Factoring Smoke Dampers into the System
While sprinklers, fire-alarm systems and firestopping are at the forefront of current fire-safety discussion, one overlooked measure is the smoke damper. Yet this device is crucial in commercial/industrial fire safety. It's the traffic cop of the system, routing smoke out of the building while keeping it away from areas where it could do harm.
While sprinklers, fire-alarm systems and firestopping are at the forefront of current fire-safety discussion, one overlooked measure is the smoke damper.
Yet this device is crucial in commercial/industrial fire safety. It's the traffic cop of the system, routing smoke out of the building while keeping it away from areas where it could do harm. It's also an ambassador between the HVAC and fire-safety systems, as it clearly ties the two together.
Smoke damper codes have remained fairly consistent over the years, and remain so in the International Building Code . Most applications require the highest classification for dampers (class 1 out of a possible 4). Classification is determined by the amount of leakage (in cfm per sq. ft.) allowed, based on the way the damper is sealed.
When it comes to designing smoke control systems, dampers, which are tested via UL-555S, are available in a variety of blade types and shapes, so there's a lot of design flexibility.
However, like many other building system components, the issue is code interpretation, and not every jurisdiction views smoke dampers the same way. "The issue tends to be how the local authority views penetrations and smoke partitions vs. one-hr.-rated walls and two-hr.-rated walls, and whether they need just fire damper protection or smoke damper protection, because they don't want any migration of smoke into paths of egress or anywhere else," says Pat Banse, P.E., Smith Seckman Reid, Inc., Houston.
Location of the damper is also an issue. "You have to determine which jurisdiction [you're dealing with], because usually, the local building code is more restrictive in terms of where they're to be placed in duct systems," Banse says. "With exhaust systems—systems that remove air from the building with an exterior fan—many times, the smoke damper can be eliminated because they have no openings in the path of egress from corridors or stair entrances, where a normal supply and return would be serving comfort conditioning to that corridor."
According to Banse, NFPA's 2003 edition of the Life Safety Code indicates where smoke dampers need to be placed in a system, depending on the occupancy. But as long as the building is fully protected by a supervised automatic sprinkler system, the code allows them to be deleted from, or not installed at all in, engineered smoke control systems. That is, unless they're required for proper pressurization or operation of the system. The Life Safety Code also allows dampers to be removed or not installed in systems where they are arranged to prevent recirculation of exhaust air under fire conditions. However, Banse notes, local building codes might require that any duct system that crosses a partition must have a damper. This is where conflict occurs. Figuring out where dampers are truly required is crucial, he says, because the more that need to be installed, the more it affects the construction cost of the building, as well as the potential for failure.
"You've got to talk to the local [code] guys and try to tell them as much about the building and its operation as you can, and get them to buy into design concepts to see if there are ways to eliminate [smoke dampers] or include them, depending on what's best," Banse says. "The question always seems to be how do you do that early enough in the process so it doesn't get to the plan review, and the owner says, 'I see that you didn't put all of the dampers in,' and then all of a sudden, you've got to add $100,000 to the project. They're never happy with that. From a design aspect, the earlier the better when it comes to sharing the operation of the system."