The state’s workplace safety agency is investigating the death of a mechanic who was fatally injured when a bus he was working on rolled on top of him Thursday morning.

Walter Pietilla, 58, was killed at a Bayview district maintenance yard owned by Cal Experience LLC, a San Francisco-based company that provides party and entertainment bus services.

Pietilla was working underneath the hood of a bus when it rolled off its support ramp, pinning him underneath, according to Dean Fryer, spokesman for Cal-OSHA, the agency investigating the incident.

Cal-OSHA is investigating what steps were taken to prevent the accident, Fryer said. Investigators will question other employees at the company, to determine if they carry out the proper procedures and safety measures when working on vehicles. Cal-OSHA will also question management at the company to determine if adequate training has been put in place for the workers, Fryer said.

If Cal-OSHA finds the company in violation of state safety rules, it could face fines ranging from a couple of hundred dollars to several thousand dollars, Fryer said. Cal Experience LLC does not have any prior record of workplace violations, he said.

Calls to the company’s San Francisco office were not returned on Friday.

wreisman@sfexaminer.com