A chain above the roller coaster snapped and dangled and ended up whacking passengers in the face and upper body as they were riding on the ride and passing beneath it at 20 mph. It's like a bicycle chain, but bigger.
Shannon McNamara, 10, was in the last car.
"Me and my friend ducked. She went like this [covering her head] and I went like this [covering my head]" said McNamara.
Alameda County Fire Asst. Chief Alan Evans said people suffered "Cuts, bumps and bruises and it was very challenging in beginning because they were covered in black grease."
"I saw that someone was getting taken by ambulance and had her neck all wrapped up and she couldn't move it," said Nadine Cobb.
The Alameda County Fire Department says one child and one adult went to Valley Medical Center to get checked out. Everyone else was evaluated and released at the scene.
"It was a manufacturer malfunction. No rider or operator error," said Alameda County Fair spokesperson April Mitchell.
Mitchell said the ride was shut down for inspection after the incident, and the California Division of Occupational Safety and Health cleared the ride for repair.
The rides are inspected every day by professional ride inspector Barry Schaible. He says the chain was new.
"Approximately three to four months old. It wasn't very old at all; it was a failry new chain. Defect in the chain itself. Yes, that's what they're coming up with now," said Schaible.
Schaible said statistically carnival rides are safe.
"You're more likely to get hurt walking across the street coming here than on the rides at the fair," said Schaible.
An independent ride inspector called Coulter & Associates is also reviewing the incident, Mitchell said.
The closure of this roller coaster has some fairgoers rethinking all the rides.
"If you look at them, they're held up on blocks of wood, and you can hear them creaking and cracking, and you just never know. I will not get on one, I will not get on a ride," said Pleasanton resident Josh Rhotan.
Despite her close call, McNamara was disappointed the ride was shut down. She wanted to go on it again.
"I felt a little scared that I was going to get hurt and go to the hospital, but I really didn't," said McNamara.
The Alameda County Fair's ride is owned and operated by Butler Amusements. Their mechanics are waiting for a replacement part to arrive and once that happens Cal/OSHA will have to re-inspect and clear the ride for reopening.
A different ride, also called the "Wacky Worm," struck a carnival worker on June 23 at the Sonoma-Marin Fair in Petaluma. That ride is operated by a different company -- Brass Ring Amusements' Midway of Fun.
In that incident, the worker walked in front of the ride as it was in motion. His leg was severed and he is still hospitalized and has no memory of what happened.
Cal/OSHA is investigating that incident as well.
Bay City News contributed to this report
