During this past week, I was contacted by two foreign companies with labor contracts that limited the annual hours of work for their employees. They wanted me to design schedules that didn't exceed an annual target (1,712 in one case and 1,816 in the other).
 

To “simplify” the assignment, I converted the annual figures into weekly numbers by dividing the annual hours by 52 weeks: 

• 1,712 hours/year divided by 52 is 32.9 hours/week
• 1,816 hours/year divided by 52 is 34.9 hours/week 

With 12-hour shifts, the average weekly hours worked depends on the number of crews. Here are the averages:  

• 4 crews work an average of 3.5 shifts a week or 42 hours a week
• 5 crews work an average of 2.8 shifts a week or 33.6 hours a week
• 6 crews work an average of 2.33 shifts a week or 28 hours a week 

A 5-crew schedule would only work with rotating shifts, whereas the 4-crew or 6-crew schedules would work with either fixed or rotating shifts. To minimize the staffing requirements, we decided to use the 5-crew approach with rotating 12-hour shifts that average 33.6 hours/week. This worked fine for the company with the higher limit (34.9 hours/week), but not for the other company (32.9 hours/week).
 

This could be resolved by either incorporating a 30-minute unpaid meal break or scheduling a vacation period every year to reduce the hours of work. This starts to get complicated quickly, so I won't go into all the details here. I just wanted to show you how this sort of challenge can be addressed.