A fatigue risk management system tells you what's allowed.CAI tells you which schedule is better.
Most FRMS programs are built as compliance floors: duty limits, minimum rest, maximum consecutive shifts. Stay inside them and you pass. But two schedules can both pass and cost the people working them very different amounts of sleep. CAIER scores that difference so it can be optimized instead of assumed.
What a fatigue risk management system actually covers
An FRMS is not a single document or a single tool. In practice it is four layers, and organizations usually invest heavily in the first and third while leaving the second — the schedule itself — to whoever has the spreadsheet.
- 01Policy and duty limits
Maximum consecutive shifts, minimum rest, hours-of-service caps. This is the floor — the line you may not cross.
- 02Schedule design
The roster itself: rotation pattern, night clustering, recovery placement, and how the burden is shared. This is where most of the fatigue is created or avoided.
- 03Monitoring and reporting
Fatigue reports, near-miss review, and staff feedback that tell you whether the published schedule is working in practice.
- 04Continuous improvement
Comparing roster variants period over period and keeping the ones that score better, instead of re-publishing last year's pattern.
What the Circadian Alignment Index scores
The Circadian Alignment Index (CAI) reads a published schedule and scores how well its temporal structure fits human circadian rhythm — higher is better. It is a schedule-design metric, not a medical device and not a wearable. CAIER is currently validating CAI in emergency medicine before extending it to other 24/7 industries. The completed v1 derivation cohort (50 emergency physicians, 626 comparisons, ~69% agreement) is available as a preprint — not peer reviewed.
How many night shifts land in a block, and whether they are clustered or scattered across the period.
Forward rotation (day → evening → night) is easier to adapt to than backward rotation.
Whether the time off after a night run is long enough to actually re-anchor sleep.
Whether the circadian cost is spread across the group or absorbed by the same few people.
Because CAI produces a comparable number, two legal rosters can be put side by side and the better one chosen — and the choice can be explained to the people who have to work it. That is the difference between an FRMS you report on and an FRMS you improve. Read the full CAI guide.
Where this applies
Fatigue risk management shows up wherever coverage never lapses. The rulebooks differ; the biology does not.
- Healthcare — emergency medicine, anesthesia, hospital nursing
- Public safety & EMS — Kelly cycles, 24/48 tours, holdovers
- Aviation — crew rostering under duty and rest limits
- Transit & logistics — hours of service, extra boards, dispatch
- Utilities & energy — grid control rooms and rotating field crews
- Industrial — continuous-process plants and distribution centers
Common questions
- What is a fatigue risk management system?
- The set of policies, duty limits, monitoring, and reporting an organization uses to keep fatigue-related risk at an acceptable level in operations that run around the clock.
- How is CAI different from duty-hour limits?
- Duty-hour limits define what is allowed. CAI scores how well a specific published schedule fits circadian rhythm, so two legal rosters can be compared and the better one chosen.
- Do we have to replace our current scheduling software?
- No. CAI is a scoring layer applied to schedules you already produce. Start by scoring what you publish today, then decide what to change.