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HARRISBURG, Pa. (AP) — Pennsylvania’s state prisons are on lockdown after staff members required treatment in recent weeks from exposure to a yet-unidentified substance described as a liquid synthetic drug.

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The Department of Corrections announced the step Wednesday, following the news that guards and nurses were treated for possible drug exposure inside an Ohio prison.

The department didn’t say how long the lockdown will last.

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In the meantime, it’s suspending prison visits, closing mailrooms to non-legal mail and requiring all employees to use gloves and other personal protective equipment.

Pennsylvania previously reported five separate cases between Aug. 6 and Aug. 13 in which 18 employees in three western Pennsylvania prisons showed symptoms that required medical treatment.

Prison staff is to use extra caution with parole violators and newly arrived inmates.

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Governor Tom Wolf issued this statement on the lockdown:

“Pennsylvania’s corrections officers put themselves in harm’s way to make our commonwealth safer, and it is up to us to provide them protection from harm. I spoke to Sec. Wetzel today and they continue to work diligently to address the emerging issue of synthetic drugs in our prison system, and my office and I have been supporting his efforts. Today’s action to lock down all of the state’s correctional facilities is a necessary step to ensure the safety of our officers and provide the department the opportunity to assess and control the situation.

It is our responsibility to keep all commonwealth employees safe while at work so that they return home each day to their families. I have confidence that the Department of Corrections, working with state agency partners and law enforcement, will determine the cause or causes of the recent sickening of staff and put in place the necessary protections and procedures to ensure staff safety.”