What is Hydrogen? How safe is it? How much do we need?

future of energy

We plan to introduce hydrogen to our gas network, as it’s much cleaner than the fossil gas we carry now and widely acknowledged as one of the solutions to the UK reaching its net zero carbon emissions targets. But, what is hydrogen? How safe is it? How much do we need? David Watson, our Head of Energy Transition, answers the questions we are often asked.

What is hydrogen?

Hydrogen is an element, existing naturally and consisting of two hydrogen atoms. It is the most abundant element in the universe, found in the Sun, most of the stars. On Earth, hydrogen is all around us, most often in the form of water – putting the H in to H2O.

In the early 1500s the alchemist Paracelsus noted that the bubbles given off when iron filings were added to sulfuric acid were flammable. It would take a further 250 years for Henry Cavendish to show that these bubbles were different from other gases, and that when burned they formed water, thereby ending the belief that water was an element. Antoine Lavoisier later gave the gas the name we use today, hydro-gen, meaning water-former.

Hydrogen is less well-known than the fossil gases we use today. It is the lightest element in the Periodic Table, known for being a very small molecule with high energy density.  At standard temperature and pressure it is a non-toxic, odourless, tasteless and colourless gas. This means that – in the same way as we do with the fossil gas used in homes today – a unique odour would need to be added to it in any future gas network.

Why do people say hydrogen is ‘versatile’?

Hydrogen’s properties mean that it can be usefully applied in a range of use cases. Because it can be either a gas or a liquid it is capable of being stored for long periods of time in either pipes, ships, tankers or even natural underground structures like salt caverns. This means that it is capable of being produced in one season and then used in another.

Once produced it can also be used for several other purposes, such as producing heat, industrial processes, making electricity or powering fuel cells. Its properties as a long-term, flexible store of energy is valuable in an energy system which is becoming more reliant on intermittent power.

Will my boiler work with hydrogen?

It is important also to note the limitations of hydrogen. The processes to manufacture it today are expensive compared to fossil gases and renewable power. Its properties as a light gas mean that if it is released it dissipates quickly into the atmosphere (good news) but also that it can pass through some materials over time (bad news).

It has a higher energy content than fossil gas but is less dense, meaning that roughly three times the volume of hydrogen is needed to generate the same amount of energy as fossil gas. Finally, it also combusts differently to fossil gas. This means that appliances using hydrogen need to be specifically designed to account for this. This means that appliances that use fossil gas today would likely need to be replaced rather than converted. That’s why manufacturers of boilers, for example, have hydrogen-ready appliances in advanced stages of production, so that when your current boiler is next due for renewal, you’d simply replace it with one that works with hydrogen, at similar cost.

How much hydrogen do we need?

It is becoming more and more likely that hydrogen will play an important role in helping us get to net zero in hard to abate sectors such as industry, heavy transport and intermittent power generation. It is also likely that hydrogen will a role to play in decarbonising home heating.

There have been a range of studies assessing the likely volume of hydrogen we will need for these uses. These studies estimate volume requirements of between 100 TWh and 300 TWh per year, by 2050. National Grid go further and estimate total hydrogen demand of over 500 TWh in one of their three net zero compliant scenarios. To put that in context, it is the equivalent of today’s UK annual electricity consumption.

The wide range of estimates on the amount of hydrogen that we might need mean that gas networks like Cadent are planning for a wide range of potential eventualities. Our focus has therefore been on establishing the technical and feasibility aspects of a gas network that can in future enable such use.

Is hydrogen safe?

Hydrogen has many advantages as an energy source, but it also suffers from some negative connotations in the minds of the public. People often assume it is inherently unsafe – even though they safely use fossil gas today. It is not enough to tell consumers that hydrogen is safe, however. We need to demonstrate that hydrogen for heating will at least achieve the high safety standards as they have come to expect from the existing fossil gas network.

Work is underway to demonstrate that hydrogen can do just that, with projects around the country testing hydrogen use under a wide variety of laboratory and real-world conditions. Each of these projects involved the development, submission and approval of initial safety evidence before the trials could commence.

How are you testing and trialling hydrogen?

The first trials to assess the effect of blending hydrogen with fossil gas took place at Keele University, and covered the distribution, supply and use of blended hydrogen in residential properties, involving approximately 100 consumers. This trial found no major safety or technical issues. Having satisfied the Health and Safety Executive (HSE) and other authorities of its safety aspects, the next stage will be to proceed with a real-world demonstration of 100% hydrogen in people’s homes - something that is now progressing.

This is not the only work underway. Cadent and the wider gas sector are actively leading a broad range of hydrogen-focused projects and programmes, designed to demonstrate safety. 

The outputs of this work will be provided to the HSE and Government so that they can determine whether hydrogen can be considered as a suitable home heating fuel. The bar for this is rightly high with conclusive, quantitative evidence needed before the HSE are satisfied that hydrogen is at least as safe as fossil gas.

Can we safely blend hydrogen and fossil gas?

Phase One of our HyDeploy project at Keele University, involving approximately 100 consumers, is now complete and has successfully demonstrated how hydrogen blended to 20% by volume with fossil gas in a plastic gas network can operate safely. While this is promising, we will need more complex ‘real-world’ trials to confirm the safety evidence for blending before it could be rolled out more widely.

Phase Two trials are therefore incorporating a wide variety of pipes and equipment, as well as more customers, including several business and commercial customers. Further research is planned which will follow this with demonstration projects incorporating a broader range of business and commercial customers, running until the end of 2023.

These projects are intended to demonstrate the technical evidence for blending hydrogen at scale from the middle of this decade with the aim of then using the hydrogen production planned in areas of heavy industry such as Aberdeen, Teesside, Humberside and the North West. By way of example, if these demonstration projects are successful, the HyNet North West project (Cadent is a partner in this) could see more than 500,000 customers in the region receiving blended hydrogen by 2027.

Can hydrogen be safely distributed around a network?

One of the merits of hydrogen in a future energy system is that we can re-use a significant amount of the gas network – a gas network which is already there and that customers have already paid for.

Cadent, like all other gas networks operators, have been replacing old iron mains with new plastic (polyethylene) pipe for the last 40 years. Although the project was originally established to replace ageing cast iron pipework, this work is effectively now making the extensive lower pressure gas network better for carrying hydrogen.

Today approximately 72% of Cadent’s overall network has been replaced with plastic. While the proportion converted to date varies by geography, we expect this figure to increase to over 95% by 2032. This is not to say that the gas network needs to be entirely plastic in order to carry hydrogen safely and effectively. Indeed, we are working with the HSE to establish just what mix of materials are compatible with 100% hydrogen across a range of situations.

A network is more than pipes

There are also assets such as valves and governors that help to safely control the flow of gas. Work is therefore needed to test the compatibility of all these different types of assets and to establish new safe working procedures to operate them both on blends and 100% hydrogen.

We are working closely with colleagues across the industry as part of the H21 project to demonstrate the safety evidence for transporting hydrogen across the gas network right now.

This work is detailed, rigorous and in-depth, testing every possible aspect. Phase One has focused on assessing the impacts of any hydrogen leaks and ignition potential from above and below ground assets. Phase Two is currently focusing on establishing new operational procedures for working on hydrogen pipes and assets. Phase Three will be to run a live trial on an existing gas network, starting with around 50 homes in 2022, followed by approximately 600-700 homes in 2023.

Is hydrogen safe to use in the home?

Establishing hydrogen safety in the home has been led by the Department for Business, Energy and Industrial Strategy (BEIS) as part of its Hy4Heat programme. This has so far found that a comparable safety profile to fossil gas is achievable if minor mitigatory measures are taken, for example the installation of excess flow valves and flame failure devices on appliances. These mitigations aside, it should be noted that one clear advantage of using hydrogen in the home is that it does not carry the same risk of carbon monoxide poisoning present when burning fossil gas.

The Hy4Heat programme has also provided answers to a number of safety related questions posed at the start of the work, such as will customers be able to see a hydrogen flame (and therefore know if it is burning), will customers be able to smell a hydrogen leak as they can with fossil gas today and will customers have to replace their internal pipework.

How does hydrogen impact on consumer appliances?

The programme has identified that changing the burner design of cookers and fires eliminates the need for any flame colourant to be added, knowledge which is now being used by manufacturers as they develop hydrogen appliances. The programme has also established that the same odorant used today with fossil gas can be used with hydrogen. Importantly the programme has also demonstrated that hydrogen behaves no differently to fossil gas in internal pipework. In other words, if fossil gas is distributed safely around the home today, hydrogen will be too.

The next steps will be important in developing this safety evidence still further. A series of demonstrations in occupied homes, starting with a small-scale trial of less than 500 homes on a new 100% hydrogen network will be followed by another small-scale project on a repurposed gas network. This will need to be followed by a deployment-scale demonstration showing how the conversion of a whole village or town could occur, involving up to 5,000 homes.

When will hydrogen be used in UK homes?

The total of these efforts means that over the coming few years consumers could expect to see a proportion of their gas delivered as hydrogen, without any need to change their appliances or invest in different equipment. It is anticipated that early blends of hydrogen will cost no more than natural gas today, encouraging consumer demand in much the same way that green electricity contracts were sold. Consumers may also come to expect that if their boiler comes to the end of its natural lifecycle during the next decade, they will be able to replace that appliance with a hydrogen-ready equivalent – i.e. a boiler that is able to burn both methane and hydrogen.


Cadent is the UK’s largest gas distribution network with a 200-year legacy.  We are in a unique position to build on strong foundations whilst encouraging the curiosity to think differently and the courage to embrace change.  Day to day we continue to operate, maintain and innovate the UK’s largest gas network, transporting gas safely and protecting people in an emergency.   Our skilled engineers and specialists remain committed to the communities we serve, working day and night to ensure gas reaches 11 million homes from Cumbria to North London and the Welsh Borders to East Anglia, to keep your energy flowing. 

Future of Gas: Here at Cadent we support the Government’s plans to reach Net Zero by 2050. That means we’re backing the introduction of hydrogen as a low carbon alternative to natural gas for the future. We know people love the controllability of gas and, with our network already in place, it makes sense to switch to the lower carbon alternative offered by hydrogen, which we believe can keep homes and businesses warm for generations to come.

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Stephanie van Rosse


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