WILSONVILLE, Ore. (AP) — About two dozen workers at the Coffee Creek Correctional Facility have been evacuated from the prison after an employee in the mailroom discovered an envelope containing a powdery substance.

The Oregonian/OregonLive reports someone called 911 about the suspicious package at 9 a.m. Wednesday.

Tualatin Valley Fire & Rescue spokesman Stefan Myers says no inmates have been taken out of the Wilsonville-based women’s prison, and the facility is on lockdown.

He says four employees in the mailroom were likely exposed to the substance and are being decontaminated as a precaution.

An investigation is ongoing to determine what the substance is.

Myers says about 20 to 30 people in the mailroom and a nearby building were evacuated..

The Department of Corrections did not immediately respond to a request for comment.

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Information from: The Oregonian/OregonLive, http://www.oregonlive.com