Developments in Brief : Psychologist Says There’s a Reason So Many Accidents Occur at Night

The explosion and radiation release at the Chernobyl nuclear power plant occurred at 1:23 in the morning. The near meltdown at the Three Mile Island power plant occurred around 4 in the morning, and four subsequent critical human errors occurred between 4 a.m. and 6 a.m.

A significant fraction of truck, train and industrial accidents also occur during that period, says biological psychologist David Dinges of the University of Pennsylvania, because “the human biological clock winds down at night.”

Humans have evolved a pattern of working by day and sleeping at night, according to Dinges, and do not adapt to changed schedules rapidly. Today, however, about 20% of the work force does night work, and the body’s attempt to cope with these changes produces lowered alertness, gastrointestinal upsets and cardiovascular problems.

The problem is compounded by automation, which requires humans to monitor dials and gauges, as in a power plant. That type of monitoring is “the one thing we do worst of all at night,” Dinges said.

One partial solution is to rotate shifts forward, rather than in the opposite direction, as is now common. Another is to allow workers a longer time on each shift so they become acclimated. Finally, he said, “age is a critical factor. Younger people adapt much better than older ones.”