Before an excavation or trench is started the employer determines where underground utilities and piping may lie and takes the precautions section 12.1 sets out. Walls 1.2 metres (4 feet) or deeper are supported by adequate shoring, bracing or caging unless the stated exceptions apply, and workers do not enter until the shoring requirements and the other conditions of section 12.3 are met. Shoring is not installed or removed from inside the trench, excavated material stays at least 609 mm from the edge, the excavation is kept reasonably free of water and free of stored hazardous liquids, gases and explosives, material is lowered only with unrestricted visibility or a signaller, a worker on the surface keeps the workers below in view, nobody stands under a load, unstable rock walls are supported, the excavation is lit and barricaded with warning lights at all times while occupied and at night, piled material that interferes with traffic is lit, power shovels are placed with care and shored where on the bank, and no excavation may endanger a worker by undermining a neighbouring building or structure.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.