f Dispersion of Helium Releases in Domestic Properties

The UK’s pathway to net zero is likely to include the use of hydrogen in place of natural gas within the gas network. From the perspective of domestic end users of gas, if a conversion is to take place, then the behaviour of hydrogen after an escape within a property needs to be fully understood. Several studies have been carried out in recent years to understand the dispersion characteristics of hydrogen in the event of an internal escape within a building. From a domestic perspective, this has always taken place in laboratory settings or purpose-built test houses which are probably not entirely reflective of UK housing stock. This work pulls together previous work on domestic ventilation and gas dispersion analysis, to provide further evidence to show how a significantly lighter than air gas will move around a range of real domestic properties in the event of an internal gas escape. Reference is then made to work carried out on the consequences of ignition of hydrogen to show how the use of risk mitigation measures such as ventilation and hydrogen detectors can be used to support early conversion projects.
The outputs of previous research into the use of hydrogen in domestic properties suggested several recommendations on a hydrogen conversion. These recommendations included the following measures:
• Integrity assurance of pipework and gas appliances, i.e. ensuring that the gas system within the property is leak-tight and all appliances are fitted with appropriate safety devices.
• Odourisation, this will continue to occur to the same concentration (ca. 6 mg/m3).
• Excess Flow Valves (EFVs) to stop the gas flow in the event of a large leak.
• Appropriate ventilation and additional ventilation in small spaces such as cupboards.
• Gas detection in the form of an alarm or alarms, with a 1000 ppm set point, located in appropriate and central locations to alert the householder if a gas leak occurs.
To solidify these recommendations this experimental programme was carried out to investigate the propagation of a buoyant gas in a variety of as lived in houses, under a range of leak scenarios. As such, the work focussed on reducing the risk/protecting individuals in situations where a leak has already occurred via the optimal application of ventilation and gas detection.
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.