Shafts, vertical or inclined, lined or unlined, give access or ventilation to tunnels or serve foundations, dewatering or underground facilities, and may be sunk from the top or raise-bored where underground access exists, which can be done remotely without people entering. Shaft openings should have controlled access, using a secure lockable cover that only a designated person can open, or alternatively with a suitable guardrail and toe board fitted with a gate for access, and the sides supported with steel frames or timber sets, or in special cases precast concrete or steel liners. Because shafts can have special features, advice on design and construction should come from a competent person such as an engineer before excavation and installation, and special ventilation may be needed.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.