Understanding Excavation Hazards
Cave-ins
- Most dangerous excavation hazard
- Can occur without warning
- One cubic yard of soil can weigh as much as a car (3,000+ pounds)
- Most fatalities occur in trenches less than 12 feet deep
- Survival rate is low once buried
Other Excavation Hazards
- Falling loads
- Hazardous atmospheres
- Water accumulation
- Underground utilities
- Mobile equipment
- Falls into excavations
- Structural collapse of nearby buildings
Key Excavation Rules
The 5-Foot Rule
- Any trench 5 feet or deeper requires a protective system
- The only exception is excavations in stable rock
- A competent person must determine if a trench under 5 feet needs protection
The 4-Foot Rule
- Ladders, steps, or ramps required for trenches 4 feet or deeper
- Must be located within 25 feet of workers
- Means of egress must be in protected areas
The 20-Foot Rule
- Trenches 20 feet or deeper require protective systems designed by a registered professional engineer
- Standard tabulated data cannot be used
The 2-Foot Rule
- Keep spoil piles at least 2 feet from trench edges
- This prevents soil from falling back into the trench
- Also reduces weight load on trench edges
Protective Systems
Sloping
- Cutting back trench walls at an angle inclined away from the excavation
- Different angles required for different soil types:
- Type A soil (most stable): 53° (¾:1)
- Type B soil (medium stability): 45° (1:1)
- Type C soil (least stable): 34° (1½:1)
- Must account for additional factors like water, vibration, etc.
Shoring
- Installing support systems to prevent soil movement
- Various types: hydraulic, pneumatic, or timber
- Must be installed from the top down
- Must be removed from the bottom up
- Requires knowledge of proper installation techniques
Shielding
- Using trench boxes or shields to protect workers
- Does NOT prevent cave-ins but protects workers inside
- Must extend 18 inches above the trench in some cases
- Can be moved as work progresses
- Workers must stay within protected area
Benching
- Creating steps or benches in the trench wall
- Only allowed in Type A and B soils (not Type C)
- Maximum height of benches equals their width
- Multiple bench levels may be required for deeper trenches
Soil Classification
Type A Soil
- Most stable soil type
- Examples: clay, silty clay, sandy clay
- Has unconfined compressive strength of 1.5 tons per square foot or greater
- Cannot be Type A if:
- It is fissured
- Subject to vibration
- Previously disturbed
- Part of a layered system with weaker layers
Type B Soil
- Medium stability
- Examples: silt, sandy loam, unstable dry rock
- Previously disturbed Type A soil
- Has unconfined compressive strength between 0.5-1.5 tons per square foot
Type C Soil
- Least stable soil type
- Examples: gravel, sand, loamy sand
- Soil with water freely seeping through it
- Submerged soil
- Has unconfined compressive strength of 0.5 tons per square foot or less
Soil Testing Methods
A competent person must test soil using at least one visual and one manual test:
- Visual tests: checking for cracks, water seepage, layered soils
- Manual tests: thumb penetration test, plasticity test, ribbon test, dry strength test
Access and Egress
Ladders
- Must extend 3 feet above the edge of the trench
- Secured at top to prevent movement
- Inspected before each use
- Positioned within 25 feet of all workers
- Placed in protected areas of the trench
Ramps and Runways
- Designed by a competent person
- Structural members of same thickness
- Connected to prevent displacement
- Free of projections that could snag clothing
- Non-slip surface
- Properly angled for safe travel
Stairways
- Must meet OSHA stairway requirements
- Handrails on all stairs with 4+ risers
- Proper illumination
- Kept clear of debris and materials
- Inspected regularly
Daily Inspections
A competent person must inspect excavations:
- Daily before work begins
- As needed throughout the shift
- After rainstorms or other water exposure
- After any significant disruption
- After any condition change that could increase hazards
Look for:
- Signs of potential cave-ins (cracks, bulges)
- Failure of protective systems
- Hazardous atmospheres
- Water accumulation
- Other hazardous conditions
Hazardous Atmospheres
When Testing Is Required
- Excavations deeper than 4 feet
- Where oxygen deficiency or hazardous gases might exist
- Near landfills or hazardous substance storage
- Where generators or equipment exhaust may accumulate
What to Test For
- Oxygen levels (must be between 19.5% and 23.5%)
- Flammable gases (must be below 10% of lower explosive limit)
- Toxic gases like carbon monoxide
- Hydrogen sulfide and methane in sewer work
Ventilation and PPE
- Provide adequate ventilation when necessary
- Use blowers or fans to move fresh air into the excavation
- Supply appropriate respirators when needed
- Never enter hazardous atmospheres without proper protection
Water Accumulation
- Never work in excavations with accumulated water
- Use water removal equipment supervised by competent person
- Inspect after rainstorms before allowing re-entry
- Special support systems may be required in wet conditions
- Wear appropriate PPE if working near water
- Have rescue equipment ready if water hazards exist
Underground Utilities
Before Digging
- Contact utility notification system (Call 811/One Call)
- Wait required time for utility marking (typically 2-3 business days)
- Respect and preserve markings
- Obtain utility location documentation when possible
During Excavation
- Hand dig within marked tolerance zones
- Expose utilities carefully by hand before using power equipment
- Support exposed utilities to prevent damage
- Report any damage immediately, even if minor
- Never assume depth or exact location of utilities
Safe Work Practices
For Workers Inside Excavations
- Always inspect before entering
- Enter only protected excavations
- Use provided access/egress methods
- Stay within protected areas
- Exit immediately if hazards detected
- Never work under suspended loads
- Maintain awareness of equipment operating nearby
For Workers Near Excavations
- Stay back from edges
- Cross only at designated walkways
- Never jump over trenches
- Be aware of traffic and equipment
- Don't add unnecessary weight near edges
- Watch for signs of instability
Equipment Safety
- Keep equipment away from trench edges
- Use spotters for equipment operating near excavations
- Never allow equipment over workers
- Maintain warning systems (barricades, hand signals)
- Check for adequate overhead clearance
- Follow designated traffic routes
Emergency Response
If a cave-in occurs:
- DO NOT enter the unprotected area
- Call 911 immediately
- Tell emergency responders exactly where victim is located
- Keep unnecessary personnel away
- Shut down nearby equipment
- If safe to do so, try to provide air to the victim
- Control traffic and crowds until help arrives