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Excavation collapses, killing worker

A crew of five workers, including the contractor, began installing underground storm sewer pipe on a street in Surrey, B.C. The contractor dumped a bucket of gravel into the excavation. Two workers entered the excavation and spread the gravel at the bottom to make a bed for the pipe. The contractor then lowered a length of pipe, and the two workers attached it to the end of the previously installed pipe. The contractor dumped more gravel into the excavation, and the workers used shovels and their feet to tamp the gravel around the pipe. One worker left the excavation. About a minute later, the east side wall of the excavation collapsed onto the remaining worker, causing fatal injuries.


Findings as to causes

  • One side wall of the excavation collapsed. The worker was buried under the loose material and died of asphyxiation.
Findings as to underlying factors
  • The excavation was not shored or sloped to prevent the side walls from collapsing. Use of an adequate shoring cage would have prevented the wall from collapsing.
  • Site supervision and inspections were inadequate and did not prevent the development of unsafe conditions.
  • The ground was very hard, which led the contractor to believe that the excavation was safe to enter.
  • A previously backfilled sanitary sewer line ran parallel to the excavation. Excessive weight of the loose materials in the sanitary sewer trench may have forced the wall of the excavation to collapse.
  • Vehicle and mobile equipment traffic next to the excavation wall would cause vibrations in the ground, which in turn may have caused the wall of the excavation to crack and collapse.
  • There was no health and safety coordinator at the site to address the hazards of the work site.

Hazard Alert

Publication Date: Dec 2005 File type: PDF (2 MB) Asset type: Incident Investigation Report Summary NI number: 2005113830569