Military helicopters equipped with lead shielding have dumped water on parts of the severely damaged Fukushima Daiichi nuclear power plant in Japan, while high powered water cannons were aimed at spent fuel cooling areas in attempts to prevent massive radiation releases. Radiation dose rates have been measured at 250 millisieverts per hour above the plant. By U.S. standards, the New York Times reports, emergency workers could only be exposed to such levels for an hour before reaching their dose limit.

For regular updates on the situation at the plant, check out the Japan Atomic Industrial Forum, which produces a table showing the status of all of the reactors at Fukushima, as well as radiation levels at the border of the plant.

Yesterday, the U.S. Nuclear Regulatory Commission recommended that the evacuation zone around the plant be extended from the current 20 kilometers to 80 kilometers. The head of the NRC, Gregory Jaczko, also said at a congressional hearing that he had seen indications that one of the spent fuel storage pools had run dry, exposing the fuel and creating a risk of extremely high radiation levels. (Reports have not specified precisely how high.)