Law enforcement officials say a fire at the Hamilton County Jail last week was intentionally set.
About 150 inmates had to be relocated Tuesday night after smoke filled several floors of the jail.
On Monday, officials with the Hamilton Sheriff's Office said the incident is believed to be arson and charges are expected pending the outcome of the investigation.
Deputy Chief Austin Garrett said he could not disclose on which floor the fire was set, but it was done within a return air duct in a secured but common area of the jail where inmates come and go.
"That's how the smoke spread," Garrett said. "Once they shut the system off and ventilated, it got the smoke out."
"We want to ensure the public understands that we take this type of incident, and any incident within that facility, seriously. And that we have plans in place that, whether we relocate within or if we had to do a mass evacuation out of that complete facility, we have plans in place," Garrett added.
Sheriff Jim Hammond said additional personnel were brought to the jail within 15 to 20 minutes "to help move people out of the danger zone and were able to contain it."
"There's not a whole lot that was burned over there, but your danger is always smoke inhalation," Hammond said.
Garrett said there was no significant damage to the facility apart from a small amount of charred insulation inside the duct system.
Garrett added that after any incident, law enforcement officials and first responders go over the situation to see what was handled well and what could be improved.
"We do that with the responding agencies to identify were there any barriers that we can remove that would make response times better, those kinds of things," he said. "It's always used as a learning experience to make us better as a team, to be able to provide a better service to the public."