IEC 62508:2010 – Guidance on Human Aspects of Dependability

This article provides an in-depth technical analysis of IEC 62508:2010 – Guidance on Human Aspects of Dependability, offering practical engineering insights for professionals involved in design, testing, certification, and compliance. The standard addresses critical aspects of engineering practice and serves as an essential reference for industry professionals worldwide.

1. Scope and Framework

IEC 62508 provides guidance on incorporating human aspects into the dependability of systems. It recognizes that human performance is a critical factor in overall system reliability, availability, maintainability, and safety. The standard covers human characteristics, performance shaping factors (both external and internal), human reliability analysis (HRA) methods, and human-centred design processes.

The Human-Machine System model presented in the standard includes goals, humans, machines, social/physical environment, and feedback loops. Statistical data indicates that 60-90% of system failures can be attributed to human error, making human factors engineering essential for system dependability. The standard provides a structured approach to understanding how human performance influences overall system reliability and how to design systems that are resilient to human limitations.

2. Human Reliability Analysis Methods

The standard categorizes HRA methods into first-generation (Technique for Human Error Rate Prediction – THERP), second-generation (Cognitive Reliability and Error Analysis Method – CREAM, and A Technique for Human Event Analysis – ATHEANA), and third-generation approaches. The quantification of human error probabilities (HEP) requires consideration of performance shaping factors such as time pressure, training quality, procedural adequacy, ergonomic factors, and organizational culture.

Common Performance Conditions (CPCs) provide a framework for assessing the context of human actions. HRA methods differ in their approach: first-generation methods focus on observable behaviors and error rates, while second-generation methods account for cognitive processes, context, and performance shaping factors that influence human decision-making. HEP baselines vary significantly across industries and must be calibrated for specific application contexts using expert judgment, simulator studies, or historical data.

3. Integrating Human Factors into the System Lifecycle

Human-centred design is integrated across all system lifecycle stages: concept, development, production, operation, maintenance, and disposal. Specific activities include function allocation between human and machine, task analysis, interface design, and usability testing. The standard emphasizes that human-oriented design should start at the concept stage and continue iteratively throughout the lifecycle.

Case studies in the annexes demonstrate how human reliability improvements can significantly reduce overall system risk in critical applications such as nuclear power, aerospace, and process industries. The standard recommends systematic approaches including task analysis to identify potential errors, interface design guidelines to reduce confusion, and training programme development to address identified weaknesses. Performance shaping factors are multiplicative in their effect – combinations of poor factors can increase error rates by orders of magnitude.