Establishing the State of the Art for the Definition of Safety Distances for Hydrogen Refuelling Stations

Hydrogen is widely considered a clean source of energy from the viewpoint of reduction in carbon dioxide emissions, as a countermeasure against global warming and air pollution. Various efforts have been made to develop hydrogen as a viable energy carrier, including the implementation of fuel cell vehicles (FCVs) and hydrogen refuelling stations (HRSs). A good network of hydrogen refuelling stations is essential for operating FCVs, and several hydrogen refuelling stations have been constructed and are in operation worldwide [1]. However, despite the potential benefits of hydrogen, its flammability creates significant safety concerns. Furthermore, even though the energy density of hydrogen is lower than that of gasoline and there is no carbon present, which means the amount of radiant heat flux released during combustion is relatively small, hydrogen must be handled at high pressure in order to make the cruising range of a fuel cell vehicle (FCV) equal to that of gasoline-powered vehicles. Therefore, it is essential to properly evaluate these safety concerns and take reasonable and effective countermeasures. Approximately 50 accidents and incidents involving HRSs have been reported globally [2]. Sakamoto et al. [2] analysed accidents and incidents at HRSs in Japan and the USA to identify the safety issues. Most types of accidents and incidents are small leakages of hydrogen, but some have led to serious consequences, such as fire and explosion. Recently, there was a serious incident in Norway at Kjørbo, where a strong explosion was observed [3] – indeed this was within a short time of two other serious incidents in the USA and South Korea showing that the frequency of such incidents may be higher as deployments increase. Use of hydrogen forklifts (and the associated refuelling infrastructure) is another challenge to consider. Hydrogen refuelling stations are often installed in urban areas facing roads and are readily accessible to everyone. Therefore, a key measure to approve the hydrogen refuelling stations is safety distances between the hydrogen infrastructure and the surrounding structures such as office buildings or residential dwellings. Whilst a lot of work has been carried out on safety distances (see e.g. [4-6), the accident scenario assumptions and safety distances varied widely in those studies. As a result, no consensus has yet emerged on the safety distances to be used and efforts are still needed to bridge the gap between international standards and local regulations (see e.g. [7-8]). The paper analyses this issue and provides guidance on the way forward.