NEW ORLEANS (AP) — Young teenagers were safety monitors along a Louisiana obstacle course when a wooden climbing framework collapsed under the weight of more than 20 "Warrior Dash" competitors in October, an investigator revealed Friday.

Nearly a year after the collapse of the "Diesel Dome," authorities filed five arrest warrants Friday against contractors accused of shoddy construction work and event staffers who officials said failed to follow written safety procedures.

"It truly is a thousand wonders that other structures did not fail," said Brant Thompson, Louisiana's deputy state fire marshal.

He said "young children" were stationed at the obstacles, given radios and told to keep an eye on safety, but given no instructions about how many people should be allowed on at a time. Asked for clarification, he said many safety monitors were about 13 or 14 years old.

Two North Carolina contractors as well as one former and two current employees of the Chicago company that runs Warrior Dash races are expected to turn themselves in to face 13 misdemeanor counts of negligent injury, Thompson said.

More than a dozen people were hospitalized after the framework collapsed during a race in the Baton Rouge suburb of St. Francisville. Competitors' injuries included broken bones, cuts and head injuries.

The investigation found nothing to contradict an organizer's statement in October that it was the first such accident in the nationwide race series, Thompson said.

Red Frog Events cannot comment about specific allegations because officials have not seen the fire marshal's report, spokeswoman Lauren King said in an emailed statement.

"We've worked closely with the fire marshal's office and investigators since the accident ... and nothing we saw, read or heard during that investigation would warrant criminal charges," she wrote. "One of the employees being charged was not even at the event or involved with the planning of the event."

Thompson identified the Red Frog workers as former employee Mary A. Kreke, 24, of Frederick, Maryland, and current employees Megan E. Gaseor, 25, of Norridge, Illinois, and Emily A. Littlejohn, 27, of Dayton, New Jersey.

King declined to say which of them was not involved.

Contractors Marcus M. Edwards and Daniel L. Lauber, both 47-year-old men from Charlotte, North Carolina, face one felony charge each of "engaging in contracting without authority" — failing to get a Louisiana contractors' license — in addition to the negligent injury charges, Thompson said.

Edwards didn't immediately respond to a phone message left with his company, North South Renovations of Charlotte. Nobody answered a possible listing for Lauber's company, Peterson Builders.

Thompson said Red Frog staffers didn't follow written company procedures such as checking on construction, monitoring each obstacle during the 5-kilometer race, and having a staffer at each obstacle to monitor safety.

Staffers told investigators they didn't realize they were supposed to check the construction, Thompson said: "That was all left to the contractors."

Thompson said construction defects included using smaller boards than called for in Red Frog's plans, such as 2-by-4-inch (5-by-10 centimeter) boards instead of 2-by-6 inch (5-by-15 centimeter) boards.

"Even the nails that were used ... were inadequate for the lumber that was used there," he said. "Clearly boards were becoming detached from the main frame" during the race.

When that happened, he said, "Rather than taking it down or cordoning it off and removing it from part of the race, they did a little patchwork on it ... but nothing that would hold up to the load of the participants there."