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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Article source: http://hse.gov.uk/research/rrhtm/rr1113.htm