Assessment of environmental risk from major accident hazards

Abstract

After reviewing various methods and criteria which are readily available in safety risk assessment, it was concluded that risk ranking is a good way forward to be further developed or modified for the assessment of environmental risk. In particular, the Mond Index is a good concept which might be used to develop a framework for the assessment of risk from major accident hazards to the environment (ICI, 1985). The Environmental Hazard Index (EHI) method which was based on the United Kingdom Department of Environment (UK DoE) criteria for major accident hazards to the environment, gives important criteria which could be used in the framework (AEA Technology, 1995). Many consequence models for different environmental hazards have been developed and continue to be developed by various authors. For example, river dispersion models such as PRAIRIE, WASP5 and RIVER were reviewed (AEA Technology, 1993, Ambrose et. Al, 1993, RIVER User Manual, 1992). Others have developed consequence models for hazards such as dispersion of toxic combustion products in air and dispersion of toxic liquids in the groundwater. Further development of consequence models is beyond the scope of this discussion. Instead, the development of a risk assessment framework which makes use of available consequence models was aimed. The developed framework will describe the overall risk to the environment from an accident scenario, in such a way that the risk can be compared with tolerability criteria. This was considered to be the main gap in the currently available methodology for environmental risk assessment. Although a number of consequence models have been developed, the user is left uncertain about how to use the output which is in terms of concentration versus distance rather than effects or risk to the environment. In order to develop the risk assessment framework, the “major accident to the environment” definitions proposed in the UK DoE Guidance Note has been used (UK DoE, 1991). These definitions are currently the most definitive statement of how to interpret major accidents to the environment for the purpose of the CIMAH Regulations and a risk assessment method based on them will be useful. However, the DoE definitions was criticised and that the DoE intends to revise them (Khayyat, 1992). It is hoped that the framework developed is capable to suit for any change to be made to the definitions of major accidents to the environment.