f 380 Air Ingress in Isolated Installations, Interim Report

The precursor to this project was an event leading to a damaged meter at the in January 2024 after the installation had been isolated for 27 days over the holiday period. The incident required two key events: an air/fuel mixture within the flammable range for hydrogen in the installation pipework and an ignition of that air/fuel mixture. The consequence of this was an overpressure in the system leading to damage occurring in the gas meter.
The initial investigations into the event suggested that there may be a mechanism allowing air ingress to occur in an isolated gas installation. The ignition itself was suspected to have been caused by an attempt to light the hydrogen fire with subsequent flashback into the installation.
This report details work carried out to date by Steer Energy, supported by Enertek, to investigate air ingress mechanisms in gas installations. The project is split into two overall work programmes:
• a detailed, experimentally led study of the air ingress phenomenon to identify and understand gas exchange mechanisms in an isolated system, leading to the creation of a flammable mixture in an installation.
• an investigation into the potential for ignition of a flammable mixture in an installation, by an appliance or component in that system.
Both programmes will then conclude with mitigating measures for each event, providing assurance for safe operation of hydrogen in gas installations during roll out.
This interim report provides details of the work carried out to date on the project. The work is not completed, however good progress has been made in understanding the causes of both events described above.
Over 100 individual tests have been carried out, air ingress has been demonstrated and a good understanding of the mechanisms has been gained. The effects have been seen with hydrogen, helium,and methane. Key observations are:
• no air ingress has been seen while pressure remains above ambient.
• no air ingress has been seen when systems are connected to an upstream gas supply.
We can therefore conclude that air ingress does not occur whilst positive pressure is maintained in a gas installation, and this can be achieved by maintaining the upstream supply.
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.