The Impact of Sleep on Safety’s Dirty Dozen

safety checklist

The Dirty Dozen was created in 1993 by Gordon Dupont while working as an employee for Transport Canada. It later became part of a training program for Human Performance in Maintenance and is now a central guideline used by transportation companies and safety training programs worldwide. The list focuses on twelve common preconditions for human error and unsafe acts. A detailed explanation of the twelve preconditions listed in the Dirty Dozen can be found at the SKYbrary repository of safety knowledge. Amongst the twelve, six preconditions are known to be positively impacted by healthy, restorative sleep. They are:


“Fatigue is a natural physiological reaction to prolonged physical and/or mental stress.” In working populations, accidents and errors caused by fatigued employees create high human and financial costs. As a result, companies who focus their resources on the root causes of worker fatigue find significant savings across many aspects of health, wellbeing and human performance. With approximately 45% of the US population reporting sleep problems each night, companies can reduce the occurrence and impact of fatigue by offering convenient access to sleep health professionals who can resolve sleep problems, sleep disorders and circadian rhythm misalignments that impact many shift workers.

FACT: Fatigued workers in the workplace are costing companies more than $18 billion a year in the U.S.


“Acute stress is that which arises from real-time demands placed on our senses, mental processing and physical body. Chronic stress is accumulated and results from long-term demands placed on the physiology by life’s demands.” Because both acute and chronic stress impair cognitive emotional responses, studies show that decisions made in this state are far less creative, show poor judgement and result in more accidents and errors. Stress that results from fatigue can be insidious in nature as people feel that they can “adapt” to stress, when actually it accumulates and reduces mental faculties. The best way to handle high levels of stress is to provide the brain and body with the proper amount of recovery time in the form of healthy sleep. The result is incredibly predictable, improved emotional resilience, reduced physical and mental tension, and significantly enhanced decision-making under stress.

FACT: Stress-related accidents including those associated with sleepiness and fatigue account for 60-80% of total reported accidents.


“Complacency can be described as a feeling of self-satisfaction accompanied by a loss of awareness of potential dangers.” Complacency increases with low energy levels, longer time on task and higher levels of mundane activity. In this state, workers are less aware of their surroundings and are less likely to react to changes requiring their attention. In addition, people experiencing complacency due to mundane activity and/or long periods without rest, are at much higher risk for accidents in the workplace. Allowing individuals to take breaks during long, monotonous tasks, as well as to start tasks with an adequate amount of sleep and recovery is paramount to combating complacency.

FACT: The inattention to detail can be a contributing factor for why 9 out of 10 workplace accidents are caused by human error.


According to the SKYbrary repository of safety knowledge, “lack of awareness is defined as working in isolation and considering only one’s own responsibilities and not the affect actions may have on others and the wider task.” Awareness is dependent on sensory input and the ability to detect information that requires a response. The brain’s ability to create awareness requires daily restoration of neurochemicals, which can be dramatically impaired by poor sleep. It goes without saying that companies do not allow employees to work while intoxicated, but neuroscience tells us that the effect fatigue has on the brain is just as bad as alcohol. Experiments show that individuals experience similar levels of cognitive impairment when they are sleep deprived or fatigued, as they do when they are intoxicated. To avoid this situation, it’s important for employees to recover from fatigue with healthy sleep and adhere to shift schedules and programed rest periods.

FACT: A study performed at the University of Pennsylvania demonstrated that being awake for 21 hours is the equivalent of a blood alcohol level of 0.08%, which is considered legally drunk.


“Distraction could be anything that draws a person’s attention away from the task on which they are employed.” While it is not uncommon to sometimes get distracted while working, it becomes even easier for a person to succumb to distractions when fatigued. As a result, people become more forgetful and have a harder time redirecting focus to work after a distraction. This can negatively affect safety by increasing the risk and degree of accidents and errors. By reducing typical workplace distractions and increasing quality and quantity of sleep, employees will be more focused on tasks at hand and eliminate the errors and mistakes that distractions create.

FACT: Data indicates that distracted drivers, for example, significantly increase the severity of accidents.


“Pressure can be created by lack of resources, especially time; and also from an inability to cope with a situation.” Some level of pressure is unavoidable and can be expected in any work environment. However, too much pressure can result in errors that compromise safety. The intensity of pressure is amplified when people are tired or fatigued. To improve resilience under pressure, individuals need to be fully rested and approach work with a clear mind. The size and complexity of a once daunting task will seem much less significant after the brain and body are no longer fatigued.

FACT: The inability to handle the stress related to pressure, results in errors and mistakes which stem from either over performing or speeding up to get the job done quickly. Both responses result in a greater chance of creating or being involved in an unsafe act.


Medical research has shown that employees who suffer from lack of sleep or fatigue are at higher risk for workforce accidents and errors. While not every precondition is significantly impacted by healthy sleep, the benefits of convenient access to solutions that effectively address employee sleep problems can significantly reduce or prevent the occurrence of six of the twelve Dirty Dozen preconditions for unsafe behavior.

Discover how much poor sleep is costing your business.

Calculate the cost at:

2. Health Advocate
3. Willis Towers Watson
4. Safety Partners, Ltd. 
5. Dr. Jeff Durmer, MD, PhD
6. APA PsycNet
7. Work and Sleep (Key words: sleep deprivation and workplace distraction, pg. 204)

The Impact of Sleep on Safety's Dirty Dozen