An excavation is 12 feet deep with vertical sides in Type B soil. The contractor chooses to use a trench box instead of sloping. What is the minimum distance the trench box must extend above the bottom of the excavation?
Correct Answer
A) 12 feet
The trench box must extend from the bottom of the excavation to at least ground level, providing full protection for the 12-foot depth of the excavation.
Why This Is the Correct Answer
CORRECT_ANSWER - According to OSHA excavation safety standards, when using a trench box (protective system) in an excavation, the box must provide complete protection for workers from the bottom of the excavation to at least ground level. Since the excavation is 12 feet deep, the trench box must extend the full 12 feet from bottom to top. This ensures no unprotected vertical soil face is exposed where workers might be present.
Why the Other Options Are Wrong
Option B: 18 inches above ground level
10 feet would still leave 2 feet of unprotected vertical soil face exposed above the protective system, which violates OSHA safety requirements.
Option D: 10 feet
8 feet would leave 4 feet of unprotected excavation wall exposed above the trench box, creating a serious cave-in hazard for workers in the excavation.
Memory Technique
Think 'FULL PROTECTION' - the trench box must cover the FULL depth of excavation, never leaving workers exposed to unprotected soil faces.
Reference Hint
OSHA 29 CFR 1926 Subpart P - Excavations, specifically 1926.652 Requirements for protective systems
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