Risk Criteria and Their Sensitivity to Building Occupant Vulnerability Modelling

Accidents like Texas City have put the risk to people in occupied buildings high on the agenda of both regulators and operators.  Regulatory regimes for ensuring the safety of those in occupied buildings are becoming more demanding and the need for accuracy and transparency has increased.  For example, regulatory guidelines like API RP752 and RP 753 provide guidance on the design and location of permanent and portable buildings to minimise risks to occupants.  This paper focuses on advances in software models for assessing risks to people in buildings from releases of flammable materials. Particular focus is given to the sensitivity of risk metrics to the building vulnerability modelling used. 

When deciding on the location and construction of buildings in the vicinity of hazardous installations, a number of factors must be considered. Key to the process of deciding where to locate buildings and what level of protection they should offer their occupants are the level of risk to which it is acceptable to expose those occupants.  Traditionally QRA has used “generic” vulnerability for people indoors where their probability of death when particular levels of different types of hazardous effects are exceeded, such as explosion overpressure, is treated as being independent of the type of building within which they reside (see for example BEVI, 2009). This is a significant limitation to using the results of traditional QRA in selecting appropriate building types in different situations or to locate buildings in the safest place from the standpoint of risk to occupants. Risk to building occupants is a function of both building location and construction.  In order to minimise risks to personnel in the most cost effective way, plant designers and safety managers need to be able to compare and assess different options with ease.

This paper describes recent advances in the capabilities of the Phast Risk QRA tool (Cavanagh et al 2009, Cavanagh 2010) which allow analysts to assess the relative benefits of using different building types to reduce risks to their occupants. These new features enable individual definition of building types and associated occupant vulnerability, along with the ability to locate buildings of a particular type in various locations to ensure overall risks can be minimised.  A case study is used to illustrate the application of the new vulnerability modelling to selecting suitable building types, and locating them in the most appropriate position to minimise risks to occupants. 

Cavanagh, N.J., Xu, Y. and Worthington, D.R.E., A Software Model for Assessing Fatality Risk from Explosion Hazards using the Multi Energy Method and Baker Strehlow Tang Approach, Hazards XXI Symposium, November 10th-12th 2009, Manchester, UK.

Cavanagh, N.J., Recent advances in software for modelling the risks associated with gas explosions in congested spaces using the Multi Energy Method, 13th International Symposium on Loss Prevention and Safety Promotion in the Process Industry, June 6th- 9th, Bruges, Belgium, 2010.

BEVI, Reference Manual Bevi Risk Assessments Version 3.1, National Institute of Public Health and Environment (RIVM), Centre for External Safety, the Netherlands, 2009.