MODULE 7: PSYCHOSOCIAL ISSUES AND OTHER MISCELLANEOUS TOPICS IN OCCUPATIONAL AND ENVIRONMENTAL HEALTH
SECTION 7: SHIFTWORK AND HOURS OF WORK:
2: Designing Shiftwork Schedules

2. DESIGNING SHIFTWORK SCHEDULES:

The most useful strategies are summarised in the box below (ILO Encyclopaedia, 1998):

  1. Nightwork should be reduced as much as possible. If this is not possible, quickly rotating shift systems are preferable to slowly rotating ones. Permanent nightwork does not seem to be advisable for the majority of shiftworkers.
  2. Extended workdays (9-12 h) should be contemplated only if the nature of the work and workload are suitable. The shift system is designed to minimize the accumulation of fatigue; there are adequate arrangements to assure that a complete recovery after work and a high acceptance of the working time arrangement are possible.
  3. An early start for the morning shift should be avoided. In all shift systems flexible working times arrangements are realisable. The highest flexibility is possible in "time autonomous groups."
  4. Quick changeovers (for example, from night to afternoon shift on the same day or from to afternoon to morning shift) must be avoided. The number of consecutive working days should be limited to 5-7days. Every shift system should include some free weekends with at least two successive full days off.
  5. The forward rotation of shifts (morning shift, evening shift, night shift) would seem to be recommendable, at least in continuous shift systems.
    6.
Permanent Night Work:

This is not the physiologically preferred system. Although when at work continuously, there may be some adaptation of the body clocks, this reverts once the worker is off work and tends to follow a day/night cycle in their social lives.

Quickly Rotating versus Slowly Rotating Shift Systems:

More rapidly rotating schedules are more advantageous compared to weekly shift rotation. This is because a fast rotation maintains the daytime orientation of the circadian rhythm. This also prevents a chronic sleep deprivation which may arise from consecutive night shifts. It is advisable to keep night shifts to between 2 – 4 days before at least two days off. Although some workers may prefer the long stint of nightshift followed by long weekends (3-4 days off), this could lead to sleep deprivation and fatigue.

Shift Duration and Timing:

Shifts should not be longer than 12 hours, although 8 is preferrable. For shifts longer than 8 hours, the work intensity should be modified to ensure that it is lighter work. Nightshifts should be preferably of a shorter duration, with only a minimum number of 12 hour shifts.

The timing of shifts must also be considered. Starting of a morning shift too early, causes fatigue of workers who may have had a reduced number of hours of sleep. However, a later start to the early shift implies a later finish to the night shift, which may be problematic, both physiologically as well as socially (consider problems with transport, for example).

Direction of Shift Rotation:

A shift system which first moves from morning shift to evening shift, and then to night shift, has a forward rotation (phase delay, clockwise rotation). An anticlockwise, or backward, rotation has a phase advance which moves from night to evening to morning shifts. The forward rotation is thought to be physiologically preferrable. A continuous shift system that has a rapid forward rotation pattern, with 8 hours of work per shift, some free weekends, at least two successive full days off and no quick changeovers, appears to be the system to be recommended. The illustration from the ILO, shown below, provides an approach to shift rotation.

Average weekly working hours:
33.6 h/week without additional rotation
35.2 h/week with 2 additional shifts/10 weeks
36.8 h/week with 4 additional shifts/10 weeks
38.4 h/week with 6 additional shifts/10 weeks
40.0 h/week with 8 additional shifts/10 weeks
(Data extracted from the ILO Encyclopaedia, 1998)