Dampers: An essential component of fire protection design
Based on an examination of NFPA data in the 1930s, in 1939 the National Board of Fire Underwriters recommended that dampers be installed in HVAC systems to interrupt the passage of smoke, flame, and heat during a fire. Since that time, numerous experts in the field of the fire sciences have substantiated the effectiveness of automatic closing fire and/or smoke dampers and automatic fan shutdown...
Based on an examination of NFPA data in the 1930s, in 1939 the National Board of Fire Underwriters recommended that dampers be installed in HVAC systems to interrupt the passage of smoke, flame, and heat during a fire. Since that time, numerous experts in the field of the fire sciences have substantiated the effectiveness of automatic closing fire and/or smoke dampers and automatic fan shutdown in HVAC systems in preventing the migration of smoke, flame, and heat to areas of a building remote from the area of origin. Throughout the world, fire protection engineers and mechanical engineers continue to incorporate fire and/or smoke dampers into the fire protection design of many types of modern buildings.
A fire damper is a device, installed an HVAC system, that closes automatically upon the detection of heat in accordance with UL standard 555. A smoke damper is a device installed in an HVAC system to control the movement of smoke in accordance with UL 555S. Combination fire/smoke dampers fulfill the function of both fire and smoke dampers, and must meet the testing requirements of both.
In the United States, the legacy model codes contained provisions for requiring construction capable of resisting smoke spread. Some of those requirements included the installation of smoke dampers. The 2000 Edition of the International Building Code (IBC) retained the requirement for smoke dampers in corridor walls when the corridor has a fire resistance rating in language similar to the legacy codes.
But the 2000 IBC added a new requirement that requires smoke dampers at the penetration of shaft enclosures in lieu of requiring engineered smoke control systems, which had also been mandatory under certain conditions in two of three of the legacy codes. This code change was accepted in the new IBC on the basis that many of the previously required fire-rated and smoke-resistant floor and wall requirements in the legacy codes were permitted to be weakened or eliminated when automatic sprinklers were installed.
Because smoke dampers installed in duct penetrations of shaft enclosures is a relatively new building code requirement, and despite the concern about smoke spread throughout buildings (including sprinklered buildings), the requirement for smoke dampers in duct penetrations of shafts has been under attack in every IBC change cycle since 2000. The opponents of smoke dampers have previously cited the installed cost and maintenance cost of smoke dampers as an “unreasonable expense” to building owners, without increasing the safety of the building occupants. The debate will occur again during the hearings for the public comment on FS 113 May 18 to 19 in Dallas at the ICC Final Action hearings for the 2012 IBC.
The reliability and effectiveness of sprinklers is often cited as a justification for removing the requirement for smoke dampers in shafts. The International Code Council (ICC) voting membership has consistently rejected proposals to entirely remove smoke dampers from duct penetrations from shafts. Although the ICC has voted to support some revisions since the proposal was approved, it still applies to many buildings. However, the valid question remains as to the cost benefit of smoke dampers in shafts in sprinklered buildings.
In 2008, the Air Movement and Control Assn. International (AMCA) contracted with Koffel Assocs. Inc. to conduct a literature search to identify credible work on this subject, and to use the research findings (if any) as the basis for additional computer modeling. The literature search resulted in two interesting findings:
First, no documents were found that would support the removal of smoke dampers in shaft penetrations. On the contrary, the literature search provided a sampling of fires from the past 25 years where smoke spread was an issue for occupant life safety. Many of the fires occurred in occupancies in which at least some of the legacy building code requirements would not specifically have required smoke dampers but would have required construction capable of preventing smoke spread, which could have included dampers. The data collection methods from the time period studied would not have specified when smoke dampers would have been required, or even if they had been provided as an above-code provision.
Second, the literature search identified a relatively recent modeling effort and some full-scale fire tests on the vertical spread of smoke in buildings via shafts. The additional modeling research, which has been contracted to be completed by Koffel Assocs., expands on these two studies in an attempt to better quantify the benefit of smoke dampers at duct penetrations of shafts in sprinklered buildings. (The report on the research and modeling conducted by Koffel Assocs. was nearing completion at the time of this article's printing, and will be available in the near future through AMCA's website at www.amca.org .)
THE SPRINKLER RELIABILITY DEBATE
At the heart of every debate in the decision to eliminate a fire or smoke protection feature in order to offset the expense of automatic sprinklers are two issues: reliability of automatic sprinkler systems and their relative cost/benefit. The fact that sprinkler systems fail to perform satisfactorily from time to time is not debated. However, the frequency and the causes of such failures stir controversy. When such malfunctions occur, a fire that would have been a nuisance can quickly become a potential catastrophe.
Sprinkler reliability figures are tossed about casually to promote their installation without much consideration given to the consequences of sprinkler failures in buildings where many other features have been eliminated. In 2009, NFPA's John Hall authored the report, “U.S. experience with Sprinklers and Other Automatic Fire Extinguishing Equipment.” The fire data used to support the study was gathered from 2003 through 2006. In the study, Hall states that “automatic sprinklers are highly effective elements of total system designed for fire protection in buildings with sprinklers cover the area of origin, they do they operate in 95% of all reported structure fires large enough to activate sprinklers. When they operate, they are effective 96% of the time, resulting in a combined performance of operating effectively in 91% of reported fires were sprinklers was present in the fire area and the fire was large enough to activate.”
In 1997, an NFPA study examined fire data from 1986 to 1995 to evaluate the extent of flame and smoke spread in sprinklered and nonsprinklered buildings. For high-rise buildings (seven stories or taller), the study showed that 11.4% of fires in sprinklered buildings resulted in smoke damage beyond the fire floor, while 15.4% of fires in nonsprinklered buildings resulted in smoke damage beyond the fire floor. For mid-rise buildings (three and six stories), 15.7% of fires in sprinklered buildings resulted in smoke damage beyond the fire floor while 34.4% of fires in nonsprinklered buildings resulted in similar damage.
While the study was unable to define the severity of the smoke damage or toxicity, it is significant that so many fires in sprinklered buildings had smoke damage beyond the fire floor. If smoke dampers were to be eliminated in sprinklered buildings, and the automatic sprinkler systems failed for whatever reason, the spread of smoke during fires would almost certainly increase.
It is important to note that neither NFPA report supports the position that sprinkler systems eliminate smoke, or that fires that are controlled by sprinklers do not continue to smoke production. G. W. Mullholland's paper entitled “Smoke Production and Properties,” recorded in the 1995 SFPE Handbook of Fire Protection Engineering, estimated that if the airborne soot particulates produced by burning an upholstered armchair filled with 9 lbs of polyurethane foam were uniformly distributed throughout 1,800-sq-ft room, a person would not be able to see his or her own hand held at arm's length in front of his or her face. Even when sprinklers successfully suppress a fire, the fire can be expected to continue to burn and produce soot particulates and toxic gases.
Numerous studies have been conducted on fires where the sprinklers' water spray was shielded by some obstruction and never reached the item that was burning. Such fires effectively became nonsprinklered fires.
Experts confirm that automatic sprinkler systems are very effective, although not infallible or a panacea. The sprinkler industry, the fire service, and the fire protection community are continually striving to improve sprinkler reliability when the causes of sprinkler failure become known. John Klote, in an article entitled “Compartmentation and Dampers are Essential,” stated, “in our ever-changing organizational functions, materials, construction methods, and architectural designs, it is reasonable to expect that new failure situations will arise. For that reason, sprinklered buildings need other fire (and smoke) protection features to ensure an adequate level of protection in the event of sprinkler failure.”
Additionally, damper manufacturers, contractors, installers, and the fire service are cooperating to ensure that the dampers are both installed correctly and periodically inspected to ensure functionality.
Building codes can control the construction materials used in a building, which is taken into consideration when sprinkler systems are designed. However, neither building codes nor designers can control the materials that occupants bring into the building. If the wrong types of materials are brought into a building a sprinkler system that would otherwise control a fire can be easily overwhelmed. Therefore, sprinkler systems are best supported by designs, systems, and devices such as smoke dampers that help to manage smoke migration, even during successful sprinkler activation.
There is little debate as to whether an HVAC system can transport smoke to areas remote from the fire area's origin. However, there is still some debate as to how best to manage the smoke in both sprinklered and nonsprinklered fires. For many years, system shutdown was the standard approach to achieving some control over smoke migration.
Since 2000, however, the operation of the HVAC system in smoke control mode is not required in most buildings constructed to the IBC. Without an engineered smoke control system, or complete system shutdown and functional smoke dampers at shaft penetrations, the HVAC system can transport smoke to every building area the system serves. Even shutting down the HVAC system without dampers will not prevent it from supplying oxygen to the fire and will not entirely prevent smoke movement throughout the HVAC system.
The installation of smoke dampers at the shaft penetration by the duct can help inhibit smoke movement through the HVAC system.