INDIANAPOLIS » The superintendent of an Indiana school district where a stage collapsed, injuring 16 high school students when they plunged an orchestra pit, said Friday that the section that gave way was only a few years old, but it’s unclear whether it was ever subject to inspection.

The uncertainty surrounding the regulation of the orchestra pit cover that collapsed during Thursday’s finale of a musical at Westfield High School, 20 miles north of Indianapolis, is reminiscent of questions that arose in 2011, when heavy winds toppled stage rigging onto fans awaiting a performance by country duo Sugarland at the Indiana State Fair.

Seven people were killed and dozens injured in that collapse, which sparked new state rules on temporary, outdoor stage rigging equipment. Thursday’s collapse wasn’t deadly, and all of the students who were injured were out of the hospital by Friday afternoon.

John Erickson, a spokesman for the state’s Department of Homeland Security, said the state rules adopted after the fair rigging collapse don’t apply to the type of permanent, indoor stages found in schools. And he said it’s unclear whether inspections of public school stages are required under any state rules.

"It does not look like plans were required to be filed" for the stage at the school, Erickson said.

Westfield Washington Schools Superintendent Mark Keen said he wasn’t sure who, if anyone, handles inspections of the district’s school stages. He said school officials are delving into records and will provide information to investigators.

The stage collapsed Thursday night as clapping and singing students performed Journey’s "Don’t Stop Believin’" in the finale of a concert called "American Pie." Video supplied to The Associated Press by Zach Rader — who was in the audience — shows students plummeting out of sight before the music cuts off and screams are heard.

Westfield police Capt. Charles Hollowell said Friday that the injured students had mostly suffered minor injuries and were "doing really well," including a girl initially reported in critical condition. She was the last student still hospitalized, but was released Friday.

The school held classes Friday, but Hollowell said the auditorium was closed except to investigators.

The State Fire Marshal’s office, Indiana State Police and Indiana’s workplace-safety agency were investigating. Indiana Gov. Mike Pence said in a statement that they would "make every effort to prevent this or worse from happening in the future."

Keen said the school often rents its auditorium to outside groups and the facility gets heavy use. He said the orchestra pit cover, which is used during some productions to get the performers closer to the audience, was replaced a few years ago after the original 1997 cover was damaged.

He said officials were checking records to determine whether it had ever been inspected.

"I know we have records when they come in and inspect our football bleachers and when they inspect the gymnasium bleachers and so we’re trying to find if there are inspection reports on (the pit cover) as well," Keen said.

Blake Rice, an 18-year-old senior who was playing guitar when the stage collapsed, said he thought the pit cover was replaced within the past two years after it was damaged and interconnecting panels that comprise the structure became warped and too uneven for use. He said the pit cover has vertical supports and crossbars beneath it that are similar to scaffolding.

Rice said the cover had been used without incident during two rehearsals before Thursday’s performance.

"There was no indication anything would go wrong, but on Thursday night, well, it was just a little too much for the floor to handle at that point," he said. "Everyone had a lot of energy and was jumping up and down a lot more than they normally would, just from adrenaline and everything."

J.T. Coopman, executive director of the Indiana Association of Public School Superintendents, said he expected the accident to "jolt people into action" at schools statewide to review the safety of stages.

"That would be the direction that I would be giving my maintenance staff: ‘Do we have a structure like this? How often do we inspect it? Are we sure that it’s absolutely safe before we use it?’" he said.