ABCD Rotation (best viewed on desktop/tablet)
Base: ABCD (24/72). Safe debit mapping (no 48s): A→+C#, B→+D#, C→+A#, D→+B#. Index # repeats per 4-day block (1→4) within a 16-day superblock. Hell week shown for A1 (3 marked days every 16).
The Prompt: Build a monthly ABCD duty calendar: split A/B/C/D into A1–A4, B1–B4, C1–C4, D1-D4; Use the safe debit mapping (A day gets C#, B day gets D#, C day gets A#, D day gets B#) so no one ever works 48 straight. Show a 16-day rotation string.
The Math
We start with three shifts: A, B, C (165 each → 495).
Add our recruit class: +30 = 525 members.
Divide operational work force into 4 shifts creating D Shift: 525 ÷ 4 ≈ 131 each → A=131, B=131, C=131, D=131.
Debit groups
Each shift is divided into four small, balanced cohorts (~33 people each):
A1, A2, A3, A4
B1, B2, B3, B4
C1, C2, C3, C4
D1, D2, D3, D4
On a given day, the on‑duty Shift (A/B/C/D) is augmented by one matching debit group to keep the day fully staffed.
Who helps whom
To prevent anyone working 48 straight, debit is always pulled from the “two‑away” shift in the A→B→C→D cycle:
A day gets help from C (labelled +C#)
B day gets help from D (+D#)
C day gets help from A (+A#)
D day gets help from B (+B#)
The “#” (1–4) is the cohort index that rotates. This keeps the workload fair and predictable.
16‑day rotation (then repeats)
Every four days the cohort index advances (1 → 2 → 3 → 4). Over 16 days every cohort appears exactly once:
The Math
We start with three shifts: A, B, C (165 each → 495).
Add our recruit class: +30 = 525 members.
Divide operational work force into 4 shifts creating D Shift: 525 ÷ 4 ≈ 131 each → A=131, B=131, C=131, D=131.
Debit groups
Each shift is divided into four small, balanced cohorts (~33 people each):
A1, A2, A3, A4
B1, B2, B3, B4
C1, C2, C3, C4
D1, D2, D3, D4
On a given day, the on‑duty Shift (A/B/C/D) is augmented by one matching debit group to keep the day fully staffed.
Who helps whom
To prevent anyone working 48 straight, debit is always pulled from the “two‑away” shift in the A→B→C→D cycle:
A day gets help from C (labelled +C#)
B day gets help from D (+D#)
C day gets help from A (+A#)
D day gets help from B (+B#)
The “#” (1–4) is the cohort index that rotates. This keeps the workload fair and predictable.
16‑day rotation (then repeats)
Every four days the cohort index advances (1 → 2 → 3 → 4). Over 16 days every cohort appears exactly once:
At a glance
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Daily pattern: A → B → C → D and repeat (one shift on duty each day).
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Base schedule for a firefighter: 24 on / 72 off (work every 4th day).
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Cross‑assignment cohorts: Each shift (A/B/C/D) is divided into four small cohorts (e.g., A1–A4). A matching cohort from a partner shift augments the on‑duty day.
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No 48‑hour tours: Cross‑assignments only occur on each shift’s safe day (two steps away in the ABCD cycle), so nobody works 24s back‑to‑back.
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Leave friendly: Full daily staffing without collapsing leave slots; fewer last‑minute mandates.
What it means for one firefighter:
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Base: work every 4th day (24/72).
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Plus: about one cross‑assignment every 16 days.
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Yearly total: roughly 113–115 tours, still lower than a 24/48 schedule.
Why this works
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Safety & fatigue: Everyone gets a minimum 24‑hour buffer between tours; base cadence is 72 hours off.
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Coverage continuity: The ABCD rhythm and cohort rotations keep daily staffing consistent.
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Leave protection: Standard leave slots remain available; the day’s cohort augmentation fills expected gaps.
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Skills & leadership on every day: Officers and specialties (RSQ, HazMat, Tech, Marine) are balanced across A1–A4, B1–B4, C1–C4, D1–D4 so daily minimums are met.
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Fairness: The 1→4 cohort index rotation shares added assignments evenly.
Common questions
Is D different from the other shifts?
No. A, B, C, and D are four equal shifts on the same 24/72 rhythm.
Will I ever work 48 in a row?
No. Cross‑assignments only occur on your shift’s safe day (two steps away in the cycle), so there are no back‑to‑back 24s.
How often is my cohort cross‑assigned?
Roughly once per 16 days for your cohort.
How do we keep qualifications balanced?
We build each cohort with the right mix of officers and specialty certifications so any calendar day meets minimum staffing.