Focus of the Month: Excavations
Trench Protection and Necessary Measures
As the weather warms and the ground thaws, workers throughout the United States will begin digging trenches, exposing them to hazards like a trench collapse. For this reason, OSHA specifies protective measures that are required for trench protection.
What is a trench?
A trench is defined as a narrow excavation made below the surface of the ground not greater than fifteen feet in width. The depth of an excavation does not play a role in determining if it is a trench, but certainly plays a major role in trench safety and protection requirements.
Trench protection is required when workers must enter trenches that are five feet deep, or more. This applies to all trenches and is not affected by how much time an employee will be in the trench. Even if an employee will only be in the trench for a few minutes, trench protection is still required. Depth is not the only consideration when determining whether trench protection is necessary. If any trench, regardless depth, is at risk of collapsing, workers must be protected prior to entering. This includes trenches with a depth of less than five feet! Your excavation competent person is the one to decide if a trench is at risk for collapse and what trench protection is necessary.
Trench boxes are a common form of trench protection, providing strong walls and a frame that protect workers inside from cave-ins. An improperly constructed trench box, though, will not protect workers in the trench. If the spreader bars aren’t properly pinned, the walls can compress if the earth cave in. If that happens, anyone within the box can be struck or crushed. Another common issue is failing to add end protection to the trench box.
Cave ins are not limited to the sides protected by the walls of a trench box, so the open end of a trench box must be protected from a cave-in exposure as well. Far too often, workers see end protection as an inconvenience that makes extra work as they move trench boxes down the length of a trench. They fail to realize how important end protection is.
Road plates are a common option for adding end protection to a trench box. To ensure they provide adequate protection, they must be set so that they are supported by both walls of the trench box. The walls provide strong support, so that if the earth caves in against the road plate, it will push against the strongest parts of the trench box, protecting workers within the box from the collapsing earth. If the plates are placed so that one or both edges rest against the spreader bars and the earth collapses against the plate, the spreaders can buckle, causing the box to collapse striking the worker and allowing the earth to collapse into the box.
Trench protection is a key component of safe trench work, and your trained excavation competent person needs to ensure that workers in the trench are properly protected from the hazard of soil collapse.
For more information about excavation safety, see our previous articles:
Trenching Safety and Excavation Hazards
Trenching and Excavation Safety Begin with Planning and Training