This article deals with the assessment of Safety Instrumented Systems using intelligence in the field devices. The integration of intelligent instruments within safety oriented applications presents a challenge. The justification for using these instruments in safety applications is not fully proven and the dependability evaluation of such systems is not trivial. The work presented in this article deals with modeling in order to evaluate the performances relating to the dependability for structures which contains intelligent instruments. This architecture constitutes a Safety Instrumented System (SIS). In the modeling of the system, the functional and dysfunctional aspects coexist and the dynamic approach using the Stochastic Activity Network (SAN) is proposed to overcome the difficulties mentioned above. Monte-Carlo method is used to assess the dependability parameters in compliance with safety standards related to SIS (IEC 61508 & IEC 61511). The proposed method and associated tools allow this evaluation by simulation and thus provide assistance in designing SIS integrating intelligence.