![]() ![]() In these cases, the failure rate is measured by the average probability of failure on demand (PFD Avg). Low Demand Mode: The demand rate of the safety system is less frequent than once per year.The SIL value for the safety system is determined by comparing the required probability of failure to the international standards of functional safety, defined in IEC 61508 and IEC 61511.īased on the demand rate of the safety system, the SIL standards are classified into the following two types: The required probability of failure is a number representing the probability that a safety system will fail in a dangerous scenario. The LOPA process uses information such as initiating event frequencies, the probabilities of failures of all safeguards, and the tolerable frequency of risk mitigation to determine the required probability of failure of the safety system. LOPA is a quantitative method for determining the SIL level for the safety system. ![]() It is the measurement of performance of a safety system under all the stated conditions within a stated period of time. The SIL value is a measure of the reliability and availability of a safety system. ![]()
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