Trench collapses kill an average of 40 workers per year. One cubic yard of soil weighs approximately 3,000 lbs — there is no outrunning or digging out of a cave-in.
OSHA 29 CFR 1926.652 requires a protective system for any trench 5 feet deep or more. Trenches 20 feet or deeper require a system designed by a registered professional engineer.
Soil is classified into three types: Type A (most stable — clay, ceite), Type B (medium — silt, medium clay, angular gravel), and Type C (least stable — gravel, sand, submerged soil). The soil type determines the allowable slope angle and shoring requirements.
Three protective systems: Sloping (cutting the trench walls back at a safe angle), Shoring (installing supports to prevent wall movement), and Shielding (using a trench box to protect workers inside). The competent person selects the appropriate method.
A competent person must inspect the trench daily before entry and after any rain, vibration, or event that could change conditions. They have the authority to remove workers from the trench immediately if hazards are detected.
DO
Have a competent person inspect the trench before anyone enters
Ensure a safe means of egress (ladder, ramp, or steps) within 25 feet of every worker
Keep spoil piles at least 2 feet back from the edge of the trench
Call 811 to locate underground utilities before any excavation
Monitor for hazardous atmospheres if the trench is deeper than 4 feet
DON'T
Enter any trench 5 feet or deeper without a protective system in place
Stand on or near the edge of a trench where soil can give way
Place heavy equipment or materials near the trench edge
Assume the soil type — it must be tested and classified by the competent person
Ignore water accumulation — pumping or other controls are required before entry
Discussion Questions
Who is the competent person for excavations on this jobsite, and what is their authority?
What type of protective system are we using today, and why was it selected for this soil type?
If you noticed cracking along the trench wall or water seeping in, what would you do?