Object oriented design of safety critical programmable equipment systems

Purpose: The purpose of this study is to provide a method for designing the software for a process control system that avoids difficulties that lead to safety problems. Design/methodology/approach: Design of real-time software for safety critical programmable equipment systems (PES) such as process control or shutdown systems needs to be approached quite differently compared to any other software. It must be designed by those who understand the equipment system not by software engineers who do not. Following the ‘Piper Alpha’ disaster in the North Sea in the late 1980s, it was realised that the software of safety critical PES, such as the shut-down system on an oil rig, was proving very unreliable. Earlier hardwired relay-based shut-down systems were designed by process control engineers who understood the functions the equipment was required to perform; however, by the 1980s, such systems had been replaced by PES designed by system analysts who did not understand the technologies involved. The safety critical real-time software for a programmable equipment system will only be reliable when it is designed by control engineers who understand the functions it has to perform. Findings: Bottom-up design of software is necessary to avoid safety issues and this can only be achieved using object-oriented methods. Originality/value: This paper describes an entirely original idea of the author based on experience of managing the design and construction of the process control, emergency shut-down and fire and gas and communication systems for a major oil and gas platform in the North Sea around the time of the Piper Alpha disaster.