Risk assessment that usually is applied to identify, control and reduce the hazardous consequences, is the main stage of risk management and for doings it, different methods in different area has been introduced and applied well. Researchers in the field, have categorized risk assessment approaches into two approaches deterministic and probabilistic. Nevertheless, our reviews indicate that many of risk assessment methods have been introduced and applied by researchers as a probabilistic method, while, others just called those method in a deterministic type. In this paper, FMEA which is a well known risk assessment method in the area of industrial processes, has been studied and investigated sense of belonging to both the deterministic and probabilistic class. Finally, an empirical study has done in the area of gas industry, which demonstrates the importance of two approaches in risk assessment of this area. Empirical results show that, the results of probabilistic approach are more reliable than deterministic approach.