Do employees’ work schedules put them at-risk? The role of shift scheduling and holidays in predicting near miss and incident likelihood

This evaluated the link between work schedules and workplace incidents and near miss reporting.

A large dataset consisting of a crew schedule calendar from 2016-2018 of a Fortune 500 company (which had 350 operators at the time of the study) were evaluated. This included day and night shifts.

Providing background they note:

·        Work schedules can restrict the rest opportunity between shifts to under 11 hours, making work physically and psychologically demanding

·        Other work highlights that daily rest periods under 13 hours don’t allow people to adequately recover from fatigue

·        Work with overtime schedules, shifts of 12 or more hours and work weeks >60 or more hours are linked to significantly higher self-reports of injury than work without those characteristics

·        Other work has linked work >41 hours a week with a greater number of reported near miss events compared to those working 35-40 hours a week. This effect was amplified further in those working >51 hours a week

·        Working multiple days in a row can exacerbate inadequate rest between shifts. One study explored the accumulation of fatigue over three consecutive 12 hour shifts in healthcare, finding that reaction time, attention and muscle function were all negatively impacted over shifts

·        The DuPont schedule, a rotating night-shift schedule as was used in the current study, has been associated with employee circadian rhythm disruptions; resulting in sleepiness and worsened job performance

·        Other data found that workers of rotating shift schedules received less sleep in the initial days of a series of consecutive shifts

·        A 2006 meta-analysis found that night shifts were the most risky type of shift: riskier than afternoon shifts, which were riskier than day shifts. 12-hr shifts were riskier than 10, which were riskier than 8-hr shifts

·        In the above study, the safest way to work a 48-hr week was to work six consecutive 8-hr day shifts, being 20% safer than working four consecutive 12-hr day shifts, 40% safer than working six consecutive 8-hour night shifts and 50% safer than four consecutive 12-hr night shifts; similar patterns was found for a 60-hr workweek

·        Another study observed that working more but shorter shifts is safer than fewer but longer shifts and day shifts tend to be safer than night shifts

·        Note: Like any study, this also had a number of limitations. One is the challenge of statistically associating performance to incidents, which tend to be rare (and thus, can require a large sample for statistical significance).

Results

Key findings were:

·        The probability of an incident significantly increased as employees worked consecutive day nights

·        However for night shifts, this pattern reversed such that the first and second night shifts seemed to have a higher risk of incident or near miss compared to shifts occurring later in the swing

·        There were more incidents and near misses occurring on day shifts compared to night shifts [** Although I can’t see if they controlled for headcount differences between shifts]

·        The proximity of the shift to an upcoming holiday break wasn’t linked to increases in incidents or near misses

Expanding on the findings, working consecutive day shifts increases the probability of an incident occurring, where the fourth consecutive shift resulting in higher risk than preceding shifts. They note “if a crew was working their fourth consecutive day shift, they faced a 5.84% probability of an incident and a 4.93% probability of a near miss occurring during their shift” (p4).

However, curiously, this relationship didn’t hold for night shifts – which had a reverse direction, where the earlier part of the swing had a higher probability of events.

Upcoming holidays had no statistical relationship with incidents or near misses in this study, nor did the link between consecutive shifts or near misses.

For near misses, it’s suggested the lack of association could be related to their (under) reporting rather than a true absent connection; that is, reporting a near miss “to be influenced by idiosyncratic reporting behaviors, which likely vary across employees and situations, introducing a larger amount of error variance in near miss measures” (p5).

In wrapping up, they argue that organisations should direct more resources and safety initiatives to addressing the risk of accumulated shift risk. This could include changes to staffing, increases in break time and other approaches [** as part of a coordinated fatigue risk management approach].

Specifically, they suggest that some exposure may be reduced by modifying shift schedules so that consecutive 12-hr shifts are limited to three consecutive days.

Link in comments.

Authors: Laske, M. M., Hinson, P. E., Acikgoz, Y., Ludwig, T. D., Foreman, A. M., & Bergman, S. M. (2022). Journal of safety research, 83, 1-7.