Fatigue, Stress, Workload, and Shift Work
Core concepts
Fatigue degrades vigilance, reaction time, and judgement, and increases variability. Know circadian rhythm effects, the post-lunch dip, and the circadian low in early morning hours, when error risk peaks. Understand sleep debt and sleep inertia after waking. Shift work creates risks from rotating schedules, insufficient rest, and long shifts; countermeasures include strategic napping, controlled lighting, and fatigue-risk management systems.
Workload is the relationship between task demand and operator capacity. Distinguish underload (boredom, vigilance failure) from overload (tunnel vision, shedding of secondary tasks). Stress can be acute (emergency) or chronic (organisational); moderate stress aids performance, excessive stress impairs it (Yerkes-Dodson). Recognise startle and freeze responses and cognitive tunnelling.
Traps in questions
- Assuming fatigue is cured by caffeine rather than sleep.
- Treating night-shift risk as uniform across the shift; the early-morning low is worst.
- Confusing workload with task quantity; it depends on capacity and complexity.
- Assuming low workload is safe; underload impairs monitoring.
- Forgetting that stress narrows attention and can cause premature closure.
Worked rule of thumb
Use the demand-capacity balance check: estimate demand (tasks, complexity, time pressure) against capacity (staffing, experience, fatigue, stress). If demand exceeds capacity, reduce demand or add resources before continuing. Example: during a complex transient at 04:00 with a short-staffed crew, call for additional support early rather than relying on heroic effort, because fatigue and overload compound error risk.