Safety Integrity Assessment of Programmable Electronic Systems

Abstract As Programmable Electronic Systems (PES’s) are introduced into the industrial environment to control or monitor possibly hazardous processes, the question arises of whether the safety integrity of such systems is adequate for a particular application. The detailed operation of many of these systems is complex and is rarely fully understood by, or even made known to, the user. This leads to a certain amount of disquiet in some applications where a hazard is possible if the PES malfunctions in a particular way, perhaps by a particular failure mode or by aberrant behaviour. A natural reaction of the user is to ask whether a particular system will be as safe as the equivalent conventional control system with which he may be more familiar. Unfortunately there are many difficulties in applying the same safety assessment techniques to PES’s as have been applied in the past to conventional systems. This paper discusses these problems and outlines an assessment methodology which is being developed to enable the user or the Inspectorate to determine whether or not a PES installation is of a suitably high safety integrity for the application.