A method for determination of hazardous zones for hydrogen installations has been studied. This work has been carried out within the NoE HySafe. The method is based on the Italian Method outlined in Guide 31-30(2004), Guide 31-35 (2001), Guide 31-35/A (2001), and Guide 31-35/A; V1 (2003). Hazardous zones for a "generic hydrogen refuelling station" (HRS) are assessed, based on this method. The method is consistent with the EU directive 1999/92/EC "Safety and Health Protection of Workers potentially at risk from explosive atmospheres" which is the basis for determination of hazardous zones in Europe. This regulation is focused on protection of workers, and is relevant for hydrogen installations, such as hydrogen refuelling stations, repair shops and other stationary installations where some type of work operations will be involved. The method is also based on the IEC standard and European norm IEC/EN60079-10 "Electrical apparatus for explosive gas atmospheres. Part 10 Classification of hazardous areas". This is a widely acknowledged international standard/norm and it is accepted/approved by Fire and Safety Authorities in Europe and also internationally. Results from the HySafe work and other studies relevant for hydrogen and hydrogen installations have been included in the case study. Sensitivity studies have been carried out to examine the effect of varying equipment failure frequencies and leak sizes, as well as environmental condition (ventilation, obstacles, etc.). The discharge and gas dispersion calculations in the Italian Method are based on simple mathematical formulas. However, in this work also CFD (Computational Fluid Dynamics) and other simpler numerical tools have been used to quantitatively estimate the effect of ventilation and of different release locations on the size of the flammable gas cloud. Concentration limits for hydrogen to be used as basis for the extent of the hazardous zones in different situations are discussed.