The FBI said there was no powder in a letter sent to the Portland VA Medical Center on Wednesday.
Federal agents are now investigating what caused the health concerns of four employees and two security guards at the medical center's administration and research building.
At 4:30 Wednesday afternoon, six people reported feeling ill after an employee opened a letter.
"Initial reports were of irritation to skin, eyes, nose, mouth and hands," said Paul Corah, of Portland Fire and Rescue. "It seemed to be similar as being sprayed with pepper spray, but we don't know what the chemical is at this time."
All six people went through an extensive decontamination process at the hospital, and they were soon released.
The envelope with the supposed powder was handed over to the FBI, and lab technicians performed a series of tests. The test results showed no harmful substances, the FBI said, and interviews revealed there was no power visible in or on the letter.
Investigators contacted the sender of the letter and determine there was no threat stated or intended.
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