RR1113 - Review of vapour cloud explosion incidents

Major incidents worldwide have involved large vapour cloud explosions, including the Buncefield explosion in 2005. It is important to learn from historical incidents to understand the risk profile of installations.

Following the Buncefield explosion, a large body of published research has improved scientific understanding of the release event, the flammable cloud formation and the explosion. This report describes work done by HSE with US safety regulators to consolidate previous research and to incorporate recently published analysis into a single, systematic review of historical incidents.

Important new conclusions have been reached that a high proportion of large vapour cloud explosions occur at nil or very low wind speeds. In these conditions, the dispersion from large and medium scale releases will be gravity-driven and the vapour cloud will continue to grow as long as it remains undetected. Large vapour clouds will almost always ignite, the probability of a severe explosion event is very high, especially for gasoline.

These findings have important implications for safety practitioners considering installations where such releases of flammable substances can occur. They reinforce the importance of the main risk control measures of overfill prevention and maintaining plant integrity; but they also suggest that the value of mitigation measures such as vapour detectors and vapour barriers should be reviewed.

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Updated 2023-12-12