam solution, a mix of water and concentrate. Compressed air is then injected into the stream on the discharge side of the pump. As the foam solution and compressed air travel through the hose, they mix to form a lightweight, frothy foam that clings to vertical surfaces and coats burning materials.

Traditionally, Class A compressed-air foam has been mixed in an equal ratio of water to air. Recent tests seem to indicate that using more water than air, perhaps as much as 2gpm:1cfm, might be more effective, and many cafs units now generate compressed-air foam closer to that ratio.

Most of the major manufacturers offer cafs. Waterous has the Eclipse system, Hale offers the CAFSMaster, Darley offers several versions of the AutoCAFS, and Pierce recently introduced the Hercules system. Each of these systems includes a 160cfm to 200cfm air compressor, which can deliver compressed-air foam to one or more 1I-inch preconnects, a 2H-inch discharge, and the deck gun for use in attacking structure fires.

Who's using foam, and why? Although there have been some wild claims about the effectiveness of foam in the past, most experts now agree that nozzle-aspirated foam is at least twice as effective as plain water in extinguishing most Class A fires, and everyone agrees that many Class B fires simply couldn't be extinguished without foam.

As for compressed-air foam, there have been even wilder claims, but the number that seems to be emerging from tests is that caf is roughly four to five times more effective than plain water in extinguishing most Class A fires.

Numbers like these are attracting the attention of many fire departments. In the West, the Los Angeles City Fire Department specified a Robwen Class A foam system on its latest delivery of 18 pumpers; Houston is getting a Hale Class B foam system on 55 new pumpers; and Tacoma, Wash., recently purchased five pumpers and quints equipped with Darley's AutoCAFS. In the East, Manchester, N.H., runs three pumpers equipped with Hale cafs; Hartsville, Pa., took delivery of a pumper-tanker with a Pierce Class A/B foam system; and Mt. Olive, N.J., received a pumper with an Akron foam system.

No matter where you live, chances are that departments in your area are specifying foam systems on their new apparatus. Roger Ruth of National Foam sits on the nfpa 1901 committee and is chairman of the nfpa foam task group. He strongly believes that the use of foam systems is going to continue to grow: "Fire departments have recognized the effectiveness of foam and are buying the most cost-efficient system for their particular application."

Ruth notes that to be accepted, foam systems, especially cafs, need to be reliable and easy to operate. He also predicts that there will be an extension of cafs technology into Class B foams for use in aircraft crashes and other large-scale flammable liquid fires.

Dominic Colletti of Hale Products has authored a new book, "Class A Foam - Best Practice For Structure Firefighters." More information is available at .

Training Officer Gary Simpson of the Manchester (N.H.) Fire Department has just completed an hour-long training video on cafs and Class A foam, filmed by American Heat of Carrollton, Texas. Copies of the April 1999 American Heat Video, "Class A Foam for Structure Firefighting," are available for sale at 800-535-5386.

Compressed-air foam offers significant advantages in both wildland and structural incidents. Here are a few.

More effective water

* Uses less water.

* Uses less foam concentrate.

* Penetrates fuels more effectively to reach deep-seated fires.

* Forms a vapor barrier around fuels to exclude oxygen.

* Absorbs heat more rapidly to lessen the chance of flashover in structure fires.

* Gives a faster knockdown to contain the spread of fire.

* Reduces the potential for rekindle

* Can be pumped twice as high as water under the same pressure.

* Allows firefighters to see where foam has been applied.

* Coats wood, metal, glass, brick, concrete and vegetation.

* Clings to vertical surfaces.

* Can be used with Class A or B foams.

Greater safety, less stress

* Produces up to three times longer stream throw, allowing greater standoff distances.

* Reduces the weight of hose lines.

* Lowers risk of heat stress during interior attack.

* Reduces smoke and steam.

* Reduces the chance of structural collapse from accumulated water.

* Permits the application of a protective foam coating up to several hours before the arrival of the wildland fire front. Firefighters can cover an exposed area, then move to a safer location.

* Reduces time at the scene, resulting in less personnel fatigue and allowing more time for recovery.

Less equipment damage

* Reduces loading on aerial devices from the weight of the filled waterway for elevated master streams. (Water adds about 540 pounds per 100 feet in a 4-inch waterway.)

* Reduces pressure drop in hose so the pump can operate at a lower discharge pressure, resulting in lower engine rpm, less wear and lower noise levels

* Fewer water refills mean less damage to apparatus traveling back and forth over rough terrain.

Less property damage

* Reduces water and smoke damage to structures and contents.

* Reduces the potential for flooded basements.

* Reduces water runoff.

* Aids fire investigation by lessening disruption of the scene by water streams.

There are some disadvantages of compressed-air foam as well. Here are a few:

* Expensive to buy and maintain.

* Creates slippery surfaces.

* Produces a large thrust when the nozzle is first opened.

* Without full pressure, hose lines kink more easily.

* May encourage the use of smaller hose lines or lower flow rates. Compressed-air foam still requires appropriately sized lines and flow rates, it just extinguishes the fire faster.