Analysis of a Propane Sphere BLEVE
Résumé
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.