Fire alarm triggered for fifth time at Fukushima Daiichi Nuclear Power Station in August; no fire confirmed on site

At 7:14 a.m. on August 18, a fire alarm was triggered on the first basement floor of the turbine building of Unit 5 at the Fukushima Daiichi Nuclear Power Station. Tokyo Electric Power Company (TEPCO) stated that after fire department personnel arrived and conducted inspections, it was confirmed at 7:55 a.m. that there was "no fire" on site. Readings from radiation monitoring stations around the plant showed no significant fluctuations.

This was the fifth time a fire alarm had been triggered at the Fukushima Daiichi Nuclear Power Station since the beginning of August. Previously, related alarms had occurred on August 8 at the maintenance building for Units 5 and 6, on August 12 at the emergency diesel generator room for the high-pressure core spray system of Unit 6, on August 13 at the main administration building, and on August 15 at the southwest stairwell of the turbine building of Unit 5. After each of the above alarms was triggered, the fire department confirmed that no fire had occurred, and no significant changes were observed in surrounding radiation monitoring data.

In response to the consecutive triggering of fire alarms in recent days, Tokyo Electric Power Company stated on August 17 that smoke-sensing detectors had previously misidentified moisture as smoke. The company believes that the high-humidity environment brought by the approaching typhoon and rainfall may have been one of the factors triggering the alarms.

Tokyo Electric Power Company plans to return the relevant detectors to the manufacturer for further inspection and will confirm through subsequent investigations whether rainfall and humidity were the direct causes.