A fire damper and a smoke damper are life-safety devices placed where ductwork crosses a fire-rated barrier: the fire damper, built to UL 555, closes on heat at about 74°C to stop flames passing through a rated wall or floor, and the smoke damper, built to UL 555S, closes on smoke detection to stop toxic gases moving between zones. Together, or as a combined fire-smoke damper, they preserve the integrity of fire compartments and smoke-control systems required by code.
Fire Damper Basics (UL 555)
A fire damper is a metal curtain or blade assembly mounted in the duct at a barrier penetration. Its fusible link or thermal release holds the blades open during normal operation; when ambient temperature reaches roughly 74°C to 165°C depending on type, the link melts and a spring snaps the blades shut. The damper and its housing are tested in a furnace to a fire-resistance rating, most often 1.5 hours or 3 hours, matching the wall or floor it serves. Dynamic fire dampers are rated to close against airflow and keep working with the fan running, while static types close after the fan stops.
Smoke Damper Basics (UL 555S)
A smoke damper is judged by leakage, not fire endurance. UL 555S classifies it by how little air passes when closed under a pressure difference, with Class I allowing at most 1.0 cfm per square foot at 1 inch w.g. and Class II allowing up to 3.0 cfm. It is driven by a smoke detector signal through an actuator, closing in seconds to seal a smoke-control barrier, stairwell, or elevator lobby. Because it must hold position against pressure, the actuator and frame are built for repeated cycling and tight sealing.
Fire vs Smoke Damper Comparison
| Property | Fire damper (UL 555) | Smoke damper (UL 555S) |
|---|---|---|
| Closes on | Heat, about 74°C to 165°C | Smoke detector signal |
| Rated by | Fire resistance, 1.5 or 3 hours | Leakage class I or II |
| Typical location | Wall or floor penetrations | Smoke-control barriers, lobbies |
| Drive | Fusible link or spring | Motorized actuator |
The comparison shows the two devices solve different problems; a combined fire-smoke damper meeting both standards is common where one penetrates a rated smoke barrier.
Key Numbers and Ratings
Three figures matter. First, the closure temperature: fire dampers release at 74°C for standard ceilings or up to 165°C for high ambient spaces. Second, the fire rating: 1.5 or 3 hours to match the assembly. Third, the leakage class: Class I at 1 inch w.g. for smoke dampers, with closure time often under 60 seconds. Actuator power is typically 24 V or 230 V, drawing 10 to 50 W, and blade sizes span 150 to 1,500 mm to fit ducts from 150 to 2,000 mm.
When to Choose Fire vs Smoke vs Combined
- Choose a fire damper wherever ductwork penetrates a fire-rated wall, floor, or shaft needing 1.5 or 3 hour rating.
- Choose a smoke damper in smoke-control barriers, stairwells, and elevator lobbies where leakage class matters.
- Choose a combined fire-smoke damper when one penetration serves both fire and smoke separation.
- Choose a dynamic-rated fire damper if the fan keeps running during a fire event.
- Choose a static fire damper only where the fan stops on alarm and airflow ceases.
Installation and Inspection
Install the damper with its frame flush to the rated barrier and the listing's required access door for service. Never pack the sleeve with material that blocks the blades, and keep the fusible link intact. After installation, run the operational test: trip the release or send a detector signal and confirm full closure within the rated time. Codes then require periodic inspection, often every 4 to 6 years for fire dampers and 1 to 4 years for smoke dampers, with records retained. A seized pivot or broken spring voids the protection, so lubricate and exercise moving parts on each visit.
Keruite manufactures this equipment at an 80,000 m² facility in Dezhou, China, with an in-house AMCA-210-style test laboratory; every unit is balanced to G2.5 and performance-tested before shipment.
Dynamic vs Static and Combined Dampers
Fire dampers are split into static and dynamic ratings. A static fire damper closes after the fan stops and airflow ceases, so it is simpler and cheaper, while a dynamic damper is tested to close against rated airflow of 2 to 10 m/s and keep working with the fan running, needed where smoke control continues during the event. A combined fire-smoke damper carries both UL 555 and UL 555S listings in one housing, with a thermal release at 74°C and a motorized close on smoke signal, sealing to Class I leakage at 1 inch w.g. Sizing follows the duct: blades span 150 to 1,500 mm and the frame is rated for the 1.5 or 3 hour wall it penetrates. Choosing the wrong type, such as a static damper in a live fan duct, voids the fire strategy.
Code, Records, and Field Care
Authorities require the damper listing to match the barrier rating, and the installation to include an access door so the device can be tested without demolishing the wall. After the initial trip test confirms closure within the rated time, codes call for periodic inspection every 4 to 6 years for fire dampers and 1 to 4 years for smoke dampers, with the report kept on file. Common failures are a missing fusible link, paint that welds the blades, or a disconnected actuator, any of which means the damper will not close. Lubricate pivots, keep the link intact, and never pack the sleeve with insulation. A documented, current test record is what proves the fire barrier still performs its rated 1.5 or 3 hour function.
Rating Plate and Traceability
Each certified damper carries a label stating its UL 555 or UL 555S class, fire duration of 1.5 or 3 hours, and serial number tied to the test report. Keep that label visible and the record with the building file; during an audit or after a fire the plate is the proof the barrier met its rated performance, and a missing or painted-over label is treated as non-compliant.
FAQ
What is the difference between a fire damper and a smoke damper?
A fire damper (UL 555) closes on heat, usually at 74°C, to stop flame spread through a rated wall or floor, while a smoke damper (UL 555S) closes on smoke detection to limit toxic gas movement and is rated for leakage, not fire. Many projects use a combined fire-smoke damper that meets both standards in one housing.
What does the UL 555 and UL 555S rating mean?
UL 555 certifies a fire damper for a fire-resistance duration, commonly 1.5 or 3 hours, in a specific wall or floor assembly. UL 555S certifies a smoke damper for leakage class, such as Class I at 1 inch w.g., ensuring it blocks smoke passage. The listing defines the approved installation and rating.
Where are fire and smoke dampers required?
They are required where ductwork penetrates a fire-rated wall, floor, or shaft, and in smoke-control systems serving multiple zones. Code typically places a fire damper at every penetration of a 1 to 3 hour rated barrier and a smoke damper in smoke-control barriers and stairwell or elevator lobby boundaries.
How often must fire and smoke dampers be inspected?
Most codes require operational testing after installation and periodic inspection, commonly every 1 to 4 years for smoke dampers and every 4 to 6 years for fire dampers in many jurisdictions, with records kept. Springs, linkages, and release devices must move freely, or the damper fails its listing.