Fire and Smoke Damper Requirements

IBC Section 717, IMC Section 607, the UL 555 / 555S listings, leakage classes, and actuation

Last updated: June 26, 2026

Overview

Building codes require fire, smoke, or combination dampers at specified duct and air-transfer openings in fire-rated and smoke-control assemblies, subject to the conditions and exceptions in IBC Section 717 and IMC Section 607. This page covers where each damper is required, the UL 555 and UL 555S listings that qualify them, the leakage classes, and how they are actuated.

Choosing a damper? The fire and smoke dampers guide covers the three types, dynamic vs static, and how to spec one, and links to a quote request.

Where Code Requires Them

IBC Section 717 (Ducts and Air Transfer Openings) and IMC Section 607 set the locations and the damper type for each. 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.

Exceptions matter: Section 717.5 sets the specific conditions and several exceptions (for example certain steel ducts in shafts, or sprinklered conditions), so not every penetration needs a damper. The required damper and location come from the project's code analysis.

The Standards

UL 555 is the standard for fire dampers. It establishes the fire-resistance rating (1.5 hours for barriers rated under 3 hours, 3 hours for barriers rated 3 hours or more) and closure performance.
UL 555S is the standard for smoke dampers. It establishes the leakage class and the elevated-temperature rating. Combination fire/smoke dampers are listed to both UL 555 and UL 555S.
NFPA 90A is the installation standard for air-conditioning and ventilating systems, referenced for duct and damper installation.
AMCA runs a voluntary certified ratings program for published damper performance data such as air leakage and air performance. Its seal is separate from, and does not automatically accompany, a UL 555 or UL 555S listing.

Leakage Classes and Temperature

UL 555S rates a smoke damper by the maximum air leakage through the closed damper at a test pressure, in cubic feet per minute per square foot of face area:

Leakage class	Approx. leakage at 4 in. w.g.
Class I (tightest)	About 8 cfm per sq ft
Class II	About 20 cfm per sq ft
Class III (loosest)	Higher leakage; not accepted for code-required smoke dampers

IBC 717.3.2.2 and IMC 607.3.2.2 require a code-mandated smoke damper to be Class I or II. Smoke dampers also carry an elevated-temperature rating, a minimum of 250°F, or 350°F where the smoke-control design requires the damper to stay operational at higher temperatures.

Actuation and Installation

Fire dampers close through a heat-responsive device such as a fusible link set to release above normal operating temperature.
Smoke and combination dampers use an actuator driven by the smoke-detection or fire-alarm system; the approved control sequence sets each damper's position, and the fail position is specified from the listing and controls.
Installation follows the listing: a listed sleeve and frame with the listed mounting, and an access door so the damper can be reached for its periodic operational test.

Frequently Asked Questions

What standards do fire and smoke dampers have to meet?

Fire dampers are listed to UL 555, smoke dampers to UL 555S, and combination dampers to both. IBC Section 717 and IMC Section 607 require the listing and set where each type is used; NFPA 90A covers installation.

Where does code require a fire versus a smoke damper?

Under IBC 717 and IMC 607, fire dampers go where ducts penetrate fire walls, fire barriers, fire partitions, horizontal assemblies, and shaft enclosures; smoke dampers go at smoke barriers and in smoke-control systems; combination dampers where both apply. Section 717.5 sets the conditions and exceptions.

What smoke-damper leakage class is required?

IBC 717.3.2.2 and IMC 607.3.2.2 require 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).

What is AMCA certification?

AMCA runs a voluntary certified ratings program that independently verifies a manufacturer's published damper performance, such as leakage and airflow. Its seal is separate from a UL 555 or UL 555S listing and does not automatically accompany it.