SGN has been forced to release additional findings, namely the final report and high-speed video footage, from safety tests which found some hydrogen explosions in homes could be more dangerous than equivalent methane explosions.
The gas distribution network said it had previously withheld the information due to concerns it “would be used out of context and could have been misinterpreted.”
In December 2022, SGN received a request by The Ferret to release findings from the experiments, which were conducted in January 2018, under the Environmental Information Regulations.
Although SGN confirmed the location, timings and parameters of the tests, the company refused to provide the measurements, videos and photographs taken, or the conclusions as given in the final report.
SGN told the media outlet that the “premature release” of this information could “unnecessarily damage participation” in its H100 Fife project, which aims to create the UK’s first ‘hydrogen neighbourhood’ and requires “informed buy-in from members of the local community.” The company said the information could cause “unnecessary alarm” and “undermine the funding and viability of the project.”
The Ferret appealed the decision to the Information Commissioner’s Office, which has now instructed SGN to release the final report on the tests.
The tests were conducted by Kiwa on behalf of SGN at the Fire Service College in Moreton-in-Marsh in Gloucestershire. Hydrogen and methane were injected at various rates into shipping containers modified and fitted out to simulate a domestic kitchen. The gas that accumulated over time was then ignited and the effects observed.
Hydrogen and methane were both tested at ‘medium’ and ‘large’ injection rates of roughly 16kW and 64kW respectively. In practice, the injections rates differed slightly from these nominal targets, with the rates for hydrogen being lower. The final report produced by Kiwa said the large injection rate represents the upper limit of any conceivable domestic use, being equivalent to the consumption of six hob burners, two ovens, two fires and a boiler. There were two tests of hydrogen injected at the large rate, which achieved slightly different concentrations of hydrogen at the ignitor of roughly 18% and 20%.
Hydrogen was also tested at a ‘very large’ injection rate of 100kW. The report said this was the rate necessary to achieve the ideal ‘stoichiometric’ air-fuel mixture (30% hydrogen) to deliver the most powerful explosion. For methane, this mix was achieved with the large injection rate.
In most of the tests of injections at medium and large rates, the overpressures measured during the explosions were “modest” and only resulted in broken windows and glass and minor structural damage. The report said: “The probability of death to occupants would have been low and injuries were more likely to be caused by flying debris and possible heat.”
However, during the hydrogen test that achieved a 20% concentration at the ignitor, “the overpressures were much larger than the other ignitions. It is likely there would have been significant damage to brickwork, and occupants of the house would probably have been severely injured.” This was the only test at medium and large injection rates in which there was damage to the structure of the shipping container, which was “bowed out” with “split welds” on two sides.
Kiwa said it believed the much higher overpressure recorded during this test was the result of the hydrogen transitioning “from deflagration to detonation. The higher flame speeds in a detonation do not allow enough time for pressure relief and therefore resulted in much higher overpressures.”
During the final stoichiometric hydrogen test, there was “severe” damage to the shipping container, which was “blown apart,” leaving window fragments up to 70 metres away (see picture below). Shrapnel from the metal shutters of the container was thrown 25 to 30 metres, damaging the tarmac in the test area in the process.
Based on these findings, the report recommended that houses converted to hydrogen should be fitted with a 64kW excess flow valve at the meter to automatically switch off the gas if the flow rate exceeds this level. SGN told Utility Week it is fitting these valves to properties participating in the H100 Fife trial, none of which have gas supplies of more than 40kW.
You can read the full report, which was released by SGN shortly before Christmas, here, and watch high-speed videos of the tests below.
The tests were funded under Ofgem’s Network Innovation Allowance. SGN said the findings were shared with industry to inform the risk assessment for hydrogen heating in homes that was conducted as part of the government’s Hy4Heat programme, which was published in May 2021.
A spokesperson for the company said: “Safety is at the heart of everything we do. That’s why we carried out these tests and shared the results with industry. The key findings were made public in 2021 as part of the government commissioned Hy4Heat programme to explore the evidence case for the use of hydrogen in homes.
“We decided not to share some of the material because of concerns this would be used out of context and could have been misinterpreted.”
SGN said detailed findings from the tests, including images of the explosions and their effects, were released as part of another report produced by Kiwa for Hy4Heat. The report said the tests “showed that for concentrations of around 10% methane and 15-20% hydrogen the consequence of an ignition would be roughly comparable.”
“Towards the higher end of this concentration band the hydrogen ignition starts to become more severe than methane,” it added. “Beyond 20% (up to around 40%) the consequence of a hydrogen ignition gets progressively much more severe.”
The SGN spokesperson said:“H100 Fife has the backing of the energy regulator Ofgem, the UK and Scottish governments and crucially hundreds of residents who are supporting this world-first green hydrogen project. SGN is committed to being open, transparent and engaging with the community to clearly explain all aspects of the project.”
A spokesperson for Ofgem said: “The safety of anyone working on or taking part in a trial of any kind on our energy system is of the upmost importance. Ofgem, along with the Department for Energy Security and Net Zero, will consider the Health and Safety Executive’s conclusions on the ability for the H100 Fife project to run safely before it can go ahead.”