Write a toolbox talk on Trench collapse

A trench collapse can happen suddenly and with enough force to crush, trap, or suffocate workers. One cubic yard of soil can weigh about 3,000 pounds, and cave-ins are the leading hazard in excavation work. Never allow anyone to enter an unprotected trench, even briefly. [1] [2] [6]

• Main hazards include cave-ins, struck-by incidents from equipment or falling loads, underground utility strikes, hazardous atmospheres, water accumulation, falls into excavations, and spoil piles or materials placed too close to the edge.
• Conditions that increase collapse risk include Type C or previously disturbed soil, rain, seepage, standing water, vibration, nearby traffic, heavy equipment, surcharge loads, and changing weather.
• There may be little or no warning before a cave-in, and escape is often impossible once the wall starts to fail.

[1] [4] [8] Cave-in prevention starts with a protective system. Under OSHA rules, trenches 5 feet or deeper require protection unless they are made entirely in stable rock. For trenches less than 5 feet deep, a competent person must determine whether there is a cave-in hazard. Trenches 20 feet or deeper must have the protective system designed or approved by a registered professional engineer. [2] [2]

Protective systems:

• Sloping: cutting trench walls back at a safe angle away from the excavation. The slope must match the soil type and site conditions.
• Benching: cutting the sides into horizontal steps. Benching is not allowed in Type C soil.
• Shoring: installing hydraulic, timber, or other supports to prevent soil movement and wall failure.
• Shielding: using trench boxes or shields to protect workers inside the protected zone; workers must stay inside the shielded area.

[2] [2] [5] [5] Soil classification is critical because it determines how stable the trench walls are and what protective method is acceptable. Type A soil is the most stable, Type B is less stable, and Type C is the least stable. Soil can effectively become less stable when it is wet, previously disturbed, granular, or subject to vibration. A competent person must classify the soil and reassess it when conditions change. [4] [10] [8]

A competent person must inspect the excavation, adjacent areas, and protective systems before the start of work, daily, throughout the shift as needed, and after any hazard-increasing event such as rain, water intrusion, or other condition changes. If evidence of a possible cave-in, protective system failure, hazardous atmosphere, or other dangerous condition is found, workers must be kept out until the hazard is corrected. [5] [2] [9]

Provide safe access and egress for any trench 4 feet or deeper. A ladder, stairway, ramp, or other safe means of exit must be located so workers do not have to travel more than 25 feet laterally. Ladders should be secured and extend above the landing surface so workers can get in and out safely. [1] [12] [11]

Keep spoil piles, materials, and heavy equipment back from the trench edge. At minimum, excavated material and other objects must be kept at least 2 feet from the edge to reduce surcharge loading and prevent material from falling back into the trench. Do not park or operate heavy equipment close enough to overload the edge, and keep workers out from under suspended loads. [4] [2] [3]

Underground utilities are a major excavation hazard. Before digging, locate and mark subsurface installations, notify the utility locating service, and verify exact locations when work approaches known utilities. Gas, electric, sewer, water, and other lines must be protected, supported, or removed as needed before employees enter the excavation. Use extra caution when digging within the tolerance zone and follow site procedures if a line is damaged. [3] [9] [8]

Hazardous atmospheres and water hazards must be controlled. Test the atmosphere before entry into excavations over 4 feet deep where oxygen deficiency or hazardous gases could be present, such as near landfills, sewers, or chemical storage areas. Do not allow workers in excavations with accumulating water unless protective measures such as pumping, special support or shield systems, and close competent-person oversight are in place. [9] [8] [12]

Emergency response for trench work must be planned before entry. Workers should know the trench emergency procedure, maintain communication, and never work alone in a trench. If a collapse occurs, call emergency services immediately, keep bystanders out, stop nearby equipment and vibration sources, and do not rush unprotected workers into the trench for rescue. Secondary collapse is a major risk, so rescue should be coordinated by trained responders with proper trench-rescue capability. [6] [6] [7]

Key OSHA excavation and trenching requirements are found in 29 CFR 1926.651 and 1926.652 within Subpart P. In practice, the core compliance points are: protect workers from cave-ins, have a competent person inspect the trench, provide safe access/egress in trenches 4 feet or deeper, keep spoils 2 feet back, locate utilities before digging, control water and atmospheric hazards, keep workers clear of suspended loads, and use engineer-designed systems for trenches over 20 feet deep. [2] [8] [8]

For a toolbox talk takeaway: No one enters a trench until the competent person has inspected it, the soil and hazards have been assessed, the utilities are located, spoil piles are set back, safe access is in place, and an adequate protective system is installed.