Shift work refers to practice of more than one person manning the same work position at different times within a 24 hour cycle. The shift work becomes essential when the position is such that in a 24 hour cycle the position needs to be manned for periods exceeding what can be comfortably manned by a single person. The considerations for designing shift schedule can be classified in two broad groups - the durations for which the positions are to be manned, and the physiological impact of the shift working on employees.
Some positions need to be manned during day time only with no night working. Other positions may need to be manned round the clock, so that night working is involved. Also it may or may not be necessary to make the shifts overlapping.
Night work can be harmful to the health of workers. In particular it has major harmful effects on sleep and gastro-intestinal functions because of changing pattern of eating. Continuous or frequent night work also affects family and social lives of workers adversely.
Several measures are taken to reduce the adverse impact of night work. These include reducing the total hours of work in a week, rotating people in different shifts, giving adequate period of rest between changeover from one shift to another, and direction of change of shift.
Typically when work is to be performed round the clock and seven days a week, the day is divided in three 8 hourly shift. Sometimes, the night shift may be made a little shorter. For example night shift may be of 7 hours, and each of the other shift may be of 8.5 hours.
To man three shifts 4, or 5 groups of crew may be used. With 4 groups crew, on any single day 3 groups work while one group rests. With 5 groups crew, 3 groups work while 2 groups rest. A crew of 4 groups requires each person to work 42 hours a week. This figures becomes 33.6 hours for 5 group crew.
It is best to effect shift change weekly following the weekly rest, and the shift change should be in forward direction - that is morning to afternoon to night shift.
The previous answers focus on the impact of the schedule on the worker. My answer will focus on the reason for the schedule and how to design one to make the most efficient use of your personnel. There are 6 considerations:
1. Coverage requirements. The starting point for all schedule design should be the coverage requirements. If the facility operates 24/7, how many people need to be working at different times of the day? Does this stay the same throughout the week? For this discussion, let's assume that the facility needs 2 people working at all times.
2. Shift length. The most common shift lengths for 24 hour operations are 8 hours and 12 hours. The reason is that these divide evenly into a 24-hour day. Although 10-hour shifts are popular with employees, they don't divide evenly into 24 hours, making them a poor scheduling option.
3. Schedule format. Once the shift length is selected, the next question is the schedule format, i.e. whether you want fixed (permanent) shifts or rotating shifts. As a general rule, employees prefer fixed shifts while employers prefer rotating shifts. Before moving on, I would like to point out the 8-hour fixed shifts are often an inefficient scheduling option. You can use them, but it may require 1-3 more employees than other scheduling options.
4. Overtime. Most 24/7 schedules have a small amount of overtime built into them. If they didn't, there would be gaps in the coverage or the facility would have to hire more staff. Most organizations find that the overtime in the schedule is much less expensive than hiring adequate staff, especially when you consider the cost of benefits for the additional staff.
5. Pay week. Since most shift workers are non-salaried, they are subject to federal labor laws that require overtime premiums after 40 hours work per week. Although people don't think about this, the start of the pay week is important to schedule design for two reasons: (a) you don't want a schedule that creates unbalanced work weeks such as 32 hours one week and 48 hours the next week, and (b) you don't want to invoke overtime payments unnecessarily because the schedule didn't match the organization's pay week.
6. Schedule patterns. Once you addressed all the previous points, now is the time to consider different patterns of days worked and days off. With 8-hour shifts, the most popular patterns tend to be those that feature 7 consecutive days of work before having one or more days off. The reason is that this provides the maximum weekends off (1 every 4 weeks). With 12-hour shifts, there are several popular patterns such as Every Other Weekend Off, Long Break, 3-on-3-off, 4-on-4-off, split weekends, fixed-fixed, etc.
Of course there are other considerations such as shift start times, break policies, paid time-off policies, relief (absence) coverage, etc. that must be considered. But this gives you the high-level view of the schedule design process. You may be able to find schedule examples online, but the options will be limited and the potential problems (particularly the pay week) will be substantial.
When looking at a shift schedule in ergonomics one needs to look at the types of shifts first: 24 hour shifts, 3 to four hour rotational shifts, 8 hour shifts, and these may vary depending on the industry.
Some of the things to look at when setting up shift schedules are: the amount of sleep deprivation that may occur, and a person's ability to cope with transitional shifts.
The direction of the rotation of the shift is important. It must moved in a forward pattern from day to afternoon to evening so as not to throw off a person's circadian rhythms.
Social customs of the workforce also need to be addressed. Getting someone working at 4-5:30 a.m. in the American culture would throw them off from their normal sleep patterns.
Safety of the employees when they go or come home from work is also important to look at. Do they have safe transportation available?
After each set of night shifts a person needs no less than 24 hours readjustment period.