SMOKE DAMPERS | High-Level Overview

Last Updated: August 16, 2023, by

Smoke dampers are used when there is a need to install a smoke control system to protect the integrity of any fire barriers and to stop the movement of smoke around a building, which, if not controlled, could cause significant risk to the occupants and people evacuating in the event of a fire.

What does a smoke damper do, and how do they work?

A smoke damper can have several main uses:

  1. Installed within a smoke barrier, usually within a duct or wall/slab penetration and, when automatically commanded to close, will restrict smoke passing through a duct or a hole containing it in a specific zone, not affecting other areas of the building.
  2. Manage smoke extraction strategies.
  3. Manage pressure regimes within the building to prevent the spread of smoke
  4. Used to aid the operational effectiveness of a gas suppression system.

The damper is activated to detect smoke or by a fire signal, provided to it from the smoke damper control system, fire system, or local smoke detector.  Once a signal is received, the factory-supplied smoke damper actuator, which usually will hold the damper open, will be used to close the damper.

When should smoke dampers be installed/when are they required

It is important to review the statutory requirements, codes, and regulations and the project specifications and drawings to know where the dampers should be placed in a building and within which systems.

Let’s take a quick look at a few of these types of documents…

Project Specifications

In a typical project design specification, we will usually see a statement to the effect of:

Incorporate the cost and work for all smoke dampers to be manufactured, installed, and tested according to all statutory requirements, even if not shown on project drawings.

In other words, dampers should still be installed, even if they are not indicated in the drawings if they are implied in the statutory requirements.


As noted above, it is important not to rely exclusively on the drawings to understand if dampers are needed or not.

We need to examine all the documents to determine if there are any areas where they would be needed that are not shown.

Statutory Requirements/Codes/Regulations etc

Ultimately, determining if and which kind of smoke damper is needed will come down to the statutory requirements, codes, and regulations.

To understand the requirements, the following documents can be referred to:

Manufacturing Requirements

UL Standard/Smoke Damper Certification

There are specific requirements outlined by the Underwriters Laboratories [UL] Standards for the design and manufacturing of smoke dampers. As a global safety science and engineering company, Underwriters Laboratories offers global safety science and engineering, enabling manufacturers to demonstrate their commitment to safety, strengthen security, and deliver quality products and services in compliance with all the relevant regulatory standards. For dampers to be manufactured, manufacturers must prove that their fire dampers comply with the following standards:

UL 555SThe standard for Smoke Dampers

The tests to be completed are as per the following:

  • Reliability – the damper must operate as per its design after 20,000 cycles (100% closing and 100% opening) if only used as a smoke damper,
  • If the smoke damper is also being used as a volume control damper, using the actuator to manage the airflow, then the requirements are that the damper must operate as per its design after 100,000 cycles (100% open and 100% opening), or
  • It may go through 20,000 full cycles followed by 100,000 ‘repositioning’ cycles of a minimum of 5° (degrees).
  • Temperature – Using the dampers from the above open closed test, the dampers are exposed to temperatures of up to 250°F (121°C), in increments of 100°F (56°C). Once exposed to the temperature for 30 minutes in the closed position, the dampers should then operate by the actuator normally for 3 open/closed cycles.
  • Leakage – The damper and class rating leakage level, as below, shall be determined during this test whilst the damper is in the closed position with pressure and temperature is maintained.
  • Operation – A closed damper will be subjected to a minimum velocity of 2000 fpm (10.2m/s) and 4″ of water (1.0kPa) + safety factor. Under these requirements, the dampers and any actuators are expected to perform by fully closing and opening. Airflow will be moved in each direction across the dampers.

Smoke Damper Leakage Class

Underwriters Laboratories require that smoke dampers meet the following leakage rates, depending upon their class.

 Maximum Leakage in CFM/sq.ft at Standard Air Conditions
Leakage Class@4.5″ w.g@8.5″ w.g@12.5″ w.g
Class 181114
Class 2*202835
Class 380112140

 Leakage Class 1 vs. 2 & which damper to use?

Whilst it is better to use the Class 1 damper as it has much less leakage, Code usually specifies class 2*.

Ultimately the designer of the Smoke System should clarify and specify the actual site requirements and class.

For Class 3 – we were a little unsure, so we spoke to Ruskin, who noted that they still offer this type of damper but only for motorized Fire Dampers.

Smoke damper vs. Fire damper

Smoke dampers are not to be confused with Fusible Link Fire Dampers or Fire/Smoke Dampers, which are covered under these separate articles [Fusible Link] – [Fire/Smoke coming soon].

A smoke damper is not fire-rated and should not be used to provide protection to a barrier designed for containing a fire.

The damper is designed for use in smoke management, where stopping smoke from flowing around a building or controlling the path of smoke is required during certain situations.

Smoke damper vs. Fire/smoke damper

A fire smoke damper is required where the smoke barrier/partition is also deemed as a fire barrier with a fire-resistance rating.

The damper will consist both of a motorized actuator and a fusible link.

Smoke damper drawing symbol

If you want to draw a smoke damper or find it on a drawing, it would usually be shown by this symbol:

Smoke damper maintenance requirements

Under the NFPA, there clear requirements that should be met to ensure smoke dampers are tested and maintained properly throughout their operating life to ensure they work as the design intent when needed:

Within NFPA 105 – Smoke Door Assemblies and Other Opening Protectives; it states the following:

7.6.2 Testing Frequency for each damperInspected and tested 1 Year after completion of acceptance testing
 After the above – testing and inspection frequency is every 4 years.
 Unless the building contains a hospital, where should be every 6 years.

Note for the Control Systems there is another Code – NFPA 92 – Standard for Smoke Control Systems, the document notes:

8.6.1 Periodic TestingDedicated Systems – Semi-Annually
 Non-Dedicated Systems – Annually

Who can test smoke dampers and systems

It’s surprising to see that the code does not require any specific qualifications for maintaining and testing these systems.

They require that the operation and testing of the dampers and systems be conducted by only engineers experienced in their operation and who fully understand the requirements.

System documentation requirements 

NFPA 1 – Fire Code [section 10.2.5] notes the following:

“The owner, operator, or occupant, or any person in control of a building or premises shall keep records of all maintenance, inspections, and testing of fire protection systems, fire alarm systems, smoke control systems, emergency evacuation and relocation drills, emergency action plans, emergency power, elevators, and other equipment as required by the AHJ.”

NFPA-105 notes that during the inspection and testing of the smoke dampers, the following should be recorded:

  • Location of Damper
  • Date of Inspection
  • Name of Inspector
  • Observations
  • How the observations were closed out

How long do inspection and maintenance records need to be kept?

The requirements of NFPA-105 [7.6.4] are to keep all test records for a period of at least ‘3 test cycles’.

The test cycles are as follows:

 InitialThere After
Building without Hospital1 Year4 Years
Building with Hospital1 Year6 Years

Access to and identification of smoke dampers


The access requirements are pretty simple.

Access should be clear and provide enough space to fully maintain the damper and actuator.


Like with the Fire Dampers, Smoke Dampers will need to be labeled under code requirements.

Each damper should be labeled with 13mm lettering with ‘SMOKE DAMPER.’ If we just stick to this labeling, we will end up with many issues, so the best way is to include some additional information such as damper location and number.

This is more for maintaining the systems etc.

Smoke damper installation requirements

In order for smoke dampers and the systems to be installed correctly, reference should be made to the manufacturer’s installation literature, as the installation will be specific to the type of damper.

From a code point of view, there is a requirement that they should be installed within 24 inches (610mm) of the partition and before any branch or opening.

Installing a Smoke damper and transfer grille

There are no issues installing a transfer grille with a smoke damper, as long as the installation requirements of the damper are met. 

Breakaway joint/connection

When installing a smoke damper, there is a requirement that a ‘breakaway’ joint is installed on either side of the partition that is being used as the smoke barrier/partition inline with the relevant Underwriters Laboratory [UL] standard 555 & 555S:

This will allow the connecting ductwork to ‘break away from the damper if required, allowing the integrity of the smoke barrier to remain.

An example of the breakaway joint being utilized is if the brackets holding up the ducting that is connected to the damper become compromised and collapse, the ducting could fall to the floor.

With the correct designed joint, the failure will not affect the damper installation allowing the ducting to fall away.

Breakaway Joint Style:

On square/ rectangular ducts, the breakaway joint can be created by using what is called transfer joints; these joints, shown below, have always been considered a breakaway type connection as the approved type of joint and fixing that can be used for connecting dampers to the common ductwork system.

Typically these would be fitted to the top and bottom of the ducting; the sides would use a drive slip joint. 

  • Hemmed “S” Slip
  • Plain “S” Slip
  • Inside Slip Joint
  • Double “S” Slip
  • Standing “S” 
  • Standing “S” Alternative
  • Standing “S” (Bar Reinforced)
  • Standing “S” (Angle Reinforced)
  • Drive Slip Joint [sides of duct]

We can’t cover everything regarding the joints, so if you need more information, we would advise checking the dampers’ websites.

Here is an example.

Smoke damper electrical requirements

An electric or pneumatic actuator will control smoke dampers. Under UL requirements, the actuator must be mounted to the damper at the factory, transported to the site, and installed.

If an electronic actuator is supplied, there will be a need for an electrical supply that should be detailed on the drawings once locations are known.

Is Emergency/Essential power required?

If the damper actuator is able to close on its own, usually by a spring return, under power failure, then there is currently no requirement for them to be provided with an emergency power supply; a normal supply will suffice.

Smoke damper control

Smoke dampers are usually split into 2 systems, which are selected by the design engineer, passive or active.


This type of control relies only on the damper to close, allowing the integrity of the smoke barrier to be maintained; usually, the fans will be disabled at the same time to inhibit them from operating.


An active system relies on the ventilation systems to provide either a pressurized system or an exhaust air system.

The pressurized system provides supply air and exhaust air at specific locations within the building to allow differing pressures across the smoke barriers, ensuring that the smoke is kept in or out of an area.

The exhaust air system is used to allow and maintain the smoke level in a space to be above that of the occupants trying to escape. This is achieved via mechanical means, and dampers are controlled to open/close.

What is a Smoke Barrier?

A smoke barrier is a vertical or horizontal continuous membrane, such as walls, floors, or ceilings, that are constructed to restrict the movement of smoke.

What is a Smoke Compartment?

A smoke compartment is an area of a building enclosed by smoke barriers from all sides, including from the top and bottom.

What is a Smoke Partition?

A smoke partition is a wall assembly that extends from the floor to the underside of the slab or the underside of the ceiling, where a ceiling membrane is built to reduce smoke transfer.

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