Date of incident: August 2021
Notice of incident number: 2021165370047
Employers: Construction company (2; one subcontracted by the other)

Incident summary
Workers at a demolition site were operating equipment inside a large commercial building to break up concrete and demolish the building from within. An excavator equipped with a concrete breaking hammer was demolishing an interior wall on the second storey, and a worker was working nearby using a water hose to supress dust. The floor collapsed and fell to the ground level, approximately 7.9 m (26 ft.) below. The worker using the hose sustained fatal injuries and the excavator operator sustained serious injuries.

Investigation conclusions

Cause

• Floor was overloaded and collapsed. The combined load of the excavator and demolition debris on the floor exceeded the bearing capacity of the supporting walls and caused the progressive failure of the masonry wall connections, resulting in the total collapse of the floor.
• Demolition plan was not followed. The instructions prescribed by the engineer in the demolition plan were not followed. Demolition debris was not removed and was allowed to accumulate on the upper floors. The excavator worked in areas with large accumulations of debris, and demolition debris was built up to be used as ramps and pads for mobile equipment, contrary to the instructions of the engineer.

Contributing factors

• Demolition plan was not communicated to workers. The demolition plan and its details, which contained procedures and precautions prescribed by the engineer to ensure the building’s structural integrity, were not made available to workers. The engineer’s instruction that debris must be cleared away before operating the excavator on the floor was not communicated to workers.
• Demolition plan was not clear. The written demolition plan’s instructions could be misinterpreted. The plan also lacked detail on how the debris would be handled and where it would be processed and stockpiled.
• Lack of oversight of demolition. The demolition debris accumulated on the second‑storey floors over a period of several weeks. There was no provision for inspection or oversight of the demolition work to monitor compliance with the demolition plan. The demolition contractor did not recognize or take any action to address the discrepancy between what was prescribed in the plan and what was actually being done.
• Lack of experience. The demolition contractor had no previous experience with a structural demolition of this type of building nor the demolition method being used to demolish the building.

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