A review of HSE's risk analysis and protection-based analysis ...

Table 5.1 Summary of Review Findings – Risk Analysis
Risk Analysis Element Review Approaches Review Findings
Hazard Identification Research comparing QRA approaches with The approach used by HSE is generally adequate for the relatively simple
accident experience
installations for which HSE currently performs QRAs.
Comparison with accident experience at UK The majority of incidents detailed in the accident records would have either
COMAH establishments
been identified in a QRA, or would have been similar or less onerous in
magnitude to the event(s) considered in a protection-based analysis. A few
incidents were described which would not have been addressed by a QRA of
the installation on which they occurred.
Findings of the ASSURANCE project The results obtained using HSE’s approach were neither consistently
pessimistic nor consistently optimistic in comparison with those of the other
participants, particularly with respect to the most significant events.
Frequency Analysis Comparison with frequency of incidents at Only a limited comparison was possible, since QRA studies have not been
UK COMAH establishments
performed for all COMAH establishments in the UK. The historical frequency
of accidents (representing an average over all establishments) was within the
range of predicted accident frequencies for several different establishments.
Independent peer review of HSE’s failure The peer review found that the data used were generally of good quality and
frequency data.
were a reasonable representation of the failure frequencies of the types of
equipment considered.
Findings of the ASSURANCE project Agreement between the various participants was poor, but was improved
somewhat when all participants used the same set of assumptions. HSE’s
results were not consistently the highest (most conservative) nor consistently
the lowest (least conservative).
Consequence Analysis Model Evaluation Exercise Not yet completed
Comparison of consequence modelling In general reasonable agreement was obtained between the predictions of
predictions with accident outcomes
HSE’s models and the outcomes of accidents as given in historical accounts,
bearing in mind that there is significant uncertainty in the definition of the
conditions under which most of the accidents occurred. Where there is
disagreement it has been possible to identify reasons as to why this may be the
case.
Findings of the ASSURANCE project There was poor agreement between the results obtained between the different
participants. HSE’s results were not consistently the most conservative or
consistently the least conservative.
Comparison of the HSE dangerous dose with HSE’s dangerous doses for a range of toxic substances and for thermal radiation
other means of predicting the dose required would generally result in risk estimates similar to, or lower than, those that
to cause 1% fatality in the exposed
population
would be obtained using other approaches.