Types of Fire Fighting Foam: AFFF, AR-AFFF, Fluorine Free, Class A and Class B
Fire fighting foam is selected mainly by the fuel it must protect and whether the concentrate contains fluorinated surfactants. Class B foams are designed for flammable liquids, while Class A foams are primarily wetting agents for ordinary combustibles. Within Class B, AFFF and AR-AFFF are fluorinated products, while fluorine-free foam provides alternatives where PFAS restrictions or environmental requirements apply. Concentration is also critical because foam concentrates are listed for specific proportioning percentages and applications.
Class A Foam: A Wetting Agent for Ordinary Combustibles
Class A foam is normally used at much lower concentrations than Class B foam, often around 0.1 to 1 percent in water. Its purpose is to reduce the surface tension of water so it penetrates materials such as wood, paper, tires and other ordinary combustibles more effectively.
Class A foam is commonly used by wildland and structural firefighting crews, including compressed air foam systems. It is not a substitute for Class B foam on gasoline, diesel or other flammable-liquid hazards because it does not provide the same fuel-surface protection and burnback resistance.
Protein and Fluoroprotein Foam
Protein foam is produced from hydrolyzed animal proteins and stabilizing additives. It creates a durable blanket with good heat resistance and burnback performance, although it generally spreads more slowly than film-forming foams.
Fluoroprotein foam adds fluorinated surfactants to the protein base. This improves fuel shedding and can support applications such as subsurface injection. Film-forming fluoroprotein, or FFFP, combines the protein base with film-forming characteristics.
These products remain relevant in some legacy tank and storage applications, but fluorinated versions carry the same PFAS considerations that have driven the move toward fluorine-free alternatives.
AFFF: Fast Knockdown for Hydrocarbon Fires
Aqueous film-forming foam, or AFFF, became widely used for Class B fire protection because it spreads rapidly across hydrocarbon fuel surfaces. Its fluorosurfactants allow an aqueous film to form ahead of the foam blanket, helping suppress fuel vapors and accelerate extinguishment.
AFFF has historically been used for gasoline, diesel, aviation fuels and other hydrocarbon hazards. However, the fluorinated chemistry contains PFAS, which has resulted in increasing regulatory restrictions, environmental concerns and owner requirements for replacement with fluorine-free products.
Existing AFFF systems should therefore be evaluated against the requirements that apply to the site, owner and jurisdiction rather than assuming that an existing concentrate can remain indefinitely.
AR-AFFF for Polar Solvents
Standard AFFF is not designed for polar solvents such as ethanol, methanol, acetone and other water-miscible fuels. These fuels can break down a conventional foam blanket and reduce its effectiveness.
Alcohol-resistant AFFF, or AR-AFFF, adds a polymer that forms a protective membrane when the foam contacts a polar solvent. This allows the blanket to remain effective for longer on solvent fires.
AR concentrates are commonly identified using designations such as 3x3 or 3x6. The numbers indicate the proportioning requirements for different fuel classes. The correct percentage must always match the foam manufacturer's listing and the fuel being protected.
Fluorine-Free Foam: What Changes?
Fluorine-free foam, also called FFF, F3 or SFFF, eliminates fluorinated surfactants and is increasingly used as an alternative to AFFF. These products rely on the foam blanket rather than a fluorochemical film to control the fuel surface.
- Application rates may be higher: the required rate depends on the specific product listing and applicable design standard.
- Discharge equipment matters: foam quality can change significantly between aspirating and non-aspirating devices.
- Proportioning may need review: fluorine-free concentrates can have different viscosity and proportioning characteristics than legacy AFFF.
- Stored quantity may change: a higher application rate can require more concentrate or greater tank capacity for the same hazard.
A conversion from AFFF to fluorine-free foam should therefore be treated as a system review rather than simply draining one concentrate and adding another. The replacement product's listing, application rate, proportioning equipment, discharge devices and required storage quantity should all be checked.
Matching Fire Fighting Foam to the Fuel
| Foam Type | Hydrocarbons | Polar Solvents | Class A | Fluorinated | Typical Application |
|---|---|---|---|---|---|
| Class A | Poor | No | Yes | No | Wildland, structural and CAFS applications |
| Protein | Yes | No | No | No | Legacy tank and storage applications |
| Fluoroprotein / FFFP | Yes | No | No | Yes | Legacy and specialized tank applications |
| AFFF | Yes | No | No | Yes | Legacy hydrocarbon fire protection |
| AR-AFFF | Yes | Yes | No | Yes | Hydrocarbon and polar-solvent hazards |
| FFF / SFFF | Yes | Product dependent | No | No | Fluorine-free replacement applications |
| AR-FFF | Yes | Yes | No | No | Fluorine-free polar-solvent protection |
Low, Medium and High Expansion Foam
Foam type and expansion ratio are separate considerations. Low-expansion foam is commonly used for direct application to flammable-liquid surfaces. Medium- and high-expansion foams produce significantly greater foam volumes and can be used for applications where filling or blanketing a larger volume is required.
These products are not automatically interchangeable. The foam concentrate, expansion ratio, discharge equipment, application rate and fuel must all match the intended application and product listing.
Where Foam Stops and Dry Chemical Starts
Foam is primarily a surface-control agent. It is not the ideal solution for every flammable-liquid fire, particularly pressure-fed or three-dimensional fires where fuel is continuously escaping from a pipe, flange, pump seal or other source.
Dry chemical can provide rapid flame knockdown in these situations, while foam can subsequently protect a liquid surface and help control reignition. This is why twin-agent systems can be useful where a site has both three-dimensional and pool-fire hazards.
Salus Global supplies nitrogen-expelled dry chemical skids in 350, 1,000 and 2,000 lb configurations for applications requiring rapid dry chemical knockdown.
Frequently Asked Questions
Can fluorine-free foam be used in an existing AFFF system?
Sometimes, but the system needs to be evaluated against the replacement foam's listing and design requirements. Concentrate viscosity, proportioning equipment, application rate and discharge devices can differ. A conversion may require changes to the proportioner, nozzles or stored concentrate quantity.
Is AFFF illegal in the United States?
Requirements vary by jurisdiction and application. There is not a single rule that makes every existing AFFF system illegal nationwide. Federal, state, owner and environmental requirements can restrict the purchase, use, discharge or disposal of fluorinated foam, so the requirements applicable to the specific site should be checked before making a decision.
What does 3x3 or 3x6 mean on an AR foam label?
The designation describes the concentrate's proportioning requirements for different fuel types. For example, a 3x3 product may be proportioned at 3 percent for both hydrocarbon and polar-solvent applications, while a 3x6 product may require 3 percent on hydrocarbons and 6 percent on polar solvents. Always follow the manufacturer's listing and technical documentation.
