For an excavation deeper than 20 feet, protective systems (such as shoring or shielding) must be:

解析

Note 3 to Appendix B is explicit: sloping or benching for excavations greater than 20 feet deep shall be designed by a registered professional engineer, and section 1541.1(b)(4) requires that design to be stamped and signed. Options (a) and (b) are the other two lawful routes - Option 3 lets the employer work from tabulated data approved by an engineer, Option 2 from Appendices A and B - and both are genuinely available to a competent person, but only up to 20 feet. That is what makes them the right kind of wrong answer: they are correct rules read past their depth limit. A building department may review shoring as part of a permit in some cities, but it has no role under Title 8 (c).