Glossary

Definitions are provided for educational clarity. Official definitions in standards, contracts, or regulations may differ.

Circadian rhythm

The internal biological cycle that regulates sleep and alertness over roughly 24 hours. Work against this cycle — particularly night shifts — increases fatigue risk.

Fatigue

A state of reduced mental or physical performance resulting from factors including sleep loss, extended wakefulness, circadian disruption, and workload.

Fatigue risk assessment

A structured process to identify fatigue-related hazards, evaluate controls, and define further actions. See the fatigue risk assessment guide.

Fatigue risk index (FRI)

A scoring method for estimating fatigue exposure associated with a roster or shift pattern. See fatigue risk index (FRI).

Fatigue risk management system (FRMS)

A documented, risk-based system for managing fatigue across an organisation. See FRMS guide.

Forward rotation

A shift rotation pattern that moves from morning to afternoon to night shifts. Often preferred to backward (rapid reverse) rotation for circadian adaptation.

Quick return

A short rest period between the end of one shift and the start of the next — typically fewer than 11 hours, though local definitions vary.

Safety-critical work

Work where fatigue-related error could directly lead to serious harm — common in transport, healthcare, and process industries.

Shift work

Any work schedule outside a standard daytime pattern, including rotating, permanent night, and extended shifts. See shift work fatigue.

Further research

Additional terms (e.g. bio-compatibility, WOCL — window of circadian low) will be added with source-aligned definitions.