A CLASSIFICATION SCHEME FOR PIPEWORK FAILURES TO INCLUDE HUMAN AND SOCIOTECHNICAL ERRORS AND THEIR CONTRIBUTION TO PIPEWORK FAILURE FREQUENCIES

This paper analyses the contribution of human error and sociotechnical failures to pipework failure frequencies. A failure classification scheme has been developed and used to analyse about 500 reported incidents involving failures of fixed pipework on chemical and major hazard plant. An important objective of the classification scheme was to make a distinction between human error as a direct or immediate cause of failure and failures of the sociotechnical system which can be either the underlying origin of the failure or a failure of a potential preventive mechanism. This has led to the development of a three dimensional classification scheme by which the 500 accidents are analysed. Results are presented for the percentage contributions of different direct (or immediate) causes, origins of failure (underlying cause) and failures of preventive mechanisms. The results are also presented in a matrix form by which the importance of specific recovery mechanisms applied to certain types of failure can be identified. The work shows that about 90% of the analysed incidents could have potentially been prevented by suitable preventive mechanisms which in theory are within the scope of management control. In addition a hierarchical scheme of accident causation is considered in which the direct cause of the accident is the carrier or symptom of underlying problems in the sociotechnical system. The implications of the classification schemes are considered with respect to the contributions which compose the generic failure rates which are used in the calculation of risk for major hazard plant.