1、 Stephen W. Duda, PE, FASHRAE, is a Senior Mechanical Engineer with Ross and a good review for the more experienced. INTRODUCTION Anecdotally, some HVAC engineers and designers are uncertain of the requirements for fire dampers and smoke dampers, especially with regard to the difference between part
2、ition types. Some play it safe and specify fire and smoke dampers where they really are not required. Some may even find they have been over-specifying protective dampers throughout their career. So this conference paper compiles this Fire and Smoke Damper Summary for HVAC engineers and designers ba
3、sed on the 2015 International Building Code1(the 2012 edition has the same requirements, and the 2009 edition also has the same requirements but with different paragraph numbering). Most States and local jurisdictions in North America use the International Building Code, either outright or as a stat
4、e adaptation. Where the IBC is not enforced, NFPA 90A2can be used for guidance. FIRE RESISTANCE RATED CONSTRUCTION There are four types of fire-resistance rated walls. Before you can know what type (if any) fire damper to use, you first must know which of the four types of walls you have. Fire Walls
5、 Fire Walls (IBC Section 706) are major separation walls between buildings or to divide one building into separate buildings. A Fire Wall actually allows you to treat the spaces on opposite sides of the wall as totally separate buildings. These are usually three to four-hour rated, and are usually s
6、tructurally independent. You cannot run a duct or air transfer opening through a Fire Wall located on a property or lot line not at all not even with a fire damper. If you run a duct or air transfer opening through a Fire Wall located within a building, use a three-hour fire damper. This is the most
7、 restrictive of the various types of fire-rated walls, and is rather rare on most building projects. Most fire-rated walls within buildings are not this extreme. Fire Barriers Fire Barriers (IBC Section 707) are the medium-rating level of the various types of fire-rated walls. Examples include exit
8、passageway enclosures, atrium boundaries, stairwell enclosures, and separations between occupancies in a mixed-use building. These are usually two-hour rated, but there are exceptions, so check with the architect. You cannot run a duct or air transfer opening through an exit passageway enclosure or
9、stairwell enclosure (not at all; not even with a fire damper) unless that duct is for the purpose of independent stairwell pressurization. If you run a duct through other types of Fire Barriers, use a 1-hour fire damper. But there is an exception: If the fire barrier is only one-hour rated, and if t
10、he building is fully sprinklered, and if the system is fully ducted (not an air transfer opening), then you dont need a fire damper. (IBC 717.5.2, Exception #3). Shaft Enclosures Shaft Enclosures (Section 713) are a special type of Fire Barrier used to enclose shafts. These are usually two-hour rate
11、d. Shaft enclosures are not required if all of the following are true: (a) fully-sprinklered building; (b) not a hospital or prison; (c) connects only two floors and no more. In this case, use a 1-hour horizontal fire damper at the floor line. Other than the above item, shaft enclosures are required
12、 anytime a duct travels vertically floor-to-floor. A 1-hour fire damper and Class I or II smoke damper (or combination damper meeting both requirements) is required at each penetration of a shaft enclosure. Design Tip: You can avoid the fire/smoke damper at the shaft penetration if you have a vertic
13、al shaft with exhaust ducts entering the shaft on every floor (such as in a high-rise hotel or dormitory), and if you build steel sub-ducts that extend vertically upward into the vertical riser by at least 22 inches (560 mm), and if there is a continuous flow of air upward to the outdoors (e.g., the
14、 exhaust fan is on the roof and is always on). See Figure 1. In some jurisdictions, the fan must be on emergency power for this exception to qualify. If the shaft does not extend all the way to the bottom of the building, some Code officials will allow you to place a horizontal fire/smoke damper at
15、the floor level where the duct emerges from the bottom of the shaft. Others will argue this is not permissible and will instead require that the shaft be extended down into the ceiling cavity of the floor below, so that your duct can emerge from the side of the shaft with a vertical fire/smoke dampe
16、r. See Figure 2. Design Tip: Note that where horizontal fire dampers at a floor penetration are permitted, most manufacturers require that the damper be supported by and framed with a concrete floor; the dampers are not listed to be supported by gypsum board. So you must coordinate with the structur
17、al engineer to provide an opening in the concrete floor sized precisely for the damper plus space for expansion and contraction as required by the damper listing. Figure 1 22-inch (560 mm) sub-duct exception Figure 2 Shaft extension at lowest floor Fire Partitions Fire Partitions (IBC Section 708) a
18、re the minimum-rating level of the various types of fire-rated walls. Examples include corridor walls, tenant-separation walls, and walls dividing dwelling units in a multi-family housing building. They are usually one-hour rated. Note that corridor walls in most fully-sprinklered buildings are not
19、required to be rated at all (IBC 1018.1). If a given fire partition is not more than one-hour rated, and if the building is fully sprinklered, and if the system is ducted (not a transfer opening), then you dont need a fire damper (IBC 717.5.4, Exception #4). Otherwise, in non-sprinklered buildings a
20、nd/or in transfer openings, use a 1-hour fire damper. SMOKE RESISTANCE RATED CONSTRUCTION There are three types of smoke-rated walls. Before you can know what type (if any) smoke damper to use, you first must know which of the three types of smoke walls you have to address. Smoke Barriers Smoke Barr
21、iers (Section 709) are found in hospitals and prisons, and are used to completely divide a building floor into two compartments. A tell-tale sign of a smoke barrier on a hospital floor is to look for a double-egress door (a pair of opposite-swinging doors) in the corridor; that door will be on the s
22、moke barrier wall (Figure 3). Smoke barriers are a more restrictive classification than Smoke Partitions. A Class I or II smoke damper is required at each duct penetration of a smoke barrier. Smoke barriers are also automatically one-hour fire partitions, so review the relevant section above to dete
23、rmine a possible fire damper requirement. Figure 3 Smoke barrier indicated by double-egress (opposite-swing) door In a hospital, every floor that features patient care or patient sleeping rooms (as opposed to floors that are exclusively administrative or educational) must have a smoke barrier that r
24、uns straight (or reasonably close to straight) across the entire floor, from one exterior wall to the other, that divides the floor into two distinct halves. The purpose is that patients may not be mobile enough to evacuate the building very quickly in a fire. To give them additional time to exit, a
25、nd to help give rescue personnel additional time to provide assistance, all the patients on the fire side of the smoke barrier will be moved to the other side of the barrier. If the floors footprint is so big that one side of the smoke barrier exceeds 22,500 square feet (2,090 m2), then an additiona
26、l smoke barrier is required to divide the floor into thirds. Ask the architects you work with to be very careful about their terminology used on the drawings. Some use the terms smoke partition and smoke barrier interchangeably, or worse they just call both a smoke wall. For HVAC reasons, architects
27、 must use the terms correctly, and to only use the term smoke barrier where they truly apply. If the terminology is used correctly, we can eliminate a lot of unnecessary smoke dampers. Use smoke dampers only in smoke barriers (or unducted transfer openings in smoke partitions). Smoke Partitions Smok
28、e Partitions (Section 710) are used to enclose storage rooms, trash rooms, boiler and furnace rooms, and similar rooms that have a higher-than-average chance of fire. These are not as significant as smoke barriers. Smoke partitions are intended to contain the smoke and heat resulting from a fire jus
29、t long enough to activate sprinklers or smoke detectors quickly. A Class I or II smoke damper is required at each air transfer opening in a smoke partition. Nothing is required in ducted penetrations of smoke partitions, and this is where over-specification sometimes occurs. Ducted penetrations of s
30、moke partitions do not require smoke dampers. Hospital Corridor Walls The final type of smoke boundaries we encounter are corridor walls in a hospital, which are required to form “barriers to limit the transfer of smoke” but are not smoke barriers. If corridor walls were smoke barriers, then every s
31、ingle patient room that opens to the corridor would have to have listed/labeled doors and automatic door closers, which is not the case. The difference between a “barrier to limit the transfer of smoke” and a smoke barrier is subtle in syntax, but important to an HVAC designer. Corridor walls in a h
32、ospital are actually considered smoke partitions, not smoke barriers (IBC 407.3). This is another area where some designers use smoke dampers unnecessarily. No dampers are required in ducted penetrations of smoke partitions, including those in hospital corridor walls. MORE DESIGN TIPS 1. Do not put
33、any dampers in Type 1 grease exhaust and clothes dryer exhaust systems (IBC 717.5.3.5). If your hood or dryer exhaust duct crosses a rated wall or floor, then instead of a damper you must encase the duct itself in a rated enclosure such as a fire-rated gypsum board shaft or a listed/labeled fire-wra
34、p insulation material (Figure 4). Use sub-ducts in lieu of dampers at vertical shafts. 2. If a fire or smoke damper placement will interfere with the operation of an engineered smoke exhaust system (such as for an atrium), approved alternate protection shall be used (IBC 717.2.1). What may be done i
35、n this case is to specify a remotely resettable fire/smoke damper addressable by the fire department at a fire command center. 3. Fire dampers are available in 1-hour and 3-hour ratings. Those are generally the only two choices. Use a 1-hour fire damper in 1-hour or 2-hour walls. Use a 3-hour fire d
36、amper in 3-hour or 4-hour walls. Figure 4 Fire-rated duct wrap used in lieu of shaft enclosure and fire/smoke dampers 4. Fire dampers are available as “static” or “dynamic”. Static fire dampers are only tested to close without air moving in the duct. Dynamic fire dampers are tested to close with or
37、without air moving in the duct. The additional cost of dynamic fire dampers is minor and it is suggested to specify this type in all cases to avoid confusion. 5. Fire damper Frames (Figure 5): Frame A means the blades, in the open position, partially block the free area of the duct. Frame B means th
38、e blades, in the open position, are completely outside the free area of the duct. Frame C is for round ducts. These frame types apply only to curtain-type fire dampers, not to multi-blade type dampers like most combination fire/smoke dampers. Figure 5 Fire damper frame styles (from left to right) A,
39、 B, and C 6. Fire dampers and smoke dampers must be accessible for service. If reaching inside the duct is necessary (for example, to re-open a closed fire damper) then you must provide a duct access door and a ceiling access panel or an accessible ceiling type. 7. For buildings where engineered smo
40、ke control is required by code, such high rise buildings and atria, smoke damper open/closed status indication is required for all dampers that affect the proper operation of the smoke control system. Typically status is indicated by switches that are physically connected to the damper blade, or aux
41、iliary end-switches from direct-coupled actuators. Dont Use Corridors as an Air Duct Some designs are not permissible even with fire or smoke dampers. It is not permissible, for example, to use an egress corridor as an air plenum, including as a path for return air. The 2015 International Mechanical
42、 Code3(IMC) in paragraph 601.2 states clearly that corridors shall not serve as supply, return, exhaust, relief or ventilation air ducts, and essentially the same clause has appeared in previous editions. Picture an office building (Figure 6) with a corridor down the middle, flanked by enclosed offi
43、ces on both sides of the corridor. If an air-handling unit is located in a room adjacent to the corridor, for example, it is unacceptable to place a return grille serving that air-handling unit directly into the corridor wall, and use transfer openings from each office into the corridor proper. This
44、 has the effect of turning the corridor into a return air duct in violation of this code clause. This is prohibited regardless of any fire and/or smoke dampers that may be used to protect the openings. Figure 6 Simplified office building incorrectly using the corridor as a return air passage The con
45、sequence of using this arrangement could be dire in a fire. Were a fire to break out in, say, a trash can in the conference room, the suction of return air by the air-handling unit in the corridor would tend to draw smoke from the conference room out into the corridor the very corridor that is neede
46、d for safe egress by building occupants. A responsible engineer should strive to keep the corridor clear of smoke, and use of the corridor as a return air path would actually encourage smoke to migrate there. To clarify, it may be proper and acceptable under IMC 601.2.1 to use the space above a corr
47、idor ceiling as a return air path if the corridor is not required to be rated. If transfer openings are placed between each office, or the ceiling cavity above each office, into the ceiling cavity above the corridor, and the air-handling unit at the end of the corridor draws return air out of the ce
48、iling cavity (as opposed to the corridor proper), then the integrity of the egress path is maintained. Smoke in the trash can fire example would then tend to be drawn into the ceiling cavity but not the corridor itself. If the architect has designed the corridor without a ceiling, then the return ai
49、r will need to be ducted so that the corridor is not violated. Paragraph 601.2 goes on to grant a few exceptions or clarifications. For example, it is acceptable to use a corridor as a source of makeup or transfer air for adjacent toilet rooms, although it remains advisable to use the corridor ceiling cavity rather than the corridor itself for this purpose whenever possible. Obviously, one may place return air grilles in a corridor to return that corridors own supply air, and it is permissible to have a minor imbalance of air in a corridor to maintain proper
