Environmental tests at an Air Force base in southern Illinois failed to pinpoint what caused three people to fall sick while handling mail Wednesday, the Air Force said.

Two workers for the U.S. Postal Service and an Air Force serviceman at Scott Air Force Base developed respiratory or skin reactions around 9 a.m. in reaction to something in the mail room, according to base commander Col. Michael Hornitschek. The incident led to the evacuation of parts of the facility.

The Air Force issued a news release Wednesday night saying that environmental tests turned up "nothing of significance" at the mail center. Base spokeswoman Karen Petitt told The Associated Press that it's possible whatever sickened the three people had dissipated by the time tests were conducted.

U.S. Postal Service inspectors are continuing to investigate the cause of the adverse reactions and the mail facility will remain closed Thursday, the Air Force said.

"Our personnel are safe and the buildings in which they work have been declared safe and we will proceed with normal business tomorrow," Hornitschek said in a statement.

Hornitschek told reporters earlier that he didn't believe there was ever any threat to the local community and that it's possible the package could have been a "very benign shipment someone had sent (and that) something had spilled or broke." However, he stopped short of assuring that it wasn't a deliberate act.

He offered no details about the package or what material was inside.

Hornitschek said hazardous materials specialists had isolated the suspicious package to one specific bin. But he could not say whether that bin contained mail that was arriving or was meant to be sent from the base.

Hornitschek, appearing relaxed, said he believed the matter was "absolutely not" connected to the pending 10th anniversary of the Sept. 11, 2001, terrorist attacks.

"We view this as an isolated incident that could have happened any particular day in any particular mail center" in the Air Force, Hornitschek said.

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