In California, the trench cave-in protection requirement mirrors federal OSHA, applying protective systems at depths of:

Explanation

Section 1541.1(a)(1) requires every employee in an excavation to be protected from cave-ins by an adequate protective system, with two exceptions: excavations made entirely in stable rock, and excavations less than 5 feet deep where a competent person's examination of the ground shows no indication of a potential cave-in. Note that the second exception has two halves and both must hold - a four-foot trench in running sand is not exempt. Option (a) inverts that exception: a competent person can exempt a shallow trench from protection, not authorise an unprotected one at any depth above two feet. Twenty feet (c) is a different rule about WHO designs the system: past that depth Appendix B stops applying and a registered professional engineer must design it. Two feet and ten feet appear nowhere in the standard as triggers.