Potentially deadly doses of radiation surround them as they work, and their suits do little to prevent radiation from seeping into their bodies.
Radiation sickness sets in after exposure to 1,000 milliseiverts (mSv) of radiation at once.
It's not clear what doses of radiation these men are absorbing, but American and Japanese regulations on radiation exposure are similar: both countries have a total dose of 50 mSv that workers are allowed to be exposed to in one year. But in an emergency situation, workers are allowed to exceed that value. According to the NHK, the Japanese raised the maximum dose allowed to 100 mSv for the Fukushima 50, and on Tuesday raised the number to 500 mSv -- the international value for the maximum allowed dose in a state of emergency.
"That is amazing, but I guess they have a major problem on their hands," said Dr. Eric Hall, a nuclear researcher at Columbia University in New York City.
Despite the massive amounts of radiation they are facing, not all experts believe the radiation levels in the Fukushima Daiichi complex will be fatal.
"These guys are not necessarily laying down their lives for their country and friends. We have a good understanding of what we can actually expose ourselves to. NHK said this morning that the workers are allowed to go in for a very short period of time, make an adjustment on a fuel generator or a pump or a valve, maybe take some data from a gage, and then they go back out," said Jere Jenkins, the director of Radiation Laboratories at Purdue University in West Lafayette, Ind.
"You've got a limited amount of expertise on those units. If your workforce is 1,000 people, you don't want to start wiping out those people because you're going to lose your experts. I know 'experts' are saying these people are charging into their death, but that's not right," added Jenkins.
While radiation-induced cancers are a serious worry for those exposed to high doses of radiation, they usually take at least a few years to set in.
"You may see an incidence of cancer 30 years down the road. Cataracts can set in in 30 to 40 years," said Jenkins.
"Leukemia showed up within a few years in the atomic bomb survivors, but solid cancers did not appear until 10 years and continue [to show up] to this day," said Hall.
The crews are not necessarily made up of strong young men. Emergency nuclear scenarios suggest asking older retirees to volunteer, not because they're more expendable, or even because they're more skilled, but because even if they're exposed to massive amounts of radiation, history has shown they would die of old age before they die of radiation induced cancers, which can take decades to develop.
"No one is sacrificing themselves. Encouraging older workers is based on the idea that they are past their reproductive life, not on the basis of cancer risk," said Hall. "It was common practice years ago when radium was used in hospitals to have 'older' workers as radium custodians... [because they are] past their reproductive years."