Safety Requirements Specification

An important output from the Analysis phase of the SLC is the Safety Requirement Specification (SRS), which details the functional and integrity requirements of the safety systems. As per IEC 61511-1, the SRS shall be prepared prior to the detailed design and engineering of the SIFs and shall be the basis for the Stage 1 Functional Safety Audit (FSA). The SRS is often a contractual document (e.g. detailed design specification for EPC Contractor / System Integrator).

The SRS contains general requirements such as operating environment, application program and SIS architecture requirements, as well as detailed information for each SIF such as: risk reduction targets, trip settings, MTTR, Process Safety Times (PST) and operational requirements such as modes of operation, alarm system functionality, override requirements, etc. IEC 61511-1 §10.3.2 identifies 29 requirements for the SRS.

As an extension of HRA/SIL/LOPA services, PSC can provide an SRS template and populate it with the necessary information as required by IEC 61511. By using data-bank based software (such as ExSILentia), the SRS is fully integrated with Analysis phase studies and can be prepared in a timely and cost-effective way. If required, PSC can take ownership of the SRS and update it after the design and engineering phase with Vendor input and as required during O&M phase (e.g. after SIF modification, or based on operational statistics).

PSC can also provide support with the control and safety system design and preparation of operating/maintenance procedures, to ensure that these provide the required Layer of Protection to meet overall risk targets.