(46d) The Buncefield (U.K.) Fire and Explosion: Improving Layer of Protection Analysis Practise to Determine the Required Degree of Protection to Meet Regulator Requirements

The Buncefield accident has been described as the biggest fire in Europe since the Second World War. The ?fall out' from the event and the requirements specified in the various reports produced by the Major Incident Investigation Board (MIIB) and the Buncefield Standards Technical Group (BSTG) has included a focus on the application of LOPA to facilities of the Buncefield type. The Health and Safety Executive (HSE) as part of its regulatory duties requested 15 similar facilities to carry out LOPA. The results showed inconsistency which caused concern for the regulator and for LOPA practitioners in the European Process Safety Centre (EPSC). The HSE has responded by asking EPSC to chair a group of industry and regulator LOPA users to devise a ?standardised' LOPA method to minimise or eliminate the main inconsistencies for this type of facility. The paper details the common errors found and what the group has recommended as best practice for LOPA in such cases. The subjects include:

? Target frequencies ? including individual and societal risk, environmental consequences

? Typical Initiating Events and their frequency ? human error, control system failures

? Conditional Modifiers ? time at risk, probability of ignition, probability that ignition leads to a vapour cloud explosion

? Layers of protection.

It is clear from the 15 studies that there is a wide interpretation of LOPA method requirements. These are very well illustrated by failure to observe the requirements of IEC 61511 in some cases and remarkable claims for Conditional Modifiers in others. We need to assure a more consistent approach by LOPA users. If this effort fails, it is likely to cast doubt on LOPA as a best practice for industry and the regulator.