Lessons Learned from the Assessment of Occupied Buildings Risk on Brownfield Sites

There have been a number of major incidents on chemical plants (e.g. Flixborough`(1974), Hickson & Welch (1992), Texaco City (1994) and Buncefield (2005)), that have highlighted the risk to people occupying buildings on process sites. The risk to occupied buildings due to brownfield modifications on existing chemical sites or from neighbouring developments has become an increasing focus of regulators and operators worldwide. The modifications can result in significant changes to the frequency of impairment due to hazardous events, the consequences modelled and the level and means of protection required to the occupied buildings under consideration.

Occupied Building Risk Assessments (OBRA) are used to optimise the location and design of occupied buildings at major hazard facilities including chemical manufacturing sites, petrochemical sites and fuel storage facilities. Such assessments are often carried out using the guidance notes issued by the American Petroleum Institute (API) – API 752 (Management of Hazards Associated With Location of Process Plant Permanent Buildings) and API 753 (Management of Hazards Associated With Location of Process Plant Portable Buildings) or the Chemical Industries Association (Guidance for the Location and Design of Occupied Buildings on Chemical Manufacturing Sites).

However MMI Engineering’s experience has shown that the application of generic vulnerability models may not adequately inform on the risk to building occupants and may mislead subsequent decision making. This paper will detail the need for a multi-disciplinary approach to adequately quantify the risk, inform on building vulnerability and the selection and design of appropriate retrofits and upgrades to existing buildings as well as detailing the lessons learned from a case study for a major hazard facility.