The carnival ride company at last year's Sonoma-Marin Fair has been fined $500 for an accident that severed a carnival worker's leg when he walked onto the track of a moving roller coaster.

According to a California OSHA investigative report, the 23-year-old East Bay man was returning from a snack break on June 23, the fair's first day, when he walked into the gated area surrounding the Wacky Worm kids' roller coaster.

The man, whose name has never been released, walked onto the tracks. The front car of the ride, which was filled with young children and their parents, struck the worker and tossed him a short distance, witnesses said. His leg was severed below the knee.

Midway of Fun, which operated the ride, received a low-level fine for the accident, Krisann Chasarik, a Cal-OSHA spokeswoman, said Tuesday.

The investigation found that Midway of Fun hadn't provided the ride operator with training for a situation where someone walks into the path of a ride that is in operation, she said. The injured man was on a break from an adjacent ride.

It wasn't determined why the man went into the fenced area of the ride, moving a three-foot-tall movable metal gate to do so. It did not appear the man was under the influence of any drugs or alcohol, Chasarik said.

The man underwent surgery later that day, but the leg couldn't be reattached.

The investigation, which concluded in the fall, included interviews with midway managers, other midway employees and witnesses. A detailed record check of Midway of Fun's performance was also included, Chasarik said.

"Everything else was in order," she said. "We didn't find any other violations."

The Wacky Worm ride, a figure-eight-style coaster about 12 feet tall, was shut down as medical personnel tended to the man but reopened later. No fair-goers were hurt and fair representatives stressed that the injury was not the result of an unsafe ride or a machinery malfunction.

The incident didn't hurt fair attendance, which increased over the previous year, organizers said. The fair averages about 65,000 patrons a year.

Fair director Pat Conklin said Midway of Fun remains the ride provider this year.

"There was nothing mechanically wrong with the ride or the ride operator, it was an unfortunate accident," she said.

The Sonoma-Marin Fair runs from June 22 to 26 this year.