Definition and Risk Overview
Under WAC 296-155-650, an excavation is any person-made cut, cavity, trench, or depression in the earth’s surface formed by earth removal. A trench is a narrow excavation where the depth exceeds the width, and the width at the bottom is 15 feet or less. If forms or structures reduce the bottom width to 15 feet (4.6 m) or less, the excavation is considered a trench.
Importantly, one cubic yard of soil can weigh up to 3,000 pounds, roughly the weight of a small car. Accordingly, trench and excavation operations carry significant risk. In fact, according to OSHA data, the fatality rate for excavation work is 112% higher than for general construction; “employee injury from collapse” is the primary hazard, and “no protective system” is a leading cause.
Competent Person (CP)
- Identifies hazards, has stop-work authority, and knows WAC 296-155-655.
- Inspects before the project, daily before work, as needed during the shift, and after rain/other events.
Soil Evaluation
- Perform visual + manual tests (plasticity, thumb, penetrometer).
- Check: cohesive vs granular, vibrations, prior disturbance/utilities, water seepage, fissures/sloughing.
Soil Types
- Type A: UCS ≥ 1.5 tsf (not A if fissured, disturbed, wet, or vibrating).
- Type B: UCS 0.5–1.5 tsf or otherwise A but fissured/near vibration.
- Type C: UCS ≤ 0.5 tsf; sand/gravel; any seeping soil.
- Increase protection as stability decreases (especially Type C).
Access/Egress (≥ 4 ft)
- Ladder/steps within 25 ft lateral travel.
- Earth ramp only if stable footing, ≤ 25 ft travel, and protected (shored) along the route.
Hazardous Atmospheres
- Test before entry > 4 ft where deficiency or contaminants are possible (e.g., landfills/near chemicals).
- Ventilate/monitor/use PPE; re-test before resuming work.
Call 811
- Request utility locates before digging to prevent strikes and outages.
Inspections & Corrections
- CP inspects excavation, adjacent areas, and protections daily/throughout/after events.
- If signs of cave-in/system failure/hazard: remove workers immediately and correct before continuing.
