The evolution of motorized life-safety dampers
Motorized fire, smoke, and combination fire/smoke dampers and their testing requirements have come a long way since their introduction during the 1970s.
Originally, life-safety dampers were standard commercial control dampers with blade locks to hold them closed. They were Underwriter Laboratories-tested to the third edition of UL 555, the standard for fire dampers, and the first edition of UL 555S, a standard for smoke dampers. Testing consisted of fire, preconditioning and heat-degradation tests. Because Underwriters did not have a test procedure for actuators, damper manufacturers would list the actuator used in the test of their product. Actuators did not have to operate under fire conditions. Instead, a fusible link connected to the damper blades and a shaft connected to the actuator was used. During a fire event, the actuator would disconnect from the shaft, a spring would close the damper, and a locking device would secure the blades closed. Because of the fusible link, full access to a damper via an access door was required for visual inspection and testing.
In the ensuing years, major changes were made to improve the efficiency of motorized fire, smoke, and combination fire/smoke dampers. Today, they have their own UL 555S test requirements, and there is a new test standard for actuators and dynamic assembly operation.
Modern life-safety dampers are specially designed to operate during exposure to high temperatures and velocities. Also, instead of relying on fusible links and blade locks to close under fire conditions, they are designed with a jackshaft with a solid connection that locks the blades into position when the dampers are closed.
Life-safety actuators, meanwhile, have evolved from oil-filled, foot-mounted motors with complicated linkages subject to breaking to specially designed anti-slip, direct-coupled devices that have passed rigorous UL cycle and holding tests.
Standards UL555 and UL555S have been updated to meet today’s building HVAC and smoke-evacuation systems. Current standards require damper and actuator assemblies to be cycle-tested for a minimum of 20,000 cycles and subjected to a heated-air dynamic-closure-and-operation test with a minimum temperature of 250°F, a minimum air velocity of 2,400 feet per minute, and a system pressure of 4.5 inches water gauge.
UL procedures include spontaneous inspections at manufacturers’ facilities to ensure life-safety dampers are being built as tested, without modifications. Additionally, UL requires installation instructions to accompany each shipment of dampers, so contractors have the most up-to-date guidance.
With non-motorized dampers operating with fusible links, visual inspection is the only way to determine if an issue exists. With motorized dampers, because of the rigorous standards to which all must adhere prior to being shipped to a job site and the documented installation instructions from the manufacturer, after an initial visual inspection and visual commissioning of a building, remote testing is possible. Remote testing can be accomplished multiple ways:
- Control panel. A control panel can be hard-wired directly to a damper with a momentary push button.
- Computerized fire-alarm panel. Requirements for damper testing vary from country to country. For example, in Europe, some countries require testing as often as every 48 hours, performed by a computerized fire-alarm panel that notifies users if something is wrong.
- Remote control. Technology similar to that allowing us to control our homes with a hand-held device is available for testing UL-listed motorized dampers.
With remote-testing capabilities, intrusion into ceiling cavities to test dampers no longer is necessary, and the cost of testing can be reduced by up to $500 a damper.
Because of improved accuracy and reliability, reduced tolerances, and the development of specialized actuators and testing equipment, life-safety dampers no longer are glorified control dampers. They are specially designed devices that play a vital role in passive fire-protection systems, preventing the spread of fire and/or smoke through openings in walls, ceilings, floors, and partitions, protecting occupants and property.
This column was supplied by the Air Movement and Control Association International’s Fire and Smoke Damper Task Force.