Negligible Extent classification and specific detailed risk assessment in a Hydrogen RefuellingStation (HRS) example

The MultHyFuel project aims to develop evidence-based and harmonised guidance for the safe deployment of Hydrogen Refuelling stations (HRS) in a multi-fuel context. In order to generate good practice guidelines, the project has developed risk assessments using three HRS configurations for the study and analysed the Hazardous Area Classification (HAC) for those examples. Firstly, the hazardous area classification has been analysed for a representative dispenser with operating pressures between

350 and 875 barg. The background concentration and release rate has been studied at different pressures and natural ventilation rates. The results suggest that Negligible Extent (NE) could not be applied for the dispenser example due to the operating pressures of that stage of the system. Although this classification would not apply for the dispenser, it has been anticipated that that NE classifications may be applied for other sections of the HRS, for instance, a hydrogen generator. Therefore, an example of the NE classification and specific detailed risk assessment requirement as per IEC 60079-10-1:2020 for an enclosure within a hydrogen generator is presented. Recommendations for the specific detailed risk assessment are proposed for this scenario with the intention to support improved definition of the requirement in IEC 60079-10-1:2020 for future revisions.