f H21 Phase 2: Ignition Considerations for Network Procedures

The objective of the H21 programme is to reach the point whereby it is feasible to convert the existing natural gas (NG) distribution network to 100% hydrogen (H₂) and provide a contribution to decarbonising GB’s heat and power sectors with the focus on decarbonised fuel at point of use. This report is one of a series of reports that look to address the work areas previously identified following a review of network procedures. It looks at the difference between the ignition sensitivities of natural gas and hydrogen, primarily regarding electrostatics and friction, and how they impact on network procedures. Equipment currently used by NGN was reviewed for its suitability for use with hydrogen. A number of further precautions have been identified for hydrogen, and the main findings are summarised below.
Ignition topics that should not require alteration with hydrogen.
The LEL based criteria (20% LEL for the use of non-ATEX equipment, when deciding upon evacuation and other safety precautions, 70% LEL for switching off electrics under emergency conditions, and 5% LEL and falling for reoccupation of buildings) remain fit for purpose with hydrogen; however, these do require accurate hydrogen gas detection. Damp rag earthing of PE pipe was demonstrated experimentally to be effective in preventing electrostatic discharges and is suitable for use with hydrogen. Protection against electrostatic discharges extends 10 cm beyond the damp rag. The continuity bonds used for natural gas remain fit for use with hydrogen. The cathodic protection remains suitable for hydrogen from an electrostatics point of view, although the location of impressed current cathodic protection (ICCP) systems should be in Zone 2 NE (Negligible Extent) areas. There is little change in the risk of pyrophoric ignition, and electrostatic discharge remains the greatest ignition risk with “black dust”.
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.