To develop safety strategies for the use of hydrogen indoors, the HyIndoor project is studying the behavior of a hydrogen release, deflagration or non-premixed flame in an enclosed space such as a fuel cell or its cabinet, a room, or a warehouse. The paper proposes a safety approach based on safety objectives that can be used to take various scenarios of hydrogen leaks into account for the safe design of Hydrogen and Fuel Cell (HFC) early market applications. Knowledge gaps on current engineering models and unknown influence of specific parameters were identified and prioritized, thereby re-focusing the objectives of the project test campaign and numerical simulations. This approach will enable the improvement of the specification of openings and use of hydrogen sensors for enclosed spaces. The results will be disseminated to all stakeholders, including hydrogen industry and RCS bodies. Keywords: hydrogen, leak, fire, safety strategy, safety objectives, space, dispersion, vented deflagration, flame, vent