Tunnel hazards stem from working underground and include instability, including rock bursts and falls of rock or earth, changing strata and stress, restricted access and space, possibly including confined spaces, contaminated or oxygen-depleted air, fire or explosion, fixed and mobile plant and its interaction with people, temporary electrics including loss of power to lighting and ventilation, compressed air and high-pressure hydraulics, large materials handling, overhead seepage and process water, slippery or uneven surfaces, people or objects falling, groundwater contamination, in-rush of water or ground gas, noise, vibration, humidity and heat, surface settlement and hazardous substances. Controls include ground support (tunnelling shields, mesh, rockbolts, shotcrete), temporary work platforms, traffic management, regular plant maintenance, dewatering pumps, mechanical ventilation, dust extraction, water scrubbers, catalytic converters, and breathing equipment where a hazardous atmosphere cannot be ventilated. Ground support designed for the specific conditions is essential, and all tunnelling excavation should be supported.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.