nighttimeResearch published in Occupational & Environmental Medicine in November, 2014, which examined the chronic effects of shift work on cognition, showed that shift work is associated with impaired cognitive function.[1]

This association was strongest for those who had been employed in shift work for more than ten years and was equivalent to an additional 6.5 years of age-related decline. The United Kingdom’s Health and Safety Executive (HSE) states in the past 25 years, there has been a gradual increase in the number of people who undertake shift work in the UK, with around 5-20 per cent of the working population now engaged in shift work that involves night work. This equates to 3-6 million workers.

The Health and Safety Laboratory (HSL) works with HSE to draw together current research and the results of accident investigations, to provide advice on the risk from fatigue on health and safety performance as a result of shift working. Shift work, particularly that which requires people to work at night (around 11pm until around 4am), interferes with the human’s biological need for night time sleep and can result in both acute (within shift) and chronic (over a longer period) fatigue.

This can have a negative impact on cognitive functions such as vigilance, decision-making and situational awareness, with the potential to contribute to poor safety performance and ultimately incidents. In the longer term, shift work has been associated with health impacts such as gastrointestinal and cardiovascular problems, along with a possible link with breast cancer. The research cited above by Marquié et al now indicates a potential for a long-term cognitive impact too.

The direct causal link between shift work, fatigue, safety performance and health consequences is yet to be established. But the link between fatigue and safety outcomes is very clear in circumstances where the impact of poor performance/ human error can be immediate, such as with drivers and road traffic accidents.

In more complex, high- hazard, low-risk occupational environments where accidents are low frequency events, the link between fatigue, poor performance and incidents is less clear. This is because additional layers of defense are used to protect against human error, such as the use of automatic shut-off valves in the petrochemical industry. In these circumstances, fatigue is acknowledged as a contributory factor to incidents.

The fatigue risk can be managed like any other health and safety risk and, while fatigue is not directly measurable, it can be minimized by well-designed and well-managed shift schedules, according to the HSE.

Simple organizational factors can increase the risk from fatigue -- not enough staff to work a planned shift schedule; not enough people in some roles; or insufficient flexibility in the schedule to cope with work demands. A well-designed shift schedule should take a risk-assessment approach to managing fatigue risk; it should include good arrangements to cover absence, training, and other demands on staff time.

Ultimately, the only way to reduce the impact of fatigue on performance and safety is through quality rest and recovery periods. This is further reinforced by the Marquie et al research, which indicates that those who had been removed from shift work for more than five years showed signs that their cognitive performance had recovered.

(1) Jean-Claude Marquié, Philip Tucker, Simon Folkard, Catherine Gentil and David Ansiau, 2014:

Source: Safety and Health Practitioner;