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Shift Work

By: Jeffrey Cusack
| Last updated: March 18, 2021

What Does Shift Work Mean?

Shift work is an employment practice that divides a single job into multiple shifts (work periods) per day. For example, a manufacturing plant that operates 24 hours per day might break its work periods into three eight-hour shifts.

Typically, this means that employees who are active during one shift will be replaced by a new group of employees for the next shift. If an employee works two shifts in a row, that is called a “double shift”.

Safeopedia Explains Shift Work

Shift work can be divided into two categories: fixed shift work, and rotational shift work.

Fixed shift work refers to any situation in which an employee works at the same time each day, and the same day each week. An employee who always works nights, for example, is a fixed shift employee.

In contrast, rotational shift work refers to situations in which the shift that employees work rotates according to a set schedule. For example, a rotational shift worker may be expected to work a day shift for a set number of days, followed by a set number of days of working the night shift, as part of their regular schedule. This type of shift work is common in a number of sectors, such as in-hospital healthcare work.

The term shift work may also be used to describe any work setting in which employees can be scheduled to come into work at multiple discrete work periods. For example, a retail store or restaurant that can schedule any employee to work a shift at 8 am, 1 pm, or 6 pm may also be said to use shift work.

Many OHS contexts do not include this retail-style type of shift work under their definition of shift work, either because employees in these industries often retain the ability to schedule themselves, or because the OHS authority is limiting their guidance or rules to a specific set of industries. Non-industry specific guidance on shift work may also limit the term to include only those whose shifts require them to work a certain number of hours within a given week.

When used in OHS contexts, the term “shift work” often refers solely to rotational-style shift work. Rotational shift work is of special interest to occupational safety experts because it is associated with negative health and psychological effects in shift workers, as well as increases in human error that can cause safety incidents and catastrophic accidents. Many of the negative effects of rotational shift work are also seen in fixed shift workers who work nights.

According to the Canadian Centre for Occupational Health and Safety, approximately 25% of the North American population participates in rotational shift work, while an article in the medical journal BMJ places the European number at approximately 20%.

Shift Work and Worker Health and Safety

According to the BMJ, rotational shift work is associated with negative health effects due to its continuous disruption and re-disruption of the body’s natural circadian rhythms. Circadian rhythms are physiological rhythms that govern a variety of human metabolic activities, including body temperature, respiratory rate, urinary activity, cell division, hormone production, and other processes. They are a natural mammalian that often operates on a 25 hour cycle in humans, and disrupting this cycle therefore disrupts the governance of numerous health-critical functions.

Disruptions to the circadian rhythm are associated with a variety of negative effects on human health and wellness, and consequently, on the efficiency and quality of their job performance.

Shift work disrupts the circadian rhythm by continuously disrupting the worker’s natural eating, sleeping, and working schedules, causing the worker to become out-of-sync with their body’s natural physiological tendencies and needs. This problem can be made worse by how shift work modifies the worker’s external environment, as circadian rhythms can be disrupted by factors such as the reversal of the day-night cycle (e.g., exposure to sunlight during a worker’s “sleep” hours) and changes to the worker’s social habits.

The negative health effects associated with rotational shift work include increased risk of fatigue, mental illness, gastrointestinal disorders, and cardiovascular disorders. Pregnant women are also at risk of miscarriage, premature birth, and low birth rate. In addition to these risks, some scientists have speculated that the effects of rotational work on human metabolic rate may increase the negative effects of worker exposure to certain toxic chemicals.

Rotational and night shift work have also been linked to accidents and increased injury rates; however, the nature of this relationship is not exactly clear. A study by the University of British Columbia found that over the ten-year period between 1996 and 2006, the percent of rotational workers making OHS claims fell from 7.7% to 3.9%, while night shift-only related claims stayed around 6.0%. A 2017 Korean study found that shift workers face a 2.7 to 1.7-fold risk of occupational injury, while a 2015 Finnish study found increased risk in the United States, but not in India or Singapore.

Despite this lack of clarity, it is generally accepted that the risk of accidents during shift-work is increased if the work involves extended work hours, which means anything beyond an eight-hour shift.

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