Half a day, half a day

The first in a series on shiftwork

I’ve recently had a client comment that he is concerned about his recently introduced 12 hour shift system (previously an eight hour shift system was in place). He has had an adverse comment in a safety audit stating that 12 hour shifts are significantly more ‘risky’ than eight hour shifts. On the face of it, this statement is accurate, but the reality and the bigger picture are a bit more complex.

There is no doubt that a 12 hour shift has issues with fatigue, particularly toward the end of the shift. Sleepiness may also be an issue on night shifts. The UK HSE recommends that 12 hour shifts are avoided for safety critical activities or where work is demanding. Does this mean that 12 hour shifts are always worse?

There are some significant advantages to 12 hour shifts that need to be considered as well as the potential adverse fatigue effects. The first of these is the number of shift changes during the 24 hour day (at the risk of stating the obvious, 2 rather than 3). Shift handover is a safety critical communication with the potential for error. We reduce the potential for error by reducing the number of handovers. Similarly, situational awareness builds up over the shift. The operator starts with lower situational awareness as he comes on shift, and this increases over the shift as he familiarises himself with the plant status. Again, we minimise these effects when we minimise the number of shift changes.

12 hour shifts allow us some options in the shift rota that 8 hour shifts don’t (at least without significant social consequences). Most well designed 12 hour shift patterns are ‘forward rotating’ with two days followed by two nights followed by a period of time off. The advantage of the short period spent on nights is that the body clock does not reset and the recovery period is much shorter. This can have a positive effect on the sleepiness factor mentioned earlier as well as making the shift pattern ‘easier to live with’.

We should also consider the peripheral activities that are impacted by the shift pattern, particularly commuting. Most people working shifts are forced into using the car as transport, with public transport being limited or non-existent at the required times. Obviously mixing driving and the potential for sleepiness is a generally bad idea. Night workers are second only to young inexperienced male drivers in the accident statistics. I interviewed an operator earlier this year who said that he often drove home after a night shift “with my windows open and the radio turn up” in order to combat sleepiness. We should ask ourselves (and our employees) whether they are experiencing effects like these and take corrective actions where necessary. On the other side of the equation, the overall yearly commuting time is reduced with 12 hour shifts as the commute happens less frequently and excessive sleepiness isn’t necessarily solely a feature of 12 hour shifts.

With fatigue, sleepiness and shiftwork, like many human factors topics, there’s no ‘right’ answer other than ‘it depends’. Shift patterns are always a compromise between the needs of the job, the needs of the employer and the needs of the employee. The trick is to have good systems of management, feedback and control of the real problems such as overtime and shift swaps. These probably have a bigger effect on the risk profile than the basic shift pattern itself, and are often an area that management is blind to; leaving shifts to self manage this important aspect.

At a future date I’ll return to the subject and talk about management of shifts for safety (rather than for cover or to minimise the overtime budget), the effect of breaks and job design on fatigue and sleepiness, long term health effects for shift workers, and the influence of the work environment.

It’s a big subject, and I’d welcome your comments.