Check Mate: A framework for optimising human-based checking

摘要

Across the high-hazard industries there is a reliance on effective human performance, particularly within complex sociotechnical systems. These systems will include a range of safeguards, both engineered and procedural, to defend against human or engineering failure. Such safeguards may be formally claimed as part of a safety case or safety justification, or serve as a defence-in-depth measure. A common procedural control that tends to recur throughout complex systems is human-based checking (HBC), usually in the form of two-person checks or independent checks. Confidence in these types of checks exists despite a lack of evidence supporting their efficacy. Nonetheless, HBC usually forms an integral role in supporting claimed overall system reliability. Whilst explicit claims can be made on the performance of specific checking tasks, there is an implicit requirement for a HBC regime to meet Human Factors relevant good practice, and deliver its intended function throughout the system. This function is to facilitate timely identification and rectification of human failures, in addition to avoiding routine challenge of engineered safety measures. Historically, the implicit requirement on HBC has not been subject to rigorous review, perhaps due to perceptions that HBC activities are prone to failure themselves, or mis-placed confidence exists in the perceived simplicity of HBC activities, and therefore, does not warrant detailed review. The concept that checking tasks are simple may influence management perceptions of the causes of failure, leading to a misplaced focus on competence or culture. In practice, it may be poor task design and/or ineffective implementation of management system arrangements that exacerbates instances of human failure. Failure to explore the impact of such arrangements on human performance, tailored with inadequate investigation mechanisms, may inadvertently reinforce perceptions that checking tasks are simple, when in fact, they are characteristically complex. Greenstreet Berman has supported a Periodic Safety Review for a UK Nuclear Licensee, which included review and substantiation of safety-critical HBC activities and the supporting HBC regime. Operational Experience data indicated that a large proportion of human failure was associated with HBC activities. Therefore, work was undertaken to better understand how workers conceptualise HBC, potential weaknesses with checking activities, and whether there were alternate approaches that would render more robust checking arrangements. As part of this work, a HBC framework has been developed to facilitate a systems approach to the optimisation of HBC activities and arrangements. The framework prompts consideration of the conceptual principles of HBC, in order to define reasonable and realistic HBC performance requirements. This then facilitates development of appropriate implementation strategies, which will enhance levels of human reliability. The framework aims not only to support the assessment of HBC arrangements by HF practitioners, but also to support system designers, engineers, and managers in understanding how to optimise human performance in relation to HBC activities and hence to achieve a balanced design that places reasonable and realistic claims on human performance. The purpose of this paper is to present an HBC framework that provides a systems approach to the implementation of HBC activities and serves as a valuable tool for the assessment of the suitability of HBC, and, importantly, supports effective integration of HBC into complex systems. It also supports communications regarding the significance of HBC in the delivery of safe and reliable operations.