Aqueous Film Forming Foam — universally known as AFFF — is the most widely specified firefighting foam agent in the world for Class B flammable liquid fires. It is the standard agent for petroleum storage tank farms, airport rescue and firefighting (ARFF) vehicles, fuel loading terminals, and petrochemical plant deluge systems across every major fire protection standard, from NFPA 11 to GB 15308.
Yet despite its near-universal use, AFFF is frequently misspecified — used where AR-AFFF should be specified, selected in the wrong mixing ratio, or confused with other foam types. This guide explains exactly what AFFF is, the chemistry behind why it works, its technical parameters, where it performs best, and where it falls short.
Contents
What Is AFFF Foam?
AFFF (Aqueous Film Forming Foam) is a synthetic foam concentrate that, when mixed with water at a 3% or 6% ratio and aspirated through a foam branch or monitor nozzle, produces a low-expansion foam blanket capable of rapidly suppressing Class B flammable hydrocarbon liquid fires. The term “aqueous film forming” refers to the defining characteristic that sets AFFF apart from all other foam types: the ability to spontaneously spread a thin, continuous aqueous film across the surface of a burning hydrocarbon fuel — ahead of the advancing foam blanket — providing immediate vapour suppression before the foam itself arrives.
AFFF was originally developed in the 1960s by the US Naval Research Laboratory in collaboration with 3M, specifically to address the need for a faster-acting foam agent for aircraft fuel fires on carrier decks, where the speed of fire control is critical to crew survival. It replaced the slower-acting protein foam concentrates that had been standard until that point, and rapidly became the dominant agent for Class B fire protection worldwide.
CA-FIRE manufactures AFFF foam concentrate in two mixing ratio models: S-3-AB (3%) and S-6-AB (6%), both tested to GB 15308 and compatible with NFPA 11 system designs. Both models are suitable for fresh water and sea water proportioning systems.
How Does AFFF Work?
AFFF suppresses fire through two simultaneous mechanisms that work together in the first seconds of application:
01
Aqueous Film Formation
Fluorosurfactants in the foam solution drastically reduce the surface tension of the water phase below the surface tension of the hydrocarbon fuel. This causes the aqueous solution to spontaneously spread across the fuel surface as a thin, self-healing film — moving ahead of the foam blanket. The film immediately suppresses flammable vapour evaporation from the fuel surface.
02
Foam Blanket Smothering
The aspirated foam blanket (6–9× expansion) rolls across the fuel surface behind the aqueous film, sealing the fuel from atmospheric oxygen and providing a physical barrier against re-ignition. Water draining from the foam blanket continuously cools the fuel surface below its autoignition temperature.
03
Vapour Suppression
By cutting off vapour generation from the fuel surface, AFFF eliminates the flammable vapour-air mixture above the fuel that sustains combustion. Without a continuous supply of flammable vapour from the fuel surface, the flame cannot be maintained regardless of the ignition source still present.
04
Self-Healing Film
One of AFFF’s most valuable properties is that the aqueous film is self-healing — if the foam blanket is disrupted by turbulence, foam cannon impact or physical disturbance, the aqueous film spontaneously flows back to reseal the exposed fuel surface, restoring vapour suppression within seconds without additional foam application.
Typical AFFF fire control timeline on a Class B fuel spill fire
0s
Foam application begins
5s
Aqueous film spreads across fuel
15s
Vapour suppressed, fire diminishing
60s
Full foam blanket, fire controlled
The Chemistry: What Makes AFFF Different
The critical component that distinguishes AFFF from all other foam concentrates — and the source of its rapid film-forming knockdown performance — is the fluorosurfactant. A surfactant (surface-active agent) is a molecule that reduces the surface tension of the liquid it is dissolved in. Ordinary hydrocarbon surfactants, used in regular synthetic foam concentrates and cleaning agents, can reduce water surface tension from approximately 72 mN/m to around 30 mN/m.
Fluorosurfactants go further — the carbon-fluorine bonds in their molecular structure give them extreme surface-tension-reducing power. An AFFF foam solution containing fluorosurfactants achieves a surface tension of approximately 15–17 mN/m. This is critical because the surface tension of a typical hydrocarbon fuel (gasoline, diesel, kerosene) is approximately 20–27 mN/m. When the aqueous foam solution has a lower surface tension than the fuel surface it is applied to, it spontaneously spreads across that surface — like water spreading across a greasy pan when a drop of detergent is added. This is the aqueous film.
Surface Tension — Why the Film Spreads
Plain water
~72 mN/m
~72 mN/m
Hydrocarbon fuel (gasoline / diesel)
~22–27 mN/m
~22–27 mN/m
Synthetic foam solution (no fluorosurfactant)
~28–35 mN/m
~28–35 mN/m
Higher than fuel → cannot spread across fuel surface → no film formation
AFFF foam solution (fluorosurfactant)
~15–17 mN/m
~15–17 mN/m
Lower than fuel → spontaneously spreads across fuel surface → aqueous film forms
In addition to fluorosurfactants, AFFF concentrate contains hydrocarbon surfactants (foam stabilisers), solvents (typically glycols, to control freeze point and viscosity), and corrosion inhibitors and preservatives to ensure long-term storage stability. The precise formulation balance between these components determines the foam’s expansion ratio, drainage time, film-forming speed and freeze point — all of which are verified by the GB 15308 and NFPA 11 Annex B performance tests.
CA-FIRE AFFF Technical Specifications
CA-FIRE AFFF foam concentrate is available in two models — S-3-AB (3% mixing ratio) and S-6-AB (6% mixing ratio) — tested to GB 15308 at our Fujian manufacturing facility.
The mixing ratio (3% or 6%) must match your proportioning system calibration. Both models produce identical firefighting performance — the ratio is determined by your system design, not by fire type or tank size. See our guide: AFFF 3% vs 6% — Which to Choose?
Where Is AFFF Used?
AFFF is specified in fixed fire suppression systems and portable firefighting equipment across a broad range of Class B hazard applications. The following are the most common installation types:
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Petroleum Storage Tank Farms
Fixed foam systems on cone-roof and open-top crude oil, gasoline, diesel and fuel oil storage tanks. AFFF is the primary agent specified under NFPA 11 for surface application on hydrocarbon storage tanks.
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Airport Rescue & Firefighting (ARFF)
ARFF vehicles carry AFFF as their primary foam agent for aircraft fuel spill fires and crash rescue operations. AFFF’s rapid aqueous film formation is essential for fast fire control on aviation fuel spills where speed directly determines survival outcome. Governed by ICAO Annex 14 and NFPA 403.
⛽
Fuel Loading Terminals & Racks
Fixed foam monitor and deluge systems at fuel loading gantries, road tanker loading bays and pipeline pump stations where fuel spill fires during transfer operations are the primary risk scenario.
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Marine & Offshore
Fixed foam systems on tanker vessel cargo decks, pump rooms, and offshore platform process modules. AFFF’s sea water compatibility makes it suitable for marine installations without a fresh water supply. Compliant with SOLAS Chapter II-2 requirements.
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Petrochemical & Refinery
Foam systems on process area bunds, transformer oil bund protection, heat exchanger areas, distillation unit bases and flammable liquid handling areas in petroleum refining and petrochemical processing facilities.
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Industrial & Power Generation
Transformer oil bund protection at power substations and generating stations, hydraulic fluid fire risks in industrial machinery, and general flammable liquid storage protection in industrial facilities where only hydrocarbon fuels are present.
AFFF System Compatibility
CA-FIRE AFFF concentrate is compatible with all standard foam proportioning equipment and delivery systems. The only requirement is that the proportioner is calibrated to the matching percentage (3% for S-3-AB; 6% for S-6-AB).
AFFF Limitations — When AFFF Is Not the Right Agent
Understanding where AFFF fails is as important as understanding where it excels. Specifying AFFF for the wrong application is a common and potentially serious error.
❌
Polar solvent fires — AFFF will fail
Standard AFFF foam collapses within seconds on polar solvent fires — ethanol, methanol, IPA, acetone, MEK and similar water-miscible fuels dissolve the foam bubble walls on contact. If polar solvents are part of the fire hazard, specify AR-AFFF (Alcohol Resistant Foam Concentrate). AR-AFFF also covers hydrocarbon fires, making it suitable for sites with both fuel types.
❌
Large oil tanks requiring extended burnback resistance
AFFF provides good initial knockdown but its foam blanket is less durable than protein-based foams under sustained heat radiation and fuel contamination. For large crude oil tanks, floating-roof tanks and subsurface injection systems where the foam blanket must remain stable for many minutes during the suppression operation, FFFP (Film-Forming Fluoroprotein) provides the superior burnback resistance required.
❌
Enclosed spaces — AFFF cannot flood a compartment
AFFF is a surface-applied agent — it suppresses fires by forming a blanket on the fuel surface. It cannot flood an enclosed space (engine room, hangar, mine roadway) with enough foam volume to suppress a fire by oxygen displacement. For enclosed-space protection, specify High Expansion Foam (YEG-3 / YEG-6).
❌
Class A solid fuel fires — AFFF is ineffective
AFFF does not penetrate solid fuels and provides no meaningful benefit on wood, timber, paper or vegetation fires. For Class A fires, specify Class A Foam Concentrate (MJABP). For mixed Class A and B hazards without polar solvents, Synthetic S-type foam concentrate covers both classes from a single stock.
AFFF vs Other Foam Types
Storage Conditions & Shelf Life
CA-FIRE AFFF foam concentrate has a minimum guaranteed shelf life of 10 years from the date of manufacture when stored correctly. Correct storage conditions are:
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Temperature: 0°C to 45°C
Keep above the freeze point at all times. S-3-AB freezes at −5°C; S-6-AB at −2°C. Sustained storage above 40°C may accelerate degradation — avoid direct sunlight on outdoor storage tanks.
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Sealed containers — original packaging
Keep in original sealed jerricans, drums or IBC totes. Opened containers should be resealed and used as soon as practicable to minimise oxidation and contamination.
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Annual testing per NFPA 11 Annex C
Sample and test installed concentrate annually. Verify expansion ratio, 25% drainage time and pH. Replace if any parameter falls outside specification — do not assume a 10-year guarantee means no testing is needed.
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No mixing with other foam types
Never mix AFFF with AR-AFFF, FFFP or any other foam concentrate. Different chemistries can interact adversely. Systems must be fully flushed before switching concentrate type.
NFPA 11 & Applicable Standards
The primary international standard governing AFFF concentrate selection, system design, application rates and testing is NFPA 11: Standard for Low-, Medium-, and High-Expansion Foam. Key sections relevant to AFFF include:
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Chapter 4 — Foam concentrate classification, mixing ratio definitions and compatibility requirements.
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Chapter 5 — Application rates for different tank types and sizes, minimum foam supply durations (typically 20–30 minutes for storage tank systems).
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Annex B — Foam concentrate performance test methods: expansion ratio, 25% drainage time, spread coefficient (for AFFF film formation), and fire performance tests.
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Annex C — In-service concentrate testing requirements: frequency (annually), sampling method, acceptance criteria and documentation requirements.
In China, the equivalent national standard is GB 15308 — 泡沫灭火剂 (Foam Extinguishing Agent), which covers performance test methods, classification and quality requirements for all foam concentrate types including AFFF. CA-FIRE AFFF concentrate is batch-tested to GB 15308 at our Fujian facility, with test certificates available on request.
📚 Standards & Technical References
→ NFPA 11: Standard for Low-, Medium-, and High-Expansion Foam — The primary standard for AFFF system design, concentrate selection, application rates and in-service testing.
→ NFPA 16: Standard for the Installation of Foam-Water Sprinkler and Foam-Water Spray Systems — Proportioner design, installation and commissioning requirements.
→ API 2030: Application of Fixed Water Spray Systems for Fire Protection in the Petroleum Industry — AFFF system design guidance for crude oil and petroleum product storage.
→ IMO SOLAS Chapter II-2: Fire Protection, Detection and Extinction — AFFF system requirements for petroleum product tankers and general cargo vessels.
→ ICAO Annex 14 — Aerodromes: Rescue and Firefighting — AFFF specification requirements for airport rescue and firefighting (ARFF) vehicles and airport foam systems.
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Get AFFF Foam Concentrate — Factory Direct from CA-FIRE
CA-FIRE manufactures S-3-AB (3%) and S-6-AB (6%) AFFF foam concentrate at our Fujian facility. SDS, TDS and GB 15308 test certificates available on request. 20 L DHL Express samples for system compatibility testing. Factory direct pricing on bulk and project orders.