🚧 Excavation & Trenching Safety
Topic: Cave-in protection, trench safety, and OSHA excavation requirements Duration: 10–15 minutes Required: OSHA 29 CFR 1926 Subpart P — Excavations
The Stats
- Trench collapses kill an average of 40 workers per year in the U.S.
- One cubic yard of soil weighs 2,700–3,000 lbs — the weight of a car
- A cave-in can happen in seconds with zero warning
- The fatality rate for trench collapses is much higher than most construction hazards — victims are often buried completely
OSHA requires: Protective systems for all trenches 5 feet or deeper. A competent person must inspect every excavation daily and after any rain event.
How Cave-Ins Happen
Cave-ins occur when:
- Soil weight exceeds the strength of the trench walls
- Water saturates the soil (rain, broken water line, high water table)
- Vibration from equipment, traffic, or adjacent work loosens soil
- Spoil pile is too close to the edge, adding weight
- Workers undercut the trench wall
- Previously disturbed soil is weaker than expected
A trench wall can collapse in under 1 second. There is no time to react. If you're in the trench, you will be buried. At 2 feet deep in soil, you cannot free yourself — you need rescue.
Protective Systems (Required at 5 Feet or Deeper)
Sloping
Cut the trench walls back at an angle so they won't collapse.
| Soil Type | Slope Ratio | Angle |
|---|---|---|
| Stable Rock | Vertical OK | 90° |
| Type A (clay) | ¾:1 | 53° |
| Type B (silt, sandy loam) | 1:1 | 45° |
| Type C (gravel, sand, soft clay) | 1½:1 | 34° |
The competent person classifies the soil. When in doubt, assume Type C.
Shoring
Install hydraulic, mechanical, or timber shoring to brace the trench walls.
- Must be designed for the soil type and trench depth
- Install from the top down, remove from the bottom up
- Workers must not enter the trench until shoring is in place
Shielding (Trench Box)
Place a manufactured trench box in the excavation to protect workers.
- Must be rated for the depth and soil conditions
- Workers must stay inside the shield at all times
- Shield must extend at least 18 inches above the surrounding grade (or spoil pile must be 2+ feet back)
Key OSHA Requirements
Competent Person
A competent person must be on-site during all excavation work. They must:
- Classify the soil type
- Select the appropriate protective system
- Inspect the excavation daily before work and after every rainstorm
- Inspect the excavation after any event that could increase hazards (vibration, water, adjacent excavation)
- Have the authority to stop work immediately
Access and Egress
- A ladder, ramp, or stairway must be within 25 feet of every worker in the trench
- Ladders must extend 3 feet above the top of the trench
- Ladders must be secured to prevent movement
Spoil Pile
- Keep the spoil pile at least 2 feet back from the edge of the trench
- Keep equipment, tools, and materials 2 feet back as well
- Never stand on the spoil pile near the trench edge
Utilities
- Call 811 at least 48 hours before digging (required by law)
- Hand-dig within 24 inches of marked utilities
- Verify utility locations with potholing before mechanized excavation
Water Accumulation
- Pump standing water out before workers enter
- Monitor for water seepage continuously
- If water is entering the trench, stop work until it's controlled
Atmosphere
- Test atmosphere if trench is deeper than 4 feet and hazardous atmosphere is possible
- Provide ventilation if oxygen is low, or gases are detected
- Rescue equipment must be available if atmosphere monitoring is required
Before Entering Any Trench — Checklist
- Competent person has inspected and approved entry
- Protective system in place (sloping, shoring, or shielding)
- Ladder/ramp within 25 feet
- Spoil pile 2+ feet from edge
- Utilities located and marked
- No standing water
- No cracks in trench walls
- Adjacent structures stable
- No equipment operating near the edge without a spotter
What NOT To Do
❌ Never enter a trench 5+ feet deep without a protective system ❌ Never enter a trench that hasn't been inspected today ❌ Never work under or near overhanging soil ❌ Never place spoil or equipment at the trench edge ❌ Never work in a trench with standing water (pump it out first) ❌ Never jump across a trench ❌ Never assume someone else checked the trench — verify for yourself ❌ Never work in a trench alone
If Someone Is Buried
- Call 911 immediately — trained trench rescue is critical
- Do NOT enter the trench unless you have trench rescue training and the trench is protected — rescuers become victims in 60% of secondary cave-ins
- Try to keep the victim's airway clear if accessible from outside
- Prevent additional soil from entering the trench
- Direct emergency responders to the exact location
Discussion Questions
- Where are we digging on this project? What soil type do we have?
- What protective system are we using? Has the competent person inspected it today?
- Where is the nearest ladder or ramp to get out?
- What would you do if you saw a crack in the trench wall?
- Has anyone on this crew been involved in a trench rescue or close call?
Today's Commitment
"I will never enter an unprotected trench, and I will speak up immediately if I see unsafe conditions in or around an excavation."
Sign-In
| Name | Signature | Company |
|---|---|---|
Presenter: _________________ Date: _________