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In November, 2012, a 39 year old construction worker from North Carolina died while working in a trench when it caved in due to improper safety precautions. In November, 2011 a nineteen year old was killed when an unprotected trench collapsed. OSHA issued violations for failing to provide proper head protection, failing to keep spoil piles 2+ feet from the edge of the trench, and failing to train employees on recognizing hazards. A Florida construction company failed to slope or shore a trench, killing one and injuring two. Trench cave-ins are the top cause for employee injury and fatalities above any other trenching safety issue. By following proper safety precautions, employees working in trenches have the tools to get home safely.
OSHA requires that all excavations that put employees at risk for cave-ins be protected by one of the following methods:
• Sloping or benching - forming an incline on the sides of an excavation.
• Shoring - Using site built structures made with timbers, planks, or plywood to support the sides of an excavation.
• Shielding - Using trench boxes or trench shields to prevent the walls from collapsing.
The most common causes of a cave-ins are not using shoring, using inadequate shoring, excavating too closely to a building or utility pole, misjudging the stability of the soil, vibrations caused during construction work that destabilizes the soil, or weather conditions that change the stability of the soil.
Soil should be tested before excavation. Type A soil (clay, silty clay, sandy clay, and clay loam) is stable and okay for excavation. Type B soil (silt, silty loam, and sandy loam) has middle range stability. Type C soil is granular soil such as gravel, sand, or watery soil. It is unstable and requires extra precautions when excavating.
Aside from cave-ins, trenches pose additional risks as well: falls, falling loads, hazardous atmospheres, drowning, and contact with underground power lines. To prevent a construction site injury or death, workers and supervisors alike must follow these guidelines.
• For trenches 4+ feet, employees need access to egress at least every 25 feet. Egress options may include ladders, steps, or ramps.
• Everyday trenches need to be inspected for signs of cave-in hazards, flaking, and hazardous conditions.
• Protective systems and equipment must be tested daily.
• Spoils and equipment need to be kept at least 2 feet from the edge of the trench.
• Wear proper personal protective equipment.
• Keep trenching machines level to prevent undercutting the soil while keeping shoring as close as possible to the trenching machine.
• 4+ foot deep trenches require air testing.
• Cross-bracing must be in place before entering a trench.
• Sheeting that forms the walls of the shored trench must reach 18 inches over the trench.
Following the OSHA recommended precautions will protect employees from serious injury or death while working in trenches on the construction site. Site safety isn't only the concern of a supervisor or safety monitor; it is everyone's concern. Save a life by following and promoting safe working practices.