Hydrogen: safety aspects

Current applications and future potential

Hydrogen usage nowadays is primarily centred on applications in the chemical industry: fuel desulphurisation, ammonia production and methanol manufacturing, for example. In Switzerland, the Cressier refinery accounts for most of the current demand. Additionally, a fleet of around 50 lorries operate using hydrogen fuel cells.

Recent innovations include using hydrogen to extract iron from iron ore. Here, the oxygen from the iron oxide reacts with the hydrogen, producing water as a by-product. This is a cleaner, more energy-efficient alternative to the traditional approach of smelting the ore in blast furnaces.

Looking ahead to the future, hydrogen will be used in other areas and become an integral part of carbon-neutral energy systems. Hydrogen can be produced using electrical energy – especially excess electricity generated by photovoltaic installations, wind turbines and hydroelectric power. This electricity can drive electrolysis processes that split water into its constituent components: oxygen and hydrogen.

The makes hydrogen a versatile energy carrier that can be stored, used or further processed at a later time, and converted into more complex chemical compounds known as derivatives. In the transport and heating sectors, hydrogen is now used for the most part in fuel cells. It will also be increasingly used in modern combustion engines or gas turbines in the future.

Future hydrogen demand

Hydrogen will play an important, stabilising role in defossilised energy supply systems in the future. Demand is therefore set to increase sharply in the future.

Table 1: Development of hydrogen demand

The driver of the enormous growth in demand is industry. Hydrogen will be used there as a raw material for other chemicals or as a fuel for process heat in high-temperature applications. Conversely, hydrogen is a basis for synthetic fuels that will be used in aviation and shipping. The sharp increase in hydrogen demand will lead to more than just localised hazards. Rather, there are concerns that a new dimension will emerge in the safety issue in connection with hydrogen. This is related to the large volumes on the one hand, and new forms of generation and applications on the other. A critical discussion of safety must therefore take into account the entire hydrogen supply system.

Hazards associated with hydrogen systems

The hazards associated with using hydrogen stem from its physical and chemical properties. This colourless, odourless, non-toxic gas weighs just one-fourteenth the weight of air, making it correspondingly volatile. These properties – its tiny molecular size, volatility and low activation energy – mean that the topic of hydrogen safety deserves special attention.

While hydrogen delivers a high energy density by mass, its volumetric energy density is very low (just 1/3000th that of petrol). So the only economical ways to store and transport hydrogen are when it is compressed (at 35 to 70 MPa) or liquefied (cooled to -253 degrees Celsius).

Rising temperatures increase hydrogen’s reactivity. The gas is highly flammable across low to high concentration ranges in air. Due to its extraordinarily low activation energy, not to mention its wide explosion range, even a small leak can trigger a vapour cloud explosion with catastrophic consequences.

For these reasons, the various stages of the hydrogen system – generation, storage, transport and use – each require their own safety precautions. The potential hazards vary depending on the application context: in energy generation (in the likes of vehicle fuel cells or in power plants), or as a raw material in industrial processes.

During electrolytic hydrogen production, the permeability of the membrane between the hydrogen and oxygen chambers creates a highly explosive detonating gas (a mixture of hydrogen and oxygen). High-voltage equipment failures during electrolysis only compound these safety concerns.

When metals are exposed to hydrogen for extended periods of time, they become brittle, escalating the risk of leaks and compromising the integrity and safety of high-pressure storage tanks.

The physical storage of liquefied hydrogen requires tanks and components engineered for extreme cryogenic conditions (i.e. resistant to temperatures as low as -253 degrees Celsius). Insulation failures can trigger rapid hydrogen evaporation, creating additional handling hazards.

A newer technique is to store of hydrogen as a solid-state chemical. With this method, hydrogen is (usually) bound to metals. But there is a risk of the corresponding storage materials being inadequately chemically and physically stable.

Faulty fuel cell vehicle refuelling puts both drivers and filling stations at risk. Leaking high-pressure storage tanks – whether at filling stations, within fuel cell stacks or in vehicle storage tanks – can result in hydrogen release. When used as a raw material in chemicals production, there is a risk of improper hydrogen handling.

Even the fossil and other fuels that we predominantly use today, not to mention various hydrogen derivatives, exhibit potentially hazardous properties. While ammonia and methanol are easier to transport and store than hydrogen, their high flammability and toxicity require that tremendous care be exercised during handling. Fossil fuels are also dangerous. Although they are far less volatile, they remain highly flammable – with petrol being a prime example.

Analysis of incidents

The European Commission’s Joint Research Centre in Petten maintains a database called HIAD (the Hydrogen Incidents and Accidents Database) to document hydrogen-related accidents. For the period between 2014 and 2023, it recorded 755 events. While most of them were minor, fatalities and injuries were occasionally recorded.

Selected hydrogen-related incidents and accidents

In 2001, a primary explosion occurred in the high-pressure hydrogen supply lines in a hydrogen production plant (with electrolysis), caused by the spontaneous ignition of an explosive mixture of hydrogen and oxygen. The subsequent failure of weld seams and joints on the storage banks led to large quantities of hydrogen gas being released, which after spontaneous ignition led to a secondary explosion and a fire. 

• In 2004, hydrogen gas escaped from the discharge valve of a liquid hydrogen delivery vehicle during transport to a commercial facility and ignited, causing a flash and a shock similar to a mild earthquake. 

• In May 2019, a hydrogen tank explosion occurred at an alkaline water electrolysis pilot plant in South Korea, killing two people and injuring six. The investigation revealed that the hydrogen separator exploded due to oxygen overflow at low load and human error. The ignition was caused by static electricity due to missing proper earthing connections. 

• In 2019, an example of electrical system failure occurred at a hydrogen filling station in South Korea. An explosion was triggered by electric arc sparks caused by outdated insulation material and electrical faults, leading to significant plant damage and personal injuries. 

• In mid-2019, a fire at a filling station near Oslo was caused by a leak in the high-pressure storage tanks as a result of an assembly error. In addition to the substantial property damage that occurred, three people were injured. 

• In 2019, failure to comply with safety regulations at a hydrogen production plant in South Korea caused plant damage and a fire, leading to an accumulation of safety risks. 

• In 2022, an incident occurred in the underground car park of a hospital in Detroit when a pickup truck’s hydrogen tank leaked and caused an explosion of enormous force that severely damaged the truck and other vehicles. Since only a few people were present at the time, only two people were injured and there were no fatalities. 

The large number of accidents illustrates that the causes of incidents and accidents are multifaceted and complex. The most frequently documented causes are: human error at 25 per cent, management factors at 23 per cent, and material and manufacturing defects at 16 per cent. For the remaining accidents (36 per cent), the cause cannot be determined with certainty or cannot be clearly assigned to any category.

Such data is important for improving safety, as it sheds light on the course and possible causes of incidents and accidents. It makes it possible to categorise them according to different aspects, such as the stages along the transformation chain from production, storage and transport to use. Alternatively, they can be assigned to types: gas or liquid leaks, equipment failures, changed environmental and operating conditions, etc.

The documented accident pattern is dominated by the use and refilling of compressed hydrogen to power fuel cell vehicles and as an industrial process gas. Leaks in pressure tanks are usually involved, and fires or even explosions are the consequences of such events.

Events relating to the widespread use of electrolytically produced hydrogen in energy supply systems do not appear in the accident statistics, because such applications have only recently reached implementation maturity and are correspondingly rare.

Studies to assess accident risks

The risk of accidents associated with handling hydrogen in industrial applications and in energy supply facilities is usually determined along the various stages, that is, separately for production, storage, transport and use. Such analyses aim to determine the probability of disruptive events and their consequences.

A procedure that is also common in other areas is to investigate and document incidents that have occurred – including their causes, sequence of events and consequences – with the aim of determining the probability of disruptive events. Such investigations provide important insights into the sequences and consequences of corresponding events.

However, such empirical methods for predicting accident risks are strictly limited in terms of scope. The number of documented hydrogen-related accidents is small, and our knowledge of the individual accidents is fraught with considerable uncertainties. It follows that analysis of actual incidents cannot cover all possible scenarios.

So more comprehensive methodological approaches are needed, such as probabilistic risk assessment methods in combination with different techniques that are not yet available in the hydrogen sector. Simplified models are used to calculate the consequences of accidents, but their applicability to hydrogen systems is questioned in the literature. It is possible that more advanced and more complex models may be required, up to and including the behaviour of hydrogen molecules.

For the traditional steps of the transformation chain, there are analyses and risk assessment methods. However, there is a lack of specific analyses for green hydrogen, including the risks of equipment failure or contamination of hydrogen with oxygen.

There is also a lack of a conceptual framework for identifying the risks encountered in an overall system. Corresponding work must be initiated and the results used to increase safety.

Safety regulations and standards

To ensure adequate safety and its harmonisation, there is a set of regulations and standards for the safe design, maintenance and operation of plants along the entire value creation chain. Here, a clear distinction is often made between recommendations (“should”) and requirements (“must”).

Recommendations are mostly derived from standards and reports from the US Fire Department, as well as from experts and their experiences. These are general instructions that primarily consider costs as opposed to strictly assessing hazards and risks.

Requirements, on the other hand, are derived from national and federal regulations. They are supplemented based on historical events and updated risk analyses.

The rules in force at present have been developed for the quantities used today. Whether they are scalable is unclear. It is therefore crucially important that science is involved in developing new specifications, standards and guidelines.

Current projects dealing with hydrogen safety focus on a single aspect of the overall system, usually the filling station. Sometimes other aspects are also covered, such as the safety of low-pressure pipelines.

There are only isolated analyses that examine the entire system. Such research projects exist in the likes of Germany. They have not been completed yet. There are no such projects in Switzerland at all.

The Swiss Pipelines Ordinance (PipeO) was updated in July 2025 and now also covers hydrogen pipelines. However, the PipeO does not lay down any hydrogen-specific safety requirements. A directive on pipelines for hydrogen from the Fachverband für Wasser, Gas und Wärme SVGW (Swiss Water, Gas and Heat Association) is currently under consultation.

It is crucial that hydrogen safety professionals review industry regulations and standards relating to fire, flames and gas systems for their applicability to hydrogen supply. Training hydrogen plant personnel in safety procedures is also important.

Conclusion and recommendations

Hydrogen is already being used for industrial and chemical processes and as a fuel. It plays a key role in the search for CO₂-free energy solutions. Its use in future energy supply systems requires significant upscaling of the quantities used. The production process will also need to be changed – from the dominant steam reforming of natural gas nowadays to electrolysis using electricity generated from renewable sources.

The use of hydrogen and its derivatives as a storage medium and energy source brings with it unique hazards and significant accident risks, given the inherent properties of the substances.

More attention should be paid to the safety of hydrogen-based systems. The risks involved, particularly in the area of energy supply, deserve a great deal more attention. Safe handling and storage require special equipment and procedures, not to mention appropriate regulations and standards.

There is a lack of specific requirements for the use of green hydrogen for electrolysers, for example. A regulatory framework and standards for the overall system are also needed. Regulations must be developed, and existing ones refined. Inadequate regulation and a lack of standards are one of the main causes of disruptive incidents according to evaluations of the HIAD database.

Clear safety requirements and responsibilities are needed at every stage of the transformation chain for the companies involved. Uniform safety standards that are tailored to new elements and cover the entire value creation chain of the green hydrogen system are needed.

New methods and models for assessing hazards and risks are needed, including systematic recording and evaluation of incidents and accidents. The aim is to use this data to identify opportunities for improvement, to reduce the number of serious incidents and to minimise risks.

Accident and risk aspects usually play a minor role, if any, in green hydrogen projects. Additionally, research into safety aspects is generally underfunded. Increased scientific efforts and appropriate funding are needed in this regard.

Hydrogen safety is a complex challenge for many stakeholders. The responsibilities of regulatory authorities need to be clearly defined and coordinated to address the diverse problems effectively.