A trench is 4.5 feet deep in stable clay soil. A Competent Person has examined the ground and found no indication of a potential cave-in. According to the exception in 1541.1, is a protective system required?

• No, only if a trench box is used.
• No, because it meets the exception for excavations less than 5 feet deep examined by a Competent Person.
• Yes, because clay soil is not considered stable rock.
• Yes, because the trench is deeper than 4 feet.