High & Low Expansion Fire Fighting Foam


Chemical formulations aside, a fire fighting foam is simply a stable mass of small, air-filled bubbles with a lower density than oil, gasoline, or water. The foam is made up of three (3) ingredients… water, a foam concentrate, and air. The water is mixed with the concentrate to form a foam solution. This solution is then mixed with air to produce foam which is very fluid and flows readily over liquid surfaces.

Fire fighting foam is generally used in the following applications:

  • Truck Loading Racks
  • Refineries
  • Pipeline Pumping Stations
  • Power Plants
  • Airports
  • Heliports
  • Marine Vessels
  • Manufacturing Plants
  • Large Spills
  • Storage Tanks
  • Chemical Plants
  • Offshore Platforms
  • Aircraft Hangers
  • Crash Rescue Vehicles
  • Mining Facilities
  • Marine Docks
  • Warehouses
  • Hazardous Material Spill Control

Ansul high expansion foam system discharge (aircraft hanger)


How do Foam Agents Work?

Fire fighting foam agents suppress fire by separating the liquid fueal from the air (oxygen). Depending upon the type of foam agent, this is done in several ways:

  • The foam blankets the fuel surface, smothering the fire.
  • The foam blanket separates the flames from the fuel surface.
  • The foam cools the fuel and adjacent heat and ignition sources.
  • The foam blanket suppresses the release of flammable vapors that can mix with air.

What Types of Foam Agents are Available?

Essentially there are six (6) general types of foam agents:

  • Aqueous Film-Forming Foams (AFFF) is based on combinations of fluorochemical surfactants, hydrocarbon surfactants, and solvents. These agents require a very low energy input to produce high quality foam. Consequently, they can be applied through a wide variety of foam delivery systems. This versatility makes AFFF agents an obvious choice of municipal fire departments, airports, refineries, manufacturing plants, and other operation involving the transportation, processing, and handling of flammable liquids and materials.
  • Alcohol-Resistant AFFF Concentrate is based on AFFF concentrates to which a polymer has been added to make them effective on fires involving polar solvents (methanol), as well as hydrocarbon-type fuels (gasoline). Thus, alcohol-resistant concentrates are the most versatile of the foam agents. The alcohol-resistant concentrate forms a polymeric membrane when used on polar solvent type fuels which prevents destruction of the foam blanket. When used on hydrocarbon fuels, the alcohol-resistant concentrate produces the same rugged aqueous film as a standard AFFF agent. The alcohol-resistant concentrate provides fast flame knockdown and good burn back resistance when used on both types of fuels.
  • Protein Foams are recommended for extinguishment of Class B fires involving hydrocarbons. Typically, these agents are used to protect flammable and combustible liquids where they are stored, transported, and processed. Protein foams are based on hydrolyzed protein, stabilizers, and preservatives. They produce highly stabilized mechanical foam with good expansion properties and good re-ignition (burn back) resistance characteristics.
  • Fluoroprotein Foam Concentrates are based on hydrolyzed protein, stabilizers, preservatives, and synthetic fluorocarbon surfactants. In applications involving hydrocarbon bulk storage and handling – such as refineries and petrochemical operations – these agents offer several advantages over protein foams. They provide better control and extinguishing ability, greater fluidity, and superior resistance to fuel contamination. Fluoroprotein foams are usually for hydrocarbon vapor suppression and extinguishment of fuel-in-depth fires and have been recognized as a very effective fire suppression agent for sub-surface application to hydrocarbon fuel storage tanks.
  • High Expansion Foams are based on combinations of hydrocarbon surfactants and solvents and are used in foam generators – both stationary and portable – for applying foam to large areas in a total flooding or 3-deminsional application such as warehouses, ship cargo holds, aircraft hangers, and mine shafts. They are especially useful on fuels such as liquefied natural gas (cryogenic fuels) for vapor dispersion and control. In certain concentrations, high expansion foams provide an effective extinguishing agent for hydrocarbon spill fires of most types and in confined areas.
  • Class A Foams are typically formulated from a combination of specialty hydrocarbon surfactants, stabilizers, inhibitors, and solvents. They reduce the surface tension of water for improved wetting and penetrating characteristics and create a clinging foam blanket that suppresses combustible vapors while cooling the fuel. Class A foams can be applied using a variety of proportioning/discharge devices and have proven effective in fighting forest fires and many deep-seated fires such as tires, paper, coal bunkers, wooden structures, etc.

Are Agent Listings and Approvals Important?

As is the case with all fire protection products, the approval process is extremely important. Recognized independent testing agencies – such as Underwriters Laboratories (U.L.) and Factory Mutual (FM) – as well as the U.S. Government established standards for product performance. These standards are designed to protect the consumer. This is why manufactures must not only meet the standards initially to secure a product listing; they also must subject their products to subsequent testing in order to retain the listing.

What is the Difference Between 6%, 3%, and 1% Concentrates?

The foam concentrate percentage refers to the amount of concentrate that is proportioned or pre-mixed with water to give the resulting foam solutions.

For Example, to make 1,000 gallons of pre-mix foam solution, a 1,000 gallon tank would require:

  • 10 gallons of 1% concentrate, or
  • 30 gallons of 3% concentrate, or
  • 60 gallons of 6% concentrate

Obviously, the more concentrated foam agent, the greater the savings in space, weight, and cost.

What Other Factors Should be Considered When Evaluating a Foam Agent?


Environmental impact and toxicity. Foam concentrates are specifically formulated to maximize performance and minimize environmental impact and human exposure hazards. All concentrates are readily biodegradable – both in the natural environment and in sewage treatment facilities. However, all foam agents should be metered into the facility to prevent overloading the plant due to foam formation. They are not considered skin irritants; however, prolonged contact may cause some dryness of the skin. For this reason, we recommend that areas of the skin which have come in contact with the foam concentrate be flushed with fresh water.

Shelf life. Shelf life is the length of time over which foam concentrates remain stable without significant changes in performance characteristics. AFFF, high expansion, and Class A foam concentrates – if stored in accordance with recommended guidelines – have a normal shelf life of 20-25 years. All other foam agents – those which are not totally synthetic – have a normal shelf life of 7-10 years.

Periodic testing. We recommend periodic testing of foam concentrates to ensure that performance standards will be maintained. NFPA Standard 11 suggests that this process be done on an annual basis and outlines procedures to accomplish the testing. For the convenience of our customers, samples may be sent directly to Ansul for testing and evaluation. Ansul provides a procedure for checking on-site the quality of foam concentrates and pre-mix solutions that it manufactures.

Compatibility. Ansul foam concentrates have been found to be compatible with most other foam concentrates of similar type and quality. However, before mixing foam agents, we suggest contacting Ansul for further information