Giant brake pads were slowing Valleyfair's Wild Thing roller coaster when the last of its six cars broke away and lurched to a tilt, sending 15 riders to the emergency room.
Those brakes under the Shakopee amusement park's signature ride will be under scrutiny as the owner, the manufacturer and outside engineers try to figure out the cause of Sunday afternoon's accident.
At the time of the accident, the ride "was well into the brakes, so probably that's going to be significant once we can get under there and see it," said Tip Harrison, director of Valleyfair's physical plant. Though he wouldn't speculate on what the investigation might reveal, Harrison doubted such an accident would have happened anywhere else during the ride.
Valleyfair officials inspected parts of the ride Monday but did not physically touch anything. They were waiting for ride manufacturer officials to fly in from California.
No government agency will investigate. Some states inspect amusement park rides, but Minnesota leaves that responsibility to the park owners and their insurance companies.
The investigation is expected to take days, Harrison said. In the meantime, riders and witnesses were reliving their experience on Monday.
Andrea Olecki, 14, of Eden Prairie was waiting in line to board the ride when she saw one of the roller coaster cars suddenly detach from the others.
Olecki said she saw what looked like a latch that connected them fly into the air.
"Everybody was just trying to run out of the line, get out of the way of the Wild Thing," said Olecki, who rode the roller coaster about nine times that day and experienced no problems. "I was scared."
Sitting with his brother in the last car of the Wild Thing on Sunday, Jay Kephart, 9, of Milaca, Minn., felt a big jerk, hit his bottom teeth on the lap bar and tipped sideways, he said. He wiggled out of the restraints, stood up and saw wheels on the track.
"Holy dang. It ripped itself apart real bad," he remembers thinking.
His brother Mitch Kephart, 13, sat in the ride unconscious with a bloody nose. By the time park officials released the lap bars, he was awake. Neither suffered serious injuries, their mother said.
Harrison said the rear wheels on the second-to-last car came off the track and broke away from the car. But he didn't know whether the derailment happened before or after the cars separated.
Valleyfair would not release its safety record because its insurance company won't let it, Harrison said, but national amusement officials tout the safety of rides in general.
The International Association of Amusement Parks and Attractions reports that 335 million people took 1.5 billion rides last year.
According to numbers self-reported by major amusement parks, there were 979 injuries serious enough to require an overnight hospital stay, said Beth Robertson, association spokesperson. On average in the past 10 years, there have been two fatalities per year. There have been no deaths from rides at Valleyfair in its 30-year history, Valleyfair officials said.
The federal government does not have oversight on theme parks, though the Consumer Products Safety Commission does oversee traveling carnival rides.
Minnesota legislators in 1992 chose to give safety responsibility to insurers that have policies with the parks.
At Valleyfair, which is owned by Ohio-based Cedar Fair L.P., inspectors hired by insurance companies inspect rides once a year before the park opens.
Valleyfair has its own staff of inspectors who graduate to various types of rides based partly on experience, Harrison said. Many go through the same training as government inspectors from other states, and one of Valleyfair's staff teaches at the training sessions.
Every winter, rides are taken apart and the integrity of the metal components are tested, Harrison said. There are also monthly, weekly and daily checklists that staff inspectors go through, some portions provided by the manufacturers of rides and others that Valleyfair has added, he said.
The daily checks are made in the morning, before the ride opens, and at an afternoon shift change.
The accident came a day after the ride was stopped twice because computerized sensors detected something. Both times, maintenance checked the ride and found no problems.
Harrison, who has been the park's physical plant director for 28 years, said those shut-downs were false alarms unrelated to the accident.
The Wild Thing is the second roller coaster by manufacturer Chance Morgan that has experienced problems in the past three years. In 2003, the company's Steel Dragon 2000 coaster at Japan's Nagashima Spaland ran off the track and came to a sudden stop, according to Japanese news reports.
A woman hurt her back when the coaster stopped and a man nearby broke his hip when he was hit by a roller coaster wheel. Several of the wheels had fallen off.
Calls to Chance Morgan in Wichita, Kan., were not returned Monday. Steven Elliott, a ride safety engineer from Wisconsin who has done work for Chance Morgan, said the company is "one of the best in the world."
Though Jay Kephart said fear from the accident will probably keep him from riding again, his brother Mitch said it won't deter him.
Their mother, Sandy Kephart, said she'll probably let them go. "I'm sure they check everything out. It's just one of those things, you never know. I mean, we could have been in an accident going there as a family."