20 Mar Excavation/Trenching Safety

Excavation and Trenching Safety

Excavation and trenching work can expose employees to extremely serious hazards. Cave-ins are the greatest risk and are more likely to result in fatalities than many other excavation-related incidents. Other hazards include falls, falling loads, hazardous atmospheres, water accumulation, underground utilities, and mobile equipment.

A trench can collapse suddenly and without warning. Never enter an excavation until the hazards have been evaluated and required protective measures are in place.

Before Excavation Begins

Good planning is essential. Before work starts:

• Identify the location of underground utilities and installations such as electrical, gas, water, sewer, communication, and fuel lines.
• Contact appropriate utility-location services before digging.
• Determine anticipated excavation depth, soil conditions, groundwater conditions, and nearby structures.
• Evaluate traffic, mobile equipment, vibration, spoil piles, and other loads that could affect excavation stability.
• Select appropriate sloping, benching, shoring, shielding, or other protective systems.
• Ensure required equipment and protective systems are available before employees enter the excavation.
• Determine whether atmospheric testing or additional precautions will be necessary.
• Establish safe access and egress.

Planning for protective systems should occur before the job begins—not after the trench has already been opened.

Competent Person

Excavation work must be evaluated by a competent person who is capable of identifying existing and predictable hazards and who has authorization to take prompt corrective measures.

The competent person is responsible for activities that include:

• Classifying soil when soil classification is required for the protective system being used.
• Selecting or verifying appropriate protective systems.
• Inspecting excavations, adjacent areas, and protective systems.
• Identifying hazardous conditions.
• Ordering employees out of an excavation when unsafe conditions exist.
• Taking appropriate corrective action before employees are permitted to re-enter.

Required inspections must be performed daily before work begins and as needed throughout the shift. Additional inspections are required after rainstorms or other events that could increase hazards, such as changing soil conditions, vibration, or water accumulation.

Cave-In Protection

Employees in an excavation generally must be protected from cave-ins when the excavation is 5 feet or more in depth, unless the excavation is made entirely in stable rock.

Excavations less than 5 feet deep also require protection when a competent person determines that there is an indication of a potential cave-in.

Acceptable protective methods may include:

• Sloping the excavation walls away from the excavation.
• Benching the sides where permitted by soil conditions and the protective-system design.
• Shoring to support the sides of the excavation.
• Shielding, such as a properly designed trench box, to protect employees if a cave-in occurs.

Protective systems must comply with applicable OSHA requirements and be appropriate for the soil, depth, loading, and conditions encountered.

Never work outside the protected area of a trench box or other protective system.

Spoil Piles and Materials

Excavated soil, materials, tools, and equipment can add weight to the trench wall or fall into the excavation.

Keep spoil piles, materials, and equipment at least 2 feet from the edge of the excavation, or use retaining devices or other effective methods to prevent materials from falling or rolling into the excavation.

Employees must also be protected from loose rock, soil, or other materials that could fall from excavation faces.

Safe Access and Egress

A stairway, ladder, ramp, or other safe means of egress must be provided in trench excavations 4 feet or more in depth.

Access must be positioned so employees do not have to travel more than 25 feet laterally to reach a safe means of egress.

Ladders must be properly positioned and secured and, where used for access to an upper landing surface, must extend as required above the landing or have another approved means of providing a secure handhold.

Never climb on shoring, trench boxes, utility lines, or other equipment as a substitute for proper access.

Water Accumulation

Water can weaken excavation walls and significantly increase the likelihood of a collapse.

Employees must not work in excavations where water has accumulated or is accumulating unless adequate precautions have been taken. Controls may include:

• Pumps or other water-removal equipment.
• Drainage systems.
• Special support or shield systems.
• Diversion ditches, dikes, or other methods for controlling surface water.

Water-removal equipment and operations must be monitored by a competent person when employees are in the excavation.

Mobile Equipment and Traffic

Vehicles and heavy equipment operating near an excavation can create vibration, surcharge loading, struck-by hazards, and collapse hazards.

Employees should:

• Stay clear of operating equipment and suspended loads.
• Remain visible to equipment operators.
• Use high-visibility garments when exposed to public vehicular traffic.
• Use barricades, warning systems, or stop logs when mobile equipment approaches an excavation and the operator does not have a clear view of the edge.
• Never stand underneath loads handled by lifting or digging equipment.

Hazardous Atmospheres

Atmospheric hazards may exist in excavations, particularly around landfills, sewers, chemical operations, fuel systems, contaminated soil, or other locations where oxygen deficiency or hazardous gases could be present.

For excavations greater than 4 feet deep where a hazardous atmosphere exists or could reasonably be expected, the atmosphere must be tested before employees enter.

Appropriate ventilation, respiratory protection, emergency equipment, and other controls must be provided when required.

Never Enter an Unsafe Excavation

Employees should never enter an excavation when:

• A required protective system is missing or damaged.
• The excavation has not received the required competent-person inspection.
• Water accumulation creates an uncontrolled hazard.
• Soil is cracking, sloughing, bulging, or otherwise showing signs of instability.
• Materials or equipment create an unsafe load near the edge.
• Safe access and egress are not available.
• A hazardous atmosphere has not been properly evaluated or controlled.
• Conditions have changed since the excavation was last inspected.

If conditions appear unsafe, stay out and immediately notify the competent person or supervisor.

Remember

There is no reliable warning before a trench collapses. Never assume that soil is safe because it looks solid, the excavation is temporary, or employees have entered it previously without incident.

Inspect it. Protect it. Provide safe access. If the required protection is not in place, do not enter the excavation.