UPDATE: We now know the fire inside the Hamilton County Jail last week was set intentionally.

Investigators revealed the new information Monday.

No one was hurt in the fire but it involved a big response from the Hamilton County Sheriff's Office, the Chattanooga Fire Department and Hamilton County EMS.

"It is a safe facility. We take the safety of those inmates extremely seriously within our care," Hamilton County Chief Deputy Austin Garrett said.

Garrett said the Hamilton County Jail is safe after revealing a fire last week was set on purpose.

The fire was located inside the air return of the HVAC unit, but Garrett wouldn't say exactly where inside the facility.

"It was a common area within the facility. Common area meaning, inmates come and go, that sort of thing. Exactly where and which floor, we're not releasing," he added.

Garrett said the fire was small and put itself out.

But it created enough smoke to fill the top three floors of the jail, forcing deputies to relocated 150 inmates to other parts of the facility while it was ventilated.

It's a situation Garrett said they train for often as part of their accreditation standards.

"We conduct fire drills monthly. They're random. Employees don't know when they're going to occur. They're done on all shifts," he said.

While investigators work to determine who set the fire, Garrett wants the person responsible to know one thing.

"Think about what you're doing when you do something like that, all the lives you endanger and the people you impact, besides yourself," he said.

Once investigators identify who is responsible, they could face arson charges.

Channel 3 asked if cameras inside the jail captured the arson on video. Garrett would only respond by saying they are using all tools available to them in the investigation.

Stay with the WRCB app for updates to this story.

PREVIOUS UPDATE: Austin Garrett, Hamilton County Sheriff’s Office Chief Deputy, tells Channel 3 that the recent jail smoke issue was caused by arson inside the jail.

Garrett says they treat incidents like this seriously to protect inmates inside the facility. The fire was created in a part of the facility's HVAC system.

 This is a developing story and will be updated.

PREVIOUS STORY: It's still unclear what caused smoke to fill the top three floors of the Hamilton County Jail Tuesday night.

Several agencies were busy Tuesday night after smoke filled three floors of the Hamilton County Jail.

No one was hurt but there are still a lot of questions surrounding what happened and the response to the scene.

Jail personnel relocated about 150 inmates to other parts of the jail where fire crews spent hours ventilating the facility.

Channel 3 wanted to know what goes into evacuating so many people at one time, quickly and safely.

The sheriff's office declined our request for an interview citing the ongoing investigation and security.

Fire officials said Tuesday night Hamilton County EMS evaluated all of the inmates and no one was hurt.

It will be up to fire investigators to determine exactly what caused the smoke.

A spokesperson for the Chattanooga Fire Department said Tuesday night a possible source was the HVAC system.

This isn't the first time we've heard of problems involving the HVAC system inside the jail.

In July, Channel 3 toured the jail during a media day hosted by the Hamilton County Sheriff's Office.

During the tour, we felt how hot it was inside the jail as temperatures reached 96 degrees outside.

Personnel and inmates both expressed their frustration about being in the heat.

Jail personnel told Channel 3 during the tour the current system is the original HVAC system that came with the 40-year-old building.

When Channel 3 requested to do a story on the system in July, a spokesperson for the sheriff's office denied our request saying the problems were being fixed.

Improvements to the jail have been the topic of discussion during several budget talks.

But the Chattanooga Times Free Press reports $20 million dollars for the next installment of county jail improvements did not make it into the 2020 budget.

It's unclear if a new HVAC unit was part of those improvements.

When Jim Hammond ran for sheriff in the most recent election, he said he wanted to move the county jail to Silverdale, but that would take some expanding.

A spokesperson for the sheriff's office told Channel 3 they are currently in the engineering and contract process and plan on breaking ground in the Spring of 2020.

PREVIOUS STORY: A possible HVAC malfunction led to smoke inside the Hamilton County Jail on Tuesday night around 6:30 p.m.

Hamilton County Sheriff’s Office spokesperson Matt Lea says smoke filled the fourth, fifth and sixth floors of the jail.

Lea says about 150 inmates were evacuated as a safety precaution.

Lea says all inmates were evaluated by EMS and no one was injured.

CFD spokesperson Lindsey Rogers says there was no fire and CFD crews were able to get the smoke out of the building.

Lea says the possible source of the smoke has been narrowed down to the HVAC system.

The exact cause of the smoke is under investigation.

Several agencies including Hamilton County EMS and extra security were brought in to help with the response, due to the size of the jail.

Stay with the WRCB app for updates to this story.