الفهرس 
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Abstract
Recently there has been a growing interest in safety instrumented system (SIS) design due to catastrophic accidents occurred at Oil and Gas industry during the second half of past century [31].
SIS is a static safety system independent of the dynamic process control system [61]. The only function of SIS is safety; no process control is performed by this system. SIS continuously monitors the process parameters and take the necessary action to put the process back to safe state in case of any abnormal deviation occurred. SIS consists of number of safety instrumented functions (SIFs). Each SIF protects against process related hazard and contributes to reduce the overall risk. Each SIF has an associated Safety Integrity Level (SIL) defines the boundaries of risk reduction factor (RRF) must be achieved by the corresponding SIF [34].
Target SIL determination for SIS greatly affect the SIS design [40]. Target SIL over estimation increases the cost meanwhile SIL underestimation increases risk. Also, Target SIL for each SIF must be verified to demonstrate, for each phase of the overall SIS lifecycles, that SIF is able to perform its function and can achieve its associated target RRF [34]. So target SIL determination and verification considered the key parameters for safety instrumented system design.
This research details the limitations, drawbacks and uncertainty associated with conventional SIL determination methods and conventional SIL verification methods and introduces a new design approach that can achieve highest safety with minimum cost through:
• Modeling conventional Risk Graph (RG) SIL determination method by employing three Artificial Intelligent (AI) techniques.
• Developing the conventional Probability of Failure on Demand PFD analytical formula for SIL verification to include all variables that can affect the ability of SIS to achieve the target SIL.
•Modeling the new developed formula by using Genetic Algorithm (GA) Intelligent technique to optimize the values of each variable of the PFD formula.