Programmable safety related systems in the gas industry

Real-time programmable electronic systems (PESs) are discussed and specific difficulties associated with their failure when used as safety systems are described. The Health and Safety Executive (HSE) guidance is summarised and the authors describe how the Institution of Gas Engineers (IGE) guidance document has been developed, taking account of British Gas experience, to provide application specific recommendations for the gas industry. The design cycle is outlined and some aspects of system configuration and fault tolerance are addressed. It is stressed that tolerance to faults, such that degraded performance rather than catastrophic failure ensues, is as important as the achievement of low error rates. The authors describe the way forward by way of formal and automated tools which are being developed. These include formal methods for writing requirements and automatic static analysers for the static verification of code