A trench is 8 feet deep with Type A soil. The contractor installs a trench box. What additional Cal/OSHA requirement must be met?
Correct Answer
A) The trench box must extend at least 18 inches above the bottom
Cal/OSHA requires trench boxes to extend at least 18 inches above the bottom of the excavation to provide adequate protection.
Why This Is the Correct Answer
Cal/OSHA Title 8 Section 1541.1 requires that trench boxes (shields) extend at least 18 inches above the bottom of the excavation. This overlap ensures that the unshored area at the very base of the trench is minimized and workers' lower bodies remain protected from soil cave-in pressure even at the floor level.
Why the Other Options Are Wrong
Option B: A competent person must be in the trench at all times
There is no requirement for a competent person to be physically inside the trench at all times. The competent person must be present on-site and must inspect the trench daily and after any hazard-altering event, but continuous in-trench presence is not mandated and would itself be a safety risk.
Option C: No additional requirements needed
Even with a trench box installed, additional requirements do apply. Cal/OSHA specifies the positioning standards for shields (the 18-inch extension), the need for daily competent-person inspections, and proper entry/exit provisions. Saying 'no additional requirements' is incorrect and dangerous.
Option D: Sloping at 3/4:1 ratio outside the box
Sloping outside the box at a 3/4:1 ratio is the requirement for Type B soil, not Type A. Type A soil (cohesive with unconfined compressive strength β₯ 1.5 tsf) requires a maximum slope of 3/4:1 only under specific conditions, and sloping the exterior when a box is used is not the primary additional requirement β the box extension height is.
Memory Technique
Think '18 inches = a foot and a half of safety margin at the bottom.' The trench box must stick up 18 inches above the trench floor β picture the box as a bathtub that must be higher than the mud line by 1.5 feet.
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