Hydrogen infrastructure - efficient risk assessment and design optimization approach

With the ambition to cut emissions from transport hydrogen fuelled vehicles and marine vessels are now being introduced several places in the society. To support this development there is a need for infrastructure to produce and transport gaseous and liquid hydrogen. The properties and safety challenges related to the use of hydrogen are very different from those of conventional fuels, thus safe design solutions may require unconventional solutions. Hydrogen has extreme properties in many ways. It is buoyant when in gas phase while a liquid hydrogen spray will develop a dense plume. The reactivity is higher, flammable range wider and the ignition energy lower than for conventional fuels. Flames may be invisible and radiation is low. When performing risk assessments for land planning purposes, bunkering assessments or passenger and crew safety these aspects must be reflected. Properties like the positive buoyancy, strong dilution for sonic releases into air, and a low reactivity and energy content for concentrations below 10% must be exploited during design to ensure acceptable risk levels. In this article a two level risk assessment and design assistance approach is presented in which risk screening with rapid consequence calculations and frequency assessments for release, dispersion, fire and explosion are performed during design review with indicative hazard distances estimated. Possible risks of concern are in this way identified, and design can be adjusted or mitigation measures introduced. When required more accurate CFD calculations are thereafter performed for more precise consequence estimates. The risk assessment approach will be described with examples illustrating the approach.