The investigation continues into the cause of a ride’s mechanical failure at Sunday’s Norwalk Oyster Fest, that injured 18 people, mostly children.

Richard Stewart, owner of Trumbull-based Stewart Amusements, which owns the Zumur swing ride, said it was an internal error that would not have been seen during recent inspections, including an official inspection Friday.

“Something locked up and it’s not something we could have anticipated,” Stewart told the Times.

None of the injuries were life-threatening and on Monday, the last child injured had been treated and released from the hospital. Stewart said he was happy the injuries weren’t more serious but it was still a nightmare situation.

“This is something new to us,” he said. “We’ve been in business 30 years or more and in this business, this is your worst nightmare.”

There will be no criminal charges in the case, according to State Police. Stewart Amusements is waiting for the ride’s manufacturer to send an inspector before the ride is dismantled to find the exact cause. He believes that will be some time next week. Other carnival ride owners, who have the same swing ride, are also anxious to hear what caused the problem, Stewart said.

“At first people were saying there was a power loss but a loss of power wouldn’t do this,” Stewart said. “This is like you are driving down the road and you pull up the break. No one was ejected from the seats but when the system locked up the seats continued to wrap around and the injuries came from riders bumping into one another or hitting the center of the ride.”

Each ride is inspected each year by a structural engineer, Stewart said, and is always inspected by the state fire marshal’s office once set up for an event like the Oyster Fest.

“It is a machine and machines do break but we need to know why,” Stewart said.

The Trumbull-based company has been operating since 1983.

“Serving Fairfield and New Haven Counties in Connecticut, and Westchester and Putnam Counties in New York, we have continually strived to provide the newest and safest amusements available,” the company website said.

Stewart Amusement didn’t provide rides at this year’s Trumbull Day, but was used for the town event in past years.