remaining three stopping after three hours. In Ibaraki, some 40 monitors stopped working for three hours until power could be restored. The first of the typhoons of the season is due to strike the area, while Japan states radiation levels at the seabed are several hundreds of times above normal levels off the coast of Fukushima. "The Science Ministry announced late on Friday highly radioactive materials were detected in a 300-km north-south stretch from Kesennuma in Miyagi Prefecture to Choshi in Chiba Prefecture, the Kyodo news agency reported." TEPCO reports that cooling has been restored for spent-fuel pools 1 to 4. Tuesday, 31 May An oil spill near reactors 5 and 6 is detected at 8:00 am, as well as an explosion heard at 2:30 pm near reactor 4. TEPCO reports that the explosion was the bursting of an oxygen cylinder damaged by unmanned machinery during debris removal. TEPCO states that there was a temporary oil leak into the sea near the plant, from an oil pipe that may have been damaged in the March disaster. It is stated as being an extremely small leak, possibly caused by recent rainy weather from Typhoon Songda. TEPCO says that the leak has stopped and oil fences have been installed to prevent the liquid from spreading into the Pacific Ocean. June 2011 Friday, 3 June The first case is confirmed where radiation levels in humans have exceeded limits since the accident at the plant. One worker in his thirties received 678 mSv, while another one in his forties received 643 mSv. Before the accident the limit for emergency situations was 100 mSv, but it was raised by the government to 250 mSv just after the accident. The two TEPCO workers were on duty in the central control rooms of reactors Nos. 3 and 4 and told the health and labor ministry that they didn't remember whether they wore protective masks or not when a hydrogen explosion occurred at reactor No. 1 on 12 March. Saturday, 4 June Air radiation readings of up to 4000 millisieverts per hour are recorded in the reactor 1 building. Monday, 6 June Japan's Nuclear and Industrial Safety Agency (NISA) gives new estimates of the times at which the reactor pressure vessels were damaged and possibly dropped fuel into the containment vessels: 5 hours after the initial earthquake for reactor 1 (20:00 March 11); 80 hours for reactor 2