22 Mar Trenching

Trenching

Trenching operations expose workers to cave-ins, falling materials, hazardous atmospheres, underground utilities, water accumulation, and mobile equipment. Because trenches have restricted working space and limited means of escape, hazards must be identified and controlled before employees enter.

Guide for Discussion

Before Trenching Begins

A competent person must evaluate the excavation and surrounding conditions before work begins.

• Locate underground utilities before excavation and have their locations properly marked.
• Determine soil type and conditions as necessary to select an appropriate protective system.
• Identify overhead power lines and other overhead hazards.
• Determine whether sloping, benching, shoring, shielding, or another protective system will be required.
• Plan safe access and egress before employees enter.
• Evaluate nearby structures, traffic, equipment, spoil piles, vibration sources, and other conditions that could affect trench stability.
• Determine whether hazardous atmospheres, water accumulation, or other special hazards could be present.
• Establish barricades, warning systems, or other controls where employees, vehicles, or equipment could approach the trench.
• Ensure emergency procedures are understood before work begins.

Competent Person Inspections

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

• Before employees enter.
• Daily before the start of work.
• As needed throughout the shift.
• After rainstorms or other hazard-increasing events.
• Whenever changing conditions could affect trench safety.

If evidence of a possible cave-in, protective-system failure, hazardous atmosphere, water accumulation, or other dangerous condition is found, employees must leave the trench until the hazard has been corrected.

Cave-In Protection

Never allow employees to enter a trench that is not properly protected when cave-in protection is required.

• Trenches 5 feet or deeper require an adequate protective system unless the excavation is made entirely in stable rock.
• Trenches less than 5 feet deep must also be protected when a competent person identifies indications of a potential cave-in.
• Protective systems may include sloping, benching, shoring, or shielding.
• Protective systems must be selected and installed according to applicable requirements and site conditions.
• Employees working inside trench boxes or shields must remain within the protected area.
• Never work beneath unsupported or overhanging soil.

Do not rely on the appearance of the soil. A trench can collapse suddenly without visible warning.

Access and Egress

Trenches 4 feet or deeper must have 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.
• Secure ladders and keep access points clear.
• Reposition ladders or other access points as work progresses.
• Do not climb on trench shields, shoring, or other protective systems unless specifically designed for that purpose.
• Keep escape routes unobstructed.

Spoil Piles and Materials

Excavated soil, materials, and equipment can increase pressure on trench walls and create falling-object hazards.

• Keep spoil piles, materials, and equipment at least 2 feet from the trench edge, or use an effective retaining device.
• Prevent loose rock, soil, tools, and materials from falling or rolling into the trench.
• Do not store unnecessary equipment or materials near the excavation.
• Never work beneath suspended loads or equipment being loaded or unloaded.

Mobile Equipment

Heavy equipment and vehicles can contribute to trench collapse and create struck-by hazards.

• Keep unnecessary vehicles and equipment away from trench edges.
• Establish safe equipment travel routes.
• Use barricades, stop logs, hand or mechanical signals, or other warning systems when equipment operators do not have a clear view of the excavation edge.
• Keep employees clear of equipment swing radiuses and operating areas.
• Use a spotter when required by site conditions or established procedures.

Water and Atmospheric Hazards

Employees must not work in trenches containing accumulated or accumulating water unless adequate protective measures are implemented.

Where hazardous atmospheres could reasonably be expected:

• Test the atmosphere before employees enter trenches more than 4 feet deep.
• Test for oxygen deficiency, flammable gases and vapors, and potential toxic contaminants as appropriate.
• Provide ventilation or other controls when necessary.
• Continue atmospheric monitoring when conditions warrant.
• Maintain appropriate emergency and rescue equipment when hazardous atmospheric conditions exist or could develop.

During Trenching Operations

Workers and supervisors must continuously watch for changing conditions.

• Follow the competent person’s instructions.
• Inspect protective systems for movement or damage.
• Watch for cracks, bulging soil, sloughing, falling material, or other signs of instability.
• Monitor weather and water conditions.
• Maintain safe access and egress.
• Keep unauthorized personnel away from the trench.
• Immediately exit and report any unsafe condition.

Remember

A successful trenching operation depends on planning, competent-person inspections, proper protective systems, safe access, and continuous attention to changing conditions. Never take shortcuts or enter an inadequately protected trench. A cave-in can occur suddenly and leave little or no time to escape.