🔥 Foam Application Rate – A Critical Factor in Fire Protection 🔥

Foam Application Rate for Different Scenarios – NFPA, EN, Lastfire and OISD

Foam-based fire suppression remains one of the most effective methods to control flammable liquid fires in refineries, chemical plants, tank farms, aircraft hangars, and process industries. The correct foam application rate and application time are critical for the successful extinguishment of liquid fuel fires. International and national standards like NFPA 11 (US), EN 13565 (Europe), Lastfire (Oil Industry Consortium), and OISD (India) provide guidance for foam system design.

What is Foam Application Rate?

Foam Application Rate is defined as the quantity of finished foam solution (water + foam concentrate + air) applied per unit area of the fuel surface, usually expressed in liters per minute per square meter (L/min/m²) or gallons per minute per square foot (gpm/ft²).

It represents the minimum foam flow rate needed to:

• Control and extinguish the fire,

• Overcome fuel vaporization and radiant heat,

• Provide safety against foam destruction or burn-back.

How is Foam Application Rate Decided?

Foam application rate depends on:

1. Fuel Type: Hydrocarbons vs polar solvents.

2. Hazard Scenario: Tank full surface fire, rim seal fire, bund spill, pool fire, or hangar fire.

3. Foam Type: AFFF, AR-AFFF, FFFP, or High Expansion.

4. Testing Performance: Fire test pans, extinguishment time, burn-back resistance, drainage time.

5. Applicable Standard: NFPA 11, EN 13565, Lastfire, OISD, etc.

Testing Methods

• Pan Fire Tests (NFPA 11, EN 1568, OISD 116): Foam applied on heptane/diesel pool fires.

• Control & Extinguishment Time Measurement.

• Burn-back Resistance: Foam disturbed and relit to check endurance.

• Drainage Time Test: Stability of foam blanket measured.

Fuels used in testing:

• Heptane/Iso-octane – hydrocarbon representation.

• Diesel/Kerosene – medium volatility.

• Isopropanol/Ethanol – for AR foams.

• Aviation Fuel (Jet A1) – aircraft fire tests.

Foam Application Rates as per Standards

1. NFPA 11

• Fixed Roof Tank (Full Surface Fire): 4.1 L/min/m², 65 min

• Floating Roof Tank (Rim Seal): 12.2 L/min/m², 55 min

• Aircraft Hangars: 6.5–10.2 L/min/m², 10 min

2. EN 13565-2 (Europe)

• Tank Protection: 4.0–6.0 L/min/m², ≥30 min

• Bund Area (Spill Fire): 6.5–10.0 L/min/m², 20–30 min

3. Lastfire (Oil Industry Consortium)

• Cone Roof Tank (Full Surface Fire): 6.5 L/min/m², 65 min

• Floating Roof Tank (Rim Seal): 12.2 L/min/m², 55 min

4. OISD (India – Oil Industry Safety Directorate)

(As per OISD-117 and OISD-STD-244, for petroleum storage installations):

• Fixed Roof Tank (Full Surface Fire): 5.0 L/min/m², minimum 65 min

• Floating Roof Tank (Rim Seal Fire): 12.0 L/min/m², minimum 55 min

• Bund Area (Spill Fire): 6.5 L/min/m², minimum 30 min

• Pool Fire (Hydrocarbon Spills): 6.5–10 L/min/m² depending on hazard, ≥30 min

Special Case: Pool Fire Application Rate

A pool fire occurs when liquid fuel spills and ignites, forming a fire across a confined or unconfined surface.

• NFPA & EN: Typically recommend 6.5–10 L/min/m².

• OISD: Minimum 6.5 L/min/m² for hydrocarbon pool fires, with application time ≥30 min.

• For polar solvents: Higher rates are needed and alcohol-resistant foams (AR-AFFF) must be used.

Sample Foam Demand Calculations

Example 1: Fixed Roof Tank (NFPA 11)

• Tank Diameter: 20 m

• Surface Area = π × (20/2)² = 314 m²

• Foam Application Rate = 4.1 L/min/m²

• Foam Flow Rate = 1,287 L/min

• Application Time = 65 min

• Total Foam Solution = 83,655 L

• Foam Concentrate (3%): 2,509 L

Example 2: Bund Spill Fire (OISD)

• Bund Area: 400 m²

• Foam Application Rate = 6.5 L/min/m²

• Foam Flow Rate = 2,600 L/min

• Application Time = 30 min

• Total Foam Solution = 78,000 L

• Foam Concentrate (6%): 4,680 L

Example 3: Pool Fire (EN / OISD)

• Pool Fire Area: 100 m²

• Application Rate = 6.5 L/min/m²

• Foam Flow Rate = 650 L/min

• Application Time = 30 min

• Total Foam Solution = 19,500 L

• Foam Concentrate (3%): 585 L

Additional Design Considerations

1. Wind Losses:

   • For outdoor fires, foam streams are affected by wind.

   • Recommended design margin: 10–15% extra foam solution.

2. Obstructions:

   • Tank appurtenances, dikes, and structures may shadow foam distribution.

3. Foam Quality:

   • Expansion ratio, drainage time, and burn-back resistance must be tested.

4. Redundancy:

   • Backup foam tanks, fire water pumps, and alternate discharge devices should be included.

Conclusion

Correct foam application rate and application time are the backbone of foam fire suppression design. NFPA, EN, Lastfire, and OISD provide detailed requirements, with OISD being mandatory in India for petroleum facilities. Pool fires, tank fires, and bund fires all demand different rates, but a safety margin (wind, redundancy, foam quality) must always be included.

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