Malcolm Cook, BAE Systems
Complexity in system design represents the most problematic aspect of systems engineering for the human factors discipline. Complexity can be an issue of system size because as system size increases analytic engineering approaches break the total system into components, or sub-systems, losing sight of transverse issues. Thus, size naturally encourages a system of systems approach to very complex designs.
Transverse functional pathways through such systems are one of the most difficult aspects of the early design process for complex systems and they represent one of the main vulnerabilities of such a system. Thus, if one considers the top level functional failures that compromise system safety or capability these invariably occur when the contextual events find a path through the system where gaps in capability exist or latent faults are present. Faults within sub-systems may not appear critical because their contribution to the system and emergent functions within the entire system are not visible. Thus, consequence driven analysis, derived from Hazard Identification, is less effective than performance driven analysis aimed at optimising functions. Early in design the difficulty with a human factors evaluation of such sub-systems is impeded by diversity of sub-system maturity. Thus, constructing early assurances and guiding the focus of human reliability assessments is unlikely to capture all significant human error events and their contribution to compromised safety or system function.
This paper explores the difficulties experienced in applying early application of HRA using qualitative and quantitative methods and proposes solutions to the difficulties that occur.