Short answer: Tunnel and metro jet fans are specified by thrust (measured in newtons), reversible operation, and fire-resistance rating per EN 12101-3 — commonly F300/120 or F400/120. EPC and ventilation consultants should define certified thrust, ambient and gas temperature limits, noise criteria, and maintenance access. Procurement decisions for infrastructure projects should be based on certified performance and compliance, not unit price.
In longitudinal tunnel ventilation, jet fans do not move air by pressure against a duct — they inject momentum. A row of fans mounted near the ceiling accelerates the airflow along the tunnel, displacing smoke or supplying fresh air. The relevant specification metric is therefore thrust (N), not static pressure. Mis-specifying on pressure instead of thrust is the most common early-stage error in tunnel ventilation design.
Parameter | What to specify | Why it matters |
Rated thrust | Single-fan thrust in N at design speed | Drives the number of fans required |
Air/gas temperature | Continuous and peak (°C) | Affects motor class and coatings |
Fire rating | EN 12101-3 class, e.g. F300/120, F400/120 | Mandatory for smoke-extraction duty |
Reversibility | Reversible vs unidirectional | Required for bi-directional smoke control |
Noise limit | dB(A) at defined distance | Tunnel portals and urban metro constraints |
Motor protection | IP rating, insulation class | Humidity, dust, heat in tunnel environment |
Access & maintenance | Hoist points, removable panels | Lifecycle cost over 20–30 year asset life |
The total installed thrust must overcome tunnel resistance. A simplified planning formula:
N (fans) = (Required total thrust ÷ Single-fan certified thrust) × Correction factor
Correction factors account for fan spacing (induction losses between units), ambient temperature, and altitude. Use the AMCA/Piper coefficients from the fan supplier's certified test data rather than catalogue peak values — certified thrust per EN 12101-3 is the only figure acceptable for compliance sign-off.
EN 12101-3 defines powered smoke-control ventilators. The classification F300/120 means the fan sustains 300°C for 120 minutes; F400/120 means 400°C for 120 minutes. For road tunnels under fire, F400/120 is typical. The rating must come from a notified laboratory, not a self-declaration.
Reversible jet fans let the operator reverse airflow direction during an incident, pushing smoke toward the nearest extraction point. Specify reversible duty explicitly — unidirectional fans are cheaper but limit emergency response options.
Specifying on static pressure instead of certified thrust.
Accepting catalogue thrust without EN 12101-3 certification.
Ignoring altitude/temperature correction in fan count.
Underestimating 20-year maintenance access cost.
Q: What EN 12101-3 class do road tunnels require?A: Most road tunnels specify F400/120 (400°C for 120 minutes) for smoke-extraction jet fans; some metro systems use F300/120. The project's fire-engineering report defines the required class.
Q: How many jet fans does a tunnel need?A: It depends on tunnel length, cross-section, required air velocity, and fan spacing. Use certified thrust with EN 12101-3 data and apply correction factors — not peak catalogue numbers.
Q: Are reversible jet fans mandatory?A: Not always, but reversible units are required where the emergency plan relies on reversing airflow to extract smoke. Many modern metro systems mandate them.
Q: Can a standard industrial fan be used in a tunnel?A: No. Tunnel duty requires certified thrust, fire rating, and continuous-operation construction under heat and vibration that general ventilation fans are not built for.