Date of incident: July 2020
Notice of incident number: 2020163750011
Employer: Excavation company

Incident summary
At a street near a multi‑resident development construction site, two workers were working inside a trench‑shoring cage (used to prevent a trench from collapsing or caving in) to install storm pipes. An excavator with a bucket attachment was preparing to pull the shoring cage inside a recently dug trench. As the bucket was being raised and positioned over the shoring cage, the bucket disengaged from the excavator’s boom. The bucket struck and fatally injured one of the workers in the shoring cage.

Investigation conclusions

Cause

• Safety key not used. For the purpose of moving the shoring cage, the bucket had been attached to the excavator boom using a hydraulic coupler. The safety key was not installed in the coupler. When the excavator bucket uncurled over the shoring cage, the bucket disengaged from the boom and fell into the shoring cage.

Contributing factors

• Manufacturer’s instructions not followed. The hydraulic coupler came equipped with a safety key and warning label. The manufacturer’s manual instructs operators not to operate the machine without the safety key. The safety key ensures that the wedge bar is securely in place to prevent an excavator attachment from disengaging. Not using the safety key created a high risk of a serious incident occurring.
• Audible alarm did not indicate proper placement of wedge bar. After the bucket had been picked up from the ground with the coupler, an audible alarm sounded. When the control button inside the cab of the excavator was pushed, the alarm stopped, suggesting that the wedge bar was in place. However, the pressure of the wedge bar against the back of the lugs on the bucket most likely disengaged the alarm.
• Inadequate hazard identification and work procedures. The employer did not have specific work procedures for moving a shoring cage or operating the excavator with a hydraulic coupler. The employer used three different methods for moving a shoring cage: pulling with the excavator bucket, pulling with tow cables, and lifting. Although the employer identified some hazards and risks, the hazard of the excavator bucket moving overhead during the process of relocating a shoring cage occupied by workers was not identified. The importance of using the safety key was also not identified.

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