Proton exchange membrane fuel cells (PEMFC) system is considered as a solution for electric vehicle autonomy. Hydrogen must be mastered to preserve safety. The risk associated with hydrogen is a consequence of these properties. This study proposes a model of explosion for reliability analysis by fault trees. Details of the PEMFC system architecture are taken into account. The data used are from professional database. Adaptation of these data is proposed to reflect the actual conditions of use of a PEMFC system and a model of degradation mechanism which is realistic. The probability calculation is performed in relation to a reference time of use. The probability of explosion of the system is thus evaluated and critical failure sequences are identified. For these minimum critical cut that are dependent on degradation due to the use of the system, inverse calculation are proposed to define the targets of the design by reliability. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.