A Tunnel Ventilation System (TVS) provides controlled airflow within railway tunnels and associated underground spaces to maintain acceptable environmental conditions and support fire and life safety.

During normal railway operation, the TVS helps manage heat generated by trains, traction equipment, passengers and other sources. Train movement itself creates significant airflow through the piston effect, which is considered as part of the overall tunnel ventilation design.

During congested or degraded operation, where trains may remain stationary in tunnels for extended periods, the ventilation system may be required to control tunnel temperatures and provide suitable conditions for passengers and equipment.

During a train or tunnel fire, the TVS performs an important smoke-management function. Ventilation strategies are designed to control the movement of smoke, maintain tenable evacuation routes where practicable and support emergency response activities.

A TVS may include tunnel ventilation fans, jet fans, ventilation shafts, dampers, ducts, air plenums, sensors, control panels and associated electrical and control equipment. System operation is typically coordinated through PLC/SCADA-based controls and may be supervised from the Operations Control Centre (OCC).

TVS design requires close coordination with tunnel geometry, stations and shafts, rolling stock characteristics, train operating scenarios, fire size assumptions, evacuation strategy, emergency response requirements and other Mechanical, Electrical and Plumbing (MEP) systems. Computational and specialist tunnel ventilation modelling is commonly undertaken to verify system performance.

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