Abstract
In recent years, hydrogen use has dramatically increased, mainly due to its growth in status as a transportation fuel. A new wave of interest in hydrogen has also been generated by actions taken by the European Union regarding ecological transition, promoting “hydrogen valleys” for the local production and use of the so-called green hydrogen.
To achieve a safe and sustainable growth in the use of hydrogen as an alternative energy vector, every actor in the hydrogen value chain shall be aware of its inherent hazards, so that the appropriate preventive and protective measures required to mitigate the associated risks are enforced.
This article shall review the main physical properties of hydrogen, and how these relate to some safety challenges such as its low ignition energy and its unusually wide flammability range. Attention is given also to the high laminar burning velocity of hydrogen-air mixtures, and how this parameter influences the sizing of deflagration vents which shall be protected against confined cloud explosions. Hazards associated with handling of liquified hydrogen are discussed as well (such as the risk of cryogenic burns).
Facilities that produce or use hydrogen shall carry out robust hazard analyses, involving multidisciplinary teams, to consider what process deviations or failures may result in situations with intolerable risk. These situations must then be brought back to safety conditions through the implementation of specific safety barriers.
In the article, a HAZOP (Hazard and Operability) analysis is carried out on a typical electrolysis unit for hydrogen production, together with its hydrogen storage tank, identifying a number of potentially hazardous scenarios. For each scenario, the effectiveness of existing safety barriers is discussed, also with respect to international codes and engineering best practices, and additional preventive and protective measures are illustrated.
