RR996 - Review of self-isolation and restoration risk assessment models

The gas distribution network operators (GDNs) must prepare emergency plans to respond to a widespread or prolonged loss of gas supply incident occurring on their part of the network. These plans are a requirement of the Gas Safety (Management) Regulations 1996 (GSMR) and form part of the safety case arrangements made by the GDNs.

This report provides an independent review of two risk assessment models that will be used in conjunction with the GDNs' gas supply emergency response plans. These models predict the anticipated number of fatalities from gas incidents during isolation and restoration of the gas supply and the anticipated number of fatalities from the effects of low indoor temperature that might be encountered during a gas supply emergency. The outputs of these models will be used by the GDNs to determine whether the gas supply to each affected property should be isolated and later restored by GDN-appointed personnel or by the gas consumer themselves.

This review covers the assumptions made in the models, the data used, and the techniques used to manipulate the data, and concludes that the overall approach adopted in the risk assessment models is appropriate. Some modifications to the models are recommended, but it is not anticipated that these modifications would affect the conclusions reached using the model, in the majority of cases.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

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Updated 2021-04-26