Part 1: About workplace fatigue

What is fatigue?

Fatigue is a physical and/or mental state caused by overexertion. It reduces a person's capabilities to an extent that may impair their strength, speed, reaction time, coordination, decision making, or balance.

A level of fatigue is a natural response to the mental and physical effort of everything we do. Normally, good quality sleep reverses the imbalance, allowing the body and the brain to recover.

However, working long hours, working with intense mental or physical effort, or working during some or all of the natural time for sleep can all cause excessive fatigue. All of these have obvious implications for workplace and public safety. Fatigue can also have longer-term effects on health.

Figure 1-The 'Bucket' model of fatigue

See larger version of the image and read the text of image

The causes of workplace fatigue

Shift work

In terms of work hours, shift work is defined as work that starts before 8.00am and finishes after 6.00pm. A biological definition of shift work would be any work pattern that causes a change in normal sleep patterns.

Shift work (in particular night work) can be a powerful cause of fatigue when it:

• limits a person's opportunities to get adequate sleep
• requires them to work in the early hours of the morning, when people are normally at their sleepiest and least functional.

The evidence available on the effects of shift work is sketchy. Interpreting it in the practical situation is difficult because the risks are different for different jobs and groups of people.

Extended work hours

Shifts that last longer than 8 hours are classed as long or extended. People may work long hours on a short-term basis to deal with a major emergency or an unexpected situation, or they may work long hours regularly for financial or other reasons. Appendix A makes some recommendations about managing long work hours in emergencies.

The effects of working long hours depend on how long the work periods are, how often they occur, and at what time of day.

Sleep restriction (having several hours less sleep than needed) has clear, negative effects on human performance. It suppresses the immune system, increases appetite, and makes the body increasingly resistant to insulin. Several nights of restricted sleep can create a 'sleep debt', which has clear effects on performance.

Effects accumulate

The combined effects of sleep restriction and extended hours of work have a short-term impact on performance, and in the long term may affect cardiovascular health, mental health, safety, and productivity.

How long people can go on working extended hours before they suffer adverse health effects is not known. We do know that:

• working more than about 55-60 hours a week (during the day) for an extended period is likely to have significant health effects
• extending a working week from 65 to 70 hours will have more impact than extending it from 40 to 45 hours, even though the amount of extra time is the same
• a period of extended work will have more impact if it follows other periods of extended work than if it is a one-off
• the effects of long periods of extended work hours (several months to years) will be greater than the effects of short periods (2-4 weeks).

Night work

All the statements above refer to day work. Working at night has a greater impact than working the same number of hours in the daytime, and the impact is even greater when the work hours are extended.

On average, shift workers lose 1-1.5 hours of sleep for each 24-hour period. This builds up a sleep debt of 6 hours after 4 nights. Working more than three or four night shifts in a row is likely to cause a significant sleep debt, with serious consequences for safety.

Night-work hours should be limited. For example, an employment contract for employees doing work where risks of errors are high could state:

The total number of hours an employee may work between midnight and 6.00am is limited to 18 over three days, after which they must have two full nights off for sleep.

The consequences of workplace fatigue

Fatigue leads to human errors

Errors made by shift workers in the early hours of the morning were critical factors in the disasters at Three Mile Island, Chernobyl, and Bhopal, as well as in the Exxon Valdez oil spillage. Fatigue-induced human errors can have major consequences for public safety, as well as for the workers involved, in one-off events like these.

A recent study showed that fatigue is common among New Zealand truck drivers^[1] and can build up over time. In this study:

• one out of four drivers reported being tired, even at the beginning of their shift
• 24 per cent of the drivers failed a standard computer test of their ability to steer, keep to speed, cope with wind gusts, and notice and respond to signals.

In a medical setting, a study of New Zealand anaesthetists^[2] found that 32 per cent recalled making a fatigue-related error in the previous 6 months. Further, 71 per cent of trainees and 58 per cent of specialists had exceeded their own safety limits for length of time at work.

Many other findings point to a clear link between fatigue and human error. For example:

• A recent study of medical interns^[3] found that every extended shift (of more than 24 hours) they worked in a month significantly increased their risk of a crash while commuting to or from work.
• In the United States, it has been estimated that fatigue contributes to between 20 and 40 per cent of all commercial vehicle crashes.These incidents are estimated to cost more than 15,000 lives in the USA and $12 billion a year in lost productivity and property damage^[4],^[5].
• Studies of error rates and productivity in round-the-clock industries, where work requirements and the work environment are comparable on all shifts, consistently show poorest performance on the night shift^[6]. Similarly, standard performance tests given to shift workers either at work, or at home between shifts, show poorest performance when they are working nights^[7],^[8].

Extreme fatigue may cause a person to 'disengage' briefly in a so-called 'micro-sleep'. If this happens at a critical time, an accident may result. Micro-sleeps have been observed in train drivers and airline pilots during periods of critical operations, with the drivers and pilots often being unaware it was happening^[9].

Fatigue affects health

A recent summary from the National Institute for Occupational Safety and Health in the USA (NIOSH)^[10] analysed 52 recently published reports that examined long working hours in relation to illnesses, injuries, behaviour, and performance. The analysis indicated that long hours of work were associated with:

• people feeling less well, less alert, and more tired
• lower cognitive function, poorer performances on psychomotor tests, and declines in vigilance
• increased injury rates, more illness, and increased mortality.

When 12-hour shifts were combined with more than 40 hours' work per week, additional effects showed up. These workers had more health complaints, poorer performance, and a slower pace of work.

Long term sleep problems

One way to measure the impact of night work is how much it restricts sleep^[11]. A 5-year study of over 18,000 French workers found that those who had worked at least 50 night shifts during 1990 were significantly more likely to have developed a sleep problem by 1995.

The study found that the more of the following conditions applied to a person's work, the more severe their problem was likely to be:

• not getting to bed until after midnight
• having to get up before 5am
• having to sleep in the daytime rather than at night.

Recovery from fatigue

Sufficient sleep

In the long term, the average amount of sleep needed for health and alertness is between 7 and 9 hours a night. Most people need at least 6 hours of unbroken sleep in any 24-hour period to remain alert, assuming a zero sleep debt.

However, people vary in many ways-including their sleep needs and working time preferences (being an 'owl' or a 'lark'). Little is known about the extent of this variation.

Breaks between shifts

The Department of Labour recommends at least two consecutive full nights' sleep (with a normal day between) in each week. Available research indicates that, other things being equal, this is enough to allow performance to return to normal, at least in the short term.

The length of break a person needs to ensure they get enough sleep depends when the break begins. A 10-hour break starting at 10.00pm will allow much more sleep than a 10-hour break starting at 10.00am. We have a strong preference for sleep at night. This is not just a social convention, but a physiological need.

The length of break a person needs to get enough sleep will also depend on how much time they need for getting to and from work, eating, washing, dressing, and socialising.

Breaks during shifts

Breaks within the working period provide for refreshment and restore physical capabilities and alertness.

Workers are often given breaks at set times determined by custom or convenience. However, shift workers need to protect themselves from fatigue. Ideally, they should take regular breaks from sustained activity, rather than waiting until their performance starts to suffer after fatigue has set in (or until a scheduled break time). Rest taken after performance begins to decline tends to be less effective and provide only temporary relief.^[12]

There is evidence to suggest that rest breaks in addition to the traditional breaks (two 15-minute breaks, and one 30-minute meal break) can improve overall productivity. This is probably due to the relief from fatigue that these extra breaks provide.

Breaks can be used to

• attend to physical needs (eating, drinking, going to the toilet)
• recover from physical effort
• relieve the effects of static postures
• relieve the effects of repetitive physical actions (such as prolonged keyboard use)
• relieve the effects of concentrated mental work (including prolonged visual work)
• recover from unusually hot or cold conditions
• take a nap.

Education and training, such as useful exercises to do, will help workers to make the most of their breaks.

Whole-of-work factors

Consider all aspects of employees' jobs when looking for ways to make their work safer, more enjoyable, and more productive.

People cope better with day-to-day workplace stressors (including fatigue) when they:

• have a balance of effort and rest
• are properly trained and supervised
• get objective, prompt feedback
• feel their efforts are acknowledged and rewarded with appropriate pay and status.

Features of work that operate over a longer time span and may make it more satisfying are:

• training and other opportunities for skill development and advancement
• opportunities for relief from shift work
• opportunities for project work (work that has a clear end) as a change from repetitive work.

A fuller account of the effect of whole-of-work factors appears in the Department of Labour Publication Healthy Work: Managing Stress and Fatigue in the Workplace, available from www.dol.govt.nz.

Key facts about fatigue, and their implications for employers

The following list of 12 key facts was developed from both practical experience and research results. It was presented at a series of workshops on workplace fatigue held by the Department of Labour in June 2003.

1. Adequate sleep is essential for maintaining and restoring full human functioning

Most humans need an average of around 7.5-9 hours of good quality sleep a night for consistent physical and mental recovery from daily activities. Getting adequate sleep is the only way to recover from fatigue, especially for the brain. Just as muscle fatigue can only be reversed through rest, mental fatigue can only be reversed through sleep.

Sleepiness, like hunger and thirst, is a signal from the body of a basic need. In extreme sleepiness, a person may begin to 'nod off' without being aware of doing so, or even fall asleep.

Work-related sleep loss is a significant public health issue. In a recent survey, 37 per cent of New Zealanders aged 30 to 60 years said that they 'never' or 'rarely' got enough sleep at night, and 46 per cent said they 'never' or 'rarely' woke up feeling refreshed.

In the short term, people who do not sleep well tend to eat more, and are more likely to pick up infections. Long-term health effects related to sleep problems include digestive system upset, cardiovascular disease, and other complaints.

Implications for employers

When employees' sleep is affected by shift work (particularly night work) they will not function as effectively as employees who work normal day shifts.

Aim to manage shift work and overtime so that employees have regular opportunities for adequate recovery through high quality sleep.

2. Stimulants provide only limited, short-term relief

The use of stimulants such as nicotine, caffeine, and some other drugs can help maintain alertness in the short term. However, this gain comes at a cost-the 'crash' when the effects of the stimulants wear off. Poor quality sleep may result from carry-over effects of the stimulants.

Sleeping tablets can reduce fatigue effectively if used appropriately and for limited periods. However, they just mask the problem if the causes of sleep problems remain unchanged. Only good quality, natural sleep will provide full recovery.

Implications for employers

Providing coffee is not a solution to workplace fatigue. You need to manage shift work in ways that reduce employees' need for stimulants.

3. Fatigue leads to physical and mental impairment

Laboratory studies indicate that fatigue impairment can be equal to or greater than alcohol impairment.

In the workplace, fatigue may cause workers to:

• feel sleepy
• find it hard to pay attention
• have slower reaction times and poorer coordination
• have slower, muddled thinking.

Implications for employers

Evaluate the risks posed by tasks performed when levels of fatigue can be expected to be high, and have systems in place to detect fatigue impairment. Design work to prevent fatigue accumulating, and support recovery by providing adequate opportunities for high quality sleep.

4. Shift work (particularly night work) can be a significant cause of fatigue

While shift work in itself inevitably produces fatigue, it is not the only direct cause. Shift work acts as a cause of fatigue along with other work and non-work factors.

Other causes of shift worker fatigue may include:

• physical and mental task demands-high workload, lack of breaks, work duration, type of work, work scheduling, unpredictability of hours of work
• environmental factors such as noise, artificial light, heat, humidity, and vibration
• biological factors-lack of sleep, less functional times in the body's daily cycle, poor health
• activities away from work-family responsibilities, social commitments, commuting.

Shift workers have more accidents commuting to and from work than non-shift workers, which are likely to be caused by fatigue.

Implications for employers

You need to be especially alert to the possibility of fatigue-induced impairment in shift workers by:

• identifying the times when workers are more likely to be affected by fatigue
• timing the starting and ending points of shift rosters to minimise fatigue
• applying and following the types of strategies described in Part 2.

5. Alertness and capability vary with the time of day

People's ability to be alert or to focus attention is not constant throughout the course of a day. There are two low points during the 24-hour cycle, which occur for most people somewhere between 3.00 and 5.00am, and again between 3.00 and 5.00pm.

These low points are reflected in the times when most fatigue-related driving accidents happen.

Implications for employers

This information has possible implications for:

• task scheduling
• performance expectations
• the number, length, and use of breaks.

Shift workers may be less able to assess their safety and modify their behaviour during the low-functionality times of day or night. You and your employees need to agree to take a conservative approach to safety at those times.

The particular measures you take to prevent fatigue-related errors will depend on the risk-how likely such errors are, and how serious their consequences would be.

6. People are programmed to be awake during the day and asleep at night

Humans have an inbuilt 'body clock' that controls daily rhythms of alertness and sleepiness.

When people do shift work they must try to override the body clock to remain active at night when the body wants to sleep, and to sleep when the body wants to be active. As a result, they may be working when they are at their least functional and most error-prone, and not getting enough sleep between shifts to recover fully.

The body clock seldom adapts fully to shift work. An exception is when workers are never exposed to daylight at all. Workers on oil platforms in the North Sea, for example, almost completely reverse their body rhythms after 2 weeks of working in this way.

Implications for employers

Try to minimise disruption to natural rhythms when planning shift work. Provide a roster that allows employees to regularly reset their body clocks to the natural rhythms.

7. The ability to fall asleep easily varies with the time of day

Generally speaking, most people fall asleep naturally somewhere between 10.00 and 11.00pm, (although people do vary, with some preferring to go to bed earlier, and others preferring to stay up later). There is a period of wakefulness before this, from around 6.00pm to 10.00pm, when it is difficult for most people to fall asleep.

It is also difficult to fall asleep when the internal drive to be awake reaches its daily peak. This happens about 6 hours after the early-morning peak in sleepiness; that is, late morning for most people. It may be slightly later after a series of night shifts.

Implications for employers

Where practicable, avoid or minimise consecutive shifts that mean employees will need to sleep at those times when falling asleep is most difficult.

8. How much time people need to recover from fatigue depends on the time of day

This fact, together with the following one (sleep loss is cumulative), means that while it is reasonable to expect employees to get adequate sleep during a normal overnight break of 12 hours, it is not reasonable to expect that they will get adequate sleep in a 12-hour break that begins in the morning.

Implications for employers

If possible, allow employees longer periods off if they must sleep during the day.

9. Sleep loss is cumulative

As a pattern of shift work continues, the effects of sleep loss and poor quality sleep accumulate, leading to increasing sleepiness and performance impairment.

Two full nights of unbroken sleep within the normal self-selected sleep time of 10.00pm to 8.00am, with a normal day in between, are a minimum requirement for adequate recovery after periods of overnight work.

Implications for employers

Provide breaks with at least 2 full nights off (and where normal day-oriented functioning is possible) as part of the normal shift roster.

Depending on when the time-off period begins, this may mean providing a period longer than 48 hours. For example, a 48-hour break beginning at midnight gives only one full night of uninterrupted sleep.

Shift workers who cross time zones (such as international pilots) will have additional problems that need special measures.

10. Various strategies can minimise fatigue and promote better sleep

Good education about fatigue leads to common understanding and appropriate workplace-specific solutions. Shift workers can be given strategies to improve their quality of life and sleep, such as improving their sleep facilities, and avoiding caffeine or alcohol within the hours before sleep.

Make sure you cover the following topics in your information and training sessions:

• adjusting the sleeping area to promote good sleep
• good nutrition while working shifts
• use and avoidance of stimulants
• recognising fatigue
• getting to and from work safely
• fitness and exercise
• effective napping
• maintaining home and family life
• childcare arrangements
• equal facilities for shift workers.

Implications for employers

Provide training in fatigue management strategies before an employee begins shift work.

Education and training are an important part of any shift work management system, but they are never a complete solution.

11. Preventing workplace fatigue requires cooperation and compromise

Shift-working arrangements are a compromise between the business's need for work to continue at a time when people are normally asleep, and employees' need to recover adequately through quality sleep.

Finding compromises that are acceptable to the greatest number of people will require employee involvement and participation. Some rosters are better than others, but everyone involved needs to accept that there is no 'perfect' night-shift roster.

Bear in mind that:

• there is a sense that the most successful roster is the one that staff prefer
• people adapt their lives to any arrangements over time, and changing arrangements can be seen as a threat to their adaptations
• if a roster never changes, it cannot be improved.

Implications for employers

The success of any shift-working arrangements will largely depend on the quality of the consultation process. People taking on shift work need reliable, basic information to make informed choices.

Changing shift-working arrangements is a major undertaking. Employees will need time to adjust.

12. Various strategies are available for managing shift work to minimise fatigue

Strategies available for assessing and managing shift work include standard audit frameworks, roster design principles, risk assessment tools, and fatigue modelling methods.

There are various tools to use in developing these systems:

• FAID fatigue safety system-see www.faidsafe.com
• Australia New Zealand Standard 4360:1999-Risk Management.

Implications for employers

No single method of shift work management will fit all circumstances. Whichever method you use, you will need to tailor it to the needs of the organisation.

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