Understanding hydrogen’s unique properties will be key to ensuring its role in the global energy transition can be carried out safely. Like familiar fuels such as natural gas, hydrogen’s behaviours significantly influence its safety profile, but these are different to hydrocarbons, requiring specific strategies to manage the associated physical and chemical hazards.
One such chemical hazard is hydrogen’s wide flammability range of 4% to 75% by volume, which is significantly wider than that of natural gas, (5% to 15%) (Fig. 1). As a result, hydrogen can more readily form flammable mixtures in air, heightening the risk of ignition upon release. Additionally, hydrogen ignites with just 0.017 millijoules (mJ) – far less than natural gas (0.290mJ). Even low-energy static sparks (0.5mJ) can trigger explosions. In 2019, a hydrogen tank explosion in South Korea was caused by ignition due to static electricity, as proper earthing connections were missing1.
Unlike most gases, hydrogen heats up, not cools, when expanding from high pressure (reverse Joule-Thomson effect), which can lead to spontaneous ignition.
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