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Reply To: Fire Control in Sulfur Pit (NFPA655)

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Paul R Orlowski

Reducing the operating liquid level in a sulphur pit or a tank should NOT affect the already designed snuffing steam system. Because in most cases, the amount of snuffing steam would have been calculated based on entire enclosure volume (empty tank or pit). This would be resulting in a higher steam flow. The idea for considering such a high steam flow is only to develop a positive pressure (lesser than 2.5 psi-g in case of API 650 tanks) in the enclosure in order to prevent the outside air entering inside and extinguishing the fire. If in case, snuffing steam flow was calculated based on HLL or HHLL (wrong approach!!), then reducing the operating liquid level – or increasing vapor space – can reduce the degree of pressure which is to be developed in case of fire. And if the inside pressure drops and equals the atmospheric pressure, then the purpose of having snuffing steam would be defeated.

Huzefa Dhinda
Process Consultant at UniverSUL Consulting
United Arab Emirates

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