f Great Britain Distribution QRA Risk Predictions

The natural gas distribution system has operated safely across Great Britain for around 50 years. It is an established means of supplying fuel for heating and cooking to residential dwellings and non-domestic buildings, and is also used in some industrial processes. In order to meet environmental targets set by the UK Government, multiple gas industry projects have been completed, or are in progress, to investigate the conversion of the existing natural gas system to carry hydrogen. This would make use of a valuable national asset and would help to meet carbon emissions targets.
As part of this programme of work across the gas industry, DNV has carried out a Quantitative Risk Assessment (QRA) of the gas distribution system across Great Britain. Note that the ‘distribution system’ in this report covers a wider scope than the common meaning of the ‘distribution network’. Here the system includes the gas distribution network operating at up to 7 bar upstream of the Emergency Control Valve (ECV) and gas use within customer properties downstream of the ECV. The primary aim of the assessment is to quantify the risks posed by a repurposed hydrogen system, and the benefits of risk mitigation measures, where necessary. To put these results in context, the risk associated with the equivalent natural gas distribution system is also quantified.
This report contains the results of the risk predictions. Separate reports gives details of the following:
• A DNV report describes the methodology reviews and modelling updates that were carried out as part of this QRA of the Great Britain distribution system.
• A DNV report describes a separate project carried out to investigate the risks associated with hydrogen use in Multi Occupancy Buildings (MOBs).
• A report produced by the Gas Distribution Networks (GDNs) evaluates each potential risk mitigation measure and justifies their adoption or rejection.
The risk predictions cover the Great Britain gas distribution system and end use within buildings for heating and cooking. The study does not consider hydrogen production or storage, gas transmission at pressures above 7 bar, industrial use of gas or vehicle refuelling stations.
This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating, which can be found at Hydrogen heating:HSE assessment of the safety evidence - GOV.UK.
Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.