By Michael Petroff
Retired battalion chief/training officer
Two basic types of foam systems are used in the fire service and industry. The least expensive is a portable system made up of a foam proportioner, hose and a foam nozzle. This system is portable and may be moved to any location, as long as water at the proper pressure can be delivered. The second type of system is a vehicle-mounted system. This system is permanently mounted on the engine.
There are several types of apparatus-mounted foam systems. The categories include eductor systems, around-the-pump proportioners, automatic proportioners (including balanced pressure bladder systems), balanced pressure pump systems and electronic direct injection systems.
Here are the main things to consider when buying new foam systems:
Design and selection
An important factor to consider in the design and selection of an apparatus-mounted foam system is the size of a foam supply tank that is needed to support the built-in system. A foam system's firefighting capacity is dictated by its "gpm" rating. Using NFPA 11 Standard on foam application rates, a 125-gpm system is rated to handle a 1250 square foot spill fire of a hydrocarbon product. The same system could handle a 625 square foot polar solvent fire. NFPA recommends that a 15 minute supply of foam concentrate be available before starting operations.
Using these figures and having a supply of 3 percent foam concentrate, a 55 gallon foam tank would be necessary to supply a 125 gpm foam system. Larger systems, such as around-the-pump proportioners, require an "off-truck foam access system" that would allow the system to be supplied from a foam concentrate bulk container.
The most common eductor system is the built-in bypass educator. These systems operate in the same fashion as portable eductors. They are sized by the foam stream flow rate that they deliver (60 gpm, 95 gpm or 125 gpm) and require 200 psi inlet pressure for proper proportioning. They have a foam concentrate metering valve that adjusts the percentage of foam added to the foam stream.
This metering valve setting must match the type of foam concentrate being proportioned (1 , 3 or 6 percent). Built-in educator systems deliver foam to only one dedicated hose line and are most commonly used for class "B" firefighting. Cost for these systems would be about $2,500-$3,000.
Around-the-pump proportioners are capable of delivering higher foam application rates. Systems are available that will deliver foam at rates from 400 g.p.m to 5,000 g.p.m. The system is adjusted by a metering valve to deliver lower flow rates. Remember that this metering valve is adjusted to match the desired foam stream flow rate, not the foam concentrate percentage.
These systems deliver foam to all outlets of the apparatus. Therefore, if a water stream is needed for exposure protection, this water stream cannot be supplied by the engine that is pumping foam. Around-the-pump systems have specific water supply hydraulic limits. Pump suction pressure cannot exceed 10 psi. Again, the foam supply tank size must be considered. At 400 gpm using 3 percent foam, a 180-gallon foam tank would be needed. This system is most commonly used for class "B" applications. Cost for an around-the-pump system would be near $3,000.
Automatic proportioning systems
These systems include balanced pressure systems and direct injection systems. They lend themselves to a combined class "A" and class "B" application. Dual foam concentrate tanks and a tank selection valve are part of the dual class systems. Direct injection systems are an electric motor-driven flow-based proportioning system that measures water flow and then injects the proportional amount of foam concentrate to maintain the preset percentage.
Foam concentrate is injected directly into the water stream on the discharge side of the water pump. Direct injection systems have a maximum foam concentrate delivery capacity. One manufacturer has a system that can deliver up to 12 gpm of foam concentrate to dedicated outlets. Using 3 percent foam, the maximum foam stream flow capacity of this system would be 400 gpm. As with a 400 gpm capacity around the pump system, a 180 gallon foam concentrate tank would be needed. Class "A" application using this system is more flexible and can deliver concentrate percentages as low as 0.2 percent. The size of the class "A" foam tank would be 20 gallons to deliver a 1000 gpm at 0.2 percent for 100 minutes. Cost for direct injection systems would be approximately $6,000 for a class "A" system, $14,000 for a class "A"/"B" combination system.
Flammable liquid firefighting
Flammable liquid firefighting is a facet of firefighting that requires specific equipment and training. With the increased use of alternative fuels, the fire service must meet new challenges. The Ethanol Emergency Response Coalition has produced a training program that describes the techniques and foam concentrate necessary to extinguish ethanol and ethanol blended fuels. The video is available for download at www.ethanolresponse.com. The program describes the physical properties of ethanol and the need for alcohol resistant foams and the proper application rate for flammable liquid fires.
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Michael Petroff is a retired battalion chief from the Ferguson Fire Department of St. Louis County, Missouri. BC Petroff served for more than 32 years, progressing through the ranks. He served on the St. Louis County Overhead response team, and is an instructor for national, state and local fire agencies. BC Petroff is a former western region director for the Fire Department Safety Officers Association, a member of the National Fire Protection Association 1021 Committee, a member of the Thomson Delmar Fire Advisory Board, and serves as the region VII regional advocate for the Everyone Goes Home Life Safety Initiatives Program.