The Buncefield Enquiry Findings and Costain’s Approach to Best Practice in Integrity Level Assessment

Tim Shaw & Robert Beresford, Costain Energy and Process

Since the Buncefield incident of 2005, when a large fire followed the largest peacetime explosion on British soil since the Flixborough Explosion, as the result of a gasoline tank overfill, the regulator in the UK requires that a fit and appropriate risk assessment of Safety Instrumented Systems is performed. 
In 2009 a nationwide review of Integrity Level assessments using Layers of Protection Analysis (LoPA) was undertaken by the Enquiry, which found many errors, shortcomings and omissions.  The issue of Integrity Level assessment has therefore received increased regulator interest and many studies at other facilities have had to be repeated.
This paper describes Costain’s approach to achieving best-practice for a client in the assessment of existing plant.  An approach is described whereby an initial assessment is completed using Risk Graph as a screening exercise, followed by the re-evaluation of higher SIL, using LoPA.  Advantages are that effort is reduced, the higher risks are addressed in appropriate detail and the safety of the resulting design is robust.  The approach reduces the effort required during the meeting, increases the overall safety of the facility and provides a better estimate of the costs, which, in turn, provides an advantage to the client company.  In the case of new-build plant the approach achieves the aims of the regulator, other interested parties, such as Local and National Government and the local community, and provides greatest benefit at lowest cost to the operating company.