Excavation and trench hazards

Too often, we underestimate the work in trenches. Even when carrying out minor work, risks remain.

Deadly cave-in

In Lachine, Québec two years ago (article in French), a team of two workers were replacing sewer lines leading to a residence. The trench in which they were working was not very large: approximately 11 meters long by 1 meter large.

After removing surface debris, the workers used an excavator to locate the aqueduct pipe. A worker needed to go into the trench to install a section of pipe. His coworker was about two meters from him in the trench.

That is when the cave-in happened. One worker was completely buried, and the other was partly buried, trapped by chunks of asphalt.

Lessons learned

In light of the information provided in the CSST report, it is clear that the victims were in a vulnerable position. Three elements could have prevented this tragedy.

1. The excavated remains were placed too close to the trench.

Around a trench, materials must be placed at least 1.2 meter from the edge. Regarding this incident, they were within this limit.

2. The angle of repose of the soil must meet certain criteria

According to the material the trench wall is made of (solid rock, clay, sand, etc.), the opening angle of the walls must meet certain criteria to ensure a high-degree of safety.

The CSST investigation indicated that despite the presence of a friable soil, the workers left the walls almost vertical. If the opening degree needed cannot be obtained, the walls must be properly shored up.

3. A safety risk analysis must be conducted before the work starts.

It ensures the implementation of adequate safety measures. In this case, the safety analysis of the work location would have allowed the necessary measures to be taken according to the type of soil.

When talking about accident prevention, there is no small work. When excavating or digging, the risks are real. Ask the experts of SPI for advice to prevent such tragedies from happening again.

Alain Daoust, cria; crsp; vea
EHS Expertise Director, SPI Health and Safety