Flights across the Midwest were delayed Tuesday because so many controllers left work.
Minor flight delays were reported Wednesday but were blamed on isolated storms rather than the controllers' illnesses, said Monique Bond, a spokeswoman for Chicago's Department of Aviation.
About a dozen controllers, or 10 percent of the staff on duty, called in sick this morning, said Ron Downen, president of the National Air Traffic Controllers Association local.
He said he feared even more would be absent from Wednesday afternoon's shift, leading him to renew his request that the Federal Aviation Administration temporarily close the Chicago Air Route Traffic Control Center in Aurora and reroute air traffic.
"People are in jeopardy because the controllers are being impaired," Downen said. "We're being told by the FAA to work until you start to feel sick. I don't believe that is a safe position to be in."
Downen said his union also asked the FAA to stop air traffic in the region Tuesday for fear of an accident.
FAA spokeswoman Kathleen Bergen said Tuesday that the agency did not close the center because it still had adequate staff to run it.
Downen said 50 controllers left work Monday and Tuesday and five went to a hospital complaining of nausea, blurred vision, headaches and rashes. He said one controller temporarily lost his sight while monitoring radar. The five were treated at Povena Mercy Center and released, a nursing supervisor said.
The air traffic control center in Aurora, about 35 miles west of Chicago, is the country's busiest and directs all traffic in the Midwest.
The illnesses caused delays of up to two hours Tuesday for flights into Chicago's O'Hare and Midway airports, but outbound flights were not affected. Traffic flying through the area was mostly rerouted to the south, which extended some flight times.
The fumes came from a nontoxic sealant applied Monday in the center's attic, the FAA said.
Bergen said the agency stopped the sealing work after the problem was traced. When the odor remained Tuesday afternoon, administrative staff were asked to leave and the control room was reconfigured to avoid an area where the odor had concentrated.
The Aurora Fire Department has declared the center safe.