Alternative Simple Fire and Explosion Models for Bousai Assessment

The Japanese word "Bousai" means "to prevent disasters". Bousai Assessment is a risk assessment, which is a set of methodologies for estimating risk based on the estimates of consequences and frequencies of accidental events such as dispersion, fire and explosion. It is similar to Quantitative Risk Assessment (QRA) but simpler than QRA. To promote the application of Bousai Assessment, the Fire and Disaster Management Agency (FDMA) of Japanese government have established a guideline, “Guideline on Bousai Assessment for Refining and Petrochemical Complexes (self-translated)”. The Guideline prescribes the formulae of conventional simple calculation methods for dispersion, fire and explosion, and then allows using other rigorous calculation methods that are not prescribed by the Guideline if required.

This paper shows that Bousai Assessment can be supplemented using rather rigorous calculation methods not prescribed by the Guideline through the application of calculation examples. It provides an account of the followings:

Estimate the total frequency of all the accidental leaks in a plant and frequency distributions for leak holes of various sizes using a leak frequency statistical database

Estimate blast overpressure from an Unconfined Vapor Cloud Explosion (UVCE) using TNO Multi-Energy Model. The estimated blast overpressure is used as design input into blast resistant design for control building and tanks

Estimate the mass of a flammable gas to explode in an UVCE based on gas dispersion calculation

Estimate the dispersion distance of a flammable gas with various release conditions

Estimate blast overpressures from a BLEVE of each LPG sphere tank with various rupture scenarios

Estimate the flame length and hazardous range of a jet fire

Keywords: Risk assessment, Bousai assessment, QRA, Consequence analysis, Leak frequency, Dispersion, Vapor cloud explosion, BLEVE, Jet fire