Читать книгу Counting Sheep: The Science and Pleasures of Sleep and Dreams - Paul Martin - Страница 21

I have an exposition of sleep come upon me.

William Shakespeare, A Midsummer Night’s Dream (1595–6)

The human errors caused by tiredness sometimes have truly catastrophic consequences, and there have been plenty of man-made disasters to prove it.

Tiredness lay behind the environmental disaster that occurred when the supertanker Exxon Valdez ran aground in Prince William Sound, Alaska, spilling 11 million gallons of crude oil into the pristine waters and polluting thousands of miles of shoreline. The official investigation by the US National Transportation Safety Board concluded that sleep deprivation was a direct cause. The accident took place just after midnight on 24 March 1989, when the Exxon Valdez was under the control of the third officer. He had slept for only six hours during the preceding 48 hours and was therefore substantially sleep-deprived. It appears that he fell asleep on duty. Media reporting at the time suggested that alcohol was to blame for the accident, but the real culprit was fatigue. In addition to the appalling environmental damage, one man’s tiredness cost his employer more than five billion dollars in punitive damages.

Tiredness contributed to the US Space Shuttle Challenger disaster. On a freezing cold morning in January 1986 the Challenger ascended for ten miles and then exploded, killing the crew of seven astronauts. It later emerged that crucial rubber O-ring seals had failed catastrophically at the low temperatures prevailing that morning. The US Presidential Commission that investigated the disaster concluded that there had been serious flaws in the decision-making processes leading up to the launch. The danger had been foreseeable, but tiredness had contributed to the bad decision to launch despite the icy conditions. Key managers had slept for less than two hours the night before and had been on duty since the early hours of the morning. They were at a dangerously low ebb when the fateful decision to launch was taken. The official report noted that ‘fatigue is not what caused the accident, but it didn’t help the decision-making process’. It also commented that ‘working excessive hours, while admirable, raises serious questions when it jeopardises job performance, particularly when critical management decisions are at stake’. Bear in mind that when official investigations search for the causes of disasters they instinctively focus on tangible, physical causes like rubber O-rings and air temperatures; intangible human factors like fatigue are seldom in the forefronts of investigators’ minds.

Lack of sleep has contributed to, if not caused, a string of disasters and near disasters in nuclear power plants. Many of them occurred in the early hours of the morning – a common feature of sleep-related accidents – and stemmed from failures by human operators to make sensible decisions when faced with the relevant information. Research has confirmed that nuclear power-plant operators who work night shifts experience real problems with sleepiness, distractibility and poor alertness. Even if they are not particularly sleep-deprived, they are unlikely to perform well in the early hours of the morning. And that is when the accidents happen.

The worst nuclear incident so far in the USA took place in March 1979, when the reactor at the Three Mile Island power station near Harrisburg in Pennsylvania came close to meltdown. The near-disaster at Three Mile Island arose in the early hours of the morning, after operators failed to recognise what their instruments were plainly telling them – namely, that an automatic valve had closed, cutting off the water supply to the coolant system. The reactor shut itself down automatically, as it was designed to do when a malfunction like that occurred. But a series of errors by the human operators led to a dangerous loss of coolant from the reactor core and almost turned an incident into a catastrophe. Radioactive gases were released from the partially exposed reactor core, but the containment vessel fortunately prevented them from escaping into the environment. Although no one died as a direct result of the Three Mile Island accident, it had a massive impact on the American nuclear industry. The damaged reactor took ten years to decontaminate and remained unusable. Fatigue is believed to have contributed to the operators’ repeated failures to handle the incident correctly.

The worst nuclear accident thus far in history occurred at the Chernobyl nuclear power station in April 1986. It too was sleep-related, and started in the early hours of the morning when the operators were at their lowest ebb. The disaster happened when the engineers operating one of the station’s four nuclear reactors made a series of irrational judgments. They attempted an ill-conceived experiment that involved shutting down the reactor’s regulatory and emergency safety systems and withdrawing most of the control rods from the core, while allowing the reactor to continue running. The operators exhibited the alarming propensity to take inappropriate risks that is characteristic of tired people. As a later report put it, they behaved ‘like intelligent idiots’.

The reckless behaviour of Chernobyl’s operators caused a chain reaction. At 1:23 a.m. on the morning of 26 April a series of explosions blew the reactor apart. There was a partial meltdown of the reactor’s graphite core and it caught fire. Large amounts of radioactive material were released into the environment – several times the amount created by the atom bombs dropped on Japan in World War Two. Some of it was carried by winds and contaminated several western European countries, including France and the UK. Thirty-two people at the Chernobyl plant died at the time of the accident and several more died soon after from severe radiation exposure. The long-term damage to the health of populations living in affected areas remains a matter of controversy, but it is undoubtedly huge. Several thousand people have died, or will die, as a result.

Over and over again, man-made disasters like Chernobyl and Exxon Valdez have occurred at night or in the early hours of the morning, when people’s reactions and judgment are at their weakest. We saw earlier that drivers are much more likely to have a serious crash late at night than in the middle of the morning. Almost everyone who works night shifts displays signs of sleepiness and impaired performance, and it is not difficult to see why. Working at night forces people to perform at a time when their biological clocks are telling them to sleep, and to sleep when their biological clocks are telling them they should be awake. They perform worse when they are at work, and they are less able to sleep when they go home, as a result of which they become tired and accident-prone. Add chronic sleep deprivation to the brew and you have a potentially lethal concoction. And we all have to live with the consequences.