Chapter 2 - Fatigue

Learning Outcomes

After reading through this chapter, you should be able to:

  • Describe what fatigue is.
  • Name factors that contribute to fatigue.
  • Identify signs of fatigue.
  • Name the times of day when fatigue is at its highest level.

What is fatigue?

Fatigue is an experience of physical or mental weariness that results in reduced alertness. For most people, the major cause of fatigue is not having obtained adequate rest or recovery from previous activities. In simple terms, fatigue largely results from inadequate quantity or quality of sleep. This is because both the quantity (how much) and the quality (how good) of sleep are important for recovery from fatigue and maintaining normal alertness and performance. Furthermore, the effects of fatigue can be made worse by exposure to harsh environments and prolonged mental or physical work.

Inadequate sleep (quality or quantity) over a series of nights causes a sleep debt, which results in increased fatigue that can sometimes be worse than a single night of inadequate sleep. A sleep debt can only be repaid with adequate recovery sleep.

Working outside the Monday-to-Friday, 9-to-5 routine can limit the opportunity for sleep and recovery in each 24-hour period. It can reduce the amount of sleep you get by between one and three hours per day. This is because these hours of work:

  • limit the amount of time available for sleep
  • disrupt the body clock, which is programmed for activity during the day and sleep at night

In addition to sleeping less, people who work non- traditional hours often obtain sleep of a lower quality.

In the current 24 hour, 7 day a week (24/7) society, there are many reasons that workers don’t obtain the quality or quantity of sleep that they require to be adequately rested. Some of these reasons are work related and some are non-work related. Examples of work-related fatigue factors are:

  • hours of work (especially night work, early morning starts, and high total number of hours)
  • task demands or time pressures that do not allow for adequate breaks during shifts
  • working conditions that may compound fatigue (for example, heat stress and time pressures)

Examples of non-work-related fatigue factors include:

  • undiagnosed or untreated sleep disorders
  • individual family or social factors that take priority over sleep


Identify at least two causes of work-related fatigue that have affected you during your working life.



Symptoms of fatigue

In general, we are poor judges of our own fatigue levels. It’s difficult to tell when our fatigue has reached a point where it’s no longer safe to work or drive. However, there are signs or symptoms that can be used as a gauge.

Fatigue-related symptoms can be divided into three categories: physical, mental, and emotional. The diagram on the following page outlines some of the major symptoms in each category. Depending on the type of work being conducted, there may be some task-specific indicators of fatigue that can be added to this list. If you experience two or more of the symptoms listed, you may be experiencing some level of fatigue or reduced alertness. Fatigue is not the only cause of all the symptoms, but when they occur together it likely indicates fatigue-related impairment.

If you exhibit fatigue-related symptoms on a regular basis, you should consider seeing an appropriate medical specialist. This is particularly important for individuals with a body mass index greater than 30 and a neck size greater than 40 cm, since they have a significantly higher risk of sleep apnea.

Symptoms of fatigue. Physical symptoms: yawning, heavy eyelids, eye-rubbing, head drooping , microsleeps.  Mental symptoms: difficulty concentrating on tasks, lapses in attention, difficulty remembering what you are doing, failure to communicate important information, failure to anticipate events or actions, accidentally doing the wrong thing, accidentally not doing the right thing. Emotional symptoms: more quiet or withdrawn than normal , lacking in energy , lacking in motivation to do the task well, irritable or grumpy behaviour with colleagues, family, or friends.

Symptoms of fatigue


Circle any of the above symptoms that have significantly affected you in the past. Reflect on these symptoms and indicate how they have affected your work.


Consequences of fatigue

A fatigued individual is often impaired and can’t continue to perform tasks safely or efficiently. For example, fatigue can affect your ability to:

  • react quickly in emergency situations
  • communicate clearly with fellow employees
  • work productively

Fatigue and falling asleep have been identified as significant contributors to incidents and accidents in a wide crosssection of industry. This relationship has been well supported by evidence from organizational and government investigations as well as industrial risk data. The incidents and accidents that result from fatigue can be severe and include fatalities, but are most often associated with employee injury or equipment damage.

How big a risk is fatigue?

In recent years, researchers have compared effects on performance of alcohol and fatigue. While most people understand that alcohol intoxication can be a significant risk on the roads, the effects of fatigue are not generally understood or acknowledged.

Studies have found:

  • The performance of a person who wakes at 7 a.m. and stays awake for 17 hours until midnight will be as impaired as that of someone with a blood-alcohol concentration (BAC) of 0.05% – the legal driving limit in many countries.
  • A person who wakes at 7 a.m. and then stays awake for 23 hours until 6 a.m. the following day will have a performance as impaired as someone with a BAC of 0.10% – more than the legal limit of 0.08% in Canada.

Although there are differences between being fatigued and being drunk, this research provides valuable information. One night of sleep deprivation can leave you more impaired than would be acceptable for driving a vehicle.

High risk times for fatigue

There are particular times of the day when the risks associated with fatigue are increased, regardless of the relationship between fatigue and recovery sleep. It is important to understand these risks when making decisions about hours of work, hours of overtime, contingency planning, and emergency responses.

Times when fatigue levels increase are:

  • midnight to 6 a.m. (and especially 3 a.m. to 5 a.m.). This is the low point in the body’s circadian rhythm that governs alertness and performance.
  • the beginning and end of shift when handover occurs. Fatigue levels can affect communication.
  • when breaks have not been taken for a number of hours. Employees who have been on duty longer may have accumulated fatigue.
  • early shift starts (before 6 a.m.). Early start times shorten sleep obtained the night before if you either neglect to go to bed earlier in compensation, or “clock watch” because you are anxious about getting up on time.
  • when employees are new to the job or workplace. Learning the new job and getting to know the environment and personnel is stressful. People may find they do not sleep as well during the first week or so of a new job while they become accustomed to the new workplace, role, commute, and hours.


Describe one or more safety hazards you have witnessed in your work environment as a result of any of the above situations.



checkmark Knowledge Check

  • What are two major causes of fatigue?
  • Name four symptoms of fatigue.
  • Compare performance in the following situations:
    - Being awake for over 17 to 23 hours
    - Being under the influence of alcohol.
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