Safety integrity level operation phase

Safety instrumentation system (SIS) life cycle operation and maintenance (O M) phase details. SIF, safety instrument functions SIL, safety integrity level. 

The reliability performance of the SIS is referred to as safety integrity in the lEC-standards. This is the probability that the SIS satisfactorily performs the required SIFs, under stated conditions and for a stated period of time (lEC 61511 2003). In an early design phase, a hazards and risk analysis is performed to establish the required level of safety integrity of each SIF that is performed by the SIS, and in design and operation, it is necessary to demonstrate that this level of safety integrity is met. 

The computer system requirements define, as a minimum, the functional and non-functional properties of the computer system that are necessary and sufficient to meet the safety requirements for the plant that have been defined at a higher design level. The specification of computer system requirements is a representation of the necessary behaviour of the computer system. Precise defiiution of the interfaces to the operator, to the maintainer and to the external systems is an integral part of the product provided as the output of this phase. At this stage, the definition of interfaces is limited to the functional and non-functional properties of these interfaces then-design or implementation may be as yet undetermined. 

Pre-use Analysis When a site is considering new equipment, chemicals, facilities, or significantly different operations or procedures, the safety and health impact to the employees must be reviewed. The level of detail of the analysis should be commensurate with the perceived risk and number of employees affected. This practice should be integrated in the procurement/design phase to maximize the opportunity for proactive hazard controls. (Section 2.d)... 

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