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Officials at Six Flags Great America said Tuesday that no disciplinary action will be taken against any maintenance employees for the weekend roller coaster accident that left 23 people hanging upside down for nearly two hours and injured four of them.

The Demon corkscrew ride became stuck in the middle of a loop Saturday when a nut came loose on a rear axle, causing a wheel that runs inside the track to separate from the rear assembly on the last car.

Six Flags representatives declined to comment on what caused the nut to come loose. Spokesman Scott Kirn said no one person was to blame for the accident, which he called a “very unique situation.”

In light of the accident, a new safety mechanism was added to the roller coaster for extra protection, Kirn said.

Carl Kimble, chief amusement ride inspector for the state Department of Labor, said the theme park has taken proper action to correct the problem. He said the state will reinspect the Demon roller coaster later this week.

Six Flags said it plans to reopen the ride this weekend.