f EUSE Hydrogen Domestic Pipework Conversion – Final Report

Greater assurance regarding the integrity of current domestic gas installation pipework is sought to enable its repurposing to hydrogen. This project needs to be viewed in the context of current leaks from natural gas (NG) of sufficient magnitude to create a fire, explosion, or injury incident. Gas systems do leak and roughly 400,000 publicly reportable escapes (PRE’s) are made each year from 24 million connections. This represents a risk per property of about one PRE every 60 years. The overwhelming majority of these leaks are extremely small, and probably better described as weeps.
Odorised gas (as distributed through the low-pressure gas network) can be smelt at about 1000ppm gas in air concentration [1], which is about 2.5% of the published lower flammable limit (LFL) of hydrogen (4% gas in air concentration). This roughly equates to a leak of 10 l/h (0.01 m3/h) in a 25 m3 room. The amount of gas from such a leak is small, but still large compared to the leak detectable by a standard IGEM/UP/1/B Edition 3, 20 mbarg tightness test, which can detect a leak greater than about 0.2 l/h (0.0002 m3/h) [2], for a typical natural gas domestic installation.
Spontaneous leaks (rather than weeps) in domestic and small commercial gas systems are extremely rare. The pressure within these systems (nearly always ca. 20 mbarg) is sufficiently low that it does not cause impromptu pipework failure. The pipes used in these systems do not corrode from the inside, and even with external corrosion, the nature of this effectively results in a small leak (initially a weep) which only grows slowly with time.
During the period from 2016 to 2022 there was an average of 25 domestic gas incidents a year that were attributed to meters, meter outlet pipes (effectively the gas carcass) or appliances, but of these, only about 0.4 to 1.5 injury incidents arose from spontaneous failure of internal pipework. Therefore, risk exposure from the internal pipework itself is very much at the lower end of the ‘Broadly Acceptable’ range, defined by the Health and Safety Executive (HSE), and so existing controls under natural gas service should be deemed adequate.
Provided appropriate precautions are taken during the conversion of each property from natural gas to hydrogen, it is expected that the risk exposure will remain Broadly Acceptable.
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.