California worker-safety regulators on Monday said they fined a Napa Valley company after the death of a 24-year-old member of a tree-trimming crew last summer.

California Division of Occupational Safety and Health (Cal/OSHA) said it cited Gorilla Tree Service for serious and accident-related workplace safety violations following an investigation of a brush-chipper accident in Napa that killed the man. An investigation found that the Napa-based company was unable to certify it had properly trained the worker, who had been employed at the company for about six months, the agency said.

On Aug. 15, the employee was working on the ground as part of a two-person crew removing limbs from a liquidambar tree in Napa, when a rope used to lower limbs from an aerial bucket was caught in the chipper and pulled in, strangling him.

"Tree work is a high-risk industry, and safety requirements are in place to protect workers from known hazards," said agency Chief Juliann Sum in the announcement. "Employers must ensure that workers are effectively trained to use brush chippers and other dangerous machinery safely."

Gorilla Tree Service was ordered to pay $23,200 for seven violations, including one serious accident–related, one serious and five general.

Those violations include failures to document required certification tree work and CPR training; to brief workers about the hazards, work procedures and appropriate protective equipment before each job; to ensure the chipper was equipped, maintained and operated per manufacturer's recommendations; and to prevent entanglement hazards and foreign material from getting into the chipper.

Investigators found that the chipper involved in the death didn’t have required guards on moving parts of belt and pulley drives, the agency said.

Tree workers are 56 times more likely to suffer a fatal occupational injury than workers in all industries combined, according to Cal/OSHA. The agency said major causes of tree worker injuries and fatalities include falls, electrical shock, tree branch collisions, chainsaw lacerations, palm tree skirt collapses and ladder accidents.

Over the past six years, brush chipper-related incidents in California killed one other worker and injured four seriously.

A worker was killed in 2012 while feeding brush into a chipper in Nevada City when a rope binding the brush became entangled in the chipper drum and looped around the worker's neck. The force on the rope was so great that the worker was decapitated.

In Los Angeles County in 2012, a worker was hospitalized from injuries caused by a chipper. Two workers were removing a tree using rope and a brush chipper. One of the workers was attached to a rope that abruptly went into the chipper pulling him toward the feeder. He was taken to the hospital with a punctured lung and fractures to his ribs, left arm, thumb and wrist.

In 2013, a Solano County worker lost his left ring finger when his wedding band suddenly became caught between the side frame of the feeding bay and the branch he was pushing into the brush chipper.

While operating a brush chipper in 2013, a worker in Concord was hospitalized. A truck rolled down a hill and jackknifed toward him while he was feeding brush into the chipper. Both of his legs became pinned between the truck's side door and the frame of the chipper's in-feed table. Both of his legs were fractured.