TUNNEL VENTILATION SYSTEMS

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AXIAL FANS

Depending on the design of the tunnel ventilation system, axial fans are usually used to blow clean air into the tunnel while exhausting the stale air and smoke in the event of a tunnel fire.Axial fans can be of the single-way type or fully reversible type.Depending on the site installation conditions, the fans can be manufactured in either a horizontal or vertical configuration.TME GRUP has experience in vertical and horizontal fans supplied in recent tunnel projects worldwide.

JET FANS

Among the different tunnel ventilation systems, jet fan longitudinal ventilation is the most widely used. Jet fans can be of the single-way type or the double-way type.Jet fans are suspended from the tunnel ceiling or tunnel walls by means of a suspension system and are mounted on the base chassis and mounted inside the tunnel. In most projects, the suspension system and chassis are within the scope of TME GRUP.

Tunnel Ventilation Systems

In highway tunnels, ventilation systems are utilized to address air pollution caused by vehicle exhaust emissions and heat generation. The combination of exhaust fumes and heat creates air pollution that can adversely affect passengers' health. Tunnel Ventilation Systems are among the critical safety measures implemented during tunnel construction. These systems were developed in the 20th century to mitigate the effects of exhaust gases. Pollution levels can be controlled to limit the number of vehicles using the tunnel and improve vehicle engine performance.

Highway Tunnel Requirements

Except for very short tunnels, ventilation is essential in highway tunnels, particularly during periods of heavy traffic. In a tunnel where traffic flows in one direction and moves freely, natural airflow can suffice for tunnels up to 1–2 kilometers in length. However, for longer tunnels or in cases where traffic is slow-moving or stationary, ventilation becomes a necessity.

Types of Pollution in Tunnels

Pollution inside tunnels primarily results from exhaust gases, including:

· Carbon Monoxide: The primary pollutant produced by gasoline engine exhaust. Even minimal concentrations can pose a fatal risk.

· Nitrogen Oxides: Produced by both gasoline and diesel engines, nitrogen oxides (NO and NO₂) are less toxic than carbon monoxide.

· Sulfur Dioxide: Known to irritate the nasal and bronchial passages. While undesirable at concentrations between 5–10 ppm, it is emitted in negligible amounts by motor vehicles and typically does not pose a ventilation challenge in tunnels.

Tunnel Ventilation Systems

Air distribution systems in tunnels are generally categorized into longitudinal, transverse, and semi-transverse types. The simplest is the longitudinal ventilation system, where air enters at one end of the tunnel and exits at the other. The airflow is driven by wind, pressure differences, vehicle movement in single-direction tunnels, or a fan system.

Transverse ventilation systems operate independently of longitudinal airflow and use two separate channels to supply and extract air along the tunnel length, facilitated by fans.

Longitudinal Ventilation Systems

In very short tunnels, particularly in mountainous areas with sparse traffic and natural airflow, ventilation occurs naturally without additional systems.

Transverse Ventilation Systems

For long tunnels, a fully transverse ventilation system is ideal for central sections, provided that installation and operational costs are not prohibitive. Air is supplied through a channel and extracted at road level. This process can also be reversed, depending on specific requirements.