Hours of Work and Performance: Knock it off or risk injury

BrooklynDodger has been hostile to arguments that reducing overtime, or fatigue associated with work schedule is an important area for prevention of occupational injuries. The Dodger feels that interventions depending on improving worker perception, judgment, reaction time, accuracy, and motivation are limited in impact compared to interventions which abate potential for injury based on engineering controls or substitution.

Nevertheless, within a determined environment, fatigue or other impairments are effect modifiers.

The study referenced below noted that after 17-19 hours without sleep (following a 7+ hour sleep), performance on some tests was equivalent or worse than that at a BAC of 0.05%. Response speeds were up to 50% slower for some tests and accuracy measures were significantly poorer than at this level of alcohol. This corresponds to 9 pm after waking at 6 am. After longer periods without sleep, performance reached levels equivalent to the maximum alcohol dose given to subjects (BAC of 0.1%).

The investigators concluded that these findings reinforce the evidence that the fatigue of sleep deprivation is an important factor likely to compromise performance of speed and accuracy of the kind needed for safety on the road and in other industrial settings.

BrooklynDodger notes that most studies of injury and work duration are based on time into shift rather than time since waking. It is fsbiologically plausible that cognitive effects are more determined by time since waking than work time. This study only measured the acute effects of one day rather than a chronic exposure schedule of 80 hour weeks back to back.

BrooklynDodger notes that when an effect level achieves statistical significance in an exposure-response relationship for adverse effect, the appropriate exposure standard must accommodate an appropriate extrapolation factor to achieve an acceptable level of risk.

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Occup Environ Med. 2000 Oct;57(10):649-55.


Moderate sleep deprivation produces impairments in cognitive and motor performance equivalent to legally prescribed levels of alcohol intoxication.

Williamson AM, Feyer AM.School of Psychology, University of New South Wales, Sydney, Australia. a.williamson@unsw.edu.au