trench

A trench is defined as a narrow excavation in relation to its length, made below the surface of the ground, where the depth is generally greater than the width, and the width at the bottom is no more than 15 feet (4.6 m) [1]. Hazards associated with trench work include cave-ins, hazardous atmospheres, water accumulation, and mobile equipment 2, 6, 20.

To mitigate these risks:

1. Cave-in Protection:

• For trenches deeper than 1.2 meters (approximately 4 feet), protect workers from cave-ins by sloping the walls, installing a protective structure (shoring or trench box), or a combination of both 1, 5. Shoring should be installed and removed in a manner that protects workers from cave-ins and structural collapses [2].
• Trenches deeper than 3 meters may require design and certification by a professional engineer 1, 12.
• A competent worker should be stationed on the surface to watch for any potentially unsafe conditions and provide assistance in emergencies for trenches deeper than 1.2 meters [2].

2. Hazardous Atmospheres:

• Test the atmosphere in the trench before entry, especially in areas where hazardous substances are stored or in landfill areas, for oxygen deficiency or hazardous contaminants 6, 20.
• Provide ventilation or respiratory protection when necessary 6, 20.

3. Water Accumulation:

• Prevent water accumulation in the trench or provide adequate precautions such as water removal equipment, special support or shield systems, or safety harnesses and lifelines [3].
• A competent person should monitor water removal equipment [3].

4. Mobile Equipment:

• Use a warning system when mobile equipment is operated near the edge of the trench, especially when the operator's view is obstructed [4].
• Ensure shoring, bracing, or caging is adequate to support the increased pressure if heavy equipment is used near the trench edge [5].

5. Access and Egress:

• Provide a safe means of entering and exiting the trench, such as a ladder, stairway, or ramp, located within 8 meters of any worker in the trench 13, 19, 20.
• For trench excavations that are 4 feet (1.22 m) or more in depth, a stairway, ladder, ramp or other safe means of egress shall be located so as to require no more than 25 feet (7.62 m) of lateral travel for employees [4].

6. Additional Safety Measures:

• Identify and mark the location of all underground pipes, cables, and conduits before commencing work [6].
• Ensure that excavated material is kept at least 1 meter away from the edge of the trench [7].
• Inspect the trench after any event that could affect its stability, such as rain or vibrations [3].
• Provide warning vests or other suitable garments marked with or made of reflectorized or high-visibility material for employees exposed to public vehicular traffic [4].

Continuous monitoring and regular review of these control measures are essential to ensure worker safety in trenching operations.