Rotation Analytics
Clarity from Complexity.
Fatigue Risk Analysis
A schedule can be fully compliant and still produce a fatigued worker. This analysis identifies where and when that happens.
What This Analysis Answers
Collective agreement compliance tells you whether a schedule follows the rules. Fatigue risk analysis tells you what that schedule actually does to the worker’s body.
This is a science-based fatigue risk assessment for every rotation line in the schedule. The model runs continuously across the entire rotation, including days off, to track each worker’s physiological state without interruption. The result is a fatigue score for every day of the rotation, risk classification for every line, and a clear picture of where the schedule creates risk that manual review cannot detect.
Compliant ≠ Safe
A rotation can satisfy every collective agreement provision and still produce a worker operating at fatigue levels comparable to those documented in occupational health literature.
Fatigue Is Measurable
Fatigue is not a feeling. It is a physiological state driven by sleep pressure and circadian rhythm. These are predictable, quantifiable, and specific to the schedule.
Full Rotation Visibility
A single shift may appear acceptable in isolation. The cumulative effect of consecutive short-rest periods, night shift blocks, and compressed recovery windows only becomes visible when the entire rotation is modelled end-to-end.
How the Fatigue Score Is Calculated
The fatigue score is produced by a biomathematical model that simulates three physiological processes operating inside the human body. The model runs a 15-minute step simulation continuously across every day in the rotation to track the worker’s physiological state.
Sleep Pressure
The longer a person is awake, the more their body builds pressure to sleep. This is a real neurochemical process. Sleep pressure builds exponentially during every hour awake (time constant of 18.2 hours) and dissipates during sleep in two phases: rapid initial recovery followed by slower deep-sleep recovery. A worker who gets shortened sleep carries a residual load into their next shift.
Contributes the largest component of the fatigue score. Peak sleep pressure during the shift is converted to a 0–100 base score.
Circadian Rhythm
The human body runs on an internal 24-hour clock that governs alertness independently of how much sleep a person has had. Even a fully rested worker experiences reduced alertness in the early morning hours (trough at approximately 04:48). Alertness peaks in the late afternoon (approximately 16:48). This cycle runs continuously regardless of sleep history.
Night shifts (23:00–07:00) receive a circadian penalty of approximately +7 points. Evening shifts receive a benefit of approximately −7 points.
Sleep Debt
When actual sleep falls short of the 8-hour daily requirement, the deficit accumulates as sleep debt. When sleep exceeds the requirement, debt recovers at 50% efficiency, reflecting that recovery sleep is less efficient than preventive sleep. This captures the compounding effect of consecutive short-rest shifts.
Adds 0.5 points per hour of accumulated debt.
The Fatigue Score
The three components combine into a single score on a 0–100 scale:
Fatigue Score = Sleep Pressure Base + Circadian Modifier + Sleep Debt Modifier
Sleep Pressure Base is the peak homeostatic value during the shift, scaled to 0–100. The Circadian Modifier is the average circadian effect across the shift, weighted by a factor of 25 (approximately −7 for evening shifts to +7 for night shifts). The Sleep Debt Modifier adds 0.5 points per hour of accumulated deficit. The score is bounded to 0–100.
Sleep Prediction and Recovery
The model does not assume workers sleep a fixed number of hours between shifts. Instead, it predicts when sleep actually occurs based on the worker’s physiological state. Sleep pressure, circadian phase, and shift timing determine when and how long the worker sleeps.
Sleep onset occurs when predicted alertness falls below a threshold, and waking occurs when alertness recovers above a higher threshold. A circadian sleep gate between 22:00 and 06:00 facilitates nighttime sleep. Daytime sleep is capped at 5.5 hours per calendar day, consistent with published research showing that night-shift workers obtain significantly less restorative sleep when sleeping during biological daytime.
Sleep Debt
When actual sleep falls short of the 8-hour daily requirement, the deficit accumulates. When sleep exceeds the requirement, debt recovers at 50% efficiency, reflecting that recovery sleep is less efficient than preventive sleep. This captures the compounding effect of consecutive short-rest shifts.
Days Off
Unlike analyses that only score worked shifts, this model simulates physiology through every day of the rotation, including days off. Recovery is visible in the data, and the worker’s state entering their next shift block is accurately carried forward rather than artificially reset.
First Night in Run
The first night shift after day shifts or days off carries the highest fatigue risk. Workers have typically been awake since their normal morning wake time and have not adapted their sleep schedule to night work. The model suppresses pre-shift sleep to reflect this, producing appropriately elevated fatigue scores for transitional night shifts.
Risk Classification
Fatigue scores are classified into five risk levels. These classifications appear in the deliverable alongside compliance findings, giving the Client a complete picture of scheduling risk.
Low
Score 0 – 44
Worker is operating within optimal physiological parameters for a standard shift.
Moderate
Score 45 – 59
Slightly elevated fatigue. Typical of evening shifts and consecutive day shifts with mildly shortened sleep. Performance may be subtly degraded. This is the expected baseline result for shift workers.
High
Score 60 – 74
Significant fatigue. Typical of night shifts and extended shifts, where the circadian trough compounds sleep pressure. Meaningful degradation in reaction time and decision-making expected.
Very High
Score 75 – 84
High fatigue consistent with extended 12-hour night shifts and consecutive night shift blocks. The circadian trough and cumulative sleep restriction compound to produce sustained performance impairment.
Critical
Score 85 – 100
Severe fatigue. Occurs with extended wakefulness, deep circadian trough, and compounding sleep debt. Performance impairment is comparable to levels documented in occupational health fatigue literature. Immediate schedule review required.
Sample Fatigue Report
The report below is representative of an actual Fatigue Risk Analysis deliverable. Each row represents a rotation line. The trend column traces the fatigue score across every day of the rotation, both worked days and days off, showing the full recovery and fatigue cycle. The days-in-risk-band columns show how many days each worker spends at each risk level across the full rotation, capturing the cumulative exposure profile.
Sample Fatigue Risk Analysis Report
Excel Spreadsheet, Biomathematical Analysis
All sparklines use a 25–100 vertical scale to show meaningful detail. 25 represents baseline, with the worker well rested on days off. Lines with visibly higher peaks carry more fatigue risk, even if both are classified at the same average risk level. The deliverable includes the full per-line breakdown, trend visualisations, and the methodology explanation.
Included With Any Compliance Engagement
Fatigue risk analysis can be elected alongside any compliance engagement. A single rotation submission flows through both the compliance engine and the fatigue model, delivering the most complete rotation risk assessment available.
See the full engagement pathway →Scientific Foundation
The fatigue model is built on the Three-Process Model published by Åkerstedt and Folkard (1987, revised through 2008), the most widely validated biomathematical model for shift work fatigue in the occupational health literature. Its parameters have been calibrated against expected fatigue outcomes for common shift patterns, including healthcare and industrial settings.
This analysis models a representative worker based on established physiological parameters. It does not account for individual variation in sleep patterns, age, chronotype, or health status. The fatigue scores represent what a typical working-age adult would experience on this schedule. The model evaluates the planned rotation design, not day-to-day variations such as overtime, shift swaps, or unplanned absences.
Full Methodology
A comprehensive white paper detailing the complete mathematical methodology, model parameters, validation references, and risk classification thresholds is available for download. Every deliverable also includes a methodology explanation section.
Download Methodology White Paper (PDF) →Ready when you are.
Independent rotation analysis. No discovery call. Findings delivered in 48–72 hours.