Safe Trenching and Excavation Procedures

This document outlines the WorkSafeBC guidelines for safe trenching and excavation procedures. It includes shoring and sloping requirements to prevent cave-ins and ensure worker safety, in compliance with occupational health and safety regulations. These guidelines are essential for preventing accidents and ensuring a safe working environment in excavation and trenching operations.

General Requirements

Before a worker enters any excavation over 1.2 m (4 ft.) in depth, or approaches closer to the side or bank than a distance equal to the depth of the excavation, the employer must ensure that the sides of the excavation are adequately protected. Acceptable methods include sloping, benching, shoring, or using manufactured trench boxes or shoring cages. These measures are critical to prevent cave-ins and protect workers from the hazard of moving ground. [2]

Sloping and Benching

Sloping involves cutting back the trench wall at an angle inclined away from the work area. The angle of slope depends on the soil conditions. Benching is a similar method. [6]

The sides of an excavation can be sloped at angles that depend on soil conditions to ensure stable faces. The slope or combination of vertical cut and slope must not exceed what is shown in Figure 20-1 of the regulations. For hard and solid soil, the maximum slope of the excavated face is 3 horizontal to 4 vertical. Alternatively, a maximum height of the vertical portion can be 1.2 meters (4 feet). [2] [5]

Shoring Requirements

Shoring systems support the sides or walls of the excavation. These systems involve installing aluminum, steel, or wood panels supported by screws or hydraulic jacks. Some systems can be installed without workers entering the trench, enhancing safety. Shoring should be installed as the excavation proceeds, and if there is any delay between digging and shoring, no one should enter the unprotected trench. [6]

Timber shoring materials must be lumber graded Number 2 or better from specific species groups: Douglas fir-larch, hemlock-fir, spruce-pine-fir, or coast-Sitka-spruce. All lumber must be graded to the National Lumber Grades Authority Standard Grading Rules for Canadian Lumber. [1]

Safe Shoring Procedures

Shoring materials must be installed from the top down and removed in reverse order. Workers must not enter an excavation to remove shoring materials if ground conditions have deteriorated so as to make entry for shoring removal unsafe. Shoring or manufactured support systems must be installed in firm contact with the faces of the excavation, ensuring no soil loss from behind or below the support system while the excavation is open. Voids between the shoring and the excavation face must be backfilled or blocked unless otherwise indicated by the manufacturer or a professional engineer. [1] [1] [1] [1]

End Shoring

If end shoring is required, the walers for the end shoring must be installed to bear against the walers that extend along the sides of the trench, or in a manner that will provide equivalent structural restraint. End shoring must be designed by a professional engineer if the end shoring waler length exceeds 1.8 m (6 ft.). Shoring must extend from at least 30 cm (1 ft.) above ground level to as close to the bottom of the trench as the material being installed will allow, but in no case more than 60 cm (2 ft.) from the bottom. [1] [1] [1]

Trench Support Structures

Trench support structures, other than those designed by a professional engineer, must comply with specific requirements based on soil conditions (Type A: hard and solid, Type B: likely to crack or crumble, Type C: soft, sandy, filled or loose). Cross braces and trench jacks must be installed horizontally and secured against dislodgment. Hydraulic or pneumatic trench jacks must have a means of ensuring they will not collapse in the event of pressure loss. [3] [3] [3]

Underground Utility Services

Before excavating or drilling with powered tools and equipment, the location of all underground utility services in the area must be accurately determined, and any danger to workers from those utility services must be controlled. Excavation or drilling work in proximity to an underground utility service must be undertaken in conformity with the requirements of the owner of that utility service. Pointed tools must not be used to probe for underground petroleum and electrical utility services. Powered equipment used for excavating must be operated so as to avoid damage to underground utility services or danger to workers. [2] [2] [2] [2]

Additional Safety Measures

Trees, utility poles, rocks, and similar objects adjacent to an area to be excavated must be removed or secured if they could endanger workers. Safe means of entry and exit must be provided for an excavation a worker enters. If workers are required to enter a trench over 1.2 m (4 ft) deep, the safe point of entry and exit must be located within 8 m (25 ft) of the workers, and the excavation must be safely supported or sloped to the entry and exit location. [2] [4] [4]

Excavated Materials and Spoil Piles

Excavated material must be kept back a minimum distance of 60 cm (2 ft) from the edge of a trench excavation and 1.2 m (4 ft) from any other excavation. Under no circumstances may excavated material be piled so that it endangers workers. If the average depth of a spoil pile adjacent to a supported excavation exceeds 60 cm (2 ft), the selection of the shoring or shielding must account for the increased lateral soil pressure. [4] [4] [4]

Inspection Checklist Considerations

A trenching and excavation inspection checklist should include verification of contact numbers for underground or utility services, confirmation that respective parties have been located, identified, and informed, and assurance that underground services are grounded, isolated, de-energized, or protected from unplanned release. The checklist should also cover housekeeping, ensuring excavated materials are placed at least 1 meter away from the edge, pumps are available to remove water, and traffic controls are established where required. [8] [8] [8] [7] [7] [7]

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