The past ten or so years have seen a steady increase in the use of risk assessment to help improve the safety of offshore facilities. This process started with the requirements for "Concept Safety Evaluations" in the Norwegian sector of the North Sea, and has gathered pace since the Piper Alpha disaster and especially since the publication of the Cullen Report in November last year. Lord Cullen has recommended a fundamental change in the regulation of offshore safety on the UK Continental Shelf; he has proposed that the current prescriptive regulations are replaced by goal setting regulations. This approach is broadly similar to that of new regulations in the Norwegian sector which came into force in January this year. An integral part of both approaches is in the use of risk assessment methods to demonstrate that an adequate level of safety has been achieved.
This means that risk assessment can no longer be seen as an academic discipline practised by the safety department and their consultants. It is going to become the basis of key and costly decisions and will be an important aspect of the interaction with the regulatory authorities. It will be important that the management of operating companies, at all levels, understand the principles, the shortcomings and the ways in which risk assessment should and should not be used.
Risk assessment is a generic term covering a wide range of techniques used to assess the level of safety by considering both the magnitude of harm or damage and likelihood of such harm occurring. Such assessments can be qualitative or quantitative or a mixture of the two.
A risk assessment will therefore involve some assessment of the damage and an assessment of likelihood. Such assessments can be presented in simple qualitative scales or be fully quantified to result in a numeric value of risk. A Quantitative Risk Assessment (QRA) can involve the use of a variety of methods or models ranging from simple correlations to complex computer codes; these will include methods for the assessment of the consequences of releases including dispersion models, flame radiation models, explosion models etc.; models for assessing the impact or damage resulting from the fire or explosion or impact; data on the likelihood of failures of various items of equipment and on the likelihood of alternative outcomes, for example, ignition and methods for utilising that data; and methods for summarising and presenting the results in a useable manner.
The basic approach of QRA techniques is to analyse a complex system (such as a platform or chemical plant), which contains hazardous materials, hardware, control and safety systems, people and management systems, with the intention of determining:
what accidents can occur? - this depends on the scope of the study and may be generated using checklists, HAZOP or previous study experience.
how frequently does each accident occur? - a combination of failure rate data and conditional probabilities.
