The aim of the study is to identify and quantify the additional risks related to hydrogen explosions during the operation of a hydrogen driven car. In a first attempt the accidents or failures of a simple one-tank hydrogen storage system has been studied as a main source of risk. Three types of initiators are taken into account: crash accidents, fire accidents without crash (no other cars are involved) and hydrogen leakages in normal situation with following ignition. The consequences of hydrogen ignition and/or explosion depend strongly on environmental conditions (geometry, wind, etc.), therefore the different configurations of operational and environmental conditions are specified.Then Event Tree / Fault Tree methods are applied for the risk assessment.The results of quantification permit to draw conclusions about the overall added risk of hydrogen technology as well as about the main contributors to the risk. Results of this work will eventually contribute to the on-going pre-normative research in the field of hydrogen safety.