Answer:
The correct answer is D. 5-15
Step-by-step explanation:
Excavation is a risky work which includes earthwork, tunneling, trenching, etc by earth removal. A trench is a narrow depression in which the depth is more than its width. In width, it is not more than 15 feet.
Most of the accident occurs between 5-15 feet deep in trenches. Cave-ins during excavation or digging trenches are responsible for most fatalities and injuries every year.
Other risks are inhalation of poisonous substance, lack of oxygen, accident from machines, fire, etc. Therefore the correct answer is D. 5-15 feet.