Dust monitorer alerted to wear full face gas mask in Fukushima plants on 15:00 1/18/2012.
It was the dust monitoring post to measure the hot particles in the air continuously, set in front of the central operating room, Menshin Juyo to.Fukushima plant workers were ordered to wear full face gas mask on 15:11 1/18/2012.
Then they confirmed there was no meaningful change of the monitoring result of other posts, re-started the dust monitorer after changing the filter on 15:40 1/18/2012.
By measuring the radiation level manually in front of the central operating room, the hot particles were less than the detectable level (1.4×10-5 [Bq/cm3]) so they announced they can put off the mask on 15:56 1/18/2012.
(Source)
Iori Mochizuki