Fire and Smoke Curtains: Meeting Atrium Code Requirements
Relatively new to the United States, fire and smoke curtains are less complex and less expensive than comparable mechanical systems and support the use of daylighting design.
Continuing Education
Use the following learning objectives to focus your study while reading this month’s Continuing Education article.
Learning Objectives - After reading this article, you will be able to:
- Discuss fire and smoke code requirements for atrium designs, interior stairs and escalators.
- Describe the sustainable features of fire- and smoke-rated curtains.
- Explain how fire and smoke curtains can be used to supplement or replace smoke evacuation systems in ways that save energy and reduce mechanical system costs.
- Summarize the ways fire and smoke curtains may be specified so they enhance daylighting by supporting atrium design.
Originally an open central court in ancient Rome, the modern atrium dates back to Victorian times when advances in manufacturing techniques enabled courtyards to be covered in glazing. Nowadays, the atrium is a design feature that gives multiple building types architectural distinction.
By expanding the amount of natural light within a building, atrium designs also contribute significantly to sustainable design. Daylighting strategies reduce operating costs and have been documented to deliver energy savings through improved life cycle costs and reduced emissions. Moreover, daylight vitalizes interior spaces and has been shown to increase user satisfaction and visual comfort leading to improved performance.
Since the 1980 MGM Grand fire in Las Vegas, with its multiple deaths on upper floors due to smoke inhalation, life safety fire and smoke code regulations have become increasingly stringent and are now one of the most critical atrium design issues. Unlike other building configurations whose code requirements focus on structural fire-resistant floors, walls and glazing, atrium building codes require more complex systems that are activated in the event of fire. Automatic sprinklers, smoke exhaust systems and even rolling steel doors have all been employed in keeping people in atrium designs safe in the event of fire.
Yet architects and their clients, driven by the growing green demand for open office floors, and eager for new structures with larger, soaring open spaces, have found that they are constrained in terms of both design and cost by familiar and conventional solutions and have often been forced to reject atrium designs. Similarly, architects planning to incorporate or add an atrium to an existing structure have learned that such solutions can add a significant amount to construction budgets.
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Shown here, vertical flexible smoke-rated curtain used to compartmentalize upper floor of atrium space in a fire event. Deployment of curtain systems can eliminate the need for costly mechanical smoke evacuation and increase usable building space. Photo courtesy of Smoke Guard, Inc. |
To address these concerns, a new and simpler solution has come on the market: flexible smoke and fire barrier curtains. They have the added benefit of not being an impediment to design aesthetics since they are invisible when not deployed. These new systems can be selected as an alternative to meeting atrium code requirements or as a supplement to conventional approaches. Well-tested and used in Europe for a number of years, these systems are now available in the United States. They offer an intriguing, energy saving and cost-savings option for addressing code requirements for unenclosed openings such as an atrium, interior stair or escalator.
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Shown here, typical fire- and smoke-rated flexible curtains partially closing in a horizontal application. Fire-rated curtains rated up to 2 hours can be constructed of stainless steel strengthened glass filament fabric. Photo courtesy of Smoke Guard, Inc. |
ATRIUM DESIGN
The International Building Code (IBC), the most widely adopted building code in the U.S., and National Fire Protection Agency (NFPA) 101 "The Life Safety Code," NFPA's standard for regulating all components of the building impacting occupant life safety in the event of fire, have extensive code provisions for atrium designs with explanatory material spelled out in the IBC commentary and Life Safety Code Handbook.
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Smoke-rated flexible curtains before (left) and after (right) deployment. This unique system has primary and back-up power sources. Photos courtesy of Smoke Guard, Inc. |
A significant change in the 2006 IBC code regarding atrium designs and open spaces is that IBC has adopted NFPA 92B: Guide for Smoke Management Systems in Malls, Atria and Large Spaces, which allows design flexibility, with a corresponding wider range of approaches that can impact costs. Codes are interpreted differently by state and local building authorities, but the basic fire and smoke code provisions for atrium designs and open spaces are as follows:
- IBC defines an atrium as an opening connecting two or more stories other than enclosed stairways, elevators or escalators, which is closed at the top and not defined as a mall.
- The 2009 IBC code for an atrium permits multiple floors to be connected to one another by a floor opening provided that the building is protected by an electrically supervised sprinkler system and smoke management system. A two-story atrium is generally exempt from smoke control requirements. A three-story (or higher) atrium generally does require a smoke control system.
- IBC 404.6 requires that the floor openings forming the atrium be separated from occupied spaces by a 1-hr. fire-resistive construction or horizontal assembly. Exceptions to this requirement include: Exception 1 permits glazing to be utilized as a substitute for the one-hour separation where the nonrated glazing is protected by sprinklers located in close proximity to the glazing. Another exception to the separation requirement permits a maximum of three floors to be open to the floor openings forming the atrium if the volume calculated for the design of the smoke control system includes the volume of the spaces not separated from the atrium.
To be in compliance with code regulations for atrium designs, design professionals specify sprinkler systems, smoke management systems and fire-rated barriers.
Automatic Sprinkler Systems
Sprinkler systems are de rigueur in response to the IBC code requiring an approved automatic sprinkler system be installed throughout an entire building—including atrium designs (one exception is when that area adjacent to or above the atrium is separated by a 2-hr. fire-resistance fire-rated barrier or horizontal assembly, or both).
Sprinkler systems are designed to control a fire, not to extinguish it. It is therefore likely that significant quantities of smoke may be generated that can travel far from the initial fire source. Since sprinkler systems are not sufficient to protect an atrium from potential smoke migration—codes require the addition of a smoke management system.
Case Study 1: Use of Horizontal Flexible Smoke Curtain in Open Plan Office |
This case study demonstrates that multiple components of a mechanical smoke control system could have been replaced by a single passive horizontal smoke control curtain at considerable cost savings. A four-floor office building was renovated to include a series of floor openings. A skylight extended above the center of the third floor in the area above the atrium opening. Height from the ground floor to skylight was approximately 53 ft. The floor openings were offset and did not line up vertically to provide a typical atrium configuration. This made it difficult to maintain smoke at least 6 ft above the highest occupant. A tenability smoke exhaust control system was therefore proposed based on performance-based requirements developed using a modeling approach. The intent of the design was to exhaust smoke from the floor containing the fire and from the skylight, also to exhaust smoke that might spill into the atrium. Supply/make-up air was delivered to the two non-fire floors. For a fire directly beneath the atrium opening where smoke would rise unimpeded up into the skylights, beam detectors in the skylights aligned the system to exhaust the uppermost third floor in conjunction with the skylight exhaust. The skylight exhaust and floor exhaust were accomplished using new, dedicated mechanical equipment. The supply air was provided via a combination of new, dedicated equipment and existing equipment that was also used to provide normal HVAC. For this project it would have been possible to replace the entire smoke exhaust system by a single horizontal 2-hr. flexible fire curtain at the second floor slab. This would separate the building into two 2-story connected spaces, neither of which would require active/mechanical smoke control. The size of the opening was nominally 20 ft x 60 ft. Activation of the flexible fire barrier would be via the fire alarm control panel upon smoke detection or sprinkler water flow. Mechanical Smoke Control System Required:
Passive Smoke Control System:
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Top: Cross-sectional view of office showing offset configuration of floor openings; Bottom left: Smoke exhaust control system design; Bottom right: Horizontal flexible smoke curtain at second floor |
Smoke Management Systems
Smoke management is required within atrium spaces connecting more than two stories (per IBC Section 404.4.) and requires all smoke control systems to be tested by a special inspector who shall have expertise in fire protection engineering (Section 909.18.8.)
Given the large volume of open space in an atrium, smoke control is the most critical design issue. Many sources report that as many as 76 percent of deaths and injuries that occur as a result of a fire are caused by smoke.
Smoke management or smoke control systems can be active, passive, or a combination of both active and passive measures. The fire protection engineer or professional system designer has the latitude to use these options without relying on the building code to spell out how this can be done. One code requirement is to address means of egress. This is typically accomplished by designing the smoke control system so as to keep smoke away from egress or escape paths.
Active System: Smoke Exhaust or Evacuation. The conventional widely used solution to smoke control is a smoke exhaust or evacuation system. This is considered an "active" system because it uses mechanical equipment to control the spread of smoke. Exhaust inlets located near the ceiling remove smoke at a rate that is greater than or equal to the rate at which it is generated, or at a rate which will allow people to evacuate the building.
Designing a smoke exhaust system is a complex engineering exercise that includes calculations regarding the size of exhaust and replacement air, number and size of exhaust fans and intake vents, smoke plume equations and meeting the current requirement of maintaining a smoke layer height of 6 ft above the highest walking surface.
IBC also requires that a registered professional develop a design fire size of 5,000 Btus, as part of the analysis (a design fire is an engineered description of a fire over time.) One potential problem is over-designing the exhaust system, which may lead to "plugholing" (where a relatively shallow smoke layer and too-high exhaust rate can lead to entrainment of cold air from the clear layer, thus blocking smoke from being exhausted.)
Smoke exhaust systems may have a dedicated power source, or draw on the building's power source and mechanical systems. In either case, a standby power source is required in the event of loss of power. For these reasons, an active smoke exhaust system uses more energy than a passive system such as flexible smoke curtains (see next section in online portion). See Case Studies 1 and 2 for examples of smoke exhaust systems and their required fans, ducts, dampers, power and control systems.
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This example of a large-opening automatic flexible smoke-rated curtain has zero percent residual opening when activated and employs a gravity fail-safe system. Photo courtesy of Smoke Guard, Inc. |
Passive System: Flexible Fire and Smoke Curtains. Referred to as "passive" because they require no mechanical systems to support them, flexible fire and smoke curtains have been successfully used for elevator fire and smoke protection for some time. But their application for atrium designs, interior stairs and escalators is relatively new in the US. Unlike an active smoke management system that only addresses smoke exhaust or evacuation, a passive system that incorporates fire-rated smoke curtains contains and compartmentalizes fire and smoke before they reach the open area of an atrium. In building applications where fire/smoke protection is of special concern the addition of such a passive system would be clearly advantageous as enhanced protection.
All smoke management systems require commissioning and the services of a fire protection engineer and mechanical engineer to certify proper operation after installation. Compared with a complex active smoke exhaust system, passive curtains are a simpler system and therefore less expensive to certify or commission.
Another appealing feature of the curtains is their invisibility. "We evaluated a number of alternative methods utilizing accordion doors or doors held open on magnets," says project manager B.A. Eastwood of PHA Architects. "Due to aesthetic impacts of doors, closets and tracks, we elected to pursue a roll-down smoke curtain."
As can be seen from their many performance and design benefits listed below, fire and smoke curtains present a productive and energy efficient option to replace or supplement traditional atrium smoke management solutions.
Performance and Design Features of Curtains:
- Controls smoke through passive containment and compartmentalization rather than by an active mechanical system which controls the movement of smoke.
- Curtains are lightweight and do not require structural re-enforcement for installation.
- Employ space-saving curtain containment assemblies.
- Containing the spread of smoke makes it easier for the fire department to locate the fire.
- As a passive operating system, smoke curtains use less energy than a smoke exhaust system.
- Available in a wide range of dimensions.
- Vertical curtains can be equipped with a gravity fail-safe function that allows them to deploy even if power is lost. Horizontal curtains may have either a spring-operated closing device for smaller openings, or a supplemental power source for larger openings.
- May be selected as the only smoke management system. One curtain can replace a whole smoke exhaust system with its extensive system of vents, dampers and so forth (see Case Study 1).
- May be selected as a supplement to an exhaust system; they can increase the effectiveness of smoke and heat evacuation.
- Curtains can subdivide space served by a mechanical smoke exhaust system, thus potentially reducing the initial cost and operating cost of the system (see Case Study 2).
- Can be configured to channel smoke evacuation so as to provide safe escape routes according to code requirements.
- Vertical curtains can be rated for smoke leakage.
- Invisible when not deployed.
- Less expensive to commission or certify.
Curtain systems should work in conjunction with the other elements of the building's mechanical smoke control systems through a properly designed sequence of operations. An improperly designed sequence of operations can result in damage to some parts of the smoke control system. This is a key feature that design professionals should be aware of.
Smoke Leakage
Not all smoke curtains are required to meet Underwriters Laboratories (UL) 1784 Air Leakage Tests of Door Assemblies, only assemblies that are called on to comply with UL 1784. Smoke curtains used to channel smoke toward a smoke evacuation system have no need of UL 1784 as the intent is to channel smoke toward the evacuation system and to keep it out of other areas along the way. For vertical separation of the atrium from adjoining spaces, like the three stories that are allowed to be open to the atrium by code, there is no requirement at present for them to meet UL 1784.
UL 1784 currently only deals with vertical barriers so an equivalency may need to be developed for horizontal barriers where the designer requires the barrier to be a UL 1784-compliant smoke barrier as well as a fire barrier.
Flexible Fire-Resistance-Rated Fire Barriers
As mentioned above, a 2-hr. fire-resistance-rated fire barrier or horizontal assembly is required if there is no sprinkler system adjacent to or above the atrium. IBC also requires that the floor openings forming the atrium be separated from occupied spaces by a 1-hr. fire resistive construction or horizontal assembly.
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Time-temperature profiles for the two EU and U.S. test protocols Figure supplied by Smoke Guard, Inc. |
In the past, there have been few options for meeting these requirements apart from structural floor, door or glazed assemblies—all of which add to construction costs and take up valuable square footage. Designers have searched for solutions, even specifying heavy rolling steel doors which required building reinforcements. Flexible fire-rated curtains offer a welcome and efficient means of complying with these requirements. Case Study 1 demonstrates the use of a 20- ft x 60-ft horizontal fire-rated smoke curtain having a 2-hr. fire-resistance rating.
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Premium fire protection curtains may be fire rated up to 2 hr. This vertical system is available in large dimensions and may use fire or smoke only rated fabric depending on the application. Photo courtesy of Smoke Guard, Inc. |
While horizontal and vertical flexible fire curtain barriers with 1-hr. and 2-hr. ratings are an obvious approach to meeting these code requirements, it should be noted that flexible fire curtains are tested in accordance with UL 10C (45 minutes or greater). The UL 10C test for fire ratings of 45 minutes or greater incorporates both the Standard Time Temperature Curve for heat exposure over time and something called the hose stream test. Fire-rating reflects the amount of time the material is anticipated to remain in place to help stop the spread of fire and smoke. The hose stream test shows how the barrier will react to the thermal shock and pressure when hit by water from a fire hose.
While a 1- or 2-hr. fire-rated flexible curtain clearly meets fire-rating requirements, it cannot, being flexible, meet the hose stream test. However, the intent of the required separation is to prevent spread of fire floor-to-floor, hence the limitation that the barrier be a fire-rated barrier only. According to NFPA 288, the fire-rating standard for horizontal assemblies, i.e., a fire-rated horizontal assembly—or flexible fire-rated curtain—does not require a hose-stream test and could, with the development of an alternate methods request, meet code requirements.
Vertical fire-rated curtains may be considered equivalent to that performance intended by IBC Section 404.6 Exception 1 (see p. 99). This is the exception that allows smoke rated glass with closely spaced sprinklers to replace the fire barrier requirement for atrium separation.
In June 2009, UL issued UL 10D to outline the requirements for performing equivalent fire tests for fire-protective curtains. The standard does not require performance of a hose stream test. While not currently an official test standard, it is the most appropriate UL fire test standard for testing fire rated curtains.
Since flexible fire and smoke barriers manufactured in Europe are a new entry to the market, testing according to the American Society for Testing and Materials (ASTM) and UL requirements is, at present, incomplete for some products. However, given the relative agreement between European Standard DIN EN 1363-1 and ASTME-119 exposure temperature requirements, fire-ratings should be accepted on an equivalent basis.
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Case Study 2: Use of Horizontal and Vertical Curtains in Laboratory |
A five-floor biological laboratory and classroom building had an atrium space approximately 90 ft high that extended from the 1st to the 5th floor (Figure 2a.) The baseline control system requirements for this building under the code of record at the time of the design required maintaining the smoke layer 10 ft (now 6 ft) above the 5th floor of the atrium, for an axisymetric 5,000 Btu/s fire located at the ground floor (base) of the atrium. Using the algebraic calculations outlined in NFPA 92B and the IBC, this would have required an exhaust quantity of 350,000 cfm. The preliminary design evaluation indicated that the required mechanical smoke control system would have been cost prohibitive. An alternate design was pursued, which incorporated operable flexible horizontal and vertical curtains. Both horizontal and vertical curtains were needed to separate the 4th and 5th floors. A horizontal curtain separated the 3rd and 4th floor. As shown in Figure 2d., 1-hr. fire barrier walls were in place as a required occupancy separation between the atrium space and the adjacent spaces on the upper levels (these fire barrier walls were not strictly part of the smoke exhaust system, so they were not included in the list of smoke control components). The computer model fire dynamics simulator was used to demonstrate a tenability approach that allowed a reduction in the total exhaust quantity to 100,000 cfm for the atrium. As shown in Figure 2c., calculations showed that this would keep smoke above the 3rd floor slab for an indefinite period of time. Occupants of the 3rd floor could exit the atrium space through newly added corridor doors. Baseline Mechanical Smoke Control System
Reduced Mechanical System Enabled Using Flexible Barriers
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| Figure 2a. Section through atrium |
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| Figure 2b. Location of flexible horizontal and vertical smoke curtains. |
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| Figure 2c. Calculated smoke layer interface for 100,000 cfm |
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| Figure 2d. Mechanical smoke exhaust control system components |
An example of a project having a complex atrium geometry, where use of flexible smoke curtains helped reduce the cost of the mechanical systems required.Figure 2b. Location of flexible horizontal and vertical smoke curtains. |
INTERIOR STAIRS AND ESCALATORS
According to IBC Section 708.2, escalator openings or stairways that are not a portion of the means of egress can be protected without requiring a smoke exhaust system as would be required for an atrium.
There are exceptions however. Exception 1 states that for openings that do not exceed four stories and where the opening size does not exceed twice the horizontal protected area of the stair/escalator, a draft curtain and closely spaced sprinklers are required.
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Typical example of a smoke- and draft-compliant curtain assembly is deployed upon a signal from the local smoke detection system. Occupants can press two wall switches mounted on opposing walls to enable egress, after which the curtain will re-deploy if the system is still in alarm. Photo courtesy of Smoke Guard, Inc. |
Exception 2 states that for larger openings or stair/escalator openings exceeding four stories, the opening may be protected by approved power-operated automatic shutters at every penetrated floor, having a fire resistance rating of not less than 1.5 hours. It should be noted that this exception does not specify whether the automatic shutters should be arranged vertically at the perimeter of the opening or horizontally across the opening at the floor.
Roll down smoke and draft curtain for stairs and escalator openings meet code requirements for openings less than four stories. One typical model for polygon and rectangular enclosures is available in dimensions up to 52 ft 5-3/4-in. per side with a maximum perimeter length of 164 ft. Escalators are often fitted with controls that permit them to continue one more cycle before the last curtain comes down.
SUSTAINABILITY FACTORS
Flexible fire and smoke curtain assemblies support sustainable design in several ways. They provide the means to deliver larger daylight-filled code-compliant structures and, by occupying less valuable square footage, increase usable productive areas. They are constructed of sustainable materials, reduce energy consumption and lessen the assumed need for code-required structural and mechanical materials. Fire and smoke curtains make a great deal of sustainable sense.
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Constructed of stainless steel strengthened glass filament fabric with polyurethane and black identification stripes, this curtain is approximately 0.02 in. thick and is fire-rated up to 2 hours. Photo courtesy of Smoke Guard, Inc. |
They are also healthier. "They are ideal for the healthcare environment," says project manager Terry Russell, AIA, LEED AP, CSI, CDI, HDR Architects. "Since they are completely hidden until fully deployed, there are no hidden areas to promote hidden growth of bacteria."
Leadership in Energy and Environmental Design (LEED®)
Following are categories where flexible fire-rated and smoke curtains could contribute LEED points under New Construction and Major Renovations:
MR Credit 4: Recycled Content 1–2 Points
Intent: to increase demand for building products that incorporate recycled content materials, thereby reducing impacts resulting from extraction and processing of virgin materials.
One provider of smoke and fire curtains has calculated that the average curtain system is comprised of as much as 30 percent of recycled materials based on the sum of post-consumer recycled content plus half of the pre-consumer content. The post -consumer portion is approximately 20 percent. The pre-consumer portion is approximately 10 percent. (Note: Some systems currently offered are awaiting recycled content calculations.)
IEQ Credit 8.1: Daylight and Views—Daylight 1 Point
Intent: To provide building occupants with a connection between indoor spaces and the outdoors through the introduction of daylight and views into the regularly occupied areas of the building.
IEQ Credit 8.2: Daylight and Views—Views 1 Point
Intent: To provide building occupants a connection to the outdoors through the introduction of daylight and views into the regularly occupied areas of the building.
An atrium supports the use of daylighting strategies, which have been demonstrated to reduce operating costs and deliver energy savings through improved life cycle costs and reduced emissions.
Many architects say they are frustrated by complex and expensive smoke control requirements when they try to incorporate atrium designs into projects. Providing a simpler and less expensive smoke control solution that supports atrium designs would allow them to consider this design option for more projects.
Materials & Resources (MR) Credit 5: Regional Materials
Intent: To increase demand for building materials and products that are extracted and manufactured within the region (500-mile radius.)
Design professionals should check with manufacturers to ascertain if particular smoke and fire curtains qualify for this credit.
ID Credit 1 Innovation in Design 1–5 Points
Intent: To provide design teams and projects the opportunity to achieve exceptional performance above the requirements set by the LEED Green Building Rating System.
Smoke and fire curtains support more innovative design by allowing simpler, more economical code compliance solutions for atrium designs, large unenclosed spaces and all building areas.
Smoke and fire curtains allow elimination of enclosed occupant and service areas and equipment-dedicated space. Square footage can then be reallocated, thus increasing the economic value of the project.
Specifying simpler smoke and fire curtains also can result in significant reduction in construction materials and mechanical equipment.
CONCLUSION
Relatively new to the United States, but well-tested in Europe, fire- and smoke-rated curtains are clearly an effective answer to meeting life safety requirements of atrium designs and the open spaces surrounding interior stairs and escalators. They are less complex and less expensive than comparable smoke exhaust mechanical systems, and are the simplest system to certify or commission. They also require less energy to operate during mandatory testing and the curtain assemblies themselves are constructed from recycled materials. For atrium designs with three floors or more, architects now have the choice of having a cost-saving, simpler and more environmentally conscious smoke exhaust system by supplementing it with fire and smoke curtains.
With their economic and performance benefits, curtain systems facilitate the inclusion of atrium designs in more projects—particularly for projects which would have rejected the inclusion of an atrium because of high code compliance costs. They thus add to a building's sustainability goals by contributing to the design of more daylighting options—which have long been proven to reduce energy costs and enhance occupants' health, wellbeing and productivity. Fire and smoke curtains clearly present cost-effective and sustainable solutions that should prove very valuable.
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| Flexible fire and smoke protection systems are the focus at Smoke Guard – and have been for more than a decade. We specialize in reclaiming usable space and providing code-compliant fire and smoke curtain solutions to protect openings throughout your entire building. In many situations, such as atriums, our flexible curtain systems can replace the need for large smoke control systems and costly additional construction. www.smokeguard.com |