(104ay) Safety and Safety-Instrumented System (SIS)

Although SIS & its related standards (ISA S84.01, IEC 61508 & IEC 61511) are quite commonly referred to in project specifications and company standards, but the correct understanding for their application throughout the safety lifecycle is rarely correctly understood. Even that the industry standards related to SIS have been matured but there is a lack of understanding on their practical implementation. What are the benefits we can get by correct implementation of IEC 61511 on Greenfield projects and especially on industries built during pre IEC 61511 era since that is the sector specifically being neglected?

Different methods being used for SIL selection and their merits/de-merits would be discussed in brief for Greenfield projects. Although availability of software tools have made calculations related to SIS (SIL Selection/Determination and SIL verification) much easier but is this taking away the skills and understanding away from the users? Are we getting more information while the knowledge is being reduced? Correct knowledge of functional safety along with process under review is the key for correct and optimal risk reduction without sacrificing safety as a result of under engineered SIS or inducing high capital and operating/maintenance cost as a result of over engineered SIS.  Proper planning, required procedures, IEC 61511 compliant management systems for maintenance & proof testing for achieving such implementation are equally important in order to achieve the required risk reduction often forgotten after the facility/project handover.

This paper will give an overview of safety lifecycle as per IEC 61511 explaining the generally misunderstood parts emphasizing on validation of SIS at different stages as required by IEC 61511 and often neglected parts of the standard and the key steps to ensure compliance based on authors experiences of SIL selection & Verification on Greenfield projects while working with EPC company and implementation of IEC 61511 on operating facility while working with the facility operator.