SIL Implementation on Safety Functions in Mass Transit System

The concept of Safety Integrity Level (SIL) has been developed within different systems of standards (IEC 61508, EN50129 and DEF-STAN 00-56). These standards are applied in different areas: control technology (IEC 61508), railway technology (EN50128 and EN 50129), and defense technology (DEF-STAN-00-56). Nowadays, a lot of the mass transit turnkey projects around the world demand the contractors to follow CENELEC standards and SIL concept for the safety function implementation. Although the concept of SIL is mentioned in these standards, the interpretation of the concept of SIL in these standards is not consistent and unequivocal. This paper is written to elaborate the anomalies of SIL interpretation among these various standards in order for safety engineers to obtain a more detailed view on the concept of SIL over these standards.