The 70°C fire damper sits on air supply and ventilation ducts. It stays open in normal use. On a fire it closes and interlocks the fan to stop it.
The 280°C fire damper sits on smoke extraction ducts. It stays open in normal use. On a fire it extracts smoke. When the smoke temperature reaches 280°C the damper closes and interlocks the fan to stop it.
The 280°C fire damper is normally open, also called a high-temperature fire damper. It is fitted in ventilation ducts with high temperatures. At 280°C the fusible alloy melts and the damper closes. It can also be driven by a 24 V signal. The 280°C smoke fire damper is normally closed. It sits in the smoke extraction duct. On a fire the control centre signals it open for extraction. At 280°C the fusible alloy melts and it closes. It is a two-action damper.
Ventilation ducts are not used during a fire. The 70°C damper closes at that point and stops the fire from spreading through the duct. In a smoke system the damper extracts during the fire. The smoke is hot; at 280°C mechanical extraction no longer works well, so the damper closes to protect the fan and other equipment.
In short: the 70°C fire damper is normally open and closes on contact with fire. The 280°C smoke fire damper is normally closed, opens on fire to extract, and closes when the air reaches 280°C.
On fans: the supply fan, positive-pressure fan and make-up fan are different names for the same kind of unit, moving air below 80°C. The smoke exhaust fan serves fire extraction and must run 30 min at 280°C; it can also extract kitchen grease. The exhaust fan moves air below 80°C.
How the dampers above relate to the fans: smoke extraction ducts use a 280°C fire damper; all other fire compartments use a 70°C damper.
The high-rise code refers to a smoke fire damper, which differs from a fire damper. In brief:
Fire class. 1. Fire damper: fire protection, closes at 70°C by thermal fuse, can be linked, used in ventilation and air-conditioning ducts. 2. Smoke-fire damper: closes on smoke detection for smoke protection and also at 70°C by thermal fuse for fire protection, used in ventilation and air-conditioning ducts.
Smoke class. 1. Smoke outlet: opens electrically, manually or remotely, links with the smoke exhaust fan, may carry a 280°C closing device, used on ceilings or walls of smoke zones. 2. Smoke valve: opens electrically or manually, links with the smoke exhaust fan, used on smoke system ducts. 3. Smoke fire damper: opens electrically or manually, closes at 280°C by fuse, used on the inlet duct of the smoke exhaust fan. 4. Smoke window: opens on smoke detection, electrically or remotely, used on external walls for natural smoke extraction.
The 70°C fire damper is generally used on ventilation and air-conditioning ducts, and where those ducts pass a fire compartment, fire wall or enter a plant room. Its main role is to cut the ventilation and air-conditioning line on a fire and stop fire spreading through the duct.
The 280°C fire damper is generally used in smoke control systems. Normally open, it closes automatically at 280°C on a fire and sends a signal to the fire control room, stopping further spread.
The 280°C smoke damper is normally used as a smoke outlet. Normally closed, it opens on a fire through a nearby detector or the fire control room to extract smoke, and closes at 280°C.