Every employee in an excavation needs an adequate cave-in protective system designed under paragraph (b) or (c), unless the excavation is entirely in stable rock, or is less than 5 feet deep and a competent person's examination of the ground shows no sign of potential cave-in. Protective systems must resist, without failure, every load intended or reasonably expected. Sloping and benching follow one of four options: (1) 1.5H:1V (34 degrees) or flatter, in Appendix B Type C configurations; (2) maximum slopes and configurations set under Appendices A and B; (3) other written tabulated data stating selection parameters, limits of use and safe slopes, with explanatory guidance; or (4) a written design naming the approving registered professional engineer and stating safe slopes and configurations. Support, shield and other systems follow one of four options: (1) timber shoring per Appendices A and C, aluminum hydraulic shoring per manufacturer's data or else Appendix D; (2) manufacturer's tabulated data, followed in full, deviating only with the manufacturer's specific written approval; (3) other written tabulated data; or (4) a written engineer's design naming the engineer and giving material sizes, types and configurations. For Options 3 and 4, and manufacturer's data, a copy (naming the approving engineer where required) is kept on site while the system is built, then may be stored elsewhere but must be produced to the Secretary on request. Appendix A applies to Option 2 sloping, Appendix C and D shoring and data built on its system. A competent person classes each deposit as Stable Rock or Type A, B or C using a minimum of one visual and one manual test (for example plasticity, thumb penetration or drying tests). Type A is cohesive soil of 1.5 tsf unconfined compressive strength or more, but never if fissured, subject to vibration, previously disturbed, or layered with layers dipping into the cut at 4H:1V or more; Type B includes cohesive soil above 0.5 and below 1.5 tsf; Type C includes cohesive soil at 0.5 tsf or less, granular soil, and submerged or freely seeping soil. Layered systems take the weakest layer's class, and changed conditions require competent person reclassification. Appendix B sets maximum simple slopes for excavations of 20 feet depth or less: 3/4:1 in Type A (1/2:1 where 12 feet deep or less and open 24 hours or less), 1:1 in Type B and 1 1/2:1 in Type C. In Type A an unsupported vertical lower portion may be no more than 3 1/2 feet high, and wherever a vertical lower portion is supported or shielded, the support must reach at least 18 inches above its top. Where distress appears the slope is cut back at least 1/2H:1V flatter than the maximum, and for surcharge loads a competent person decides and secures the needed reduction. For trenches up to 20 feet deep, Appendix C tabulates minimum timber sizes and spacings and Appendix D aluminum hydraulic spacings (2-inch cylinders rated at least 18,000 pounds, 3-inch at least 30,000 pounds) by soil type. The tables are not adequate, and another 1926.652 design is needed, where equipment over 20,000 pounds surcharges the trench, crossbrace vertical loads exceed 240 pounds (timber) or 100 pounds (hydraulic) on a one-foot centre section, or only the lower part is shored beneath a slope of 3H:1V or steeper without members sized from the trench top; for timber, also where adjacent loads exceed a two-foot soil surcharge. Materials must be defect-free and used and maintained per manufacturer recommendations; damaged items go to a competent person and, unless assured safe, stay out of service until a registered professional engineer approves them. Support members are securely connected against sliding, falling or kickout and never overloaded; installation and removal must protect workers, temporary removal needs added precautions, and removal runs bottom up, slowly, with backfilling keeping pace. In trenches, digging up to 2 feet below the bottom of supports or a shield is allowed only if the system is designed for the full trench depth and no soil loss appears, and support installation is closely coordinated with digging. Nobody works on sloped or benched faces above unprotected employees. Shields must not be overloaded, must be installed to limit lateral movement, must be entered and left without cave-in exposure, and must be empty while installed, removed or moved vertically.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.