An analysis of the risk of failure in the safety valve – tank with propane-butane (LPG) system has been conducted. An uncontrolled outfl ow of liquid LPG, caused by a failure of the above mentioned system has been considered as a threat. The main research goal of the study is the hazardous analysis of propanebutane gas outfl ow for the safety valve – LPG tank system. The additional goal is the development of an useful method to fast identify the hazard of a mismatched safety valve. The results of the research analysis have confi rmed that safety valves are basic protection of the installation (tank) against failures that can lead to loss of life, material damage and further undesired costs of their unreliability. That is why a new, professional computer program has been created that allows for the selection of safety valves or for the verifi cation of a safety valve selection in installations where any technical or technological changes have been made.