02 Mar Trenches

Trenches

Trenches can expose workers to cave-ins, hazardous atmospheres, falling materials, water accumulation, mobile equipment, and other serious hazards. A trench can collapse suddenly and without warning, so workers must never enter an excavation unless it has been inspected and required protective measures are in place.

Guide for Discussion

Competent Person Inspections

A competent person must inspect trenches, adjacent areas, and protective systems:

• Before employees enter.
• Daily before the start of work.
• As needed throughout the work shift.
• After rainstorms or other hazard-increasing events.
• Whenever conditions change or evidence of a possible hazard develops.

If an inspection identifies a hazardous condition, employees must be removed from the trench until the necessary precautions have been taken.

Cave-In Protection

Cave-ins are one of the greatest hazards associated with trenching.

• Never enter an unprotected trench when a protective system is required.
• Trenches 5 feet or deeper generally require an adequate protective system unless the excavation is made entirely in stable rock.
• Trenches less than 5 feet deep also require protection when a competent person identifies a potential cave-in hazard.
• Protective systems may include sloping, benching, shoring, or shielding, depending on soil and site conditions.
• Never work outside the protected area of a trench box or shield.
• Do not assume there will be warning signs before a cave-in. Soil can collapse suddenly.

Safe Access and Egress

For trenches 4 feet or deeper, provide a stairway, ladder, ramp, or other safe means of egress.

• Position access so employees do not have to travel more than 25 feet laterally to reach it.
• Keep ladders and access routes unobstructed and properly secured.
• Reposition access points as work progresses to maintain the 25-foot maximum travel distance.
• Never climb on protective systems unless they are specifically designed for access.

Water Accumulation

Employees must not work in trenches where water has accumulated or is accumulating unless adequate precautions have been taken.

• Remove employees when water creates an unsafe condition.
• Use pumps, drainage systems, diversion ditches, or other appropriate controls when necessary.
• Monitor water-removal equipment when it is being used.
• Inspect the excavation after heavy rain or other conditions that could affect soil stability.

Spoil Piles, Materials, and Equipment

Keep excavated materials, equipment, and other loads from creating additional hazards.

• Keep spoil piles and materials at least 2 feet from the edge of the excavation or use retaining devices sufficient to prevent material from falling or rolling into the trench.
• Keep vehicles and heavy equipment a safe distance from trench edges.
• Use warning systems, barricades, stop logs, or signals when mobile equipment operates near an excavation and the operator does not have a clear view of the edge.
• Protect workers from materials or equipment that could fall or roll into the excavation.

Hazardous Atmospheres

Atmospheric hazards may exist in trenches, particularly around utilities, contaminated soil, sewers, landfills, or other locations where hazardous gases or oxygen deficiency may occur.

• Test the atmosphere when hazardous conditions could reasonably be expected.
• Provide ventilation or other controls when required.
• Do not enter an atmosphere that is unsafe for entry.
• Maintain emergency and rescue equipment when hazardous atmospheric conditions exist or could reasonably develop.

Protect Workers and Others

• Notify subcontractors, visitors, and other affected personnel of trench locations and hazards.
• Use barricades, warning signs, or other protection around excavations as necessary.
• Provide fall protection where required.
• Identify underground utilities before excavation begins.
• Protect or support exposed utilities as necessary.
• Never work beneath suspended loads or equipment being loaded or unloaded.

Employee Responsibilities

Before entering a trench:

• Verify that the competent person has inspected and approved the excavation.
• Inspect the work area and protective system for obvious problems.
• Use designated access and egress points.
• Stay within the protection provided by trench boxes, shields, or other protective systems.
• Remain alert for changing soil, water, equipment, atmospheric, and weather conditions.
• Immediately exit the trench and report cracks, movement, falling material, water accumulation, protective-system damage, unusual odors, or other hazardous conditions.

Remember

A trench can collapse without giving workers time to escape. Never enter an unprotected trench when a protective system is required, and never assume soil that appears stable will remain that way. Follow the competent person’s instructions and exit immediately whenever unsafe conditions develop.