Laboratory and on-site thermal testing confirms that fire smoke exhaust fans keep running at 280°C for a continuous 2-hour period, the acceptance benchmark for life-safety ventilation in commercial and industrial buildings.
Why the 280°C / 2-Hour Rating Exists
Smoke control is a life-safety function, not a comfort function. When a fire breaks out, occupants need a clear, tenable escape path and firefighters need visibility to attack the seat of the fire. A smoke exhaust fan must therefore continue to extract hot, buoyant gases even after the surrounding air has far exceeded normal operating temperatures. The 280°C for 120 minutes requirement originates from European classification work for powered smoke and heat control ventilators and is widely referenced in project specifications across the Middle East, Southeast Asia, and China.
The rating describes a worst-case duty, not a design operating point. In a real fire the gas layer near the ceiling can reach several hundred degrees, but the fan is expected to survive long enough to perform its extraction duty and then be taken out of service. Specifying the correct duration (30, 60, 90, or 120 minutes) is a function of building height, firefighting strategy, and local code, and the selected duration should be confirmed against the authority-having-jurisdiction before order placement. Overspecifying simply adds cost; underspecifying leaves the escape route unprotected at the worst moment.
Temperature classes are not interchangeable. A ventilator declared for 200°C over 120 minutes and one declared for 400°C over 90 minutes protect different building types, and the class has to follow the smoke-control calculation rather than a supplier's stock list. Designers also need to remember that hot gas is far less dense than ambient air: at 280°C the density of air falls to roughly 0.62 kg/m³ against 1.2 kg/m³ at 20°C, so the same impeller moving the same volumetric flow develops only about half the static pressure and draws far less shaft power. Duct sizing and motor selection must both be checked at the hot condition as well as the cold one, otherwise the extract train looks adequate on paper and underperforms in the event.
Test Setup and Acceptance Criteria
A thermal performance test is normally conducted in a controlled chamber where the fan is brought to its design speed and then exposed to a rising and stabilized hot-air stream. Instruments record impeller temperature, motor winding temperature, bearing condition, and continuous rotation. The unit passes only if it keeps running for the full rated duration and still meets its declared airflow and pressure afterwards, because a fan that survives but can no longer move air has failed its purpose.
| Item | Specification | Note |
|---|---|---|
| Test temperature | 280°C | Stable hot-gas exposure, not transient spike |
| Endurance duration | 120 min | Equivalent to the stated 2-hour class |
| Motor protection | Class H insulation, 180°C | Withstands conductive heat from shaft |
| Airflow retention | ≥ 90% of rated volume | Measured at end of test |
| Post-test inspection | No structural cracking | Impeller and housing visually verified |
| Air density at 280°C | ≈ 0.62 kg/m³ | Against 1.2 kg/m³ at 20°C |
| Cold-condition check | Full duty at 20°C | Motor sized for the denser case |
The same fan family often shares a housing with a standard ventilation unit, but the fire-rated version adds a heat-protected motor, a cooling disc or air-shielded shaft, and high-temperature paint and gaskets. These details are what separate a smoke exhaust fan from a general-purpose centrifugal or axial unit, and they must be documented in the type-test report so the buyer can prove compliance during fire authority review. A catalog claim without the underlying test certificate is not acceptable evidence.
Two details are missed more often than any others in a type-test review. The first is the cold-start duty: the fan spends its whole service life at ambient temperature and only minutes at 280°C, so the motor has to be sized for dense cold air where absorbed power is highest, roughly 1.9 times the hot-condition figure. The second is everything outside the fan casing. Power cabling, control wiring, damper actuators, and flexible connections in the hot zone need their own temperature ratings, and a fire-rated fan wired with standard cable will still stop when the cable insulation fails. The type-test report covers the ventilator; the designer covers the circuit that feeds it.
What Buyers Should Verify
- Duration class: Confirm 30/60/90/120 min matches the fire strategy, not just the lowest price.
- Test house report: Ask for the original type-test certificate naming the exact model and size.
- Motor location: Prefer shaft-mounted motor outside the gas stream where the layout allows it.
- Mounting: Verify the bracket and isolators are rated for the thermal duty, not just the cold weight.
- Spares: Confirm bearings and seals are serviceable after a thermal event is not expected, but stocking simplifies replacement.
- Check hot and cold duty: Confirm declared airflow at 280°C and absorbed power at 20°C both sit inside the motor rating.
- Rate the whole circuit: Cable, actuators, and flexible joints in the hot zone need temperature ratings matching the fan class.
Standard Background and Project Significance
Selecting a verified 280°C / 2h fan removes a major uncertainty from a smoke-control design: the designer no longer has to assume the extract train will fail exactly when it is needed most. Keruite applies this test discipline in its own performance laboratory, so the declared thermal class is backed by measured data rather than a catalog claim, and the project file carries defensible evidence for the approving authority.
For the buyer the practical value is auditability. A ventilator whose thermal class was measured in an in-house performance laboratory, on a production unit rather than a prototype, gives the fire engineer a document that survives scrutiny. The company has built ventilation equipment for more than 30 years from an 80,000 m² plant in Dezhou, Shandong, holds CCC and ISO 9001:2015 certification, and ships to more than 50 countries, so the same test discipline applies whether the fan is destined for a metro contract or an overseas high-rise. That consistency lets a specifier reuse a proven selection across projects instead of re-qualifying a supplier each time.
Our engineers respond to selection enquiries within 24 hours, including help matching fan class, duration, and airflow to the project's fire and life-safety drawings.