In the risk assessment process (RAP), the need to obtain reliable decision is imposed on risk analysts for reducing these risks. This decision can be obtained through different tools and methods using sources such as, databases, expert’s knowledge...etc. In this context; expert knowledge plays a crucial role supplying the process by estimated data of events and safety barriers failures. In fact, the resort to this source is often advisable to support decision-making as regards Safety Barriers performance. When we need to consult risk assessment experts, we can obtain a different expert opinions, the aggregation of their opinions is required using specified methods according to the expert opinions. Using these methods, the analysts are able to combine these judgments in order to make better evaluation/decision about performance of safety barriers.  In this paper we have attempted to show how the decision maker can assess the safety barriers performance by aggregating Expert Knowledge in the Framework of BORA Approach. Finally, the proposed methodology is applied to case study on an operational process, a combustible gas balloon (G01-VN-45-01) within the unit of gas treatment (UTGA), Sonatrach, Algeria).