Firefighting Foams
Firefighting foams are specialized chemical agents used in commercial aviation to suppress and control fires, particularly fuel-based fires involving jet fuel (Class B fires). These foams rapidly blanket flames, cool hot surfaces, and prevent re-ignition, playing a vital role in aircraft rescue and firefighting (ARFF) operations on runways and near terminals.
Background and Evolution
The development of firefighting foams began in the early 1900s, with protein-based foams derived from animal byproducts. In the 1960s, aqueous film-forming foam (AFFF) was introduced by the U.S. Navy in collaboration with 3M and the Naval Research Laboratory. AFFF revolutionized aviation firefighting by creating a thin film that suppresses flammable liquid vapors while spreading quickly across fuel surfaces. By the 1980s, AFFF became the global standard for ARFF services, used in both military and civilian airports.
In recent decades, environmental concerns have driven the development of fluorine-free foams (F3s) as alternatives to legacy AFFFs that contain PFAS (per- and polyfluoroalkyl substances)—persistent chemicals linked to environmental and health hazards.
How Firefighting Foams Are Used
- Airport Rescue and Firefighting (ARFF): Primary tool for first responders during aircraft fires on runways, taxiways, or near terminals.
- Hangar Fire Suppression: Deployed through foam-dispersing sprinkler systems to rapidly suppress fires in maintenance hangars.
- Fuel Spill Fires: Applied to suppress or prevent ignition of flammable liquids spilled during fueling, maintenance, or accidents.
- Training Exercises: Used in controlled burns to train ARFF teams, often with environmentally friendly substitutes.
Why Firefighting Foam Is Used
- Rapid Fire Suppression: Foams cool fire zones and isolate oxygen, extinguishing flames quickly.
- Vapor Suppression: Thin aqueous film (in AFFF) seals flammable vapors, preventing re-ignition.
- Surface Cooling: Water content in foam cools hot aircraft surfaces and prevents fire spread.
- Adherence to Surfaces: Clings to curved or vertical aircraft structures, maintaining suppression over time.
- High Visibility: Foam blankets clearly mark treated areas, aiding coordination during chaotic fire events.
Types of Firefighting Foam in Aviation
Technical Specifications
- Expansion Ratio: Typically 6:1 to 10:1 for ARFF applications (low-expansion foam).
- Application Rate: ~6.6–7.6 L/min/m² (0.16–0.19 gpm/ft²), depending on aircraft fire scenario.
- Drainage Time: ~3–6 minutes (indicates how long the foam holds its blanket).
- Operating Temperature Range: Typically −5°C to 49°C (23°F to 120°F), with some variants rated lower.
- Foam Proportioning: 3% or 6% concentrate mixed with water using onboard proportioning systems in ARFF vehicles.
Comparison to Alternative Fire Suppressants
| Type | Key Features | Use in Aviation |
|---|---|---|
| AFFF (Aqueous Film-Forming Foam) | Fast-spreading, vapor-suppressing, effective on hydrocarbon fires | Standard in ARFF for decades |
| AR-AFFF (Alcohol-Resistant AFFF) | Contains polymers for fires involving polar solvents | Rarely used in aviation but applicable in hangars |
| Fluorine-Free Foam (F3) | PFAS-free, biodegradable, environmentally safer | Increasingly adopted at airports worldwide |
| Protein and Fluoroprotein Foams | Biodegradable, slower spreading | Mostly phased out in aviation |
Role in Modern Aviation
Firefighting foam is a required component of airport fire safety as mandated by ICAO (Annex 14) and FAA Part 139. Airports must equip ARFF vehicles with appropriate foam supplies, including roof and bumper-mounted turrets capable of delivering high volumes quickly. Aircraft hangars, especially for widebody jets, use foam deluge systems that deploy automatically when sensors detect fires.
Since the 2010s, many commercial airports (e.g., London Heathrow, LAX, and Sydney) have begun transitioning to fluorine-free foams to meet environmental regulations and reduce PFAS contamination.
Environmental and Economic Considerations
- PFAS Contamination: Legacy AFFFs contain persistent fluorinated chemicals (PFOA, PFOS), prompting regulatory bans and costly cleanup efforts.
- Cost: Fluorine-free foams tend to be more expensive up front but are less costly in the long term due to reduced remediation liabilities.
- Storage and Shelf Life: Most foams have a shelf life of 10–20 years when stored properly.
- Training Foam Substitutes: Water-based or synthetic alternatives are used for drills to reduce environmental impact.
Future Trends
- Global PFAS Bans: Nations and aviation authorities (e.g., EASA, FAA) are phasing out PFAS-based foams.
- Improved F3 Formulations: New fluorine-free foams aim to match AFFF performance with minimal environmental tradeoffs.
- Hybrid Fire Suppression Systems: Integrated use of water mist, foam, and dry chemicals for faster and cleaner suppression in airport hangars.
- Smart Foam Systems: Automated proportioning and delivery systems enhance response time and reduce waste.
Summary
Firefighting foams are essential to commercial aviation safety, enabling rapid response to aircraft and fuel fires. Though AFFF has long dominated the field, environmental shifts are pushing the industry toward fluorine-free alternatives. These foams protect lives and property on the runway and in hangars, representing a critical line of defense in aviation’s multilayered fire safety strategy.
| Material | Pros | Cons |
|---|---|---|
| Dry Chemical Agents (e.g., Purple-K) | Very fast knockdown, compact storage | Poor re-ignition protection, no cooling |
| Water Spray | Simple, cooling effect | Ineffective on fuel fires without foam additive |
| Clean Agents (e.g., Halotron) | Safe for electronics, clean residue | Expensive, limited in open-air fires |
| Fluorine-Free Foam (F3) | Environmentally safe | Slightly slower knockdown compared to legacy AFFF |
Parts that are made of or use Firefighting Foams
| Part Number | Name | Alt Part Number | ATA Chapter | Cage Code | NSN | Rotable | Repair Stations | Suppliers |
|---|