Master Sgt. Cristy Duncan in the J5 area of StratCom’s headquarters. Workers repaired an air-handling unit serving the J5 department on Oct. 3. “I can tell there’s a difference,” Duncan said. “Something’s been changed.”

In July, a worker in the U.S. Strategic Command’s underground headquarters got mysteriously sick.

Then another in the same area did. And another.

Eventually seven employees reported similar illnesses, some of which required hospitalization.

Dozens of other workers reported headaches, burning eyes and dizziness.

StratCom officials now believe they’ve found the culprit: a buildup of carbon dioxide in one group of basement offices.

The Air Force has since moved 22 workers and is now cleaning the 37,000-square-foot suite of offices in the aging StratCom building at Offutt Air Force Base near Bellevue. The rooms, one floor underground, are the workplace of 200 people from StratCom’s J5 (Policy and Plans) department.

Their job includes preparing the nation’s plans for nuclear war and for defense against other large-scale threats to the United States.

Citing privacy concerns, StratCom officials would not describe the illnesses suffered by workers, but several visited hospitals, said Maj. Gen. Dan Karbler, StratCom’s chief of staff. None have suffered long-term health effects. All have returned to work. A survey showed that many other workers have experienced irritated noses and eyes, fatigue and dizziness.

Indoor carbon dioxide is the result of human activity and is given off when humans exhale. It builds up to higher levels later in the day. Excessive CO2 indoors is usually tied to poor ventilation, experts say.

Typical symptoms of exposure to high levels of carbon dioxide can include headaches, dizziness, drowsiness and loss of attention. Recent studies have suggested that even slightly elevated CO2 levels may impair a worker’s ability to complete complex tasks.

Workers in the J5 area began reporting in the summer that the air seemed stale.

“It just didn’t feel like fresh, clean air,” said Air Force Master Sgt. Cristy Duncan, who works in J5.

But the command didn’t fully realize the scope of the problem until several more workers became ill.

“It took awhile to understand (that) maybe there is a connection,” said Col. John Cotton, StratCom’s surgeon general.

Cotton recommended an occupational health inspection of the J5 section.

Officials also conducted a survey of J5 workers during the summer regarding health effects. Of 84 who responded, 65 percent reported an irritated or stuffy nose, 62 percent reported fatigue, 48 percent suffered from headaches, 41 percent had itchy or burning eyes and 19 percent reported dizziness.

The results led StratCom to suspect elevated carbon dioxide.

In September, tests of the carbon dioxide levels in each room showed that levels exceeded standards set by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) of 1,000 parts per million almost daily. But they didn’t reach the 5,000 parts per million considered unsafe under federal Occupational Safety and Health Administration rules. Afternoon readings reached as high as 1,600 parts per million.

“It’s above comfort levels, but below OSHA permissible exposure limits,” Cotton said.

Workers were allowed to move out of the affected spaces if they wished.

“We said ‘If you are uncomfortable, we will move you,’ ” said Col. Jeff Hagan, StratCom’s deputy chief of staff. Twenty-two workers accepted the offer.

StratCom officials said they aren’t sure why carbon dioxide has built up in these offices. The space doesn’t have a history of air-quality problems, Cotton said.

One theory, he said, is that it is related to the loss of an air-intake vent that was toppled in an EF1 tornado that hit Offutt on June 16. That vent brought fresh air into the underground spaces at StratCom. It was fixed late in the summer.

Workers also repaired an air-handling unit serving the J5 space on Oct. 3. After that, CO2 levels began dropping and have been consistently below the ASHRAE standard since, peaking on most days below 800 parts per million, according to data provided by StratCom.

“I can tell there’s a difference. Something’s been changed,” Duncan said.

“I feel it is (better). The air’s cleaner, fresher,” said Al Gay, a civilian who has worked at StratCom since 2003.

Cotton said the problem may simply be the structure’s age. It was built in 1957 to house the headquarters of what was then known as the Strategic Air Command.

“When you have an old building, you’re going to have issues,” Cotton said.

That’s especially true in buildings with basements, he added. Much of StratCom’s work is done underground, in a facility built to serve as a command bunker.

“Our basements have basements,” Karbler said.

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With no definite cause, it’s not clear what else StratCom may do, though officials are planning a deep clean of the space in January.

The ultimate solution may be completion of the $1.2 billion StratCom headquarters under construction across the street. That project has had several delays since workers broke ground in 2012, including the persistent discovery of mold in ductwork for its heating and air-conditioning system.

Earlier this year, U.S. Army Corps of Engineers officials estimated that the building will be fully completed and occupied by July 2019.

But the current building won’t be empty for long. After StratCom moves out, the 55th Wing headquarters staff is scheduled to move in.

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