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Green hydrogen: Energy remedy or safety headache?

Green hydrogen, a clean and sustainable energy source, presents potential risks. Read more about how to mitigate these hazards and ensure the safe storage and use of green hydrogen.

Demand for green hydrogen has increased in recent years during the UK’s push toward net zero. Green hydrogen can provide numerous benefits and has the potential to be a clean and sustainable source of energy. However, there are various risks associated with its production, storage, and use in industry, that require careful consideration and mitigation.

Potential risks with green hydrogen

Green hydrogen is produced through the electrolysis of water using renewable energy sources. The following examples illustrate potential hazards involving the storage and use of green hydrogen:


As with all forms of hydrogen gas, green hydrogen is highly flammable. On release, it will readily mix with air to form a flammable gas atmosphere, with detection being very difficult as leaked hydrogen gas is colourless, odourless, and tasteless. The following flammability characteristics highlight the risks of handling green hydrogen:

  • Extremely sensitive to ignition from electrostatic discharges, such as propagating brush, spark, cone, brush, and corona discharges (ignition energy = 0.016mJ).
  • Wide flammability range (4% to 75%), with abnormally high upper flammable limit – resulting in releases that will likely be flammable.
  • May spontaneously ignite if released under high pressure (Reverse-Joule Thomson Effect).
  • More susceptible to the transition from deflagration to detonation (DDT).

In gaseous form, hydrogen is buoyant and will rise on release, whereas cryogenic hydrogen will fall and accumulate at a low level before rising. A small amount of energy is required to ignite a hydrogen-air mixture, which can result in a flash fire or explosion. Hydrogen burns with an invisible flame with little radiant heat. It is notoriously difficult to extinguish.

An appropriate risk assessment will quantify the required level of ventilation to control releases, include a detailed ignition source identification, and install sufficient mitigation processes. Additionally, safeguards, such as gas detection, ATEX equipment, and potential explosion protection devices, should also be considered to counter fire and explosion risks.


Green hydrogen is often stored and transported under high pressure to maintain it in a gaseous state or as a cryogenic liquid. This creates the potential of pressure-related hazards, including potential leaks. Hydrogen molecules are small and can permeate joints or fittings that have only been proved leak-tight for use with other gases, such as nitrogen. Carefully designed, robust storage means – with continuous pipework – are required to ensure these hazards are effectively controlled.


Green hydrogen can react with certain materials, such as metals, causing embrittlement. This could compromise the integrity of transfer equipment and storage systems – possibly leading to leaks or even failure. Assessments must consider if materials used are compatible and appropriate to prevent such reactions.


While green hydrogen is not toxic, it can displace oxygen in confined spaces – creating oxygen-deficient atmospheres. Consequently, if the oxygen concentration drops below safe levels, it could pose an asphyxiation risk. Adequate oxygen depletion monitoring systems should be in place and interlocked to mechanical ventilation to mitigate this concern.

Next steps

A comprehensive operations review is crucial for mitigating hazards associated with the generation, storage, transportation, and use of green hydrogen. Additionally, a full and sufficient risk assessment – in accordance with DSEAR 2002 or ATEX 153 –  is important for protecting your business and its employees.

For further information and assistance on the safe storage and processing of green hydrogen gas, contact your Marsh advisor.