Hydrogen heating, village trials and explosion risk

With possibly just days to go before the UK government announces its decision on the Redcar Hydrogen Village heating trial, rumours and misinformation about safety are swirling - many of them propagated by Northern Gas Networks (NGN) - the gas distribution company promoting the trial.

The story so far

For those that have not been following the blow-by-blow, the government started laying the groundwork for hydrogen heating in the UK in 2018, via a programme called Hy4Heat. This consisted of ten Work Packages, of which Work Package 7 was a Safety Assessment and Work Package 9 covered how a community trial might be prepared and run.

In November 2020, as part of his 10-Point Plan for Green Industrial Revolution, then Prime Minister Boris Johnson announced his administration would "support industry to begin a large village hydrogen heating trial [by 2025], and set out plans for a possible pilot hydrogen town before the end of the decade."

To be fair, the government has always been clear that safety was of paramount importance, saying from the start that "Before any community trial can go ahead the Health and Safety Executive (HSE) will need to be satisfied that it will be run safely."

The government has also said, repeatedly, that no hydrogen trial will go ahead against the wishes of locals. Ellesmere Port was knocked out of the running when it became clear that it did not enjoy "strong local support" among residents.

Bait and switch on safety

Throughout their promotion of the Hydrogen Village Trial in Redcar, NGN has referred to the five years of work undertaken on safety. For instance, on its main Redcar Hydrogen Community information page, it says "The plan to provide communities with 100% hydrogen has only been made possible following exhaustive research over the last five years to ensure it can be supplied as safely and reliably as natural gas is today."

What NGN has been less open about is the fact that it is not planning to follow the recommendations of those five years of work. The Safety Case that emerged from Hy4Heat Work Package 7 was based on passive, or "inherent" safety, with measures including two free-flow valves (which shut off the gas supply in the event of a large leak), and 10cm by 10cm non-closable vents in each room with a hydrogen appliance or substantial plumbing. The residents of Ellesmere Port, made aware of Cadent's plan to knock in their walls at a public meeting with experts (of which I was one), gave that idea short shrift.

Verbally, NGN has told residents it is not planning to implement the measures laid out in the Hy4Heat Safety Case, but to switch to an "active" safety strategy based on the use of hydrogen sensors. Its problem is that although it is working with the HSE to develop the sensors, no Safety Case based on hydrogen sensors for space heating has yet been published - let alone approved by the HSE, let alone communicated by NGN as part of the trial, let alone discussed by residents, let alone accepted by them as adequate.

NGN has repeatedly accused me and the other experts who appeared at the public meetings in Ellesmere Port and Redcar of spreading misinformation. They say they would never do anything unsafe - but that is gaslighting: I never said they would, and in any case the HSE would not let them. What I did say, and continue to say, is that NGN are not planning to follow the published Safety Case, approved by the HSE for the hydrogen heating trials.

If NGN provides me evidence of an HSE-approved Safety Case for the protocol they intend to follow, I will of course issue a correction and apology. Until then I will continue to pursue what I consider my public duty to inform.

The Hy4Heat Safety Case - in detail

In 2018, the Department for Business, Energy & Industrial Strategy [now part of DESNZ] appointed Arup as programme manager for Hy4Heat. Arup worked with technical and industry specialists: Kiwa Gastec, Progressive Energy, Embers and Yo Energy. Together the group formed a consortium refered to as Arup+

All the relevant documents relating to Hy4Heat Work Package 7, the Safety Assessment can be found here.

The main report, entitled "Safety Assessment Conclusions Report incorporating Quantitative Risk Assessment", is dated May 2021 and is 144 pages long. Don't worry, there's no need to read it all because there are shorter versions of the important stuff, as we shall see. It is, however, a great source document. It contains lots of good stuff, including a summary of the modelling which showed hydrogen heating would result in 4x as many injuries as natural gas, unless enhanced safety measures were taken. (Section 9.1.2, natural gas, 9 explosions per year and 16 injuries. Section 9.2.2, hydrogen, 39 explosions and 65 injuries).

The full report also contains the background behind the safety measures required to "reduce the overall risk to a level that is comparable to natural gas". The measures themselves can be found in Section 14, "Summary of Recommendations" on Page 101. Look in particular at the ones on pipework and ventilation.

These extra safety measures (as can be seen from the table in Section 10.1.2) reduce the number of injuries back to 16 a year (comparable with the 17 from natural gas), but that's from 26 explosions rather than 9. The average hydrogen explosion, as the hydrogen boiler development leader from Worcester Bosch explained to the public meeting in Ellesmere Port, is less severe than the average natural gas explosion - so if your goal is “comparable” numbers of injuries to natural gas heating, you should expect more explosions. [Note: electricity carries different risks (fire, electrocution) but "kitchen explosions" and the dreaded "whole downstairs explosion" are not among them]. 

The additional safety measures required to make hydrogen heating as safe as natural gas heating are also listed in the shorter (27-page) WORK PACKAGE 7 Safety Assessment: Precis.

They are then reprised in the key document from Work Package 7 which is the Annex To Site Specific Safety Case for Hydrogen Community Demonstration. It is just 9 pages long, and forms the basis of the submission to HSE for approval of the safety provisions governing the trial. If you are looking for one document that contains the full list of safety recommendations, this would be it. They include such gems as:

• "Rooms with gas appliances or substantial pipework installed should have non-closable vents with equivalent area of 10,000 mm2, located as close to the ceiling level as possible and no more than 500 mm below ceiling level."

• "Vents that can be fully closed, either automatically or manually shall not be used. The use of stops to ensure provision of at least 10,000 mm2 could be considered."

• "Mechanically ventilated buildings are excluded from the trial."

• "A tightness test shall be undertaken to current natural gas standards prior to conversion and subsequently prior to commissioning by a second person. The tightness test shall be assessed in accordance with IGEM/H/1 or other installation standards (e.g. BSI). Where this is not the case, then the pipework shall be replaced to meet current natural gas standards."

• "Any cast iron components found during the inspection shall be removed or replaced."

• "The Hy4Heat assessment did not include [...] commercial properties with gas usage significantly greater than domestic environment, i.e. installed gas usage greater than 100kW (e.g. sports facility with a swimming pool)."

• "The Hy4Heat assessment did not include [...] Buildings that use mechanical (or forced) systems for background ventilation."

It is worth remembering that while conversion work is being done, the resident has no cooking or heating.

The Annex also places the onus on the resident to maintain the safety measures in their home: "Householder agreement shall be in place and shall agree to ensure appropriate safety management of appliances and other infrastructure, including maintaining the system and appropriate reporting of incidents throughout the trial period. This should also include any information about the use of hydrogen that is considered relevant." 

HSE’s approval of the Hy4Heat Safety Case

The HSE wrote a fairly detailed (8 pages long) BEIS/Arup+ Hy4heat Case for Safety Project, Conclusions Memo in May 2021, which concluded as follows:

"It is recommended that HSE issue a letter of assistance to BEIS confirming that the Safety Case annex, relating to the risks from the supply of 100% hydrogen gas downstream of the ECV [Excess Flow Valve], and supporting documentation provides an adequate basis, if applied appropriately by the relevant duty holder, for:

• Designing the scope of future hydrogen trials,

• Assessment of the risks arising from those trials, and

• Management of those risks in accordance with a suitable and sufficient risk assessment for those trials."

Now you see why the Annex to the Hy4Heat Work Package 7 report is the key document: the HSE assessment, recommendations and Letter of Assistance all refer back to it. 

Following up on its Conclusions Memo, HSE wrote the second of the two key documents you might want to read, called a Letter of Assistance to the minister at BEIS [now DESNZ], confirming their approval of the Safety Case contained in the Annex. HSE is an independent agency, so this is the form in which it provides advice to ministers. It is just one page long and very much worth reading.

HSE was very careful in its Letter of Assistance to note that their approval relates only to Version 1.0 of the Annex submitted by Arup+. It repeats the formula from its Conclusion Note, namely that:

"HSE is satisfied that this [Safety Case annex] provides an adequate basis, if applied appropriately by the relevant dutyholder, for:

• Designing the scope of future hydrogen trials,

• Assessment of the risks arising from those trials, and

• Management of those risks in accordance with a suitable and sufficient risk assessment for those trials. 

It goes on to say:

"This letter relates only to those risks identified in the Annex. Other duties to ensure the safety of the public from the distribution of hydrogen in pipes remain unaffected by this letter,  for example:

• Emergency response to gas escapes,

• Pipeline pressure management,

• Gas odorisation,

• Up-to-date and accurate asset record-keeping,

• Repair and maintenance of assets, 

• Any other applicable duties under relevant health and safety legislation."

HSE's response to the Arup+ Annex and Safety Case is by no means HSE's only work on hydrogen. They have a full programme of research and a Gas Network Hydrogen Testing Facility, which was "purpose-built by Northern Gas Networks for Phase 1a of their H21 project but now available for other work". I leave you to decide whether it is appropriate to test NGN's safety approach and equipment in a facility originally funded by NGN, whether HSE can be impartial on the Hydrogen Village Trial at Redcar being promoted by a funding partner, and whether the relationship between NGN and HSE is altogether too cosy.

The main point here, however, is that up to today, as far as I am aware the HSE's Memorandum of Conclusions and Letter of Assistance constitute the sum total of their official statements on the safety of the Redcar trial. As always, if I am wrong, could NGN or anyone else please point to the evidence, and of course I will issue a correction.

Sounding the ALARP

Another way in which, in verbal discussions with some residents, NGN has said it plans to deviate from the approved Hy4Heat Safety Case Annex relates to the standard against which safety will be measured during the trial.

For the Hy4Heat work, the standard applied was that the risk from hydrogen heating should be "comparable" to that posed by natural gas. Hence all the modelling of numbers of injuries per year, and then proposed set of measures in the Annex, designed to bring them back to the level caused by natural gas.

What is now apparently being discussed with HSE is that the risk should instead just be "As Low As Reasonably Practicable" or ALARP. This is a standard frequently used in industry, where eliminating all risk would be unfeasibly expensive, and so a somewhat lesser standard is used.

One major problem when ALARP is applied to the hydrogen trial - setting aside the issue of polling residents for support and then entirely changing the Safety Case - lies in defining "Reasonably Practicable". Is that ALARP for any sort of heating system (a heat pump, for instance, or district heating), ALARP for a gas heating system (i.e. comparable to natural gas), or ALARP for a hydrogen heating system? How does one decide what ALARP means, for a technology that has not been tried before? And does ALARP mean that the government can decide that the residents will be guinea pigs in the hydrogen trials, and then only "Reasonably Practicable" efforts need be made to keep them safe?

Another challenge relates to the use ALARP in the context of public trial of a new technology, particularly when one based not on inherent safety, but on active safety, so that the safety outcome is heavily dependent on the human behaviour of participants. How much education in the use of hydrogen sensors is "Reasonably Practicable"? This is why, while ALARP is often used in medical environments, for instance to reduce the exposure of staff to radiological risk, it is not used to govern clinical trials, which are always governed by an independent research ethics committee.

Summary

So there you have it. As soon as NGN starts talking about hydrogen sensors, they are departing from the "five years" of safety work that has been undertaken on the Hydrogen Village trials to date.

Could they get approval from HSE for a new Safety Case based on hydrogen sensors? It is hard to tell. The problem with relying on "active safety" is that you have moved from a situation where the resident is safe without having to take action, to a situation where the resident, or someone else has to actively do something in order to be safe. That involves answering questions like the following:

• What are residents supposed to do if their sensors go off?

• What happens if an occupant is out and the sensor goes off?

• What happens if the sensors go off in an empty property?

• How many

• Are the sensors connected to NGN's control room, and if so, is that connection certified for safety-critical use?

• Do NGN have the right to break in to an empty property if the sensor goes off?

• How do you make sure everyone (including for instance the elderly, the babysitter, etc) knows what to do if the sensor goes off?

• Who is responsible for changing the batteries on the sensor (remember that hydrogen rises, so the sensors presumably have to be installed on or near the ceiling, out of reach of frail residents)?

• Is it safe to access high spaces (lofts etc) without first undertaking forced ventilation, since any accumulated hydrogen may not automatically clear?

• How often must sensors be maintained or calibrated? In industrial environments, it is recommended that maintenance and recalibration of leak detectors should be performed every 3-6 months and recorded in facility records, unless otherwise specified in manufacturer's instructions.

The US's Lawrence Livermore National Lab maintains a very useful resource on hydrogen safety called H2Tools, with a whole page on best practices in leak detection.

The context here is that hydrogen is much more flammable and explosive than natural gas. Deep in the detail of the Work Package 7 Safety Assessment: Conclusions Report, on page 50, we learn that "toasters and hair dryers, whose filaments grow red-hot when operating (i.e. the filament temperatures are likely to be in excess of 600 °C)... led to immediate ignition of hydrogen but not of methane". NASA's Safety Standard for Hydrogen and Hydrogen Systems notes that "Personnel should avoid wearing clothing made of nylon or other synthetics, silk, and wool because these materials produce charges of static electricity that can ignite flammable gas mixtures".

In the UK, the Institution for Gas Engineers and Managers (IGEM) has published a Reference Standard for Low Pressure Hydrogen Utilisation, which is an excellent technical primer on the safety issues. However, it raises more questions than it answers - for instance noting that "Mechanical ventilation systems will not be designed to handle flammable gases (including NG) and so in the event of a gas leak, ignition within the system could not be ruled out" - and highlighting the need for more research in many areas.

The point here is not that the risk of a hydrogen explosion in Redcar is high. It remains very, very low. Even if it were four times the risk of a natural gas explosion, as estimated by Arup+ for hydrogen heating in a typical UK home in the absence of mitigating measures, that would still only be an explosion risk of one in 185,000 and risk of injury or death of one in 350,000 per year.

The point here is about consent. Any claim that residents support the trial, based on telling them that safety is a non-issue because of the five years of work undertaken under Hy4Heat, is nonsense. The only way to obtain informed consent would be to publish a new Safety Case, approved by HSE, let residents discuss it and take advice from independent experts, and only then hold a vote - a real vote, properly run and overseen, not just asking a few leading questions and then claiming support.

Bonus question: was town gas actually safe?

While I am at it, I also want to deal with one other issue on which misinformation abounds. During any discussion with supporters and promoters of the Hydrogen Village Trials, it is only a matter of time before they point out that many millions of homes in the UK used to be heated with Town Gas, a synthetic gas made from coal which consisted of around 50% hydrogen, before the switch to natural gas in the 1970s.

They will use this fact to claim first that fears over the safety of hydrogen are overblown, and second that switching 23 million gas consumers to hydrogen cannot be that difficult.

Their argument ignores four key facts. First, there were far more gas explosions when we used Town Gas; second, that the switch to natural gas was from an inherently more dangerous gas to an inherently safer one, while a switch to hydrogen would be the opposite; third, that in the 50 years since the conversion we have dramatically improved the airtightness of our homes and don't want to reverse that progress; and fourth, that the cost of converting our heating to hydrogen would be of the same order of magnitude as converting to electrical heating, according to the gas industry's own figures (as I explained in a previous piece on hydrogen heating).

In terms of the number of explosions, the best data I have found to date shows that in 1968, when there were approximately 13 million homes heated with town gas and 600,000 other supply points, there were 156 gas explosions. Today, there are 23 million natural gas customers and an average of 31 explosions per year. What this means is that any gas customer was over 8 times as likely to suffer an explosion in 1968 than today.

Of course there are other factors at work, such as improved installation quality under CORGI - although Gas Safe Register estimates that one in six gas boilers in the UK is in some way unsafe - but the fact remains, Town Gas customers were nearly an order of magnitude less safe than today's natural gas customers, even though it was only 50% hydrogen. We know from the work of Arup+ under Hy4Heat Work Package 7 that in the absence of safety mitigation measures, hydrogen would be four times less safe than natural gas.

Second bonus question: what about NOx pollution?

In the US, a recent study found that 12.7% of childhood asthma cases were attributable to gas stove use. In the UK, the prevalence of indoor cooking with gas hobs is around 60%, compared with the US's 35%, so 20% or more of childhood asthma cases here could be caused by gas cooking.

Could cooking with hydrogen make this figure worse? We simply don't know, because it was not part of the Hy4Heat research, not mentioned in the Arup+ Report or Safety Case Annex, and not mentioned in the HSE Conclusions Memorandum or Letter of Assistance.

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Post-script: NGN has been fighting demands by residents to invite independent experts attend a planned information meeting on 18 December. According to them, only those who have actually run gas networks are qualified to comment on safety issues associated with the potential distribution and use hydrogen. For six years, between 2012 and 2018, I was deputy chair and then the chair of the safety panel of the board of Transport for London. I would venture that this experience, taken together with my engineering background and work on the energy system over the past two decades, may have given me a better understanding of safety governance than many promoters of the hydrogen village trial.