The aim of this article is to carry out an assessment of the risks of fires and explosions in the field of hydrocarbons, which have harmful impacts on the safety of people, property and the environment, in the gas dehydration system at the Alrar gas complex in the STAH region of the SOUNATRACH Company. In order to control these risks, we used quantitative and semi-quantitative approaches to concretize the accident scenarios. Preliminary risk analysis (PRA) and overpressure risk analysis (APR) must be used in order to evaluate the thermal and overpressure effect distances of the hazardous phenomena based on the PHAST program. We were able to determine the dangerous phenomena that are likely to follow the occurrence of undesirable occurrences that are caused by a combination of system faults, drifts, or external attacks thanks to the preliminary risk analysis (PRA). We estimated the probabilities of occurrence of the central feared events and the probabilities of occurrence of their consequences