Avoiding SIL Misconceptions

Engineers must refine their foundational understanding of process safety in order to avoid common misconceptions about safety instrumented systems, including safety integrity level (SIL) definitions Learnings from major industrial process accidents occurring over the past half century have driven awareness of functional safety and resulted in the development of two performance-based standards for manufacturers in the chemical process industries (CPI). These standards, introduced by the International Electrotechnical Commission (IEC; Geneva, Switzerland; www.iec.ch), are known as IEC 61508 and 61511. A safety integrity level (SIL) is utilized as a measurement of required risk-reduction targets, as well as a way to represent achieved risk reduction. Although the functional safety standards have been in existence for many years, there are many common misconceptions around industry standards, as well as around the concept of SILs themselves.   Introduction to functional safety Safety, in its most basic form, can be defined as freedom from unacceptable risk. Risk is a function of the likelihood of an incident occurring combined with its resulting consequence — specifically, a personal injury, loss of life or damage to the environment…