The hazard
Soil is heavy, and a trench wall can give way with little or no warning. A cave-in can bury or crush a worker before they can react, and a coworker who jumps in to help can be caught by the next collapse. These rules keep the walls off people and give everyone a way out.
The action
Keep spoil piles, materials and equipment at least 2 feet back from the edge, or hold them back with retaining devices, or both. Never stand under loads handled by lifting or digging equipment (29 CFR 1926.651(e)). When mobile equipment works near the edge and the operator cannot clearly see it, a warning system such as barricades, hand or mechanical signals, or stop logs must be used (29 CFR 1926.651(f)). Workers exposed to public traffic must wear a warning vest or other high-visibility garment (29 CFR 1926.651(d)). (29 CFR 1926.651(j)(2))
ASK THE CREW
What do you do if you see cracks at the edge or water seeping in?
From the talk: Trenching and excavation. Read it in full, free, with the questions and the sign-in sheet.