(45c) Selection of Appropriate Ignition Models for Fire and Explosion Assessments

A release of flammable substances can result in various fire or explosion events depending on whether there is an immediate or delayed ignition.  Although developments have taken place in producing fit-for-purpose ignition models, there remain significant uncertainties, including how to identify the most appropriate ignition models, and how to estimate the split between immediate and delayed ignition and no ignition.  These issues significantly impact both the fire and explosion assessment and the overall risk result. 

This study compares different ignition models, including

• For onshore installations: Purple Book approach, DNV model and Atkins Model
• For offshore installations: JIP TDIM model and OLF model
• For both onshore and offshore installations: Cox, Lees &Ang model and UKOOA model

This paper addresses the type of installation, availability of ignition sources, level of detail of the study, and suggests fit-for-purpose ignition models most appropriate to use.

Although there is a general consensus on overall ignition probability, there are significant differences between practitioners on the split between immediate (early) and delayed ignition.  Immediate ignitions are assumed to result in pool and jet fires, but not a large vapour cloud capable of explosion.  Immediate ignition does not afford the opportunity for workers to escape the area prior to ignition.    Depending on how the values are subsequently applied in the fire/explosion modelling, the appropriate split between early/immediate and delayed ignition are recommended.