The events in March of 2011 in Japan have provided us with an example of what can happen when large LPG spheres are exposed to severe fire engulfment. This paper presents an approximate failure analysis of a sphere exposed to a severe fire engulfment scenario. It estimates the expected failure time of the sphere based on predicted wall temperatures and internal pressure buildup. The prediction of the pressurization rate is based on a two-zone, thermally stratified liquid model. It shows that the pressurization rate depends strongly on the initial fill level. At high fill levels, the sphere can pressurize much faster then would be expected if the liquid were well mixed and isothermal. This rapid pressurization can lead to early failure. The analysis considered two fire heat flux conditions and shows how prediction of failure time can be affected by high temperature stress rupture. The analysis also considers various initial fill conditions to predict BLEVE hazards at failure. The results are in reasonable agreement with limited observations and data from the March 2011 incident in Japan.
