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 has delivered a detailed understanding of air ingress in isolated domestic pipework
following depressurisation. The work has improved understanding of the conditions under which
air may enter pipework, the mechanisms involved, and the potential consequences for hydrogen
reinstatement activities. The project has also delivered an agreed practical mitigation approach to
manage the identified risks.
During the current reporting period, the project has moved into a practical readiness phase. The
main technical outcomes have already been achieved, and the remaining work is focused on
enabling deployment of the agreed mitigation method within the H100 Fife project.
The outstanding activity relates to final design verification, performance approval and readiness
confirmation for the component required to support the clean purge process before any hydrogen
is intoroduced. Once this has been completed, the component will allow the mitigation approach
to be applied in the H100 Fife project.
The outcomes of this project are expected to support safer engineering practice, improved
operational procedures and enhanced customer safety during the trial. The learning may also be
relevant to future hydrogen transition activities.
Lessons Learnt
The project has demonstrated the importance of allowing flexibility within research and
development projects, particularly where new or poorly understood safety issues are being
investigated. What began as a focused assessment of depressurisation and air ingress developed
into a wider investigation covering the mechanisms of air ingress, the consequences for hydrogen
reinstatement, and the practical measures needed for safe implementation.
A key lesson is that early-stage research can identify wider operational and safety considerations
that may not be fully apparent at the outset. Future projects should therefore allow sufficient
flexibility in scope, programme and budget to respond to emerging findings where they are
relevant to safety and practical deployment.
The project also showed the importance of considering practical application early in the process.
The mitigation approach developed through this work is intended to support clean purging during
hydrogen works and reduce the risk of air being retained within domestic pipework before
hydrogen is introduced.
Another lesson is the need to identify practical delivery dependencies as early as possible. Even where the technical approach has been agreed, deployment can still be affected by final design verification, performance approval and readiness requirements for specific components or tools required for use on site. Future projects should therefore allow sufficient time for these assurance activities before implementation. The learning generated by this project is expected to support future hydrogen trials and may inform wider hydrogen deployment in domestic networks, particularly where domestic pipework depressurisation, reinstatement and purging need to be managed safely.
