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Class A Foam Q&A

by Dominic J. Colletti

Although the new generation of Class A foams were originally developed for forestry firefighting in the mid-1980s, practical experience and testing has shown that it can be a valuable tool to manually combat other Class A type fuels, including structure fires. New foam application equipment has reduced the logistical requirements burdened on the pump operator to efficiently supply Class A foam on the fireground. This has made its use feasible for municipal fire operations. What follows are some frequently asked questions about this technology.

Why is Class A foam more effective than plain water on Class A type fires?

Plain water has inherent limitations in cooling and penetrating Class A fuels because of a naturally high surface tension. This high surface tension causes water to form into droplets, and consequently, the majority of the droplets roll off fuels, impeding water's heat absorption potential.

Class A foam concentrate treated water (foam solution) has reduced surface tension and allows more surface area of water droplets applied to contact the ordinary combustible surface. This provides increased heat transfer through conduction.

Class A foam concentrate is technically known as a synthetic detergent hydrocarbon surfactant, and when mixed with water at the recommended ratios, is biodegradable. Because it is a hydrocarbon surfactant, it also has an affinity for carbons and causes the water (as foam solution) to penetrate into wood fuels.

Class A foam solution can be aspirated (entrained with air) by application through a fog or air aspirating nozzle, or a Compressed Air Foam System (CAFS). Different quality finished foam blankets can be formed using these foam generation devices. Forming a low expansion, quick draining finished foam bubble blanket will yield additional fire suppression proficiency upon direct attack by enabling the foam solution to adhere to horizontal and vertical three dimensional fuels. Foam bubbles adhering to fuels will cause the foam solution to remain on it where it will penetrate or evaporate, until it is all gone. The net effect of using Class A foam in this fashion is that the available water supply is efficiently used to cling to and cool the fuel. This maximizes water's ability to suppress the fire, rather than being wasted by running off of it.

How can Class A foam help our daily fire operations?

The major percentage of working alarms that municipal departments respond to are Class A fires. From that standpoint, methodologies that increase fire suppression capabilities should be closely investigated because of the potential benefit to the total number of incidents. In simple terms, using Class A foam correctly can provide a tool to increase the effective application of water on these hazards. The benefits of adopting Class A foam may include increased firefighter safety, increased fire operation efficiency and reduced property damage. In most scenarios, using water more efficiently will mean reduced knockdown and total extinguishment time, and as a prime effect, firefighter stress from exposure to heat and toxic products of combustion will be lessened. Rural departments depending on a labor and equipment intensive water supply can extend the capability of water shuttle operations. Because of faster fire control, less total water may be needed for extinguishment when using Class A foam. This can help reduce total fire and water damage, and thus the environmental and financial impact of fire on the community.

Can the benefits justify the cost?

From a cost standpoint, Class A foam concentrate is generally proportioned at 3/10 to 5/10 of 1% when used for direct attack. This is only a fraction of the proportioning ratio typically used with Class B flammable liquid foams (usually 3% and 6%). This low proportioning ratio, and its ability to make water a more effective firefighting agent makes usage cost effective. Each individual department should prepare an analysis of required implementation/operation costs. These costs should then be weighed against the potential benefits to the total fire operation and the community. This should be performed after a thorough review process of Class A foam technology.

Can Class A foam be utilized for interior structural attack? If so, what are the benefits?

Most municipal departments have hydrated fire districts with good water supplies. With proper training, Class A foam can be utilized very effectively for both interior and exterior structure attack. At least one reason why Class A foam should be used for interior attack, even though a good water supply may be available, can be better understood through examining plain water application requirements, such as the Iowa formula, and by looking at actual interior gpm flows used today. Some have said that water flow formulas developed years ago are no longer valid today because of the increased interior fire loading characteristics of home furnishings manufactured from synthetic materials, whereas all natural fires were ordinarily used years ago when these formulas were developed. While it is true that these synthetic materials have considerably increased fuel loading, it is also true that many departments have replaced 1 1/2" hose and variable gallonage nozzle with 1 3/4" hose and automatic nozzle. In as much as this larger hose line and nozzle is capable of delivering the higher flows primarily found with 2 1/2" diameter hose line, aggressive interior attacks are only normally delivering 95 to 150 gpm water flow. It is difficult to realistically use higher interior flows because of high nozzle reaction force, the inability of the attack team to advance awkward hose line from the higher pressure required and because there are limited firefighting personnel found on the responding engine. Realizing that there are practical limits to interior attack flow rates, adding Class A foam concentrate can be a justifiable alternative to increase the fire-killing and fuel securing action of interior fire streams. This may help offset higher interior fire loading found in most residential occupancies today.

When talking about Class A foam, the term CAFS is often discussed. Can CAFS be used by municipal fire departments, and do they offer any advantages?

Compressed Air Foam Systems or CAFS, describes a high energy foam generation system that utilizes an air compressor to generate the foam bubbles within the hose line. This system can offer advantages over conventional application equipment. CAFS are becoming widely recognized as giving quicker flame knockdowns, increased reach and more finished foam product variability for a wide range of tactical uses. There are several municipal fire departments using CAFS for structure attack.

What equipment is needed to produce Class A foams in municipal fire operations?

Most departments have some experience with Class B flammable liquid foams. Class B foam concentrates are mixed with water (proportioned) and then aspirated (air-added) to create finished foam blankets. Class A finished foams are produced in this way also. The major difference in producing Class A foam is that lower proportioning ratios are required.

What is the typical equipment installation for departments that are using Class A foam?

Many are installing variable speed direct injection, discharge side foam concentrate proportioning systems. These systems offer advantages over common educators and other methods of integrating foam concentrate with the fire stream. They are available in 12 volt DC, are small in size and usually mounted in a storage or pump compartment. These direct injection foam concentrate proportioning systems allow reliable, easy to control foam production, and keep foam concentrate out of the fire pump and water tank. They are unaffected by changes in suction and discharge pressures within their design specifications. Many apparatus installations include dual foam concentrate tanks, one holding Class A foam concentrate, and the other holding 1% Aqueous Film Forming Foam Concentrate. This allows for suppression of Class A type fuels and also normal hydrocarbon Class B flammable liquid fires. Conventional smooth bore and automatic nozzles are compatible with Class A foam. Nozzles can be swapped or attachments added to aspirate the foam solution and create finished foam blankets of varying degrees for a variety of tactical uses, such as exposure protection.

Is training required to place Class A foam agents in fire operations?

Training is essential for the successful implementation of Class A foam into fire operations. The benefit of any new firefighting concept is directly proportionate to the knowledge of the user. It is important that the entire department become involved in the education and training process. This could begin with the truck committee gathering all the technical information available on the subject through contacting various manufacturers and users of Class A foam systems. Training and educational manuals and videos should be purchased through nationally recognized training agencies. Some equipment and foam agent distributors are available to demonstrate their wares. Hosting a live fire demonstration would be an excellent method to introduce the Class A foam concept to the department and obtain some hands-on use. A qualified instructor that has experience with Class A foam should be the instructor-in-charge of the foam portion of the live fire demo.

After the decision has been made to purchase Class A foam equipment, a systematic training program should be formulated and placed into action upon system delivery. This should include but not be limited to:

  • Classroom instruction on Class A foam methodology and implementation.
  • Pump operator training in the operation and maintenance of the foam equipment.
  • Procedures for handling Class A foam concentrate to protect personnel, equipment and the environment.
  • A standard operating procedure to designate when and how Class A foam will be used.
  • Hands-on training before actual fire responses.
  • Training on new foam application techniques if new nozzles or CAFS will be utilized.
  • Performing live fire training if Class A foam is to be used for structure attack. All training should follow relevant NFPA standards including NFPA 1403, and any other regulations of state and local authorities having jurisdiction.

Fire departments looking at Class A foam should realize that when the technology is used correctly it can present a tangible gain in fireground operational effectiveness and firefighter safety. However, it is not a "cure all" for all the problems encountered in fire operations. A successful training program will result in maximizing its benefits and communicating its limits and capabilities to fire personnel.

About the author: Dominic J. Colletti is the foam systems product manager at Hale Fire Pump Company in Conshohocken, PA. A former volunteer firefighter in New York state, he is a fire protection system engineer, specializing in foam systems design/application.