Oak Ridge, TN – A three-story apartment building was evacuated and a 56-year-old woman was taken to the hospital after firefighters found a carbon monoxide leak in a boiler in the basement of the building on Tuesday night.

The cause of the leak in the boiler on Vanderbilt Drive wasn’t immediately clear. The boiler is used to heat water in that building, and it won’t be used again until it’s repaired and re-inspected, authorities said.

At about 8:30 p.m. Tuesday, the Oak Ridge Fire Department received a call that a woman who lives directly above the boiler at Rolling Hills Apartments was dizzy and throwing up. Her father, who uses oxygen, told ORFD Captain Ray Burney that the family’s dog was “acting funny.”

“He just couldn’t stand up,” Burney said. The fire captain helped the dog up, but “he fell over,” Burney said.

Recognizing the symptoms, Burney got his gas meter. It showed a carbon monoxide concentration of 1,270 parts per million, or ppm, in the first apartment.

“That’s really high,” firefighters said.

A low alarm level is 25 ppm.

Other apartments had levels as high as 999 and 714 ppm, said Eric Rackard, Oak Ridge Fire Department battalion chief.

High carbon monoxide levels can produce flu-like symptoms. Carbon monoxide is a deadly gas that is colorless and odorless. It is produced by the incomplete burning of various fuels, including coal, wood, charcoal, oil, kerosene, propane, and natural gas.

Authorities said the apartment building has electric heat, but the boiler uses natural gas.

Oak Ridge Fire Department Chief Darryl Kerley said a few residents reported that they had smelled something, possibly the results of incomplete combustion, for a few days. Some of them reported symptoms on Tuesday, Burney said.

Firefighters opened all the apartments in that building to check them and, when necessary, ventilate them with the help of fans. They would have to go back and check levels after ventilating, Rackard said at about 9:40 p.m. Tuesday, when one unit was reported to have a reading of zero.

They were getting good levels, but they also had to make sure the carbon monoxide was out of the crawlspace, Rackard said.

Firefighters said Tuesday night that residents would probably be able to return to the building, but wouldn’t be able to use the boiler for hot water.