Human Factors
Core concepts
Human factors is about performance and limitation. Know the SHELL model and the dirty dozen; the senses (vision, hearing, proprioception) and their limitations; memory (short and long term) and attention; information processing and decision making; stress, fatigue, circadian rhythm and sleep; motivation and peer pressure; teamwork, leadership and communication; and error models (slips, lapses, mistakes, violations). Understand the Swiss-cheese model and how defences fail.
Traps to watch
- Fatigue versus stress: both degrade performance, but fatigue accumulates over time and is worsened by circadian disruption.
- Complacency: familiarity reduces vigilance; it is a recognised hazard, not a personality flaw.
- Vision: night vision uses rods and is poor at colour discrimination; scanning off-centre improves detection at night.
- Hearing: noise-induced loss is typically gradual and unnoticed by the individual.
- Error classification: a slip is a correct intention executed wrongly; a mistake is a wrong intention. Questions test this distinction.
Worked example
A technician intending to fit the correct bolt (correct intention) fits a visually similar but wrong-length bolt (execution error) - a slip. If the technician reasons that the shorter bolt is acceptable without checking the manual, that is a mistake. The remedy differs: slips are reduced by checklists and physical constraints; mistakes by training and knowledge.
Rule of thumb
For any human-factors scenario, identify the error type first, then the defence that would have caught it. Answers that blame the individual rather than the system are usually wrong.