Understanding safety integrity levels

Abstract

Modern software safety standards employ the concept of safety integrity levels (SIL). The SIL concept is presented as it is defined and used in the International Electrotechnical Commission's standard, IEC 61508, which is the best known and most influential safety standard for software-based systems. The SIL concept appears to offer simple rules for the development of safety-related systems. However, the rules are not so simple and may even be misleading. The SIL concept is only properly applicable in the context of safety, and it is inappropriate and dangerous to use it outside this context. It is as important to be aware of the dangers of the SIL concept as it is to understand its appropriate use.