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Current LNG transportation practice provides for pressure relief systems, designed with credit for the tank's insulation in order to to prevent gas cargo pressurisation due to boil-off and fire, as per IMO IGC Code 8.5. However, it is uncertain to what extent any insulation degradation, in a fire situation, is taken into account in the design of PRV systems. As foam plastic insulation materials are subject to possible melting, degradation and/or ignition at temperatures lower than might be achieved during such fire exposure, there is concern that the PRV systems may not be capable of relieving the vapour flows that would result from the increased boil-off due to partial or total insulation failure. This SIGTTO publication covers following matters - the origins of the IGC Code, fire scenarios, LNG carrier pressure relief systems, simplified reapplication of the Code for loss of insulation, heat transfer into the tank; time based heat transfer, response of insulation materials to heat, and others.