Trench Collapse

Trench collapse is one of the deadliest hazards in construction, and one of the most preventable. Victims are usually buried quickly; even a partial burial can crush the chest so the worker cannot breathe.

Why walls fail

Soil holds its shape until it does not. Water, vibration from traffic or equipment, the weight of the spoil pile at the edge, and previously disturbed ground all reduce its strength. OSHA sorts soil into stable rock and Types A, B and C, from most to least cohesive, and each type has a maximum allowable slope.

Protective systems

• Sloping: cut the walls back to a safe angle.
• Benching: cut the walls in steps.
• Shoring: brace the walls with hydraulic or timber supports.
• Shielding: set a trench box that protects workers even if the wall fails.

A protective system is required at 5 feet, unless the excavation is entirely in stable rock. Beyond 20 feet, the system must be designed by a registered professional engineer.

Before and during the dig

Call 811 so underground utilities are marked. Keep spoil and equipment back from the edge. Provide safe access: a ladder, ramp or stairway within 25 feet of workers in trenches 4 feet or deeper. Test the air in deep trenches for low oxygen or toxic gases. A competent person inspects the excavation daily and after rain or any event that could change conditions.

Learning it here

Trench safety is taught in OSHA 10 and OSHA 30, in Heavy Equipment Operation, Plumbing & Pipefitting, Electrical Lineworker and Water/Wastewater programs, and demonstrated at the sand table beside this panel.