How To Use Firefighting Foam On Fire

How Does Foam Stop A Fire?

Firefighting foam stops a fire by simultaneously cooling the fuel, separating the flame from the oxygen source, and suppressing the escape of flammable vapors through the formation of a cohesive aqueous film.

The primary mechanism of AFFF 3% foam concentrate lies in its "Aqueous Film Forming" capability. When the foam solution is applied to a hydrocarbon fire, the fluorinated surfactants within the AFFF foam reduce the surface tension of the water. This allows the liquid to spread rapidly across the surface of the burning fuel. Even if the foam blanket itself is broken, the invisible aqueous film remains, continuing to suppress vapors and prevent the fire from flashing back.

Beyond the chemical film, the physical foam blanket acts as a thermal insulator. In large-scale industrial fires, the heat radiation is immense. AFFF 3% foam concentrate creates a stable, air-filled structure that reflects radiant heat away from the fuel. This cooling effect is vital for lowering the temperature of the liquid fuel below its flashpoint, ensuring that the fire does not reignite once the initial flames are knocked down.

Furthermore, the density of the AFFF foam is significantly lower than that of the fuel it is suppressing. This buoyancy ensures that the extinguishing agent stays on top of the liquid rather than sinking to the bottom, which is a common failure point when using plain water on oil fires. By maintaining this surface-level integrity, the foam ensures a complete "smothering" effect that is the industry standard for Class B fire suppression.

Key Suppression Mechanisms

1. Smothering: Prevents oxygen from reaching the fuel.

2. Cooling: Absorbs heat from the fuel and surrounding metal structures.

3. Separating: Creates a physical barrier between the flame and the fuel surface.

4. Suppressing: Seals in volatile vapors to prevent re-ignition.

What Is Necessary When Applying Firefighting Foam?

Effective application of firefighting foam requires the precise proportioning of AFFF 3% foam concentrate with water, followed by aeration through specialized discharge devices to create a stable foam blanket.

The first critical component in the application process is the proportioning system. For AFFF 3% foam concentrate, the system must be calibrated to mix exactly three parts of concentrate with ninety-seven parts of water. If the mixture is too lean, the AFFF foam will lack the structural integrity to withstand heat; if it is too rich, the concentrate is wasted and the film-forming properties may be compromised. Common tools for this include balanced pressure proportioners and around-the-pump systems.

Secondly, aeration is mandatory. While AFFF 3% foam concentrate is a liquid in the tank, it must be expanded into a foam to be effective. This is achieved through foam nozzles or "aspirating" discharge heads. These devices pull air into the water/concentrate solution, creating the bubbles that form the blanket. The expansion ratio—the volume of finished foam compared to the volume of the original liquid—must be carefully managed based on whether the fire is in an open tank or a confined spill area.

Lastly, the technique of application, known as "foam surgery," is vital. One should never "plunge" the AFFF foam directly into the burning liquid, as this can splash the fuel and spread the fire. Instead, firefighters use the "roll-on" method, the "bank-down" method (bouncing foam off a wall), or the "rain-down" method. These techniques ensure the AFFF 3% foam concentrate forms a gentle, continuous layer that migrates across the hazard without disturbing the fuel surface.

Essential Equipment for Foam Application

• Proportioners: Venturi-style eductors or high-accuracy displacement pumps.

• Storage Tanks: Atmospheric or bladder tanks designed for AFFF 3% foam concentrate.

• Discharge Devices: Foam cannons, monitors, and air-aspirating nozzles.

• Water Supply: High-volume pumps capable of maintaining pressure during the expansion of AFFF foam.

Which Foam Is Used For Ethanol Fire?

For fires involving ethanol or other polar solvents, a specialized Alcohol-Resistant Aqueous Film-Forming Foam (AR-AFFF) is required because standard AFFF foam will be dissolved by the alcohol.

The challenge with ethanol and similar "polar solvents" is that they are miscible with water. If you apply standard AFFF 3% foam concentrate to an ethanol fire, the alcohol will immediately pull the water out of the foam bubbles, causing the foam blanket to collapse instantly. This "foam-destructive" nature of polar solvents makes regular AFFF foam completely ineffective for protecting distilleries, pharmaceutical plants, or ethanol blending facilities.

To combat this, AR-AFFF concentrates contain a special polymer. When this version of AFFF 3% foam concentrate contacts a polar solvent, the polymer precipitates and forms a tough, physical "polymeric membrane" between the fuel and the foam. This membrane acts as a chemical-proof shield, preventing the ethanol from attacking the foam structure. This allows the AFFF foam to sit on top of the alcohol and perform its cooling and smothering functions just as it would on gasoline.

It is important for facility managers to identify their specific fuel risks. If a site handles both hydrocarbons (like diesel) and polar solvents (like ethanol), an AR-AFFF 3% concentrate is often the most versatile choice. It can act as a standard AFFF foam on oil fires and as a membrane-forming agent on alcohol fires, providing a "multi-purpose" solution for complex industrial environments.

Differences Between Standard AFFF and AR-AFFF

Is Firefighting Foam Safe?

Modern AFFF 3% foam concentrate is designed with a focus on environmental compliance, though users must follow strict containment and disposal protocols to prevent groundwater contamination.

The safety of AFFF foam has undergone significant evolution over the last decade. Historically, foam concentrates contained long-chain PFAS (Per- and Polyfluoroalkyl Substances). Today’s premium AFFF 3% foam concentrate products are typically "C6" compliant, meaning they use short-chain surfactants that are considered to have a lower environmental impact and do not bioaccumulate to the same extent as older formulations. Manufacturers are now focused on creating high-performance AFFF foam that meets rigorous international standards like UL162 or EN1568.

From a human health perspective, AFFF 3% foam concentrate is generally classified as a mild skin and eye irritant in its concentrated form. Standard Personal Protective Equipment (PPE), including gloves and goggles, should always be worn when handling the liquid. In its expanded AFFF foam state, it is primarily water and air, but direct inhalation or ingestion should still be avoided. Training programs emphasize the importance of "containment and recovery" during drills to ensure no foam runoff enters local waterways.

Safety also encompasses the reliability of the product. Using a certified AFFF 3% foam concentrate ensures that the foam will work exactly as intended during a crisis. The "safety" provided to the facility—in terms of preventing a catastrophic fire spread—often outweighs the managed risks of chemical storage, provided that the facility has a robust foam management plan in place for post-fire cleanup.

Best Practices for Foam Safety

1. Containment: Use dikes or drainage systems to catch AFFF foam runoff.

2. Disposal: Consult with local environmental agencies for high-temperature incineration of used foam.

3. Transition: Replace legacy "C8" stocks with modern C6-compliant AFFF 3% foam concentrate.

4. PPE: Ensure operators use chemical-resistant gear during proportioning.

Is Fire Fighting Foam Corrosive?

While AFFF 3% foam concentrate is not highly corrosive to most specialized firefighting equipment, it can cause localized corrosion in carbon steel pipes and certain copper alloys if left stagnant over long periods.

The chemical makeup of AFFF foam includes surfactants, stabilizers, and solvents. In its concentrated form, AFFF 3% foam concentrate can be slightly acidic or alkaline depending on the specific formulation. If stored in a standard carbon steel tank without an internal coating, the concentrate may lead to "pitting" or surface oxidation. This is why most industrial systems utilize stainless steel (304 or 316) or high-density polyethylene (HDPE) for long-term storage of AFFF foam supplies.

When the foam is mixed with water for application, the corrosivity is significantly diluted. However, the residual salts and surfactants in AFFF 3% foam concentrate can still leave deposits inside pipes and nozzles. If these systems are not "flushed" with fresh water after use, the drying foam can create a sticky residue that may clog small orifices or cause "galvanic corrosion" at the joints of different metals. Maintenance protocols should always include a thorough freshwater flush of all delivery hardware.

In the context of the vehicles and infrastructure being protected, AFFF foam is generally considered safe. It is far less damaging than dry chemical powders, which can be highly abrasive and corrosive to electronics. Because AFFF 3% foam concentrate is primarily water-based, its impact on the structural integrity of a facility is minimal, provided the area is cleaned after the fire event.

Maintenance Tips to Prevent Corrosion

• Material Selection: Use Stainless Steel or GRP for storing AFFF 3% foam concentrate.

• System Flushing: Always run fresh water through the lines after any AFFF foam discharge.

• Periodic Testing: Conduct annual foam quality tests to ensure the concentrate hasn't degraded or reacted with the storage container.

• Gasket Integrity: Check seals and gaskets regularly, as some AFFF foam solvents can swell or degrade certain types of rubber.