The California Division of Occupational Safety and Health on Monday said it cited an Oakland, California-based general contractor for dismantling a trench box while an employee was still working inside and later killed by a loosened support rail.

Investigators examining the cause of the April 27 fatal incident found the employer committed “willful-serious safety violations by unsafely removing a linear support rail that fell and fatally crushed the worker,” Cal/OSHA said in a statement.

Bay Construction Co. assembled a trench box to install underground pump station equipment at the Martin Luther King Jr. Regional Shoreline in Oakland. Four days later, the crew was finishing up the underground work when a worker was compacting dirt inside the trench box and another was using an excavator with a four-hook bridle sling to remove the shoring system’s 5,000-pound linear rails. The hooks used for the sling were not adequate for this operation and one failed, dropping a rail and fatally crushing the worker inside the trench, according to an account provided by Cal/OSHA.

“Shield systems are designed to protect employees from cave-ins when working in an excavation,” Cal/OSHA Chief Juliann Sum said in the statement. “Employers must ensure that no one is inside of the excavation when the protective system is being installed or removed.”

Cal/OSHA issued nine citations to Bay Construction Co. with $141,075 in proposed penalties, including five classified as general, two serious, one serious accident-related and one willful-serious accident-related.

The willful-serious accident-related citation was issued for failing to ensure that no employees were in the trench shield while it was being dismantled. The serious accident-related citation was issued for the employer’s failure to use adequate hooks to remove the heavy linear rails. The citations for serious violations were issued for failing to conduct daily inspections of the excavation site to identify any potential hazards and failure to implement multiple sections of the employer’s injury and illness prevention program, which includes training and instruction to employees working in excavations.

Officials with Bay Construction could not immediately be reached for comment.