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The Risks of Shift Work

Posted by Siriya Mitsattha on August 17, 2017 . 0 Comments

What is shift work?

Shift work refers to any work that occurs outside of regular daytime hours (8 AM to 5 PM), and also involves irregular, on call, and rotating shifts. In 2005, approximately 28% of 14.6 million Canadian workers worked some type of irregular shift. 

Industries where shift work is common include healthcare (doctors, nurses and hospital staff), services (police, fast food and commercial workers) and transportation (airline staff and truckers). 

Working against natural biological clocks could have a detrimental impact on shift workers both physically and mentally. Shift work was categorized as a Class 2A Carcinogen by the World Health Organization in 2007. In addition, studies have shown that night shift workers have almost twice the risk of being injured when compared to regular workers.

Why does shift work pose a risk?

Biologically, humans evolved to rest at night and be active during the day. This cyclic sleep wake pattern is known as the circadian rhythm. 

Shift work forces the body to go against its natural sleep wake pattern. The disruption of normal sleep patterns can result in drowsiness or fatigue at inappropriate times. And since shift workers are required to perform their duties at irregular times, they may make a mistake resulting in an accident or injury. 

The relationship between shift work and performance has been closely studied. Shift workers have been known to be at greater risk of reduced cognitive performance, poor decision-making, slower reaction time, and poor concentration. 

Risks of shift work

A recent study conducted by Maltese et al (2016) titled Night Shift Decreases Cognitive Performance in ICU Physicians found that cognitive abilities of physicians was significantly worse after night shift work. The study assessed the impact of night shift on cognitive performance of 51 staff in the Intensive Care Unit (ICU). The staffs were tested on a series of cognitive tasks following a night of regular sleep and again after a night of shift work. Regardless of experience and age, performance of all cognitive tasks worsened significantly. Performance of critical tasks such as working memory capacity, speed of processing information, perceptual reasoning and cognitive flexibility were shown to decrease.

Infamous accidents that occurred during irregular shifts

Some of the most infamous accidents that occurred have been attributed to human error as a result of shift work.

1. The Methyl Isocyanate Chemical Accident in Bhopal, India.

Bhopal disaster

Almost an hour after midnight on December 3, 1984, a gas leak from Union Carbide’s pesticide factory in Bhopal resulted in about 558,125 injuries and at least confirmed 3,787 deaths. Operating errors made by shift workers was found to be a factor in the magnitude of the disaster. The immediate effects of gas exposure on the surrounding population were coughing, choking, severe eye irritation and burning respiratory tract.

2. The Three-Mile-Island Nuclear Accident, Pennsylvania, USA.

The release of radioactive gases occurred in an early morning of 4 AM of March 28, 1979 at Three Mile Island nuclear generating station in Pennsylvania. Subsequent investigation found that the workers forgot to open a valve – a regular operating procedure. The accident brought increased attention to risks of accidents caused by tired shift workers.

3. Chernobyl Nuclear Accident, Pripyat, USSR.


The Chernobyl accident is widely considered as the worst nuclear power plant accident in human history. The accident occurred at 1:23 AM on April 26,1986. In terms of cost and casualties, the explosion was considered as the maximum Level 7 Event on the International Nuclear Event Scale. The accident occurred during the test of a new voltage regulating system, which was supposed to occur during the day but delayed to the night shift.  During the test, a young engineer erroneously handled the control rods, which set off a chain of events resulting in the reactor meltdown. 

4. The Exxon Valdez Oil Spill, Alaska, USA.

exxon valdez oil spill

The Exxon Valdez Oil Spill is considered to be one of the most devastating human-caused environmental disasters. The accident occurred 12:04 AM on March 24,1989.  The Exxon Valdez ship spilled over 11 million gallons when it ran into a reef. The accident was partly attributed to errors made by the crew, who had previously worked 12 – 14 hours shifts.

What can be done to minimize risks associated with shift work? 

The demands of society today mean that shift work is unavoidable.

However, many steps can be taken to reduce the risk of accidents and injuries that may be caused by drowsiness of fatigue associated with shift work. Changes such as: shift adaptation, work shift planning and management systems, and compliance with worker safety regulations stipulating rest periods between shifts.

Getting restful sleep before the shift work is also a very important factor.

There are lots of resources to help people looking to learn more about shift work:  Learn more about coping with shift work and other risks and problems associated with shift work.


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