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
When workers will be exposed, a competent person must inspect the excavation, nearby areas and protective systems daily before work, as needed during the shift, and after every rainstorm or other hazard-increasing event. A competent person can spot existing and predictable hazards and is authorized to fix them promptly (29 CFR 1926.650(b)). If they find signs of a possible cave-in or other hazards, exposed workers must be removed until it is safe (29 CFR 1926.651(k)(2)). If you see cracks, bulging walls or water seeping in, get out and tell them. (29 CFR 1926.651(k)(1))
ASK THE CREW
Who is our competent person today, and what do they check?
From the talk: Trenching and excavation. Read it in full, free, with the questions and the sign-in sheet.