NASHVILLE, Tenn. >> Security upgrades at a troubled youth detention center in Nashville were not enough to prevent 13 teenagers from escaping Friday, the second major breakout from the facility this month.

Tennessee Department of Children’s Services spokesman Rob Johnson said several teens overpowered a guard at the Woodland Hills Youth Development Center about 11 p.m. Friday. They took the guard’s radio and keys and let themselves out of a dormitory. All but one were recaptured within hours.

The breakout was the latest in a series of problems that have alarmed Tennessee authorities, including a mass breakout by 32 teens on Sept. 1. The state has since begun conducting a review of youth detention security in the state.

Security improvements since the Sept. 1 breakout include securing the bottom of the fence that surrounds the facility in concrete. Workers also have reinforced aluminum panels under the dormitory windows that the teens were able to kick out during the first escape.

“A lot of shortcomings were exposed after that first breakout,” Johnson told The Associated Press in a telephone interview. “They’ve been working hard and fast and have made a lot of improvements, but there’s still more work to do.”

Johnson said Friday’s breakout began while a guardhouse was empty and a guard was out checking the perimeter. According to the official, the teens smashed the guardhouse window with a rock and one went through the broken window and opened the gate for the others.

The guard who was overpowered in the dormitory was treated at a hospital and released, Johnson said. Another worker also was injured, but not seriously.

Within hours of the breakout, Nashville’s Metro police and Tennessee Highway Patrol officers had regained custody of all but one youth, a 16-year-old. The recaptured teens were taken to the juvenile court detention center. The 52 other teens being held at the Woodland Hills complex remained calm during the disturbance, Johnson added.

Thirty-two teenagers escaped from the same center on the night of Sept. 1. Two days later, riots broke out on the grounds of the facility, with teens brandishing fire extinguishers and sticks.

Johnson said many of the teens who participated in Friday night’s breakout were involved in the previous disturbances. Two of the teens who escaped in the earlier breakout remain at large.

Gov. Bill Haslam was in Afghanistan on Saturday. His spokesman, Dave Smith, said in an email that officials have brought in a national expert to review the situation at Woodland Hills, and DCS Commissioner Jim Henry has been visiting other states to learn about best practices.

“As the governor has said, our goal is to find the right balance of providing educational and rehabilitation opportunities for the youth we’re serving there along with their safety, the safety of others,” Smith wrote.

The Woodland Hills center has a history of violent clashes, breakout attempts and attacks on guards.

The recent problems have shed light on the difficulty of maintaining order at a center where most of the 14- to 19-year-olds have committed at least three felonies, and the challenges faced by Tennessee’s Department of Children’s Services in trying to fix the issues.

In an interview earlier this month, DCS Commissioner Henry said policies were being reviewed to see if guards could be given weapons such as stun guns to help control unruly detainees. Currently, he had said, guards do not carry weapons and must rely on talking with the inmates to quell disturbances.

However, some lawmakers in Tennessee have said that’s not enough. They want the state to reopen a facility closed in 2012, Taft Youth Development Center, which primarily housed older, more violent offenders. They say the inmates at Taft were transferred to Woodland Hills, which then saw a spike in assaults.