From 2006 to 2009, INERIS alongside with CEA, PSA PEUGEOT CITRO?N and IRPHE were involved in a project called DRIVE. Its objective was to provide data on the whole reaction chain leading to a hydrogen hazard onboard a vehicle. Out of the three types of leakages identified by the consortium (permeation, chronic and accidental), the chronic leakage taking place within the engine was judged to be more problematic since it can feature a high probability of occurrence and a significant release flow rate (up to 100 NL/min). Ignition tests carried out within a real and dummy engine compartment showed that pressure effects due to an explosion will be relatively modest provided the averaged hydrogen concentration in this area is limited to 10 %2vol/vol, which would correspond to a maximum release flow of 10 NL/min. This maximum concentration could be used as a threshold value for detection or as a target while designing the vehicle. Jet fire experiments were also conducted in the frame of the DRIVE project. It was found that pressure-relief devices (PRDs) might be unsuited to protect humans from the explosion of a tank caused by a bonfire. Other solutions are proposed in this paper.