Emergency TunnelVentilation Systems

Emergency Tunnel Ventilation Systems are vital auxiliarysystems installed in railway, metro, and highway tunnels to protect human lifeand support evacuation in the event of accidents, fires, or gas leaks.

Why Are They Critically Important?

Especially in underground environments such as metrotunnels, where access is limited, proper system design and installation are ofcritical importance. These systems enable:

• Prevention of uncontrolled smoke propagation
• Rapid extraction of toxic gases
• Maintenance of adequate visibility for passengers and evacuation teams

Tunnel Ventilation Systems in Metro Projects

The main components and operating principles of tunnelventilation systems designed for metro projects are detailed below:

• Reversible Axial Fans

At each ventilation shaft located at station ends, two (2)primary axial fans are installed, integrated with bypass and isolation dampers.These fans are designed to provide equal performance in both supply and exhaustmodes. Each fan is equipped with double silencers to minimize noise pollution.In emergency conditions, the system is capable of reversing the airflowdirection to full capacity within a maximum of 60 seconds.

• Air Intake Shafts and Piston Relief Dampers

To control the high pressure generated by train movement(piston effect), dedicated air intake shafts are installed at station ends andservice stations. These shafts are equipped with controllable bypass dampers.During normal operation, bypass dampers remain open to balance pressure, whilein emergency situations they automatically close to completely isolate airflowinteraction between tunnel sections.

• Temperature Sensors and Automatic ClimateControl

Highly sensitive temperature sensors are installedapproximately 20 meters away from station ends and shafts to continuouslymonitor tunnel air temperature. If the average tunnel temperature exceedsdesign limits, ventilation fans are automatically activated to cool the tunnelto predefined safe temperature levels.

Emergency Tunnel Ventilation System OperatingModes

1. Normal Operation Mode

Under normal operating conditions, when train services runaccording to schedule, tunnel environmental conditions are managed in line withpassenger comfort and design criteria.

• Piston Effect and Air Exchange

Ventilation shaft dampers are configured to utilize the“piston effect” generated by train movement, extracting warm air from thetunnels and drawing in fresh air. This approach aims to achieve natural aircirculation throughout stations and tunnels.

• Strategic Shaft Placement

While most airflow is supplied through station entrances,ventilation shafts are positioned at both ends of stations to provideadditional fresh air intake and to discharge accumulated heat.

• Active Fan Support

During hot seasons, natural ventilation may beinsufficient if tunnel temperatures exceed design limits. In such cases, tunnelventilation fans (TVS) are automatically activated to exhaust hot air andsupply fresh air, thereby cooling the environment.

2. Congested Operation Mode

When trains are held inside tunnels due to planned orunplanned stoppages, airflow generated by train movement (piston effect)ceases. Mechanical ventilation is therefore required to maintain acceptableenvironmental conditions.

• Push-Pull Principle

Fans at one end of the station or tunnel section operatein supply mode, while fans at the opposite end operate in exhaust mode. Thissynchronized operation ensures continuous and fresh airflow along the tunnel.

• Automatic and Manual Control

Congested operation mode can be activated automaticallyvia the signaling system when prolonged stoppages are detected, or manually bythe control center.

• Thermal Balance

This mode prevents heat accumulation generated bystationary trains, providing a comfortable environment for passengers andprotecting tunnel equipment from overheating.

3. Emergency Operation Mode

Emergency Operation Mode refers to scenarios such as trainfires or underground fires occurring within the tunnel, without any operationalconstraints. The tunnel ventilation system supplies clean (ambient) air to thefire zone to reduce the effects of combustion products, remove smoke and toxicgases, and lower air temperature.

Additionally, the tunnel ventilation system controlsairflow patterns to ensure safe evacuation of passengers and operatingpersonnel, while facilitating access for emergency response teams.

Depending on the location and magnitude of the fire, fansmay be operated under different scenarios.

a) Train Fire in a Tunnel

In the event of a train fire within a tunnel, tunnelventilation fans operate according to the “push-pull” principle described undercongested operation. To generate the required fresh air for firefighting,multiple fans on both sides of the fire zone may be simultaneously activated ineither supply or exhaust mode.

b) Critical Velocity

The minimum air velocity required to prevent smokeaccumulation in the tunnel and to direct hot smoke in the desired direction isreferred to as the “critical velocity.” The capacity of tunnel ventilation fansis calculated based on this critical velocity, and fan inlet and outlet airvelocities are designed to exceed the critical velocity value.