Tokyo Electric Power Company (TEPCO) recorded a second source of an extremely high radiation exposure amid the wreckage of its Fukushima Daiichi nuclear power plant destroyed by the multiple unit hydrogen explosions and nuclear meltdowns as a result of the March 11, 2011 earthquake and tsunami.
On August 3, 2011, geiger counters used by TEPCO workers entering Unit 1 shot up to 5 seiverts per hour (500 REM/hr). This is considered a deadly dose of radiation forcing the workers to retreat from the area. On August 1, 2011 workers first encountered a radiation field that sent instrument readings offscale at more than 10 seiverts per hour.