This project aims to assess the depressurisation of domestic pipework and entrainment of oxygen into the pipework after depressurization. By undertaking the experimental work we aim to understand this depressurisation rate during the process, and at what stage and up to what extent the oxygen ingression may occur in the pipe.
In addition to the test work, the project will present potential mitigations to prevent health and safety risks to the end user and safe methods/procedures to reinstate gas in the pipework after such depressurisation. It also investigates whether and how to disable a gas appliance and/or the gas supply after the supply has been shut off.
Benefits
The H100 Neighbourhood Trial is aiming to convert around 300 properties to hydrogen. In this trial SGN is committed to providing safety of customers through a thorough safety case which is based on the Hy4Heat Safety Annex and recommendations from industry experts where other industry hydrogen standards such as IGEM/H/2 have fallen short. While so far many questions have been closed and many gaps have been addressed, a few are still outstanding due to lack of information or ongoing research.
One of the gaps remaining to be addresses is related to the depressurisation of domestic pipework and entrainment of oxygen into the pipework after depressurization to atmospheric pressure. This question needs to be answered immediately so that we can assure HSE that all gaps have been addressed for the delivery of H100.
Benefit of this project is that it helps understand the mentioned risk and offer mitigations for addressing this health and safety consideration. This enables H100 to proceed in a safe and timely manner which will produce vital evidence for the potential roll-out of hydrogen across UK.
Learnings
Outcomes
The project delivered a comprehensive understanding of how air ingress occurs in isolated domestic pipework, particularly under conditions of changing pressure and temperature. Through extended-duration experimental testing using two bespoke rigs, the team explored the rate and extent of diffusive mixing, as well as its consequences.
As a result, a range of mitigation measures were identified and developed, including procedural and design interventions to reduce the risk of flashback and improve reinstatement safety. These outcomes will be trialled in live settings within the H100 Fife project and are expected to contribute to safer engineering designs, enhanced operating procedures, and improved customer safety during hydrogen transitions.
The insights and recommendations generated from this project provide a strong foundation for future projects to build upon and refine these mitigation approaches further through practical implementation.
Lessons Learnt
This project has highlighted the value of maintaining flexibility in research and development work, particularly when addressing new or poorly understood safety challenges. An agile approach allowed the team to adjust course as needed, ensuring timely and targeted investigation.
A key takeaway is the importance of real-world testing early in the process. Practical experimentation was instrumental in identifying challenges that may not have been revealed through theoretical or desktop analysis alone.
In addition, the project demonstrated the benefit of aligning efforts across different organisations. Knowledge gained here has already contributed to other industry initiatives, and future projects would benefit from similar coordination to accelerate learning and reduce duplication.
These findings will support future trials and may inform the wider deployment of hydrogen in domestic networks. The work conducted so far has produced consistent, actionable results, and the approach taken is considered suitable for further application—pending confirmation of its effectiveness during the H100 Fife trial.
