IEC 61508 and IEC 61511 assessments - some lessons learned

In recent years we have conducted about 25 assessments using IEC 61508 or IEC 61511, working mainly to Safety Integrity Level (SIL) 2, but on some occasions to SIL 3. In this paper we present some of the lessons we have learned and offer advice to those seeking certification for components, systems or generic process capability. We cover the three main parts of the IEC 61508 standard: Functional Safety (FS) Management; Hardware; Software. More recently, our work has included software products whose assessment has entailed building complex arguments for their compliance. This has led us to use argument structuring techniques that we comment on at the end of this paper.