COTS in Safety-Related Systems Issues and an Illustration

Abstract

This paper discusses the use of COTS software products for a safety-related system. A real example is described of 4GL application software for an airport baggage handling system (BHS). For the example a methodology, loosely based on IEC 61508 [IEC97] was mandated and all software was categorised as Developed, Customised, or Standard and Non-Essential, Essential or Safety-Related. A standard bag of techniques was then specified for the differing categories of risk defined by the resulting likelihood/consequence matrix. The example demonstrates the applicaton of the ALARP principle to ensure that the acceptance of the risk associated with the system is justifiable. Because of it’s lack of susceptibility to assessment there is often greater risk associated with using COTS software. The ALARP principle is a practical approach to the problem of assessing this risk.