Focus on Fatigue

Working With Risk

By March 10, 2019 No Comments

Welcome to Focus on Fatigue!

The past couple of months seem to have been a study of extremes. Extreme cold in some parts of the world, and extreme heat in others. As someone who is firmly located in the heat, I know firsthand that such extremes can have a significant effect on how well we sleep at night.

So, whatever part of the world you’re in, I hope you’re managing to get a good night’s sleep, whether that’s bundled up in blankets or cover-free with the ceiling fan on high.

Best wishes,
The FRMS Team



InterDynamics Pty Ltd
320 Adelaide Street Brisbane Qld 4000
Tel +61 7 3229 8300

Views expressed in articles and links provided are those of the individual authors, and do not necessarily represent the views of InterDynamics (except where directly attributed).


Working with Risk

When we talk about Fatigue Risk Management, we are talking about managing increases in the risk of accident and injury associated with increases in fatigue. It’s all about keeping people safe. One part of managing such risk is knowing when accidents at work are mostly likely to occur.

A number of studies have examined this issue in detail and the following trends have been identified.

Risk across different shifts

There is a consistent tendency for the relative risk of accidents to be lowest for morning shifts, increased for afternoon shifts, and highest for night shifts (on 8-hour shift systems). Across a number of studies, the relative risk for incidents was 30% higher on the night shift than on the morning shift.

Risk over successive night shifts

In a group of studies that examined the risk of accident over the course of four consecutive night shifts, it was found that risk increased substantially for each night. Indeed, the risk of having an accident on the fourth night was 36% higher than it was on the first night. This same increase was found in the day shift, but to a much milder degree.

Risk over successive hours of work

Risk of accident tends to increase exponentially after the 8th hour on shift. Relative to this first 8-hour period, 10-hour shifts are associated with a 13% increase in risk. The increase in risk for a 12-hour shift is 27%.

Risk between shift breaks

The risk of having an accident rises in the time between breaks, with accidents most likely to happen in the 30 minutes prior to a rest break.

What about the Circadian Rhythm?

The circadian rhythm is an internal body clock that cycles between periods of sleepiness and alertness throughout the day and night. It’s one of the reasons we get sleepy after the sun goes down, but it’s also responsible for that post-lunch slump that makes us want to take a nap. For most adults, the biggest dips in energy occur between about 2am and 4am, then again between 1pm and 3pm. Therefore, it seems natural that there would be an increase in risk of injury for shift workers who are working during the circadian dip in the early hours of the morning.

While this is far from proven, there is some evidence to support the theory. For example, a study of truck drivers found a major peak in accidents occurring around 3am. This increase was not necessarily due to drivers falling asleep at the wheel, but seemed to be due more to a decrease in driving performance. So, if you are working during this time of the morning, it may be useful to schedule a break if possible.


  • Folkard, S. and Tucker, P. (2003) Shift work, safety and productivity. Occupational Medicine, 53, 95-101.
  • Folkard, S. (1997) Black times: Temporal determinants of transport safety. Accident Analysis and Prevention, 29(4), 417-430.
  • Folkard, S., Lombardi, D. A. and Tucker, P. T. (2005) Shift work: Safety, sleepiness and sleep. Industrial Health, 45, 2-23.


In the News

Provided below are a selection of articles from around the web on the issues associated with fatigue. We hope you find them useful and interesting.

Article: 8 weird facts about sleep science learned in 2019 alone
JR Thorpe, Bustle (6 February 2019)
Maybe it’s because 2018 was a hell of a year and we all want to spend most of 2019 in sweet, sweet slumber, but there was a lot of research published in January this year about sleep. Like, a lot of research. This article checks out what we’ve learned so far.

Article: The connection between sleep and pain
Lydia Denworth, Psychology Today (5 February 2019)
A new study reveals how sleep loss changes brain processing to increase pain.

Leave a Reply