In this 2002 photo, workers examine equipments inside one of the reactor units of the Fukushima DaiIchi nuclear power plant in Okumamachi, northeastern Japan. (The Yomiuri Shimbun/Associated Press)

They have been called "the faceless 50," a band of brave technicians still working in the crippled Fukushima Daiichi nuclear plant about 250 kilometres northeast of Tokyo, five days after a devastating earthquake and tsunami set off a series of explosions and other problems at the plant's six reactors.

By Wednesday, the number of workers had grown to 70, all wearing protective gear and being rotated in and out of the danger zone, often for only minutes at a time, so as to limit their radiation exposure. They work in the dark since power and generators at the plant have failed, using flashlights, like miners with headlamps working the depths of the world's deepest mines.

This at a time when Japan's prime minister, Naoto Kan, is warning of the "high risks" of radiation in the vicinity of the nuclear plants. Kan has advised anyone living within 20 kilometres of the plant to leave the area and those within 30 kilometres to remain indoors. Japanese officials also introduced a 30-kilometre no-fly zone to prevent planes from spreading any radiation.

Most of the workers who stayed behind did so voluntarily. At great personal risk, they worked frantically to pump seawater into the reactors to cool the overheated fuel rods within and to release the steam that was boiling off just as fast. Like heroes with their fingers in a dike trying to contain a massive flood, the technicians are trying to prevent a meltdown of the uranium fuel in the rods, which, in the worst-case scenario, could seep through the steel and concrete containment vessels that surround them and unleash radiation.

Esprit de corps

There is reportedly an admirable esprit de corps among these workers, which many observers liken to the high morale among firefighters and special military units. Their bravery has been compared to that of the firefighters who risked their lives after the attacks on the towers at the World Trade Center in New York in 2001.

"They're taking action, they're fully engaged and they know they're saving lives," Francois Perchet, a former manager of nuclear reactors for London's World Nuclear Association, told AOL News on Wednesday. "They might need help for trauma later on, but right now, they're doing the right thing."

The bravery and skill of these workers is similar to that seen during large mining emergencies, such as the massive underground explosion at the Giant Mine in Yellowknife in 1992 that killed nine miners.

A special rescue team trained in emergency life-saving procedures descended at great personal risk to the site of the explosion only to find the mangled bodies of the miners killed by a deliberately set charge, the result of emotions fuelled by an ugly labour dispute.

These emergency operations involve great risk and often great sadness. Jim O'Neill, head of the Giant Mine rescue team, happened to find the body of his best friend, Chris Neill, among the nine dead miners.

­Radiation levels

A New York Times story, which was the first to describe the workers as the "faceless 50," said Japan's Health Ministry authorized raising the legal limit on the amount of radiation to which each worker could be exposed to 250 millisieverts from 100 millisieverts.

The higher limit means emergency workers can remain longer on the site, but it is unlikely it will be raised again. "It would be unthinkable to raise it further than that, considering the health of the workers," Yoko Komiyama, Japan's health minister, told a news conference.

On Thursday, Hidehiko Nishiyama, deputy director-general of Japan's Nuclear and Industrial Safety Agency, said that radiation of about 250 millisievert an hour had been detected about 30 metres above the nuclear plant.

Smoke billows from the No. 3 unit at the Fukushima Daiichi nuclear plant on Tuesday. Workers were ordered to leave the site Wednesday amid a surge in radiation but returned hours later. (Associated Press/Tokyo Electric Power Co.)

Health Canada lists the exposure limits for licensed sources of radiation as 100 mSv over five years and 50 mSv in a year for workers and 1mSv in a year for members of the public.

In Japan, five nuclear plant workers have been killed since the earthquake struck. Another 22 have been injured, and one is missing.

"One worker was hospitalized after suddenly grasping his chest and finding himself unable to stand," the Times reported, "and another needed treatment after receiving a blast of radiation near a damaged reactor."

Echoes of Chornobyl

The Times article describes the "natural bonding" among workers at Japan's nuclear plants. It quotes Michael Friedlander, a former senior operator at several U.S. power plants, who said these workers invariably warn their families to flee but themselves remain at their posts.

"You're certainly worried about the health and safety of your family, but you have an obligation to stay at the facility," Friedlander said. "There is a sense of loyalty and camaraderie when you've trained with guys, you've done shifts with them for years."

Friedlander said jobs in Japan confer identity, command loyalty and inspire a particularly fervent kind of dedication. Recent economic problems have chipped away at the hallowed idea of lifetime employment for many Japanese, "but the workplace remains a potent source of community," he said.

The same kind of heroics happened in Chornobyl, Ukraine, in April 1986 when a nuclear reactor exploded and spewed radiation over a period of 10 days. As with the workers in Japan, the emergency workers at Chornobyl stayed at their posts through the worst of the danger; within three months, 28 of them had died from radiation exposure.

The Fukushima accident has been upgraded from a 4 to a 6 on the seven-point INES scale for nuclear incidents, the highest rating since Chornobyl, which was rated a 7. A 2005 UN study predicted that 4,000 people could eventually die of radiation exposure from Chernobyl.