An aerial view of the damaged Reactor No. 4 at the Fukushima Daiichi nuclear… (Reuters )
Bursts of radiation being released at the stricken Fukushima nuclear plant could mean workers there will have to be quickly rotated out, and some could rapidly reach their annual exposure limit, complicating efforts to contain Japan's continuing nuclear crisis.
"Those are pretty brave people," David Brenner, the director of the Center for Radiological Research at Columbia University Medical Center, said of the workers. "There are going to be some martyrs among them."
Disaster officials could face a grim choice: Scale back their containment efforts or allow workers to face radiation levels that could significantly increase their risk of cancer.
Photos: Crisis continues in Japan
Reports on Thursday indicated that at times radiation was intense enough to exceed even Japan's newly raised annual limit in as little as an hour.
The new limit — 250 millisieverts — is five times the allowable exposure in U.S. nuclear plants and 125 times what workers typically receive each year.
That level of exposure raises the chances that workers will eventually die of cancer by 1 percentage point, according to John Boice, a cancer epidemiologist at Vanderbilt University and radiation safety expert.
Considering the scope of the disaster — and the fact that at least 20% of people already die of cancer — many workers may be willing to accept the danger. The situation becomes more complicated at higher doses, because radiation risk is cumulative. In other words, the risk of dying of cancer rises an extra percentage point with each additional 250 millisieverts.
It is not clear for how long the government will abide by its new limit.
There were conflicting reports about the amount of radiation the workers may have received so far. It also was not clear if the releases were planned and whether the workers were sheltered at the time.
At one point on Thursday, a level of 400 millisieverts per hour was recorded at the plant. That reading was an instantaneous measurement, and it was not clear how long that emission rate was sustained. But at that rate, a fully exposed worker would have to leave in 37 minutes, 30 seconds and not come back for a year to avoid exceeding the limit.
The Japanese government has tried to protect workers by keeping as few people on-site as possible, monitoring how much radiation they receive and limiting helicopter missions to drop water on the plant. Special clothing and respirators provide some protection from the damaging emissions.
"The main danger is gamma radiation," said Elmer Lewis, a nuclear plant safety expert at Northwestern University in Evanston, Ill. "Gamma can penetrate your body no matter what you're wearing out there. It's like a high-powered X-ray."
The plant workers are trained to react to crisis through simulated disasters, Lewis said.
But, he said, "there's really no way to anticipate what we're seeing here. They're professionals who are doing the best with what they have."
The most acute danger would come from a sudden release of radiation from which workers could not escape — an explosion, for example. That could cause radiation sickness, a devastating illness that is often fatal.
In the 1986 Chernobyl disaster in Ukraine, then part of the Soviet Union, the worst nuclear plant accident in history, workers who battled a weeklong fire were exposed to radiation at levels thousands of times higher than the Japanese yearly limit.
At first, people exposed to that much radiation might look normal. In a week, things change drastically.
"People's hair starts to fall out and the burns appear and the bone marrow damage starts," said Dr. Robert Peter Gale, a hematologist who flew to Moscow days after the accident to try to save workers airlifted there. He is scheduled to fly to Japan on Saturday to help with the Fukushima relief efforts.
Gale treated Chernobyl exposure victims with antibiotics and experimental hormones. In 13 cases, he performed bone marrow transplants in an attempt to revive their immune systems.
Of 600 workers present when the Chernobyl accident occurred, 134 developed radiation sickness, and 28 of those died within four months, according to the United Nations. Many of the rest have continued to battle health problems. Several developed cataracts.
The number of workers at the damaged Fukushima Daiichi plant during the crisis has varied from about 50 to 180, except for an hour or two when all workers had withdrawn.
Still, it is difficult to compare the accidents.
Some firefighters sent to the burning Chernobyl reactor later said they were not warned about the radiation danger, and many workers lacked protective suits and breathing devices. Soviet officials sent helicopters into the clouds of radioactive smoke to help douse the fire.