Hydrogen Safety and Quantitative Risk Assessment – Key Knowledge Sharing

Hydrogen has significantly different physical and chemical properties to conventional natural gas and other hydrocarbons. Hydrogen storage, distribution and applications pose unique challenges due to hydrogen’s wide flammable range, low minimum ignition energy, high buoyancy, wide range of explosion consequences, and its ability to embrittle metals. In addition, liquid hydrogen represents cryogenic hazards and challenges due to the low temperature it requires.

Hydrogen has a much lower density than natural gas so a H2 leak may disperse more rapidly than escaped natural gas. When released, the buoyancy of hydrogen enhances mixing with air and dilution, and this typically implies shorter dispersion distances (i.e., distance to flammable limits tends to be less in comparison to hydrocarbons).

Hydrogen explosions range from minor consequences to extreme outcomes for relatively small changes in ventilation, outflow rate, confinement, and congestion. Hydrogen detonations are entirely credible, even for small release scenarios, and are one of the worst-case events resulting from a H2 release. A detonation results in a shock wave that has great potential for causing personnel injury and/or property damage.

This paper provides an overview of hydrogen hazards and properties, focusing on dispersion and flammability (fires and explosions). In addition to a summary of a methodology to conduct H2 Quantitative Risk Assessment (QRA). H2 QRA methodology is similar to the one applied to hydrocarbons; however, some adjustments need to be performed, especially for estimating the leak frequency of release events. Nowadays, there is significant uncertainty to estimate the frequency of severe H2 explosions.

For hydrogen to gain broad acceptance and adoption, industry and regulators will need to establish robust safety standards and methods to quantify the risk associated with production, transportation, and usage cases, just as done for other potentially hazardous substances.