Firefighting Foam

What Is Firefighting Foam?

Firefighting foam is a water-based extinguishing agent mixed with a foam concentrate (typically at 1%, 3%, or 6% proportioning ratios) that produces an expanded blanket of air-filled bubbles over burning or unignited flammable liquids to suppress vapors and prevent ignition. Class A foam (0.1–1% mix) wets and penetrates solid fuels like wood and brush, while Class B foam (AFFF, AR-AFFF, or fluorine-free alternatives) floats on hydrocarbon and polar solvent fuel surfaces to smother Class B fires. PFAS-containing AFFF is being phased out in many jurisdictions due to environmental contamination concerns, with fluorine-free foams (F3) replacing them per NFPA 11 guidance.

Why Firefighting Foam Matters on the Fireground

Water alone runs off the surface of burning hydrocarbons and does not suppress the vapor that feeds the flame. Foam blankets the liquid surface, cutting off oxygen and suppressing vapor release simultaneously. In structural firefighting, Class A foam dramatically improves water's penetration of compacted fuel loads (like baled materials or deep-seated attic fires) by reducing surface tension.

Relevant NFPA Standards

• NFPA 11: Standard for Low-, Medium-, and High-Expansion Foam
• NFPA 1150: Standard on Foam Chemicals for Fires in Class A Fuels

Field Procedures & Tactical Steps

1. Select the correct foam type — Class A (0.1–1%) for structural/wildland, Class B (1–6%) for flammable liquids — and set the proportioner accordingly.
2. Apply foam gently using the rain-down or roll-on technique to build a uniform blanket over the liquid surface without plunging through it.
3. Maintain the foam blanket until the fuel has cooled below its flash point and vapor suppression is confirmed.
4. Contain all foam runoff in berms or portable dams to prevent environmental contamination, especially with PFAS-containing AFFF.
5. After use, flush all foam equipment (proportioner, hose, nozzle) with clean water to prevent corrosion and clogging.

Common Context & Application

Used on flammable liquid spills and fires (Class B), wildland-urban interface brush fires (Class A), deep-seated structural fires, and airport crash rescue (ARFF) operations.

Frequently Asked Questions about Firefighting Foam