FAI Spring 2023 Process Safety News.ai

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Hydrogen Properties & Potential Hazards Hydrogen has many properties that make it attractive as a source of energy, and many of which are inherently safe features, however there are potential hazards associated with any fuel source. Here are some of hydrogen’s properties, and how they might relate to potential hazards to consider depending on the application: ▪ Hydrogen is a colorless, odorless, and tasteless non-toxic gas typically in the form of a diatomic molecule (H 2 ). While rare, hydrogen is a potential asphyxiation hazard in confined spaces. In addition to the gaseous form, hydrogen flames are also nearly colorless, and the low radiant heat and low emissivity of the flame can make it difficult for early identification. ▪ Hydrogen is non-corrosive, however it can cause embrittlement leading to unexpected failures or leaks. Properly selected materials and system layout, periodic visual checks, adequate passive or active ventilation systems, and safety systems (e.g. leak or hydrogen detection sensors) are important aspects of a safe design. ▪ Hydrogen has excellent energy density, however its vapor density is incredibly low (around 1/15 th of air). This is excellent when considering the dissipation of a buoyant vapor cloud following a leak, however this can make it difficult to store large quantities of hydrogen. In the gaseous form, high pressure vessels can be employed. Alternatively, hydrogen can be compressed, and stored at cryogenic conditions. Both options should be considered for potential overpressure hazards, and unignited releases (e.g. loss of temperature control in cryogenic storage or fire exposure in gaseous storage, both of which can lead to rapid pressurization and a loss of containment).

▪ Hydrogen has a very large flammable range (typically considered 4% to 75% by volume in air) and a very high burning velocity when compared to other typical fuel types. This increases the likelihood and potential consequences of combustion (via fire or explosion). Despite hydrogens propensity to diffuse quickly in air, high-pressure leaks can lead to unconfined jet fires or explosions, and the low minimum ignition energy of hydrogen makes it difficult to eliminate all potential ignition sources. Confined vapor cloud explosions (i.e. deflagrations or deflagrations that transition to detonations) are also a hazard to consider with potentially severe consequences. Proper siting and barriers can help to protect against this hazard.

Expansion of Initially Choked Jet and Entrainment after Depressurization

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