Disasters Traced to Micro-Sleep as Brain Takes Nap
If it’s 2 p.m., be careful: You’re probably sleepy--and you’re not the only one.
Disasters due to human error are most likely to occur during two periods of the day, scientists say. These are when the human brain has a tendency to fall asleep, and brief, even imperceptible, moments of nodding off may contribute to deadly human errors, causing car crashes and even industrial accidents like the Chernobyl and Three Mile Island incidents.
For reasons not understood, the human body apparently favors sleep in the mid-afternoon and pre-dawn hours. If circumstances or a sleep disorder cut into a person’s regular sleep, the chances of performance errors during those periods are greatly increased, according to a recent report by top researchers.
Peak Time for Accidents
They found that the peak times of fatigue-related, single-car accidents are between 1 a.m. and 4 a.m. and 1 p.m. and 4 p.m., times correlating with the sleepiness periods.
Involuntary sleep can range from long periods of more than 15 minutes to “micro-sleeps” of just seconds. In either case, a person may not even realize that he or she has been asleep--yet the results can be disastrous.
“It is possible for someone to fall asleep for as little as a second and not know about it,” said Dr. Merrill Mitler, chairman of the Assn. of Professional Sleep Societies’ committee on catastrophes, sleep and public policy.
Mitler said falling asleep at a red light until another motorist honks or slams into the back of the car are “classic examples of someone succumbing to this need.”
International Problem
He said international studies have shown that brain processes controlling alertness and sleep lead to drowsiness from 2 a.m. to 7 a.m. and from 2 p.m. to 5 p.m.
“These two windows when sleep is most likley to occur are part of the way the body is built. If, for some reason, a person is not getting enough sleep, the tendencies are exaggerated,” said Mitler, who also is director of research for chest, critical and sleep medicine at the Scripps Clinic and Research Foundation in La Jolla, Calif.
Scientists from the National Aeronautics and Space Administration and from Brown, Harvard, Pennsylvania and Stanford universities and Scripps collaborated on the study of the relationship between workloads and work schedules and public safety.
Most likely to suddenly fall asleep are people who suffer from a disorder known as sleep apnea, a condition in which the air passages close repeatedly during sleep.
Depending on its severity, sleep apnea may stop a person’s breathing for as long as a minute many times in a night. This causes them to wake briefly, but without being conscious of it, in order to take a breath. The constant disruption of the sleep cycle leaves the person “pathologically sleepy,” said an expert in sleep disorders.
“It’s like someone is choking them all the time they are sleeping and they struggle out of it” to take a breath, said Dr. Larry Findley, who led a study at the University of Virginia linking higher auto accident rates to the disorder.
“These people are pathologically, severely sleepy to the point where they may fall asleep while standing up, or giving a lecture (or) interviewing for jobs they want,” Findley said.
Sufferers of sleep apnea who are deprived of the deeper stages of sleep may be unaware of their condition and not realize that they are falling asleep, even while operating machinery or driving.
“You can ask them how they slept and they’ll say fine. But what they think is sleep is really terrible,” said Findley.
Typically, someone with severe sleep apnea is overweight and a chronic, loud snorer “to the point where neighbors ask them to close their windows,” he said.
Treatments for the condition, ranging from surgery to remove oversized tonsils that block airways to a mask that blows air into breathing passages to keep them open, usually are successful.
In the case of the Challenger disaster, Mitler said studies showed that the people who made key decisions in the ill-fated launch had suffered extreme sleep deprivation in the days leading up to the explosion.
Accidents involving nuclear plants at Three Mile Island and Chernobyl similarly indicated connections between lack of sleep, time of day and human error, he said.
“The main point is that anyone can have unintentional sleep disrupt their performance if they are not getting enough sleep,” he said.
He said his committee was urging labor, management and government leaders to consider sleep physiology when designing workloads and schedules, such as for the movement of hazardous materials or other sensitive assignments.
