Proportioner Failure During a Fuel Spill Fire
At 11:40, during a refueling operation at Gate 7, a fuel hose separates and approximately 80 gal of Jet A spills under the left wing of an Airbus A320. The fuel ignites, producing a pool fire roughly 25 ft by 40 ft beneath the wing and fuselage. ARFF Truck 3 arrives with 2,000 L of water and 120 L of 3% AFFF. Its around-the-pump proportioner is set to 3%, and the front handline is flowing 500 L/min. The operator opens the foam tank valve and sees no foam in the sight glass; the stream is clear water with poor blanketing. The fire is impinging on the wing skin and has not entered the cabin. Twenty passengers are evacuating from the forward left door, away from the fire. Truck 4 is six minutes out. The truck has a 50 L in-line eductor and two 20 L pails of 3% AFFF. What do you do?
1. Diagnose the likely cause of the proportioning failure and state your immediate action.
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No foam in the sight glass with clear water means the proportioner is not inducting foam. Check the simple causes first: foam tank level and valve position, clogged foam strainer, air leak on the suction side, proportioner setting, and pump discharge pressure outside the proportioner's operating range. If the tank is not empty and the valve is open, the likely causes are a failed foam pump, a stuck check valve, or a blocked inductor. Immediate action: stop relying on the clear-water stream as a foam attack. Keep the handline in a fog pattern to protect the evacuation and cool the wing, and switch to the 50 L in-line eductor with a 20 L pail. Set the handline to a flow the eductor is rated for, usually 200 L/min, not 500 L/min. If the eductor cannot be placed in service, use water fog to cool and protect exposures until Truck 4 arrives, and do not open the wing panels.
2. Calculate the expected foam and water duration at 500 L/min, then compare it with the in-line eductor at 200 L/min using one 20 L pail.
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At 500 L/min and 3%, foam flow is 500 × 0.03 = 15 L/min. With 120 L of foam, duration is 120 ÷ 15 = 8 minutes. Water duration is 2,000 ÷ 500 = 4 minutes, so water limits the attack to 4 minutes at full handline flow. With one 20 L pail and a 3% eductor at 200 L/min, foam flow is 200 × 0.03 = 6 L/min; the pail lasts 20 ÷ 6 = 3.3 minutes. Water at 200 L/min lasts 2,000 ÷ 200 = 10 minutes. So the eductor gives a shorter foam supply but a longer water supply and better foam quality. Use one pail to establish a blanket on the leading edge of the pool, then switch to the second pail. Do not run the eductor at 500 L/min; it will not pick up 3% and may fail to foam.
3. Should you continue the handline attack with clear water, or change tactics? Explain the fire behavior and agent limitations.
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Do not continue a straight clear-water attack on a fuel pool; it can spread the fuel and provide no vapor suppression. Use fog only to cool the wing and protect the evacuation path, and apply foam from the eductor in a sweeping motion from the far edge of the pool toward the fire. If the fire is impinging on the wing and the foam supply is insufficient, use water fog to cool the wing skin and prevent structural failure while awaiting Truck 4. Do not use a straight stream into the pool. If the fire enters the cabin or a running fuel fire develops, withdraw to a defensive position, protect the evacuation route, and request additional foam. The dry chemical, if available, is for a small localized flame, not the pool fire. Keep the 20 L pails controlled; one pail is a limited resource.