What is the difference between Smoke and Fire dampers?
March 2, 2019
Smoke and Fire Dampers
The fire protection plans that are the most effective and efficient consist of detection, suppression and containment and is endorsed by Safeflow Ventilation. This requires both active and passive fire protection. Active fire protection consists of all systems designed to extinguish a fire once started e.g. sprinklers. It is important to note that active fire protection does not inhibit the spread of smoke and toxic gases which is the leading cause of fire related deaths. Passive fire protection is designed to prevent smoke and toxic gas from spreading and compartmentalising the fire. A critical feature is to compartmentalise a building using fire walls etc. When penetrating these walls by the ductwork of the heating, ventilation or air conditioning (HVAC) system their integrity is sustained by the use of smoke dampers, fire dampers or a combination of both.
Smoke and fire dampers serve a similar role in that they facilitate occupants escape from the building, reduce property damage, strengthen the active systems effectiveness and enable easier access for fire fighters. Throughout the world fire protection engineers continue to incorporate fire and/or smoke dampers into the many types of modern buildings. Their importance cannot be overemphasised.
Fire dampers are crucial passive fire protection products and are used in air conditioning, ventilation and heating systems. In general a fire damper works when heat from a fire causes the normal temperature of a room to rise to approximately 165 degrees Fahrenheit i.e. it is designed to close automatically on the detection of heat. The fusible link which is attached to the damper melts causing the dampers' door to close. More specifically they are located in ductwork at the intersection of fire rated barriers in building zones like partitions at the point of duct penetration in order to retain the fire rating of the wall or floor. The fire damper secures the integrity of the existing barrier thus preventing fire penetration before temperatures reach the fire rating level of the barrier itself. Its primary function is to prevent the passage of fire from one side to the other of a fire-rated separation. The damper is manufactured to a high standard of integrity being designed to resist high temperatures for as long as possible.
Intumescent types of fire dampers are passive air transfer dampers which expand to block their aperture upon exposure to elevated temperatures (intumescence). They are designed for fire resistance, direct flame resistance in the open state or for smoke resistance or a combination of the two. Air transfer fire dampers unlike ordinary fire dampers are not protected by ductwork, therefore their closing time is crucial to avoid fire passing during its open state.
Dynamic fire dampers are installed in vertical barriers and the HVAC system fan will continue to function even in the event of a fire. As the fan stays on, the spring loaded design facilitates the damper to spring shut against air pressure.
Static Fire Dampers. These are installed where the HVAC system fan shuts down in the event of a fire. The most common type is the curtain damper and consists of a 'curtain' held up by a fusible link allowing the damper to fall and shut due to gravity. Multiple-blade dampers have blades located in the airstream. This type offers greater restriction to air flow than the curtain type.
Fire dampers are required to be installed in 'sleeves'
Whilst fire dampers function to help stop the passage of fire, smoke dampers work in a similar way to preserve the integrity of physical smoke barriers e.g. floors and walls. They can also be found within air conditioning and ventilation ductwork. They also serve the same purpose as fire dampers to enable building occupants to escape and fire fighters to have easy access. However smoke dampers do not have the same stringent temperature restrictions as fire dampers. They are routinely situated in areas where smoke penetration would present particular challenges.
Smoke dampers have two general functions:
- As part of a passive smoke system where they are generally activated by smoke detectors, which would also be situated within the duct. They close upon the detection of smoke and prevent the circulation of smoke and air through the duct or ventilation opening.
- As part of an engineered smoke control system. This is designed to control the migration of smoke using walls and floors as a barrier.
Smoke dampers close by either an electronic or pneumatic actuator or a spring actuator. They can be reset manually or forced open on a reset signal to the actuator. Pneumatic actuators need air to function properly whilst electrical actuators need power to function successfully. Smoke dampers do not have to be installed in sleeves - they can be installed directly into the duct. However the joints between the damper frame and the duct must be sealed. This is to prevent any air leakage.
Combination - Fire/Smoke Dampers
These are self explanatory and fulfil the dual role of a fire and a smoke damper. They are commonly used in HVAC penetrations where a wall or ceiling or floor requires both smoke and fire dampers. When smoke is detected they close (via smoke detector) or by heat detection (via duct temperature). Whereas fire dampers require fusible links there are fire/smoke dampers that have electric heat release devices. These are resettable and allow the closure of the damper to be controlled rather than slamming shut causing pressure problems within the HVAC system.
Fire dampers and smoke dampers are an essential and integral part of a buildings passive fire protection system. As has been seen smoke and fire dampers fulfil very similar roles and are put in similar locations. They are both designed to prevent ducting becoming a weak point in a buildings fire safety provision. Essentially they are louvered vents or shutters placed within ductwork which under normal circumstances allows air through but in the event of a fire they shut. As with any building system, the regular maintenance and inspection is imperative to ensure proper operation.
At Safeflow Ventilation we offer regular Fire / Smoke Damper Testing for companies nationally. If you require this service then please contact us on 0333 358 3382 or via our Contact Form for a free quote.