WILSONVILLE, Ore. (AP) — An administration building at an Oregon prison was evacuated Friday when workers found an envelope in the mail room with an unknown substance inside.

The mail room at the Coffee Creek Correctional Facility in Wilsonville was secured after the envelope was found Friday morning, according to the Department of Corrections.

Tualatin Valley Fire and Rescue Hazardous Materials Team, the Oregon State Police, and the Federal Bureau of Investigations were on site to evaluate the powder for any hazardous substances.

Seven employees were in the mail room at the time and one was taken to a local hospital for evaluation. Mail room employees are critical to operating safe and secure institutions because they help keep drugs and other contraband out of the state’s prisons, the agency said.

It’s the third time that the administration building has been evacuated in recent months, officials said.

The prison houses approximately 1,200 adults.