Fire and Smoke Dampers

The three types, where IBC 717 and IMC 607 require them, the UL 555 / 555S ratings, and how to choose one

Last updated: June 26, 2026

Overview

When ductwork or an air-transfer opening passes through a fire-rated wall or floor, that opening would let fire or smoke through and defeat the barrier. Fire and smoke dampers close the opening to keep the barrier's protection intact, and building codes require them at specific rated-barrier penetrations. This guide covers the three damper types, where code requires each, the UL ratings, dynamic versus static operation, and how to spec one.

Need the code detail? The fire and smoke damper requirements page covers IBC 717, IMC 607, the UL 555 / 555S listings, and leakage classes.

The Three Common Types

Fire damper: closes when it senses heat (through a fusible link or other heat-responsive release) to keep fire from spreading through a duct or air-transfer opening in a fire-rated barrier. Listed to UL 555.
Smoke damper: at a smoke barrier it typically closes on a smoke-detection or fire-alarm signal to resist smoke movement; in an engineered smoke-control system the approved control sequence drives it to the required position. Listed to UL 555S.
Combination fire/smoke damper: does both jobs and is listed to UL 555 and UL 555S. Used where the penetrated barrier is both fire-rated and a smoke barrier.

Where Code Requires Them

IBC Section 717 (Ducts and Air Transfer Openings) and IMC Section 607 list where each damper is required and which type. In general terms:

Fire dampers where ducts or air-transfer openings penetrate fire walls, fire barriers, certain fire partitions, horizontal assemblies, and shaft enclosures.
Smoke dampers where ducts penetrate smoke barriers and at points in an engineered smoke-control system, plus certain shaft and corridor conditions.
Combination dampers where the penetrated barrier requires both fire and smoke protection.

Work from the drawings: Section 717.5 sets the specific conditions, ratings, and exceptions for each location, and several common penetrations are exempt. The required damper and its location come from the project's code analysis, not a rule of thumb.

Ratings (UL 555 / 555S)

Damper	Standard	Key rating
Fire	UL 555	Fire-resistance rating: 1.5 hours for barriers rated under 3 hours, 3 hours for barriers rated 3 hours or more
Smoke	UL 555S	Leakage class (code requires Class I or II) plus an elevated-temperature rating, 250°F minimum or 350°F where the smoke-control design needs it
Combination	UL 555 + UL 555S	Both of the above

Class I is the tightest leakage class and Class II allows more; IBC 717.3.2.2 and IMC 607.3.2.2 require a smoke damper to be Class I or II.

Corridor dampers are a separate case: they are a distinct listed application for specified corridor-ceiling conditions and carry their own listed rating (for example UL 555 1-hour with UL 555S Class I). Follow the model and rating on the damper schedule for those, not the general fire-damper values above.

Dynamic vs Static

Dampers are rated for the airflow condition they must close against:

Dynamic: rated to close against moving air, for HVAC systems designed to keep fans running during a fire. The rating includes a maximum airflow velocity and pressure.
Static: for systems that shut the fans down on a fire signal, so the damper closes in still air.

Only dampers labeled for dynamic use may be installed in systems that run the fans during a fire. Confirm which condition your HVAC design calls for before selecting.

How to Spec One

Match the barrier: pick fire, smoke, or combination to match what the penetrated barrier is rated for.
Confirm dynamic or static from the HVAC design.
Size to the opening: dampers install in a sleeve with a breakaway connection to the duct.
Actuator: smoke and combination dampers use an electric or pneumatic actuator wired to the fire-alarm or smoke-detection system. Specify the fail position (commonly fail-closed for smoke-barrier dampers) from the listing, the controls, and the approved smoke-control sequence.
Access: provide an access door so the damper can be reached for its required periodic test.

Get a Quote

To quote dampers, send your damper schedule: the type (fire, smoke, or combination), the barrier rating, the sizes, whether the system is dynamic or static, and the quantities. We match listed US-made dampers to the schedule and quote the order.

Pricing a damper schedule?

Send the damper types, barrier ratings, sizes, and quantities, and we'll match listed US-made dampers and quote the order. Typical turnaround: one business day.

or call 714-248-6555 · email partners@usmadesupply.com

Frequently Asked Questions

What is the difference between a fire damper and a smoke damper?

A fire damper closes on heat to stop fire spreading through a duct or opening in a fire-rated barrier (UL 555). A smoke damper closes on a smoke or alarm signal to resist smoke through a smoke barrier or smoke-control system (UL 555S). A combination damper does both.

When does code require a fire or smoke damper?

IBC Section 717 and IMC Section 607 require them where ducts or air-transfer openings penetrate specific fire-rated or smoke-rated barriers, with the type, ratings, and exceptions set in Section 717.5. The project's code analysis and drawings determine each location.

What is the difference between a dynamic and a static damper?

A dynamic damper is rated to close against moving air, for systems that keep the fans running during a fire. A static damper is for systems that shut the fans down. Only dampers labeled for dynamic use may go in fans-on systems.

What leakage class does a smoke damper need?

IBC 717.3.2.2 and IMC 607.3.2.2 require a smoke damper to carry a UL 555S leakage rating of Class I or II, plus an elevated-temperature rating of at least 250°F (or 350°F where the smoke-control design calls for it).

Do fire and smoke dampers have to be inspected?

Yes. They are operationally tested after installation and then on a periodic cycle under NFPA 80 (fire dampers) and NFPA 105 (smoke dampers). See the damper testing and inspection guide for the schedule.