Aqueous Film Forming Foam
What Is Aqueous Film-Forming Foam (AFFF)?
Aqueous Film-Forming Foam (AFFF) is a specialized firefighting agent designed to suppress and extinguish flammable liquid fires, particularly Class B fires involving hydrocarbons (e.g., gasoline, diesel, jet fuel) and polar solvents (e.g., ethanol, acetone). Developed in the 1960s, AFFF combines water, fluorochemical surfactants, hydrocarbon surfactants, and stabilizing agents to create a highly effective foam solution.
How AFFF Works
When AFFF concentrate is mixed with water and aerated, it produces a low-viscosity foam that spreads rapidly across the surface of burning liquids. Its dual-action mechanism involves:
Formation of an Aqueous Film: The fluorosurfactants in AFFF reduce the surface tension of water, allowing it to spread as a thin, continuous film over the fuel. This film separates the fuel from oxygen, suppresses vapor release, and cools the fuel surface.
Foam Blanket: The foam layer acts as a physical barrier, smothering flames and preventing reignition by blocking oxygen and fuel vapor contact.
AFFF is typically proportioned at 1%, 3%, or 6% concentrations depending on the fire risk and equipment specifications.
Key Advantages of AFFF
Rapid Fire Suppression AFFF's unique ability to form both a foam layer and an aqueous film allows it to extinguish fires significantly faster than conventional foams. The film penetrates fuel surfaces quickly, interrupting the combustion chain reaction.
Long-Lasting Protection The foam blanket remains intact for extended periods, providing sustained protection against reignition-a critical feature for high-risk environments like fuel storage facilities.
Versatility AFFF is effective on Class B fires (flammable liquids) and can also be used on Class A fires (ordinary combustibles like wood or paper) when combined with water.
Low Water Consumption Compared to water-only systems, AFFF requires less water to achieve fire control, making it ideal for water-scarce environments.
Adaptability to Various Fuels Modern AFFF formulations are tailored to combat both hydrocarbon-based fires (e.g., oil, gasoline) and water-miscible polar solvents (e.g., ethanol), broadening its application scope.
Environmental Innovations While traditional AFFF contained per- and polyfluoroalkyl substances (PFAS)-linked to environmental concerns-newer fluorine-free foams (F3) have been developed to offer eco-friendly alternatives without compromising performance.
How to Use Aqueous Film-Forming Foam
Proper application of AFFF is crucial for maximizing effectiveness and safety. Below is a step-by-step guide:
Equipment Setup
Proportioning System: Use an inline inductor, bladder tank, or balanced-pressure proportioning system to mix AFFF concentrate with water at the correct ratio (e.g., 3% for hydrocarbons, 6% for polar solvents).
Nozzle Selection: Choose air-aspirating nozzles to generate high-quality foam with uniform bubble structure.
Mixing and Application
Dilution: Mix the concentrate with water according to manufacturer guidelines. For example, 3% AFFF requires 3 parts foam to 97 parts water.
Application Techniques:
Gentle Application: Apply foam gently onto the fuel surface to avoid submerging the foam layer.
Roll-On Method: Direct the foam stream at a vertical surface (e.g., tank wall) to allow the foam to flow across the fuel.
Raindown Method: Spray foam from above to cover large areas (e.g., airport runways).
Critical Considerations
Pre-mix Testing: Verify foam solution quality using a refractometer or conductivity meter.
Expansion Ratio: Aim for an expansion ratio of 5:1 to 10:1 (foam volume to solution volume) for optimal performance.
Reapplication: Monitor the foam blanket and reapply if degradation occurs due to wind, heat, or fuel agitation.
Safety Protocols
Personal Protective Equipment (PPE): Firefighters should wear full gear, including respiratory protection, as AFFF exposure may cause irritation.
Environmental Containment: Use booms or dikes to prevent foam runoff from entering waterways, especially with PFAS-containing formulations.
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