New Fire and Smoke Actuator Offering Higher Torque and Temperature

Posted on Tue,May 17, 2016 @ 09:00 AM

Belimo Americas launches the new FSAF*A high torque fire and smoke damper actuators.  The FSAF*A electronic actuators are integrated into a life safety control system on smoke and combination fire and smoke dampers. This protects against dangerous low temperature smoke that is produced before fire breaks out and the large quantities of smoke generated in fully developed fires.  The primary result is fast smoke containment so that occupants are able to egress a building fire safely. Additional benefits are less smoke damage to furnishings and property and increased visibility for fire fighters.

The FSAF*A spring-return actuator is designed for operation of smoke and FireandSmoke.jpgcombination fire and smoke dampers in ventilation and air-conditioning systems.  Designed for maximum safety in all situations, the FSAF*A design incorporates the following features and standards: 

  • In addition to UL 60730 listing the actuator has been tested to UL 2043 and may be installed in plenums per NEC Section 300.22 (c) and the IMC Section 602.2.
  • Meets all codes for commercial buildings in the US.
  • Passes UL 555 & UL 555S at 350ºF.
  • Tested for 30,000 open-closed cycles. This also exceeds UL’s requirement of 20,000 cycles at damper static load.
  • Designed for the extreme conditions incorporates a steel housing, tamper-proof construction, and high temperature integrity. Gearing is made of steel and the internal, heat-resistant spring guarantees safety closure.
  • High motor reliability. With a reduced current at the end position, the FSAF*A motor cannot burn out, even after extended stall periods.

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Tags: Belimo News, Fire and Smoke Control

Active Safety with Motorized Fire and Smoke Dampers

Posted on Mon,Mar 07, 2016 @ 10:00 AM

Ensuring the safety of human life and property in buildings is one of the toughest demands that planners, builders, owners and operators are called upon to face. Smoke related injuries and deaths outnumber fire related injuries and deaths four to one. This is a rising concern for the safety of people and fire fighters who need to travel through building emergency exit routes as quickly as possible.

Tactical methods for smoke control are: fans, smoke vents, and closed doors in combination with dampers. Strategy varies with each situation.

  • Warehouses employ smoke vents to release smoke to the outside. NFPA 204M allows fans in the roof with louvers and dampers in the side walls to control the smoke.
  • Stairwell pressurization systems combine fans and dampers to prevent smoke from entering the stairwell from a burning floor.
  • Building HVAC ducting systems use motorized fire and smoke dampers to seal off individual zones. Dampers which are actuated electrically can be controlled from a central point and be integrated into safety control systems allowing a relatively smoke free exit for occupants and entrance of fire fighters.

Fire and smoke dampers are an integral part of distribution systems and are critical links in the life safety systems associated with most buildings. They offer extra protection against the dangerous amounts of low temperature smoke often produced before a fire actually breaks out. Restricting fires to the area of origin not only helps stop fire spread but has been proven to allow sprinklers to operate efficiently, and helps to ensure safety of human life.


Attend this upcoming webinar. Larry Felker, Product Manager for Fire and Smoke Damper Actuators will help you understand further how the new FSAF A series fire and smoke damper actuators are an integral part of distribution systems and are critical links in the life safety systems associated with buildings.


Fire & Smoke Product Release and Essential Retrofit ApplicationsLarry_Felker.jpg

In this webinar, you will learn why the new Belimo FSAF A Series of Fire & Smoke actuators are the perfect retrofit solution. The discussion will provide information on key applications and about the optimized functionality that provides maximum safety. A question and answer session to follow.

Join Us on Wednesday, March 23 at 1:00 EST


For further information on fire and smoke damper actuators, visit our online resourceor contact us via email.

Tags: Fire and Smoke Control

Modulating Control of Fire & Smoke Dampers in Smoke Control

Posted on Tue,Aug 19, 2014 @ 10:00 AM

In the US, Canada, and Latin America fire, smoke, and combination fire and smoke dampers are used in two general categories:
  1. Containment of fire and/or smoke to maintain building compartmentation. These are installed based on Chapter 7 of the International Building Code (IBC) which is the primary model code. These are sometimes referred to as passive systems although the dampers do close and fire alarms operate when a smoke detector operates.
  2. Engineered smoke control systems use dampers, fans, and some architectural features in a wide variety of applications. These are based on Chapter 9 of the IBC.

In the Americas smoke dampers are always actuated; fire dampers use mechanical means of sensing heat (fusible links that melt and gravity or spring release for closure). They and can be actuated for ease of periodic inspection and maintenance. Smoke must be sensed using electrical sensing – smoke detectors. Spring return actuators are used to close the dampers and then the actuator motor used to open the damper. Combination fire and smoke dampers are actuated due to the smoke function.

Many smoke control applications require modulating control of dampers. Stairwell pressurization and underfloor air-conditioning are examples where they can be utilized.

In this article the common control methods for fire and smoke dampers (typically Chapter 7 applications) are described in order to help distinguish among applications. Then modulating control of the same dampers in different applications (typically Chapter 9 applications) is discussed and explained.

Containment fire and smoke damper controls
Figure 1 shows (from left to right) a duct smoke detector, high temperature switch,[1]  and actuated damper. Roughly 80% of fire and smoke dampers are installed this way although the smoke sensing may be via area smoke detection and a relay employed to operate the damper. The damper protects the integrity of the wall to maintain compartmentation so that neither smoke nor fire can pass to an adjacent compartment.

Figure 1 Typical installation of a combination fire and smoke containment damper

Figure 1 Typical installation of a combination fire and smoke containment damper.

Figure 2 shows the wiring. Starting at the far left, hot power is run to the smoke detector. As long as smoke is not present the detector passes power to the temperature switch. Power to the actuator drives the damper open and holds it in the open position.

If smoke is detected power is removed from the actuator and the alarm contact on the detector closes to issue an alarm. If an area smoke detection system is used, the smoke control system has a relay connected in place of the smoke detector contact.
In case smoke is not detected but the temperature at the damper rises to 165°F (74°C), then the temperature responsive switch opens. This cuts power to the actuator and the damper springs closed. The temperature switch is manual reset so the damper remains closed during the event.

In the cases where the damper is only a smoke damper, the temperature switch is not present. The smoke detector or a relay from the smoke control system is the only operating control.
Figure 2 Smoke detector and combination fire and smoke damper wiring

Figure 2 Smoke detector and combination fire and smoke damper wiring.


Engineered Smoke Control System Dampers
Roughly 80% of fire and smoke dampers are installed in containment applications as shown above. About 20% are installed in more customized applications that are designed by the fire protection and mechanical engineers. Typical applications are atria, stairwell pressurization systems, underfloor air conditioning, underground floors, and large spaces like malls, auditoriums, and stages.

Figure 3 shows the basic controls employed in a smoke control system for one damper. The Fire fighters’ Smoke Control System (FSCS) panel allows override control and provides status indication for all components of the system.

Figure 3 FSCS panel and remote smoke damper wiring
Figure 3 FSCS panel and remote smoke damper wiring.

The dampers used for smoke control are typically of the same construction as containment. The primary difference is in the control methods. The damper blade position indication switches may be auxiliary switches on the actuator, damper blade switches, or magnetic contact switches. The smoke control system has a relay that allows the FSCS panel switches to place it in automatic, closed, or open position. Figure 3 also shows the connections to a networked system. The relays or cards are isolated from the line or 24V power used to operate the actuator.

The smoke control system components are UL 864, UUKL listed. The actuator has UL 873 or UL 60730 electrical listing and UL 2043 low smoke generation listings. The damper and actuator as a unit is UL555S listed.

Figure 4 shows a reopenable damper. Wiring for the Auto-Off-On Override switch is shown connected directly to the FSCS panel although typically there are network relays present to perform the functions. This damper serves both in containment and smoke control functions. It is connected to the FSCS panel so that the fire department incident commander can reopen the damper to remove smoke or pressurize a space. Status indication is provided.

Figure 4 Reopenable damper

Figure 4 Reopenable damper.

Sequence of Operation
In Automatic mode the smoke relay responds to the programming of the control panel to cut power and spring the damper closed when appropriate. Alternately, if a fire is present and the temperature in the duct rises to 165°F (74°C) the primary temperature switch opens and the damper springs closed.

If the panel switch is moved to Override, then the smoke relay and primary sensor are bypassed. The actuator is again powered and the damper opens. However, if the temperature at the damper continues to rise then the secondary sensor opens at 250°F (121°C). (The fire is close enough that there is danger of flames or heat moving through the damper to the other side of the wall.)

In addition, if the fire department moves the switch on the FSCS panel to Off, then power is removed from the actuator and the damper closes.

Modulating Control System Dampers
Some systems require proportional control of the dampers in the fire and smoke applications discussed above. The controls must combine typical temperature and/or pressure control methods as well as fire and smoke functions.

Figure 5 shows the simplest of modulating control methods for a fire and smoke damper. It is used commonly for corridor ventilation. The potentiometer sets a balance position for the damper during normal operation. The relay can close the damper in event of fire avoid smoke spread.

Power is placed on the actuator terminals 1 and 2. The potentiometer has a varying signal of from 2 to 10VDC that goes to terminal 3, the signal input. The actuator positions from 0 to 100% to open the damper to the balanced position. The common acts as a source of electrons and carries both AC and DC currents. In an event, the Override relay can cut power to the actuator which then springs the damper closed.

Figure 5 Potentiometer control of a smoke damper with override closed

Figure 5 Potentiometer control of a smoke damper with override closed.

Figure 6 shows the same smoke damper as in Figure 4 with an added relay to override the damper open. By shorting hot power to terminal 3 of the actuator, it will drive open. While not always necessary, a contact opens to disconnect the signal terminal on the potentiometer. This prevents hot 24VAC from damaging the signal output. On DDC systems this is important.

There are optional wiring configurations that work just as well as that shown. For example, Override relay 2 could be placed in the common 24VAC wire. At times it is important to arrange the relay contacts so that in case of failure of one relay, the failsafe condition is the safest.

Figure 6 Potentiometer control of a smoke damper with override open or closed

Figure 6 Potentiometer control of a smoke damper with override open or closed

In Figure 7 instead of a minimum potentiometer controlling the actuator, a building automation system, direct digital control sends the signal to terminal 3 and the actuator is continuously adjustable. (Default is 2V, closed and 10V, full open. This is reversible when needed for some applications.) The signal path is from Sig + on the controller to 3 through the actuator electronics to 1 and back out to the controller Com. A complete loop is always needed for current flow out and into any device.

Figure 7 Typical analog 2-10VDC actuator control circuit

Figure 7 Typical analog 2-10VDC actuator control circuit.

Figure 8 adds a high temperature switch. It is shown here in the common wire, but could be placed in the hot wire also. If the temperature at the damper rises to 165°F (74°C) the switch opens to cut power to the actuator and it springs the damper closed.

Figure 8 Control of a fire and smoke damper showing high temperature switch

Figure 8 Control of a fire and smoke damper showing high temperature switch.

Normally, the damper modulates based on the output signal from the BAS controller. Typically, if smoke is detected, the automatic response is to make Override relay 2 and spring the damper closed. If the FSCS panel is set to Open, then Override relay 2 is de-energized and Override relay 1 is energized. The damper is then open 100%. However, if the temperature in the duct going into the damper reaches 165°F (74°C), then the damper again closes.

Figure 9 adds a secondary high temperature switch and a bypass relay in the common wire.

Figure 9 Reopenable combination fire and smoke damper

Figure 9 Reopenable combination fire and smoke damper.

The sequence of operation is as follows:

With 24VAC present and all controls in the normal[2] state, the actuator opens damper to the position the Signal indicates. Actuator will modulate to maintain the setpoint.

Cutting 24VAC power or making Override relay 2 closes the damper.

If the temperature at the damper reaches 165°F (74°C), the primary sensor opens and the damper springs closed.

If the FSCS panel switch is set to Open, several actions occur.

a. The primary sensor is bypassed reconnecting the common power to the actuator.

b. Override relay 1 is made and Override relay 2 goes to normal. This causes the actuator to drive full open. (Hot 24VAC is shorted to the actuator terminal. Hot 24VAC is not allowed to reach Signal of DDC controller as that would destroy the output’s electronics.)

However, if the duct temperature reaches 250°F (121°C), then the secondary temperature switch opens and the damper again closes. The FSCS panel cannot override this and manual reset is necessary. It is presumed that the fire is too close to the damper and compartmentation is at risk.

Underfloor Air Conditioning Example
Figure 10 shows an example of an underfloor air conditioning system and how a modulating actuator could function.

The shaft wall is a fire barrier and a smoke partition and therefore requires either separate dampers or a combination fire and smoke damper. The pressure under the floor must be maintained at somewhere between 0.05 and 0.10 in. w.c. (12 to 25 Pa). This would require another damper and modulating actuator. However, by using a modulating fire and smoke damper, only one damper and actuator can do the job of three. This saves material and labor costs and also helps alleviate space constraints.

Figure 10 Underfloor air conditioning example

Figure 10 Underfloor air conditioning example.

It would be up to the fire protection engineer and the local authority having jurisdiction to determine if this damper is considered part of containment (Chapter 7) or part of the engineered smoke control system (Chapter 9). It could be used for both. If it is part of the smoke control also, then status indication and overrides would be required.

The sequence of operation is:

  • During normal operation the pressure under the floor is maintained by modulating the damper mounted in the shaft wall.
  • If a fire occurs and the temperature at the damper reaches 165°F (74°C), then the damper closes.
  • If smoke is present in duct (or space area), then damper closes.

There are a large number of methods to modulate fire and smoke dampers and apply fire and smoke safety controls. In containment applications, the damper is closed when either high temperatures or smoke is observed. In smoke control systems a number of ways exist to either open or close the damper to purge or pressurize spaces to prevent smoke from spreading.

Some, not all, of the methods of control are shown and explained in this article. Consult the referenced Codes and Standards or contact the author for additional information. 

Author - Larry Felker
Larry Felker is a mechanical engineer and member of ICC (International Code Council), NFPA (National Fire Protection Association), and a life member of ASHRAE (American Society of Heating, Refrigeration Air Conditioning Engineers). He is a Product Manager for Fire & Smoke Actuators for Belimo Americas who has specialized in fire and smoke dampers and actuators since 2002. Previously he was a temperature control system designer and before that a mechanical and electrical contractor. He is the co-author (with Travis Felker) of Dampers and Airflow Control, ASHRAE Special Publications, 2010.

(IBC) International Building Code, 2012, International Code Council, Inc. (ICC), Country Club Hills, IL 60478-5795

(IFC) International Fire Code 2012, ICC, ibid.

(IMC) International Mechanical Code 2012, ICC, op. cit.

UL 555 Standard for Safety for Fire Dampers, Edition 7, 2006, Updated 2010, Underwriters Laboratories Inc. (UL), 333 Pfingsten Road, Northbrook, IL 60062-2096

UL 555S Standard for Safety for Smoke Dampers, 4th Edition, 1999, Updated 2012, ibid.

UL 864 Standard for Safety Control Units and Accessories for Fire Alarm Systems, 9th Edition, 2010

UL 873 Standard for Temperature-Indicating and -Regulating Equipment (Ed. 12), U, 2007

UL 2043 Fire Test for Heat and Visible Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces, Standard 2043, Edition 4, 2013

UL 60730 Standard for Automatic Electrical Controls for Household and Similar Use, 2010

[1] “Primary heat responsive device” in UL 555 terminology.

[2] “Normal” is defined as the de-energized or low variable condition. For example, low smoke is the normal condition.

Tags: Technical Tips, Fire and Smoke Control

A Method of Damper Control for Corridor Ventilation and Smoke Extraction

Posted on Tue,Aug 05, 2014 @ 10:00 AM


Corridors are typically a means of egress during fires or emergency events. During normal operation they require ventilation. In some code jurisdictions or building design requirements, pressurization or smoke extraction is also required.

This article presents several means to provide pressurization or smoke extraction with ventilation and details the operation of the controls, dampers, and actuators.

The operation of corridor smoke exhaust influences and is influenced by the other smoke control tactics in a fire and the fire protection and mechanical engineers model the airflows with respect to one another. Figure 1 shows a larger picture than just the corridors.

Fiqure 1 Elements in fire and smoke controlFiqure 1: Some of the strategic elements in fire and smoke control.

The model codes used in the United States and some other countries – International Building Code ((IBC 2012) and the International Fire Code (IFC 2012) along with the International Mechanical Code (IMC 2012) have various requirements for corridors in commercial buildings. The walls must be constructed as smoke partitions and in some cases as fire partitions. Minimum widths are established. Mechanical ventilation, travel distances, and other requirements are also covered. Chapter 4 of the IBC establishes requirements based on occupancy type. Chapter 7 details the requirements with respect to structure. Chapter 9 details the active or engineered system

All smoke control equipment status must be indicated on the fire-fighter’s smoke control system (FSCS) panel. This includes smoke control dampers (IFC 909.16.1). Control of all smoke control equipment must be possible from the FSCS (IFC 909.16.2) with the exception of complex systems where other provisions are allowed.

Smoke Extraction
In corridors there are jurisdictions and individual projects where corridor damper and fan systems are required to clear the corridor of smoke and prevent spread to adjacent floors. Since ventilation is also required, the two functions must be coordinated. This can be achieved with dedicated or common (non-dedicated) equipment.

Either a “sandwich” or “building” pressurization type of approach is usually used. See Figure 2.

In a sandwich pressurization system –

a) The corridors on the fire floor are negative with the fan pulling smoke out of the floor. (Supply closed, return or exhaust open fully.)

b) The floors above and below the fire floor are pressurized more than other floors. (Supply fully open, exhaust off or closed.)

c) The corridors on other floors of the building operate normally. (Typically partially open supplies and exhausts.)

In a building pressurization system approach –
a) The corridors on the fire floor are negative with the fan pulling smoke out of the floor.

b) All other floors operate normally. They are under a positive pressure with ventilation air. Since the fire floor is very negative, the difference in pressure is large enough to prevent smoke spread to the non-fire floors.

BuildingSystem resized 600

Figure 2: “Building” vs. “sandwich” pressurization system.

Figure 2, shows the overall concept of a non-dedicated system – the ducts move ventilation air under normal circumstances and are used for smoke control only in an emergency. However, variations are common in corridor systems as there are a number of ways to achieve the goals. Among the possible methods are:

a) Two rooftop fans (supply and exhaust) and separate ducts to the corridors.

b) One reversible fan that delivers ventilation air in normal operation and exhausts air during an event. In this case there are other provisions for make-up air, reliefs or local exhausts. Various factors influence the approach that is best. All pressures – positive or negative – due to stack effect; lobbies, elevators, or natural ventilation, or attached rooms and spaces are considered.

c)  If there is sufficient make-up air elsewhere, an exhaust fan alone may be used to move air out of the corridor. No supply fan.

See Figures 3 and 4 for drawings of the two approaches. Figure 5 shows a vertical representation of a high-rise corridor duct system in a multistory building. The point is that the same duct feeds or draws from all of the dampers. The system must be balanced in order to provide the correct amount of ventilation air on each floor. When a fire event occurs, the air flow requirements change.


Figure 3: Separate supply and exhaust ducts in a corridor.

Figure 4

Figure 4: Single duct serves as supply and smoke exhaust in a corridor.

Figure 5

Figure 5: Fan and ducts in 10 story building.

The pressure at the discharge of the fan is higher than at the bottom of the building. However, the required quantity of air going through each damper is the same during normal operation.

The damper at the top of the building will be open much less than that at the bottom of the building. Even with careful calculations to use different sizes of dampers, balancing will be needed to get the correct flow through each damper. In addition to pressure losses in the duct and across the dampers, local exhausts and some stack effect will cause variations that cannot be precisely calculated. The goal will be to have the furthest damper full open to use the least fan energy while delivering the right amount of ventilation air on every floor.

The fan sequence for each of the cases above is straightforward. With the Figure 3 two duct system both the ventilation supply fan and exhaust fan are on when occupied (or optimizing or under control of an air quality sensor). If a fire alarm activates or smoke is detected during unoccupied periods, the fans are turned on again. This is the same for both sandwich and pressurization systems. At the same time the stairwell pressurization system is activated and alarms are issued. This is beyond the scope of this article.

If using the Figure 4 geometry, then the fan is on and supplying air during normal occupied times. In event of a fire, the fan goes to the reverse air flow direction – exhaust mode.

Any individual damper in either type of system must perform several functions. These dampers can be parallel blade (PB) or opposed blade (OB). In most cases an OB will have more accurate resolution for setting minimum position and full open the flow is the same for either type.

The dampers must be UL 555S (UL 555S) listed as smoke dampers (IFC 909.10.4). In some cases the damper must also be a fire damper that meets UL 555 (UL 555) as well so combination fire and smoke dampers would be required. Most corridor walls must be fire rated. However, if the fire damper function could interfere with the smoke control system operation, then installation of a fire damper is not required (IBC 717.2.1).

The actuated damper operation will be similar for all cases. Here we will discuss the detailed operation for only the Figure 3 supply and return duct case in a sandwich pressurization system.

Normal operation. Both supply and exhaust dampers open to a minimum position. Balancing dampers in series with the smoke control dampers cannot be used. They would block some flow when the damper went to 100%.

In event of a fire:

Fire floor
a) Supply damper closes so that smoke is not pushed into other areas.

b) Exhaust damper opens 100% to remove smoke.

c) In some cases the dampers are also fire dampers and will close if temperature inside damper frame reaches 165°F. The FSCS panel has override switches to reopen the damper with a secondary sensor to again close damper if the temperature reaches 250°F. This is discussed below.

Floors immediately adjacent to fire floor
a) Supply damper opens 100% to pressurize and restrict smoke entry

b) Exhaust damper closes 100%

All other floors
a) Dampers remain in normal operation

b) Variations do exist

Belimo FSAF24-BAL Solution
Figure 6 shows a corridor damper with the FSAF24-BAL. Several manufacturers produce similar products. Not shown is the front grill. The damper is installed in the corridor wall and the actuator provides the sequence needed for ventilation and smoke control. The actuator is three position – closed, adjustable mid-position, or open 100%. Figure 7 shows operation.


Figure 6: Ruskin FSD60-FA-BAL

Fire and Smoke Damper


With no power the actuator springs closed – unoccupied, fire present at damper, or smoke control stop air flow.

With 24V on wire 2, the actuator opens to the balancing position as set by the potentiometer on the face – this is the normal operation ventilation air position. Each actuator is set at a different potentiometer position as balancer measures flow.

When wire 3 receives 24V the actuator opens 100%. – full pressurization or smoke exhaust mode.

These are the positions needed for the corridor ventilation and smoke control.

Figure 7

Figure 7: Detail of FSAF24-BAL.

Smoke control system program mapped to actuator function

The sequence detailed above under dampers can be mapped against the needed actuator operation and programmed into the smoke control system panel as shown below.

Normal operation:  Wire 2 is powered, damper in ventilation position.

Fire floor
a) Supply damper:   No power, damper closes.
b) Exhaust damper:   Wire 3 powered to open damper 100%.
c) For fire dampers Wire 1, common, is always connected unless the primary sensor opens. See Figure 8 description.

Floor(s) immediately adjacent to fire floor
a) Supply damper:  Wire 3 powered to open damper.
b) Exhaust damper:  No power, damper closes.

All other floors
:  Wire 2 is powered.

Figure 8, adds more detail to how the damper is controlled. (Note that there are other wiring variations not covered here. For example the secondary sensor could be between the Override relay and wire 3.) A smoke damper would have neither the 165°F high temperature primary sensor nor the 250°F secondary senor.

Figure 8

Figure 8: Control of FSAF24-BAL-S actuator.

In Figure 8 the smoke relay is normally closed and power is delivered to the actuator. The damper drives to the minimum position setting.

Combination fire and smoke dampers have two t”emperature sensors (“heat responsive devices” per UL555) – primary and secondary. If the temperature rises to 165°F (74°C) the primary opens and the damper springs closed. It does not go to the potentiometer position since it does not have power. If the Override relay is made by intervention from the FSCS panel then wire 3 is energized. This bypasses the primary sensor. The damper then opens to the 100% position instead of the ventilation position.

If the temperature at the damper again rises and reaches 250°F (121°C), then the secondary sensor opens and damper springs closed and stays closed until manually reset.

To summarize:

By powering wires 1 and 2 with 24V the actuator drives the damper to the required position for ventilation.

By cutting power the actuator springs the damper closed.

By powering wires 1and 3 the actuator drives the damper 100% open regardless whether wire 2 has power or not.

Figure 9, shows the Fire Fighters’ Smoke Control System panel with indication lights that are given status by the auxiliary switches on the actuator. Each fan and damper has its own status lights and override switch. The signals for light indication at the panel are carried via the network from actuator auxiliary switches, damper blade switches, magnetic contact switches, or programmable actuator signals.

Exhaust Damper

Figure 9: Portion of Fire Fighters’ Smoke Control Panel.

Proportional actuator with Minimum position control

Another way to achieve the same sequence is provided by use of a proportional 2-10V actuator and an SGA24 minimum position switch.  This is a different actuator than the BAL shown above. It is a standard 2-10VDC control actuator.

The wiring schematic is shown in Figure 10. Figure 11 shows the minimum selector which can be used to set the mid-point balancing position of the actuator.

Figure 10

Figure 10: Proportional actuator controlled by minimum potentiometer.




Figure 11: Proportional minimum potentiometer




The sequence of operation of the wiring diagram in Figure 10 is as follows:

With no power on both Com and Hot, damper springs closed. This would be the typical unoccupied position. The “closed” auxiliary switch indicates the damper is closed and the network card transfers the position indication to the FSCS panel.

With power going to the SGA24 and actuator, the signal out of the SGA on 3 goes to the actuator input 3. (4 is not used in this sequence. It would allow modulating control of the damper in addition.) The 2-10 VDC signal positions the actuator and damper from zero to 90 degrees to be set by the balancing contractor.

If Override relay 1 makes 24V power is delivered to 3 of the actuator which causes it to drive full open. At the same time the 165°F sensor is bypassed. (The 250°F remains in the circuit as a final safety should fire be present too close to the wall.) This would open the damper fully if it is an exhaust on the fire floor or a supply on an adjacent floor.

If Override relay 2 makes, power is cut to 2 of the actuator and it springs closed. This would achieve needed closure of a supply on the fire floor or an exhaust on an adjacent floor in a sandwich pressurization system.

Thus the damper can be placed in closed, open, or partially open as needed for corridor smoke and ventilation control.

Figure 10 shows the primary and secondary sensors for a combination fire and smoke damper along with the override contact on Override relay 1. These are not present if the wall is not a fire barrier or partition requiring a damper. In that case the drawing in Figure 12 would accomplish the smoke damper functions for ventilation or open or closed as required. This is one example where the presence of sprinklers (that might derate the wall) works synergistically with the engineered smoke control system.

In Figure 12, when both relays are normal, the damper goes to its balancing position.

If the damper must open 100% for purge or pressurization, then Override relay 1 is made. Shorting hot to 3 of the actuator drives it full open.

If the damper must close then Override relay 2 makes. This cuts power and the actuator springs closed.

As in Figure 10, actuator auxiliary switches signal damper blade position to the FSCS panel.

Figure 12

Figure 12: Proportional control of a smoke damper by a minimum potentiometer.

Reversible Fan Ventilation and Smoke Removal

Where there is sufficient relief by local exhausts or return airs in adjacent areas, a reversible fan and only one duct run to all floors is possible. In some cases, a make-up air damper can provide for needed relief. A gravity relief damper is another possibility. This removes the need for a second duct and second damper on each floor. Figure 13 shows the concept.

Figure 13

Figure 13 Reversible fan for ventilation or smoke extraction as needed


A sandwich or building pressurization system approach can be used for corridor smoke control to facilitate egress during a fire or other event. The same duct(s) and damper(s) can be used for ventilation during normal occupancy periods.

There are a number of duct and damper choices available for corridor ventilation and smoke extraction. The Belimo FSAF24-BAL or the FSAFB24-SR with an SGA potentiometer can provide the different sequences of operation needed.


International Building Code, 2012, International Code Council, Inc. (ICC), Country Club Hills, IL 60478-5795

International Fire Code 2012, ICC, ibid.

International Mechanical Code 2012, ICC, op. cit

UL 555 Standard for Safety for Fire Dampers, Edition 7, 2006, Updated 2010, Underwriters Laboratories Inc. (UL), 333 Pfingsten Road, Northbrook, IL 60062-2096

UL 555S Standard for Safety for Smoke Dampers, 4th Edition, 1999, Updated 2012, ibid.


Written by: Larry Felker, Mechanical Engineer and member of ICC (International Code Council), NFPA (National Fire Protection Association), and a life member of ASHRAE (American Society of Heating, Refrigeration Air Conditioning Engineers). He is a Product Manager for Fire & Smoke Actuators for Belimo Americas who has specialized in fire and smoke dampers and actuators since 2002. Previously he was a temperature control system designer and before that a mechanical and electrical contractor. He is the co-author (with Travis Felker) of Dampers and Airflow Control, ASHRAE Special Publications, 2010.

Tags: Technical Tips, Fire and Smoke Control

Code Required Testing of Fire, Smoke, and Combination Dampers

Posted on Mon,Sep 30, 2013 @ 10:00 AM

Periodic testing of life safety systems and dampers is required by the codes. While there is some state or local variation, the requirements are shown in Chart 1. While the focus of this article is the dampers, the entire smoke control system is required to be tested according to the schedule labeled “Smoke Control Systems & Dampers.” A clear distinction must be made among the damper applications in order to determine the schedule that conforms to codes. The second part of this article explains the differences among the dampers and applications.

Chart 1: Periodic testing requirement for dampers.

Chart 1

Codes and Referenced Standards
    Chart 1 originates with two primary codes – the International Building Code (IBC)1  and the International Fire Code (IFC).2 It is the IFC that defines or references most testing requirements. It references NFPA 803 (fire) and NFPA 105 4 (smoke) directly for the containment damper requirements. These two standards have details on what to test or inspect, periodic requirements, and replacement information. The IFC does give the smoke control system requirements directly – 909.20.4 for dedicated systems and 909.20.5 for non-dedicated systems. NFPA 90A5 , NFPA 92A6 and NFPA 92B77 are frequently referred to with respect to testing. However, they are not referenced by the IBC or IFC and only with respect to smoke protected seating by NFPA 101, the Life Safety Code.8

Dampers Required by Chapter 7 of the International Building Code (IBC)
Chapter 7 of the IBC regulates fire resistive rated construction. Fire dampers are installed in fire walls, fire barriers, fire partitions, and horizontal assemblies. Smoke dampers are installed in smoke barriers, and smoke partitions. Combination fire and smoke dampers that are required by Chapter 7 can be installed in any of the applications that require both fire rated construction and smoke containment. They are meant to resist the passage of flames and smoke particulates.

Most fire dampers have fusible links that melt at (typically) 165°F (74°C) allowing gravity or a shaft spring to close the damper. Fire dampers are rarely actuated in the Americas (although they are regularly actuated in Europe so that they can be automatically tested). See Figure 2 for a typical curtain fire damper. There are several types and ceiling dampers are similar.

Figure 2 Curtain fire damper (photo courtesy of Greenheck Fan Corporation).

Curtain Fire DamperA smoke damper is connected to a duct smoke detector or to a relay from the fire alarm or smoke control panel. In event of a fire and concomitant smoke, an actuator springs closed to close the damper and prevent smoke movement from one area to another. All smoke dampers are actuated since there is no method to physically sense smoke and electrical control is required.

A combination fire and smoke damper looks very similar to a smoke damper, but has a high temperature sensor to close the damper from heat along with the local smoke detector.

Figure 3: Combination fire and smoke damper (drawing courtesy of Ruskin Company).

Combination fire and smoke damper

Combination fire and smoke dampers can be controlled several ways. Most commonly on modern dampers is use of an electrical temperature activated sensor-switch. When the contacts are closed, the actuator is powered and drives the damper open. When fire/heat is detected, the contacts open and the damper shuts. See Figures 3 and 4. In addition, a smoke detector or relay contact from the area smoke detection system panel is wired in series with the temperature switch. If smoke is detected, the contact opens and the actuator springs the damper closed. See Figure 3. The smoke detector is installed within 5 ft. of the damper or an area smoke detection system may control the damper’s closing. The wiring for the typical combination damper is shown in Figure 4.

Though not required by Chapter 7, in order to automatically test these dampers, position indication switches may be installed. They can power locally exposed monitoring lights or, typically via a network, indicate position to a testing panel.  These dampers are best referred to as containment or compartmentation dampers as that is their function; this clearly distinguishes them from smoke control dampers discussed below. They are often referred to as “passive” protection although they are active in as much as they move to close holes in fire or smoke walls, barriers, and partitions.

Figure 3: Containment fire & smoke damper with smoke detector.

Containment fire & smoke damper


Figure 4: Controls and wiring for a combination fire & smoke damper.

Controls and wiring


Dampers required by Chapter 9 of the International Building Code (IBC)
IBC Chapter 9, Fire Protection Systems, regulates installation of engineered smoke control systems (as well as alarms and sprinklers). In order to remove smoke or prevent the movement of smoke into protected spaces, dampers, fans, architectural reservoirs, and smoke chimneys may be employed. These are considered active systems.

Some of the occupancies where smoke control systems are required are in atria, stairwells, underground buildings, and large spaces like malls and auditoriums. Some local codes also require additional protection in corridors and any exit passages.
The dampers employed for smoke control are generally of the same physical construction as those for containment. Some smoke dampers are aluminum whereas fire & smoke dampers are galvanized or stainless steel.

It is the control capability of the smoke control system damper that is different. The system is more sophisticated and requires coordination among alarms, sprinklers, fans, doors, and dampers. The containment damper is closed by only a local duct smoke detector) or in the case of the combination fire & smoke damper, by the detector or a single high temperature sensor. The detector can be mounted at the factory or field installed. UL555S requires that both the sensor and actuator be factory installed initially.

In particular, smoke control dampers are connected to the fire fighters’ smoke control system panel for manual override control and position indication and verification. These dampers are often referred to as “re-openable” since they can be manually opened or closed although they are normally in automatic mode. See Figure 5 for an example damper. Figure 6 shows the full wiring for override and position indication. Note that modern systems typically use a network for the long wire runs. For this example, discrete wiring is shown.

Figure 5: Smoke control system damper with sensors (photo courtesy of Pottorff).

Smoke control system damper with sensors

Figure 6: Auto-Off-Manual switch and re-open able damper with sensors and actuator.

Auto Off Manual switch and re open able damper with sensors and actuatorIn addition to distinguishing between Chapter 7 and Chapter 9 dampers, there are two types of smoke control system dampers – dedicated and non-dedicated. A dedicated system is used for no other purpose than smoke control. For example, an atrium make-up air damper and atrium smoke exhaust fan damper are not used in day to day operation. A non-dedicated system is used for normal HVAC or ventilation and is operated on a regular basis. If it fails, a service call would be generated and it would require immediate repair. Failure of dedicated system dampers will not be evident without operation so they must be tested more frequently to ensure safety.

Testing procedures
Other than stating that both initial and periodic inspection and testing of dampers are required, the codes do not detail how or precisely what steps are to be taken. However, the intent is clear – compliance with NFPA 80 and NFPA 105 along with damper manufacturer instructions are expected.

It is beyond the scope of this article to detail the standards; however, a brief description is provided below.

In NFPA 80, section 19.3 Operational Test, fire damper testing is detailed. The essential test is that the damper will open and close and no obstructions are present. NFPA 729 is referenced when any smoke detection is present. The operation must be under the airflow conditions that the system will encounter. Fusible links must comply with NFPA 90A and UL33.10 Documentation must be maintained and any deficiencies reported and corrective action noted. It also states that “repairs shall begin without delay” and following repair shall be operational tested again.

Both standards state the requirement for testing one year after installation and then every 4 years (hospitals 6 years).

NFPA 105 is worded very similarly to NFPA 80 and contains many of the same requirements. Chapter 6 Installation, Testing, and Maintenance of Smoke Dampers is the most important chapter with respect to testing smoke and combination dampers. An operational test is required upon installation and all indicating devices must work correctly. NFPA 92A is referenced for periodic inspection and testing. Repairs must “begin as soon as possible” and all maintenance must be documented.

One provision that bears examination is found in section 6.5.5: “The damper shall be actuated and cycled as part of the associated smoke detector testing in accordance with NFPA72, National Fire Alarm Code.” Smoke detectors must be tested yearly and when they are released, the actuator of the smoke or combination fire and smoke damper will spring closed (or for smoke dampers that must open, spring open). The sound of the actuator and the time it takes are tantamount to a test. Thus a sample inspection for blockage – very rare after construction is completed – could reduce cost of testing.

The Air Movement and Control Association (AMCA)11 have published a document with input from all the damper manufacturers titled Guide for Commissioning and Periodic Performance Testing of Fire, Smoke and Other Life Safety Related Dampers. It contains some of the material found in NFPA 80 and NFPA 105 along with other details. AMCA does not require the need for visual inspection of motorized dampers with end switches that communicate to a panel or lights.

Belimo Americas has also published a cross reference and instructions for replacement actuators on dampers.12 Included is a form to leave on site for the fire marshal or building official which complies with the documentation requirement of NFPA 80 and NFPA 105. These instructions focus on the old obsolete actuators from the 1980s to date. Often the dampers are in perfect condition and only one or more of the electrical components are defective.


The first step in establishing a periodic testing schedule for dampers is to identify whether they are employed for Chapter 7 or Chapter 9 code requirements. Once that is achieved, operational testing itself is straightforward. To what extent manual inspection is required for smoke control dampers is up to the local inspector. Since smoke control dampers have blade switches or their actuators have auxiliary switches, a test of the entire smoke control system will test the dampers and position indication is automatically shown on the fire fighters’ smoke control panel.




1International Building Code, 2012, International Code Council, Inc., Country Club Hills, IL 60478-5795.

2International Fire Code 2012, ibid.

3NFPA 80 Standard for Fire Doors and Other Opening Protectives , National Fire Protection Association, NFPA, 1 Batterymarch Park, Quincy, MA 02169-7471.

4NFPA 105 Standard for the Installation of Smoke Door Assemblies and Other Opening Protectives, ibid.

5NFPA 90A Stadard for the Instalation of Air-Conditioning and Ventilating Systems, op.cit.

6NFPA 92A Standard for Smoke-Control Systems Utilizing Barriers and Pressure Differences, op.cit.

7NFPA 92B Standard for Smoke Management Systems in Malls, Atria, and Large Spaces, op.cit.

8NFPA 101 Life Safety Code, National Fire Protection Association, op.cit.

9NFPA 72, National Fire Alarm Code, op.cit.

10UL 33, Standard for Heat Responsive Links for Fire-Protection Services, Underwriters Laboratories Inc. (UL), 333 Pfingsten Road, Northbrook, IL 60062-2096.

11 Air Movement and Control Association International, Inc. 30 West University Drive, Arlington Heights, IL 60004-1893 U.S.A.

12 BELIMO Automation AG.

Tags: Fire and Smoke Control

Dampers and Airflow Control

Posted on Mon,May 27, 2013 @ 10:00 AM

Allow us to recommend this publication: Dampers and Airflow Control BookDampers and Airflow Control written by Laurence G Felker and Travis L Felker provided by ASHRAE Special Publications.

Fans, duct systems, duct elements (such as filters and coils), dampers, and actuators all work together to control airflow. This book provides the resources for building good judgement of the engineering principles needed to size, select, install, and adjust control dampers.

Here’s part of the contents covered in this book:

  • Mechanical System Design and Airflow
  • Dampers, Mixing, Geometry, and Pressure Loss
  • Damper Pressure Losses
  • Damper Proportional Flow Characteristics
  • Diverting and Mixing Damper Pairs
  • Multistage Damper Control
  • Summary of Damper Characterization Methods
  • Actuation
  • Minimum Outdoor-Air Control Methods
  • Space Pressurization Control Methods
  • Coordination of Outdoor-Air Ventilation with Space Pressure
  • Damper Installation
  • Control Loops and Applications
  • Balancing
  • Control Systems
  • Smoke Control
  • Summary

This book: Dampers and Airflow Control book can be purchased at ASHRAE online.

[1] ISBN 978-1-933742-53-3 ©2009 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 1791 Tullie Circle, NE, Atlanta, GA 30329


Tags: Fire and Smoke Control

Dampers, Mixing, Geometry, and Pressure Loss

Posted on Mon,Apr 15, 2013 @ 10:00 AM

Fire and Smoke Dampers

A damper restricts airflow by obstructing the duct. Some multi bladed dampers have flanged frames to which ductwork is butted, and the open area is restricted only by blades and hardware. Most dampers in the U.S. are inserted into a sleeve, duct, or wall, and the frame obstructs part of the open area. The maximum free area for this type is about 80% for 48 x 36 in. (1200 x 900 mm) and larger-size dampers, and the minimum is about 40% for an 8 x 8 in. (200 x 200 mm) damper. The frame takes up most of the reduced space. The free area changes slightly with comer braces, linkage in airstream versus frame, airfoil versus triple V, and with type of frame. In round dampers, the blade is the only significant restriction.

Commercial flanged dampers of the type more commonly used in Europe may have 90% free area, and U.S. insulated blade and industrial dampers may have a maximum of only 70%. Check specifications in all cases. The information in this article is specific to U.S. hat-frame commercial dampers.

Fire and Smoke Figure 1

Figure above shows the two basic types of control dampers: parallel blade (PB) and opposed blade (OB). Sometimes, PB dampers are called single acting and OB dampers are called double acting in reference to the linkages. "The linkages from blade to blade can be located on the blades themselves but are more commonly located on one side within the frame. (Refer to the damper manufacturers' product reference manuals for construction details.) Figures below show the various details of dampers that affect flow and pressure losses.

Fire and Smoke Figure 2

Fire and Smoke Figure 3

In some dampers, not all the blades are the same height. A 24 in. (600 mm) high damper has slightly different size blades than one that is 22 in. (560 mm). Usually, one blade is larger than the others. On most blades, the damper shaft is mounted in the middle. Some are unbalanced, with the shaft located at about two-thirds position or at the end. Differences in flow characteristics result from these blade differences.

Blade seals can extend beyond the blade and affect the flow, particularly during the initial15° of opening. Different methods of sealing cause differences in flow characteristics. High-quality dampers have better linkages, and repeatability is easier to obtain. The Air Movement and Control Association   International (AMCA) certifies airflow pressure loss testing.

Fire and Smoke Figure 4

Motors, linkages, and jackshafts that block a damper opening affect flow. Many installation practices affect the predicted response of a damper. Figure above shows the difference in flow profiles coming off PB and OB dampers. PB dampers cause air to tum direction during most of their rotation. Airstreams tend to reconnect easily after separation by the blades. The pressure drop through the wide-open damper is a function of free-area ratio. The pressure drop as the blades modulate is more a function of the turning during the first 60° of blade rotation.

OB dampers change the free area quickly during rotation, and turning only occurs at blades not opposed by another airstream. A vena contract forms between opposing blades, and turbulence is high.

There is little experimental data available about the details of airflow around and inside dampers. Thick-walled orifices and airstream obstruction data are the main sources of theoretical data. Testing data from manufacturers is the main source of hard data. Since testing is so expensive, and purchases tend to go to the lowest-cost vendor, most manufacturers provide only basic information in their data sheets, and the effects of various irregular flow profiles have yet to be studied.

This article is based on an excerpt from the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. book “Dampers and Airflow Control” by Laurence G. Felker and Travis L. Felker. You can purchase online at


Tags: Fire and Smoke Control

Pressure Losses Through Dampers

Posted on Mon,Feb 18, 2013 @ 10:00 AM

The pressure loss through any damper is a function of the entering flow profile, the free area ratio, F,  of the open damper area to that of the damper frame or wall area, the geometry of the damper installation, and the exit conditions as air leaves the damper. The most complete testing of dampers was performed for ASHRAE’s Research Project 1157. A complete analysis of the results is available in the book Dampers and Airflow Control published by ASHRAE Special Publications. Not only the full open losses, but also the modulating characteristics of dampers are experimentally defined.

The method for getting accurate prediction of damper pressure loss is too extensive to repeat here, but using several Tables found in the book, very accurate results can be obtained.

In general, DP = Co Pv , that is the pressure drop is equal to a loss coefficient times the velocity pressure.

The trick is obtaining the right Co based on the other conditions by applying engineering judgment.

Co = Fg x f(F2) where Fg is a factor based on flow profile and F is the free area ratio. The function depends on the AMCA[1] defined geometry.

Below a typical drawing from the Damper and Airflow Control book is reproduced.

Belimo Damper ExampleEngineered Damper Assembly

Dampers and Airflow Control, Laurence G. Felker and Travis L. Felker, ISBN 978-1-933742-53-3 ©2009 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 1791 Tullie Circle, NE, Atlanta, GA 30329

[1] AMCA Air Movement and Control Association, 30 West University Drive, Arlington Heights, IL 60004


Tags: Fire and Smoke Control

Smoke Control Tactics

Posted on Mon,Dec 17, 2012 @ 10:00 AM

Where strategy looks at the overall picture, the individual tactics are used to achieve the goals.  The main purpose of the booklet "Actuator Dampers in Smoke Control Systems" is to explain details of how these mechanical and electrical systems operate with respect to dampers.  The Fire Marshals, Building Officials, design engineers, and contractors are often called upon to go beneath the overall operation of a subsystem and look at the details.
Where devices and wiring interconnect two disciplines, there is a tendency for those involved to have only a fuzzy concept of the whole, interrelated design.

Figure below shows the primary mechanical systems that are used in smoke control.  While all the different tactics work together in the smoke control system, they can be divided into two basic groups – those that contain fire and smoke to ensure compartmentation and those that use mechanical means to manage the movement of smoke.  It is this latter that is more complicated and is the main subject here.

Actuator in Smoke ControlSome system dampers are applied in other ways to control air flow and smoke.  Air Handling Units (AHU) are often shut down if any smoke detector in the area they serve senses smoke.  However, in engineered smoke control systems the fans may continue to run while the AHU dampers position so that all return air is dumped outside and only fresh air is brought into the building.  For large spaces that exhaust smoke in case of an event, dampers located on outside walls (with ducts where appropriate) open to allow outside air to enter to replace air and smoke pulled out by exhausts.

Download "Actuator Dampers in Smoke Control Systems" booklet and learn more about smoke control strategy and tractics.

Tags: Fire and Smoke Control

A Comprehensive Look at Engineered Smoke Control Systems

Posted on Mon,Nov 05, 2012 @ 10:00 PM

Smoke control systems use any and all methods possible to protect from smokeBelimo Fire Escape Figure spread.  Doors, fans, sprinklers, dampers, and alarms are unified into one coordinated system.  Coordination of all the smoke control tactics is typically performed by a fire alarm/smoke control panel.  In most systems, fire fighters have override control from a Fire Fighters’ Smoke Control System (FSCS) Panel located in a lobby or a protected area.  Overrides and status indication of all equipment are present on the face of the FSCS or a computer screen display.  Figure to the left shows a detail of a typical override switch and indicator lights on a FSCS panel.
Vestibule variation and supplemental stairwell pressurizationFigure 1: Relief damper variation of stairwell pressurization.

Stairwell pressurization
Stairwell pressurization can be accomplished a number of ways. The IBC (IBC. 2012) requires vestibules in unsprinklered buildings.  This can be supplemented with stairwell pressurization.  In sprinklered buildings pressurization alone is allowed.  One should consult the IBC for details of requirements.

One method uses a constant volume fan capable of pushing air through any stair door that opens.  A barometric damper in the stairwell roof or wall relieves excessive pressure.  See Figure 1. In Figure 2 a combination vestibule with barometric is shown. There are designs by different fire protection engineers that use lobbies under positive pressure and others using negative pressure (IBC method) by exhausting. For the most part these designs do not use automated dampers in the periphery.

Since most buildings are sprinklered, pressurization systems alone are more common. A duct system can be run the height of the stairwell and proportional actuated dampers located every few floors with local pressure sensors.  If a floor door opens, the damper(s) nearest it modulate(s) open as necessary to maintain pressure.  A certain amount of smoke may enter the stairwell when any door is opened if there is a lot of pressure behind it.  Typically, the expansion of heated air does provide pressure.  It takes some time for the sensor, controller, and actuator to respond and open the local dampers further.  See Figure 3. The fan may be controlled by a VFD for better control.

Other variations are possible and research is incomplete with regards to which is best in what geometric arrangement of stairs, stack effect, or height of stairs.  One variation is a second fan that turns on when the egress level door is opened.  Then that door does not relieve all the pressure necessary for the floors.  Some research has shown that sufficient ventilation alone during a fire will keep the stairwell tenable.  This employs a supply fan at the bottom of the stairwell and an exhaust fan at the top.  It can be combined with door pressurization by using variable frequency drive (VFD) fans.

Actuated Dampers in Smoke Control Systems 9

Figure 2: Vestibule variation and supplemental stairwell pressurization

Stairwell pressurization system using proportional damper control

Figure 3: Stairwell pressurization system using proportional damper control.

Stairwells are built to be smoke proof compartments.  The occupants can escape into the stairwells and be protected from smoke while they escape the building.  When floor doors are opened, smoke must not enter the stairwell.  Since several architectural and control design methods are used examination of each system is necessary to understand its intent.  Testing using smoke generators helps to ensure the system works as required. Pressure in the stairwell must be below that which would hinder the opening of doors.

Download Guide: Actuator Dampers in Smoke Control Systems.

Tags: Fire and Smoke Control