For a trench 1.5 metres or deeper, the PCBU must also minimise the risk of trench collapse to any person by making sure every side is adequately supported using one or more of: shoring by shielding or a comparable method; benching; or battering. A combination may work best depending on the environment and the material dug. In streets or built-up areas the excavation may need partial or full sheeting or support so local vehicle movement does not cause collapse. A competent person such as an engineer should be the one to design support systems or to help choose other collapse controls such as trench shields.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.