This project aims to conduct a quantitative risk assessment (QRA) to identify, quantify, and mitigate risks associated with direct and indirect purging operations from 32mm to 250mm diameter Polyethylene (PE) pipelines on the H100 Fife Neighbourhood Distribution Network. Current industry practice recommends indirect purging of Hydrogen gas systems in various situations to prevent the potential development of a temporary flammable atmosphere within the pipework. However, indirect purging is a non-routine operation (NRO) for most Gas Distribution Networks (GDNs). Indirect purging carries risks such as nitrogen sourcing and transportation challenges, delivery competencies, over-pressurization, and asphyxiation, which are not present during direct purging. Therefore, it is essential to understand the overall difference in risk between direct and indirect purging for hydrogen systems.
Benefits
The project's deliverables encompass the development of a comprehensive Quantitative Risk Assessment (QRA) tailored to purging activities. This will entail a thorough comparative analysis of the risks associated with both direct and indirect purging methods. Furthermore, the project aims to produce a set of recommended procedures and advisory documents. These resources will facilitate the evaluation of responses to diverse emergency scenarios in a prompt and secure manner.
Learnings
Outcomes
Kiwa and Steer have successfully completed the Quantitative Risk Assessment (QRA) for emergency purging on the H100 Fife Distribution Network. This assessment highlights that the main risks stem from potential injuries due to gas escapes igniting due to significant third-party damage and electrical arcing from faulty electrical distribution.
To address these concerns, a comprehensive workflow chart has been proposed for emergency purging activities. This chart offers clear, step-by-step guidance for initiating, investigating, decommissioning, repairing, and recommissioning the H100 Fife network in the event of a gas escape on the parallel Natural gas and Hydrogen networks.
Additionally, Steer Energy has developed modified procedures for both direct and indirect purging during commissioning and decommissioning operations on the H100 Fife Distribution Network. The recommended isolation techniques—valve-to-valve, valve-to-double squeeze-off, and double squeeze-off to double squeeze-off—provide a robust isolation techniques for ensuring safety and purge efficiency. Furthermore, non-routine procedures that include detailed steps for executing both direct and indirect purging with the recommended isolation techniques have been produced.
For future projects, exploring the time required for flammable fuel air inventory buildup in the mains after applying an isolation method presents an excellent opportunity for operational improvement. Gaining insight into this timeframe will significantly enhance the response times of network operatives during gas escapes. The QRA emphasizes the importance of initiating purging operations immediately after isolating the gas mains to effectively prevent the accumulation of flammable inventory. This proactive approach will contribute to the safety and reliability of the network.
Lessons Learnt
One of the key lessons learnt from the completion of this project was that significant effort is required to transform research out puts into actionable policy documentation for Hydrogen network operations. Significant technical guidance and inputs from the project team was required to ensure suitable gas industry acceptance and local integration is achieved. Another challenge highlighted by this QRA is that current industry standards such as IGEM SR22 need to be updated to include Hydrogen operations.
