The four-crew 8-hour rotation
A common pattern gives each crew 2 mornings, 2 evenings, 2 nights and 2 rest days in an 8-day cycle, with crews starting 2 days apart. On any day three crews work, one on each shift, and one rests. Each person works 6 shifts in 8 days, which is 48 hours in 8 days or 42 hours a week on average. Shifts run 6 am to 2 pm, 2 pm to 10 pm and 10 pm to 6 am, and many plants prefer this forward rotation from mornings to nights because each change leaves at least a day between shifts.
Crew minimums and trained people
Each crew needs a written minimum. For example: 1 shift in-charge, 3 panel operators, 4 field operators and 1 chemist, with at least 2 people trained in fire fighting and 1 in first aid on every shift. Leave, training and sickness will take people away, so plants keep a reliever pool trained on the same units. Without relievers, the only cover left is a double shift, which is exactly what a hazardous plant should avoid.
Worked example: sizing the reliever pool
A unit needs 9 people per shift, so four crews of 9 put 36 people on the rolls and 27 on duty every day. Suppose each person is away 22 days a year: 13 days of earned leave, 7 of casual and sick leave and 2 of training. Across 36 people that is 792 missed shifts a year. A reliever working 6 days in every 8 covers about 273 shifts a year, so the unit needs at least 3 relievers to cover planned absence without double shifts.
Plastics units: three shifts and mould changes
Injection moulding and extrusion units usually run three 8-hour shifts six days a week, with a weekly off on a fixed day or staggered by machine. Mould setters are the constraint. A mould change needs a trained setter, so roster at least one on every shift with a planned change, and plan changes for shifts where a setter is present. Swaps between operators are simple; swaps between setters need the production head's approval.
How to set it up in ZeniaHR
- In Shifts & Roster, create morning 6 am to 2 pm, evening 2 pm to 10 pm and night 10 pm to 6 am, with the night shift flag on nights.
- Build an 8-day rotation template of 2 mornings, 2 evenings, 2 nights and 2 rest days, and stagger the four crews by 2 days.
- Roll the crew cycle out in bulk, up to 92 days at a time, then place relievers day by day wherever a gap shows.
- For plastics lines, set weekly off patterns per shift and roster setters on shifts with planned mould changes.
- Enable Shift Swaps so crew members can swap across two dates, with the shift in-charge and HR approving before the roster changes.
- Check the day grid a week ahead for shifts below the crew minimum and fill them before anyone is asked to double.
Read more about shifts and rosters in ZeniaHR.
Roles this applies to
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What is a four-crew shift system?
A four-crew system runs a continuous plant with four teams on 8-hour shifts. Each day three crews work, one on each shift, while the fourth rests. A common cycle is 2 mornings, 2 evenings, 2 nights and 2 days off, which works out to 42 hours a week on average for each person.
How many relievers does a continuous plant need?
Work it out from planned absence. Add the days each person is away in a year for leave and training, multiply by headcount, and divide by the shifts one reliever works in a year. For 36 people away 22 days each, that is 792 shifts, which needs at least 3 relievers working 6 days in every 8.
Can women be rostered on night shifts in a chemical plant?
Yes, with her consent and under the safety conditions the government has set for night work by women. For hazardous processes, also check your state's rules on the operations in which women may be deployed. Record consent, put the notified safety conditions in place, and review the roster with the safety officer.