Foam System Change to Ethanol Service
An existing foam-water deluge system protects a 60-foot-diameter open-top floating-roof tank containing gasoline. The system uses 3 percent AFFF supplied by a bladder tank, a ratio controller, and eight foam makers on the rim seal. The design application rate is 0.10 gpm/ft² over the seal area, with a 20-minute duration. The terminal now wants to store 95 percent ethanol in the same tank. The foam concentrate inventory is AFFF, and the proportioner is set at 3 percent. The water supply is a 500,000-gallon pond with a diesel fire pump rated 1,500 gpm at 90 psi. The owner asks whether the existing system can be used without changes because the tank and foam makers are in good condition and the pump test passed last month.
1. Assess the compatibility of the existing AFFF with ethanol and determine whether the system can remain as-is.
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The existing AFFF is not suitable for 95 percent ethanol. Ethanol is a polar solvent, and ordinary AFFF forms a foam blanket that is destroyed by the solvent, so it will not seal the fuel surface or provide the required extinguishing performance. The system cannot remain as-is. The service change requires an alcohol-resistant concentrate listed for polar solvents, and the design must be reviewed by the engineer. The fact that the tank and foam makers are in good condition and the pump passed its test does not address concentrate compatibility, which is the governing issue.
2. What changes to concentrate, proportioning, and testing would you require?
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Change to an AR-AFFF or AR-FP concentrate listed for ethanol. Verify the manufacturer's proportioning rate for polar solvent; do not assume 3 percent is correct. The bladder tank, ratio controller, and pump must be compatible with the concentrate, and the proportioner must be set to the listed rate. Flush the system and test with foam solution at the farthest foam maker, verifying induction, expansion, and reach. Update the concentrate inventory and placard. Document the listing for the ethanol service and have the engineer confirm that the application rate and duration are adequate for the changed hazard.
3. What other foam-system design issues should be reviewed for the ethanol service?
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Review the application rate and duration for polar solvents per NFPA 11, foam maker spacing and coverage of the rim seal, water supply duration, and whether the existing foam makers are listed for alcohol-resistant concentrate. Check tank drainage and containment, and confirm that the water supply can sustain the required duration at the required pressure. The diesel pump test should be at the system demand, not only at rated flow. Also verify that the foam concentrate is not contaminated by residual AFFF and that the system can be flushed without damaging the bladder tank or proportioner.