The assessment of PESs in safety related applications: an update

A number of assessments of major industrial installations incorporating programmable electronic systems (PES) have been carried out in recent years, some of these being on PESs which were used in safety related applications. This paper identifies the reasons why the author believes that the assessment of PESs is essential in safety related applications. Three methods of assessment are identified, test by demonstration, test by inspection and test by analysis, and practical techniques in use at ERA are described. The considerations which should be made when planning an assessment are discussed based on the experience gained