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taoxianwen123
08-11-2010, 06:58 PM
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uzbarry
09-02-2010, 12:01 PM
Hi,
i don't think that NFPA 11 recommends a foam concentrate backup time of 55 minutes for crude oil tanks, can you please share the reference clause? So far, i know, for all the system involving foam concentrate, the maximum foam backup required is for 30 minutes!

Further, 4.1L/m2/min is the factor which has have to be multiplied with the diameter of the tank to decide how many foam chambers @ what flow will be required for the crude oil tank. Although we can calculate the foam concentrate required round the way, but the perfect way would be calculate the capacity after deciding the flow through foam chambers (multiply the flow with 0.03 (mixing ratio 3%) x 30 (time) = foam concentrate required for 30 minutes for 1 tank protection).

For proper estimation, i suggest, go for some fire scenarios and select the worst fire case, what can be possible area of fire? By then you can decide , whether the 2 hoses would prove to work or you have to operate foaming system on another tank in the tank yard for the protection of the vicinity. Normally 500 US gpm is standard hose allowance and this has to be incorporated in the pump and foam estimation.

regarding your question, on fire in non-diked area, it depends what maximum quantity of flammable liquid can spill by then we can estimate the total spill area and thus calculating the foaming agent required. Go for Clause 3-8 "Non-Diked Spill Areas" in NFPA 11, you will get the answer.

best regards,
Uzair Barry