Development of Functional Safety Arguments for Electronic and Programmable Electronic Systems in Accordance with IEC 61508

The current regulatory regime for the safety of operation and installation across a number of industries, requires that a safety case is produced to demonstrate that risks asociated with operating dangerous plant and machines are acceptable or at least tolerable.

This report provides guidance on producing safety arguments, in accordance with IEC 61508, for systems which contain electronic and programmable electronic components.

IEC 61508 is a complex draft standard parts of which are due to become Full Draft International Standard (FDIS) in 1998, but it contains little guidance on what form an overall argument for the adequacy of a safety-related system should take.

The report discusses the contents of safety arguments, the specific problems of programmable electronic systems, and standards and regulations.

There is also a short introduction to IEC61508. Based on a simplified version of the safety lifecycle in IEC 61508, a model is presented for the production of safety arguments.

The model can be refined for specific applications. More detailed guidance is given on individual elements of a safety argument including: safety management, derivation of safety requirements, requirements allocation and the system architecture, design and implementation of subsystems, operation and maintenance.

Much of the guidance is also applicable to arguments for electronic and programmable electronic systems which can affect the environment or have a high financial impact associated with their operation.

Appendices contain an overview of some of the sector standards which are based on the same principles of risk assessment and safety integrity levels as embodied in IEC 61508, and the contents of a safety case as presented in Railtrack ESM.

A companion report providing guidance on the performance of hazard analysis for electronic and programmable electronic systems (98-0127R) is also available.