At times, emergency workers at the nuclear plant have had to retreat from critical cooling operations, but it would take a catastrophic explosion to force them to abandon their effort to stabilize the plant.
Tokyo Electric Power Company (TEPCO) has 180 workers in protective gear, working in crew shifts of 50, who are using fire hoses and other equipment in a desperate attempt to keep reactor cores and spent fuel pools filled with water.
At one point Wednesday, the crews were pulled out of action - it is unclear whether that was due to an unexpected spike in radiation or a planned venting of steam.
"These workers are under lots of risk already, but if they are to have any hope of controlling these reactors, then there needs to be people on the ground as these sea-water pumping operations can't be done automatically," said Tom Grieder, an analyst with IHS Global Insight Inc.
The workers will likely remain on the job unless there is another explosion or a complete meltdown of fuel rods that would drive up radiation to extreme levels, Mr. Grieder said.
But even in that case, TEPCO would look for volunteers -workers willing to undertake what could amount to a suicide mission - to try to contain the damage. "Even in the extreme event of Chernobyl, they did pull a lot of people out but they still had people there on site to take some basic measures," said John Luxat, professor of nuclear physics at McMaster University and former safety manager at Ontario Hydro.
The workers wear protective clothing and breathing masks, but the suits are effective only against alpha radiation. They offer much less protection against deadly gamma rays that would be emitted from melted fuel.