Practical SIL Calculation

Abstract

Each safety-critical system which is addressed with the provisions of functional safety usually contains a safety-related system (SRS) implementing a variety of safety functions that can bring the system to the safe state in case of any malfunction. Hazard and risk assessment yields scores which are then transferred to the safety integrity requirement of the safety functions, which need to be compliant with this requirement in terms of their definition, design, implementation, and verification standpoints. In this chapter, an exemplary process commenced in Chap. 6 is finalized concerning the requirements of functional safety for machinery, having in mind standards IEC 62061 and ISO 13849. Each safety function is assessed according to its relevant metrics, such as mean time to failure/failure rate, diagnostic coverage and hardware fault tolerance (redundancy) configurations, and final safety integrity level calculated and evaluated with the initial requirement to decide if the implementation is compliant with the safety prescriptions.