The giant fans you see in tunnels are heavy-duty tunnel ventilation fans designed to move large volumes of air along the tunnel and toward exhaust points. They are usually axial fans, often called jet fans when installed within the tunnel itself, and they form the backbone of the tunnel’s longitudinal ventilation system. Similar technology is also used in mining access tunnels and underground haulage routes.
In a typical road or rail tunnel, a series of jet fans is mounted in the ceiling or high on the walls. Each fan takes in air and discharges it at high velocity along the tunnel axis. Through momentum transfer, these fans induce a bulk airflow in the tunnel, pushing exhaust-laden air toward portals or ventilation shafts where larger exhaust fans may be installed to discharge the air to the atmosphere.
These giant tunnel fans serve several key functions:
- Routine air quality control: they help maintain acceptable levels of vehicle exhaust gases by continuously moving air and preventing stagnant pockets where pollutants can accumulate.
- Smoke control during fires: in a fire event, jet fans and main exhaust fans are controlled according to an emergency strategy that directs smoke away from evacuation routes and towards exhaust points.
- Temperature management: by moving air and exchanging it with outside air, the fans help manage temperature in the tunnel, limiting heat build-up from vehicles, lighting, and equipment.
- Operational flexibility: fan speed and operating modes can be adjusted based on traffic conditions, pollution sensor readings, and emergency scenarios.
The fans are “giant” not only in physical size but also in performance. They are engineered to deliver high airflow and significant thrust, often operating in harsh conditions with dust, moisture, and occasional exposure to high temperatures in fire situations. Their construction typically includes robust casings, corrosion-resistant materials, high-specification motors, and, in many cases, provisions for high-temperature operation to ensure they continue to function during tunnel fires long enough to support evacuation and firefighting.
In mining and industrial tunnels, similar large axial fans may be installed at portals or access points to provide intake or exhaust ventilation for underground workings. Whether in public infrastructure or in mining, these giant fans are critical components of the ventilation system, providing the airflow needed to control exhaust gases, dust, smoke, and heat inside long tunnel structures.
