OSHA 29 CFR 1926.650,29 CFR 1926.651, and 29 CFR 1926.652, Subpart P, Excavations, states that the greatest construction site risk is excavating. To reduce the probability of injury and potential for death, contractors are required by the Occupational Safety and Health Administration, to follow OSHA trench box requirements, to prevent soil from collapsing during trenching and excavation operations.
Trench boxes offer a safe, OSHA compliant work environment to expedite cast iron pipe, conduit, fiberglass tank and reinforced concrete pipe installation in trenches, restricted right-of-ways, and unstable soil areas. The boxes don’t prevent cave-ins but decrease the probability of a soil collapse trapping a worker. Trench boxes fortify a trench against unstable soil resulting from tension cracks, sliding, bulging and heaving.
Details of OSHA Trench Box Requirements
The Occupational Safety and Health Administration requires that a trench box must be used for all trenching or excavations five feet or greater in depth. Trench boxes must extend eighteen inches above the surface and be no more than two feet from the bottom of the trench. Should the trench depth exceed twenty feet, an OSHA trench box requirements stipulate a certified, professional engineer must design the trench box.
Prior to a contractor excavating a site, the contractor must inspect and classify the soil using visual and manual test procedures. Once the tested soil content is verified, the contractor can use contemporary shoring equipment or approved sloping methods to provide additional support for the trench box.
There are four classifications of soil:
Type A Soils: standard, silty, sandy clay and clay loam with a 1.5 tons per square foot (tsf) (144 kPa) or greater of compressive strength.
Type B Soils: angular gravel, silt loam with 0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa) of compressive strength.
Type C Soils: gravel, sand and loamy sand, submerged soil, water seeping soil, with 0.5 tsf (48 kPa) or less of compressive strength.
Layered Geological Strata; soils are configured in different layers
Another one of OSHA trench box requirements is that the contractor must provide a safe access and egress with the trench box. Ladders, steps, and ramps are to be situated within twenty-five feet of workers to allow a quick exit should the soil collapse.
Understanding the rules of the Occupational Safety and Health Administration and using common sense will ensure that trenching and excavating activity will go according to plan without worker injury.