Occhealth Bulletin
11 September 2009
Increased number of workplace injuries after changing to DST
Category: Reviews
Barnes and Wagner (2009) have published research following two studies into the effects of Daylight Saving Time (DST) on workplace injuries. The 24-hour cycle of the earth’s rotation has entrained human behavior to two periods of activity: sleep and wakefulness. The internal body clock (Circadian rhythm) is a major process that regulates sleep and wakefulness in accordance with this 24-hour cycle. Daylight Saving Time, advancing clocks one hour in the spring and adjusting them back one hour to Standard Time in the fall, is used to better match the sleep/wake cycle with the daylight phase of earth’s rotational cycle. This adjustment is considered advantageous to human behavior and their activities including work.
The first study was completed on a NIOSH database of Mine Safety and Health Administration (MSHA) injury data derived from a 24 year period (1983-2006). The study was carried out to examine “the influence of time changes on workplace injuries”. By law, all mining injuries must be recorded accurately including details of the time and date of the injuries. The researchers were able to analyze the details of some 576,292 injuries over the course of the period. They found that 98% of the injured workers were male, the mean age of the injured workers was 39.01 years old and the mean level of work experience, at the time of injury, was 6.49 years. The researchers also wanted to discover the relationship between work experience and injuries following Daylight Saving Time changes. Barnes and Wagner determined that when an hour is lost, there was no relationship to employee experience on the job. However, when an hour is gained (Standard Time), more experienced employees had injuries than at other times of the year. This suggested that newer employees were less likely to be injured on a day following phase delays (gaining an hour) perhaps due to the novelty of tasks and the hour extra sleep allowing for increased levels of attention and cue recognition.
The second study was carried out using information recorded by the Bureau of Labor Statistics called the American Time Use Survey. The survey is carried out nearly every day of the year, every year, and is used to measure the amount of time people engage in various activities such as work, volunteering, socializing and sleeping. The survey samples American civilians (non-institutionalized) aged 15 years or over. Barnes and Wagner used the survey data from the period 2004-2006 and their study was completed in order to determine the “link between phase changes and sleep quantity”. They showed that people sleep on average 40 minutes less following a phase advance (DST) (losing 1 hour) than on other days in the year.
The researchers showed that on Mondays following the switch to DST when one hour is lost, workers sustained more injuries at work and those injuries were of greater severity. When switching back to Standard Time when one hour is gained, there appeared to be no “significant differences in sleep, injury quantity or injury severity”. The workers conclude that “these findings beg for immediate attention given to employee schedules, sleep, and safety, because, as this study reveals, DST may save daylight, but not without painful costs.”
Find further information about this and other Occupational Health matters from the Examinetics, Inc. website at www.examinetics.com.
REFERENCE:
Barnes, C.M. and Wagner, D.T. (2009) Changing to Daylight Saving Time cuts into sleep and increases workplace injuries. Journal of Applied Psychology 94 (5) pp 1305-1317.