Working in and around trenches is particularly dangerous, particularly if the excavation is at risk of collapsing. Whether a trench is safe for workers depends on several factors, including the type of soil, the dimensions of the excavation and whether the walls are at the appropriate angle.
Improperly sloped trench walls endanger workers and can result in fines.
Example: Two workers in Saskatchewan were seen in a trench that wasn’t properly sloped and had been undercut to locate a gas line. They weren’t protected from cave-ins or sliding material by means of cut back or shoring. Their employer pleaded guilty to a trenching violation and was fined $4,200 [Dmyterko Enterprises Ltd., Govt. News Release, June 13, 2012].
To simplify the process of accessing the safety of the walls of a trench or excavation, the Michigan Infrastructure and Transportation Association sponsored the development of the Trench Right app.
The idea behind the app is that if you’re not using a trench box or shoring, then the trench must be excavated to the proper angles of repose (that is, the angle made between the sides of your trench and the level ground around it) for the type of soil you’re excavating. Trench Right makes these calculations easy. Workers or supervisors just enter information about the trench’s dimensions, the soil type (such as solid rock, stiff clay or granular soil) and the tonnes-per-square-foot reading from a penetrometer, and the app uses the information to determine whether the excavation is safe.
While using the app can simplify calculating a trench’s angle of repose, remember, of course, that you must ensure that your trenches and excavations comply with the requirements in your jurisdiction’s OHS laws, including any requirements for the angles of a trench’s walls and shoring.
The OHS Inside has additional information to help you ensure that trenches and excavations are safe for workers, including:
- The steps to take to comply with trench and excavation requirements in the OHS laws
- A trench/excavation inspection checklist
- SPOT THE SAFETY VIOLATION: Don’t Let Safety Hazards Get En-Trenched.