Fire Safety Science Digital Archive

A new technique is described for the gas-freeing of large storage tanks used for aviation fuel. The technique involves the use of natural and mechanical ventilation, together with an air-driven pump for removal of liquid residues from the irregular bottom of the tank. An assessment was made by gas-freeing a 4500 m^3 (1 M imp. gallon) tank in which the atmosphere was monitored using portable flammable gas detectors and checked by the analysis of samples using chromatography. The new technique was much quicker than the traditional method of gas-freeeing and was more controlled so that a work schedule could be devised in advance with confidence. The portable gas detectors were shown to under-estimate gas concentrations; it is thus imperative that the concentration levels at which various inspection and maintenance operations are permitted in tanks should reflect the likely errors of the instrument used to measure ccncentrations.