Temporal conditions of work environments — practice questions

Circadian rhythm: Core body temperature and alertness dip at night — performance on monitoring tasks falls in the 02:00–04:00 window (circadian trough), increasing human error risk.

Shift work: Rotating shifts prevent full adaptation — workers remain desynchronised from natural sleep-wake cycle, causing fatigue and microsleeps.

Safety (Reason's Swiss cheese): Fatigue is one hole aligning with procedure lapses and equipment complexity → accidents (see 4.4.3).

Flexitime for day staff: Separate issue from nights but improves day-worker satisfaction (JCM autonomy) without fixing night errors — need scheduled breaks, light exposure, limit consecutive nights.

Evaluation: Chronotype means some 'owls' cope better on nights but most do not. Economic cost of shift premiums vs accident cost must be weighed. Flexitime fairness argument is weak — different roles have different temporal demands.

Step 1: Calculate Predicted Accidents

• Current accidents = 30
• Predicted reduction = 35% = 0.35
• Reduction in accidents = 30 * 0.35 = 10.5
• Predicted new total accidents = 30 - 10.5 = 19.5 accidents (or approximately 19-20 accidents).

Step 2: Calculate Predicted Sick Days

• Current sick days = 920
• Predicted reduction = 20% = 0.20
• Reduction in sick days = 920 * 0.20 = 184
• Predicted new total sick days = 920 - 184 = 736 sick days.

Step 3: Psychological Rationale

• The current backward-rotating system (e.g., nights → evenings → days) works against the body's natural circadian rhythm, which tends to phase-delay (drift later). This causes significant desynchronisation, leading to chronic fatigue, poor sleep quality, and increased stress, contributing to both accidents (impaired cognitive function) and sickness absence (weakened immune system).
• The proposed forward-rotating system (days → evenings → nights) is less disruptive as it aligns better with the natural phase-delay of the circadian rhythm, making it easier for the body to adjust between shifts.
• The rapid rotation (e.g., changing every 2-3 days) prevents the body clock from attempting a full, but ultimately unsuccessful, adaptation to the night shift. This reduces the cumulative fatigue associated with slow rotation, leading to better alertness, fewer errors (accidents), and improved overall health (reduced absenteeism).