Safety Instrumented Systems

Operating companies are legally obliged to ensure safety in the workplace. Risk reduction measures have to be put in place and managed through a safety management system. A safety case justifying the risk management position must be completed for inspection by the regulatory authorities.

Safety instrumented systems must be seen to be capable of providing the level of safety improvement that is claimed in the safety case.

Conformity to IEC 61508 or IEC 61511 is a very effective way to demonstrate that the safety instrumented protection measures are able to provide the claimed reduction in risk.

IEC 61508 is a generic standard for functional safety using electronic and programmable electronic equipment. IEC 61511 is the standard for functional safety systems within the process industry sector.

The standard emphasises the life cycle approach to the overall safety system. It includes all project stages from initial concepts and hazard studies through to operation, maintenance and modification. Safety Instrumented System design requirements and safety integrity level (SIL) analysis are also covered.

The discipline that is required for SIL targeting improves management of safety as it defines the risk and the tolerable risk policy.