For the second time this week, corrections officers from the Mercer Correctional Institution have been hospitalized after being exposed to an unknown substance.

Prison spokesperson Andrea Schiok tells 21 News that the guards were taken to a hospital on Friday after coming in contact with the mystery material.

The spokesperson could not say how many officers were taken to the hospital, or if they were treated with Narcan, the opiate overdose antidote.

The incident comes just four days after six prison employees were taken to Grove City Medical Center where they were treated for exposure to an unknown substance while searching a cell and packing inmate property.

One of those employees were treated with Narcan.

The entire hospital was shut down for decontamination at the time.

A spokesperson for Grove City Medical Center says the guards from Friday's incident are not being treated at their facility.

Schiok tells 21 News that the investigation is being handled as an internal matter.

Stay with 21 News for the latest on this developing story.