After the safety system has been designed and each SIF configured, but before any safety functions are implemented, the performance requirements of the safety functions must be verified against the requirements as documented in the Safety Requirement Specification.
For SIS, this involves splitting a safety function into three subsystems – the sensor subsystem, the logic solver subsystem, and the final element subsystem. Each subsystem is then evaluated using the failure mode and failure rate data for the subsystem components, the proof test interval, the diagnostic coverage factor, and the common cause (Beta) factor (if required). What results is a value for the average probability of Failure on demand (PFDavg) which is directly related to the Safety Integrity Level (SIL); and the determination whether the architectural constraints for a particular SIL have been met, based on the hardware fault tolerance (redundancy) and safe failure fraction (diagnostic coverage).
Elite Technical Consulting’s consultants have the necessary experience to take what is a relatively complex process and use certified safety performance modelling tools to provide an independent probabilistic safety and reliability analysis of Each safety function; and deliver a comprehensive report detailing every aspect of the Verification. Our Reliability Engineers have experience of modelling complex safety functions such as Subsea HIPPS Functions using Fault Trees.