NEWPORT, Mich. --Aug 1 - McClatchy-Tribune Business News Formerly Knight Ridder/Tribune Business News - Tom Henry The Blade, Toledo, Ohio

As many as 50 workers at the Fermi II nuclear power plant were evacuated yesterday from the auxiliary building that sits between the plant's reactor and the building that houses its steam generators.

Fire alarms, which may have been triggered by the region's extreme humidity, prompted the evacuation, said Viktoria Mitlyng, a Nuclear Regulatory Commission spokesman.

The National Weather Service indicated the heat index in Monroe, which is near the plant, was the highest in the Toledo area yesterday at 107 degrees from 1 to 3 p.m.

The index, a combination of heat and humidity as measured in shaded areas with light winds, is expected to again exceed 100 degrees today throughout the region.

Eileen Dixon, Detroit Edison Co. spokesman, said the plant's fire brigade responded to the alarms. She said the utility notified the NRC at 1:44 p.m. yesterday of an "unusual event" in progress -- the lowest of four emergency action levels.

No smoke or fire was detected. Nor were any injuries or property damage reported. However, the alarm response systems activated the release of a fire-suppressant gas, carbon dioxide, in one part of the affected building. The gas had to be vented before employees were allowed to return, Ms. Mitlyng said.

"The plant is in a stable condition," she reported late yesterday afternoon.

Though Ms. Mitlyng said humidity is believed to be a culprit in the alarm system malfunction, she also said that "the cause for this is not clear" and that Nuclear Regulatory Commission officials are still trying to determine the root cause.

"We have people in our incident response center on line with Fermi until the situation is resolved," she said.

John Austerberry, another Detroit Edison spokesman, said the gas was released in a large work area inside the auxiliary building where cables are spread before installation.

As of last evening, the utility was still in contact with officials from the NRC's regional office in suburban Chicago, hoping to resolve the matter by phone and restart the nuclear plant.

The Fermi II plant, 30 miles north of Toledo in northern Monroe County, was unexpectedly shut down Saturday by an electrical problem shortly after this latest heat wave began.

The plant's reactor was automatically shut down by safety systems at 3:50 p.m. Saturday, when the site's pair of offsite power feeds failed.

The utility identified a problem with an electrical relay and has corrected the malfunction, Mr. Austerberry said.

Fermi operators began restarting the plant at 11:30 p.m. Sunday.

Power ascension was expected to reach 20 to 25 percent of the reactor's capacity last night, enough to have the plant putting electricity back on the grid, Mr. Austerberry said.

Barring any complications in getting the fire-suppression event resolved, Detroit Edison hopes to have Fermi II's reactor back at full power late tonight, he said.

The plant's power is needed because of extreme demand for electricity during heat waves like the one gripping the region.

DTE Energy, the parent company of Detroit Edison, yesterday asked utility customers to monitor their power consumption, including air conditioning and major appliances, between noon and 9 p.m. today.

Contact Tom Henry at:

thenry@theblade.com

or 419-724-6079.