A common misconception is that installing SIL certified equipment into an interlock circuit will provide automatic compliance with IEC 61511. Unfortunately it’s not that simple. Nor is there a tick-box checklist which can be easily followed.
Compliance with IEC 61511 is more about culture and commitment to process safety than merely installing SIL rated equipment.
IEC 61511, like its parent IEC 61508, is a risk based standard which allows a great deal of flexibility and judgement in its implementation. The engineer must use his/her judgement to satisfy himself, his client and the HSA, that the standard has been applied to a sufficient degree and with the necessary rigour.
Because IEC 61511 is not a prescriptive standard, compliance may not be the correct term.
It might be better to talk about adoption or implementation of the standard i.e. to use it as a guide to best practice to ensure functional safety .
It provides a ‘cradle to the grave’ solution to the management of the risk, from the initial identification of the hazard through to decommissioning, when the hazard is no longer present.
Steps to Compliance
| Predesign | Hazard Identification Risk Analysis Identify the required Safety Instrumented Functions (SIF) if any. Set Target SIL for each SIF (or interlock) |
| Design & Installation | Detailed specification for the Safety functions Detailed design of the Safety Instrumented System (SIS) , bearing in mind testing requirements. Installation and Commissioning. Validation |
| Operation and Maintenance | Documentation Testing Change control |
| Verification | Verification is the ongoing process to ensure that each of the phases above have been carried out in accordance with the requirements of IEC61511 |
