Tunnel & Underground Construction

Tunnel workers (sometimes called sandhogs) build subways, water tunnels and shafts underground, where air quality, ground collapse, fire and limited escape are constant concerns.

• Construction

Top hazards

• Ground falls and collapse
• Hazardous atmospheres: methane, hydrogen sulfide, low oxygen, diesel exhaust
• Fire and explosion with limited escape routes
• Flooding
• Moving equipment and rail haulage in tight spaces
• Compressed air work (decompression illness)
• Noise and silica dust

Key requirements

• Check-in/check-out system so everyone underground is accounted for.
• Air monitoring by a competent person and mechanical ventilation.
• Emergency procedures, self-rescuers where required, and rescue teams.
• Ground support installed and inspected; scaling of loose rock.
• Communication between the face and the surface.
• Strict decompression procedures for compressed air work.

How tunnels are built

• Tunnel boring machines (TBMs): large machines that excavate and install lining segments as they advance.
• Drill and blast: drilling holes in rock, loading explosives and mucking out after each blast.
• Sequential excavation: excavating in stages and spraying concrete (shotcrete) for support.
• Shafts: vertical access shafts with hoists for people and material.

Air underground

• Ventilation must deliver enough fresh air for the people and diesel equipment underground.
• Gassy tunnels (where methane or other flammable gas is present) have extra rules for equipment, monitoring and smoking.
• Watch for diesel exhaust and carbon monoxide from equipment. See Diesel Exhaust.
• Drilling, blasting and shotcrete create silica dust. See Silica.

Emergencies underground

• Know where the nearest exit, refuge chamber and self-rescuer are.
• Know the alarm signals and the evacuation plan.
• Fire underground spreads smoke fast. Report any smoke immediately.
• Never go past the last ground support without permission.

Before going underground

• Checked in on the board or tag system
• Lamp, self-rescuer (where required) and gas monitor
• Hard hat, glasses, hearing protection and boots
• Know today’s work area, haulage traffic and signals
• Know the evacuation route and refuge location

Last updated: October 1, 2026