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4.8 Excavation Safety

4.8 Excavation Safety

These are best practice guidelines to help protect persons from injury while working in excavations. Employees working in and around excavations must be trained on these guidelines and any additional local regulations.

4.8.1 General

  • Prior to opening an excavation, use the local utility companies to estimate the location of underground installations, such as sewer, telephone, fuel, electric, and water lines.

  • When excavation operations approach the estimated location of underground installations, the exact location of the installations should be determined by safe and acceptable means.

  • A stairway, ladder, ramp, or other safe means of exit must be located in trench excavations that are 4 feet (1.22 m) or more in depth. Employees cannot travel more than 25 feet (7.62 m) horizontally without access to an exit.

  • Employees working in and around excavations must wear a hard hat and high-visibility vest.

  • Employees are not allowed to be underneath suspended loads.

  • A warning system, such as barricades or hand signals, must be utilized to prevent vehicles and mobile equipment from inadvertently entering the excavation.

  • If you suspect that a hazardous atmosphere, such as one that is oxygen deficient, exists in an excavation pit greater than 4 feet (1.22 m) in depth, the air in the excavation pit must be tested before employees enter. If necessary, take precautions such as providing ventilation.

  • Take adequate precautions in excavations where there is accumulated water or the potential for accumulating water.

  • Protect employees from loose rock or soil that could fall into the excavation. This can be done by removing loose material, installing protective barricades, and keeping materials or equipment at least 2 feet (.61 m) from the edge of excavations.

  • If the stability of adjoining buildings, walls, or other structures is endangered by excavation operations, support systems such as shoring and bracing must be approved by a professional engineer to ensure the stability of such structures.

  • Sidewalks and slabs must not be undermined unless a support system or another method of protection is provided to protect employees from the possible collapse of such structures.

  • When employees are working in an excavation, daily inspections must be performed by a qualified person prior to the start of work, as needed throughout the shift, and after every rainstorm. These inspections must examine the following:

    • Adjacent areas

    • Situations that could result in possible cave-ins

    • The protective systems, looking for any indications of their failure

    • Any potentially hazardous atmospheres

    • Other hazards

  • Employees must be removed from an excavation if hazardous conditions exist.

4.8.2 Protective Systems

Each employee in an excavation must be protected from cave-ins by systems such as shielding or sloping unless the excavations are less than 5 feet (1.52 m) in depth.

Shielding

  • Trench boxes are a common shielding system and are intended primarily to protect workers from cave-ins.

  • The excavated area between the outside of the trench box and the face of the trench should be as small as possible. The space between the trench box and the excavation side must be backfilled to prevent lateral movement of the box. Trench boxes should not be subjected to loads beyond those which the system was designed to withstand.

  • Trench boxes may be used in combination with sloping.

  • The box must extend at least 18 inches above the surrounding area if there is sloping toward the excavation.

  • Any modifications to the trench box must be approved by the manufacturer.

  • Trench boxes may ride two feet above the bottom of an excavation, provided they are calculated to support the full depth of the excavation and there is no caving under or behind the system.

  • Workers may not remain in the trench box while it is being moved.

Sloping

The following diagram shows the maximum slope allowed for excavations less than 20 feet based on soil type and angle to the horizontal. The soil must be classified by the soil classification of the weakest soil layer.

Image
rock and soil diagram

  • Type A (most stable)—clay, silty clay, and hardpan (resists penetration).

  • Type B (medium stability)—silt, sandy loam, medium clay, and unstable dry rock.

  • Type C (least stable)—gravel; loamy sand; soft clay; submerged soil; dense, heavy, and unstable rock; and soil from which water is freely seeping.