f Air/Oxygen Ingress in Domestic Gas Installations, Phase 1 Summary Paper

Air ingress is not a new phenomenon that is exclusive to hydrogen - it already occurs in natural gas installations today (but has not previously been recorded as a challenge). Subsequent ignition events are highly unlikely, requiring a very specific combination of actions and conditions to occur. However, the likelihood, and potential consequences, of an ignition event occurring are greater with hydrogen systems (if unmitigated) compared to natural gas. Therefore, additional safeguards are recommended for hydrogen systems, to appropriately manage these risks. This work has concluded that, theoretically, any ignition events in hydrogen installations in the future should be prevented by requiring additional assurances within the formal testing and certification process of hydrogen appliances. However, as good-practice, extra layers of protection are also being recommended as precautionary measures - to inhibit the mechanisms of air ingress, and to minimise the consequences of any (now unforeseeable) flash-back events, respectively. Air ingress can be successfully mitigated in the short-term using existing technology and methods. Opportunities exist for significant improvements on mitigation measures in the future, by deploying evolving technologies and ‘smart’ systems.
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.