The Importance of Engineering Judgments for Perimeter Fire-Containment Systems

The curtain-wall system has been common for many years and continues to be specified today, especially in new commercial high-rise constructions. These nonstructural exterior building coverings typically consist of exterior cladding made from lightweight, durable materials such as aluminum framing with vision glass infills in a combination of glass, aluminum, stone, or metal cladding spandrels.

Curtain-wall systems enable distinctive and dynamic design aesthetics while protecting the building against the elements. But as curtain-wall systems are specified, it is imperative that they are designed and installed to mitigate the risk of fire. Curtain-wall systems present a specific feature that makes them prone to spreading fires. Their installation creates a void between the edge of the fire-rated floor slabs and the nonrated curtain wall. In the event of a fire, this unprotected space at the slab edge acts as a chimney for fire and gases, helping a fire rapidly spread from floor to floor.

The void between the fire-rated floor slabs and the nonrated curtain wall is often, unfortunately, only filled with mineral wool as a way of addressing the perimeter fire-containment system. This approach is wrong and will not satisfy the requirements of a perimeter fire-containment system. To make matters more challenging, the void space is hidden from view after construction, which presents additional problems. In any case, a building that does not have an appropriately designed and properly tested system is a serious fire risk.

A recent tragedy highlights the issue. In 2017, a fire broke out in the Grenfell Tower, a 24-story residential building in West London. The fire spread rapidly through the building exterior and expanded to all four sides within just 2 hours before consuming the entire structure. Seventy-two people died.

Efforts to improve the safety of buildings for occupants can be categorizes as active or passive. Active measures are those that suppress fires. Detective systems include smoke alarms and fire sprinkler systems. Passive measures are those that utilize fire-rated systems to compartmentalize a fire and keep it from spreading. These include perimeter fire-containment systems, also referred to as perimeter firestopping. Such systems use Intertek or Underwriters Laboratories (UL) approved mineral wool curtain wall and safing insulation to provide a barrier to flame and hot gases at the perimeter void between the curtain wall and the slab edge.

The International Building Code (IBC) defines firestopping as “an assemblage consisting of a fire-resistance-rated floor, floor/ceiling, or wall assembly, or the materials or devices…installed to resist the spread of fire through the assembly for a prescribed period of time.” Thus, perimeter fire-containment systems are designed to provide as much escape time as possible for building occupants in the event of a fire.

These insulation systems serve several important functions. By blocking openings with tested and rated fire-resistant materials, these systems can help contain the fire to a single floor or room, giving building occupants time to escape. They protect buildings by preventing fire, hot gases, and toxic smoke from traveling upward into other levels through the floor slab edge and exterior assembly, or curtain wall. Firestopping also protects a portion of the curtain wall referred to as the spandrel area, which typically consists of aluminum framing and spandrel glass, stone, or aluminum so that it can retain its structural integrity for as long as possible.

On the most basic level, the 2018 IBC requires that interior fires be controlled by installing a system that has been tested to ASTM E 2307 so that it remains securely in place for the time period equal to the fire-resistance rating of the floor assembly. The fire ratings of the firestop systems must match the fire ratings of the floor assembly. In other words, a perimeter fire-containment system must be designed and tested not only to verify that it functions properly but also to ensure that its F rating is the same as the floor it is protecting.

Most curtain-wall assemblies are designed around a tested and listed third-party perimeter fire-containment system. Though these systems vary when it comes to exterior spandrel panels, heights, and locations relative to the floor, all of them share the six basic design components. These components, detailed below, are critical to achieving the published hourly rating.

1. Use mineral wool insulation. Mineral wool insulation, at the required densities and thickness, is the only tested and proven material that will provide protection to both the curtain-wall spandrel and interior joint. Of the many insulation options available, mineral wool is best suited to the challenges of perimeter fire containment, primarily because its fibers are noncombustible and products made from rock and slag have extremely high melting temperatures (upward of 2,600 degrees Fahrenheit). It is also important to utilize the mineral wool insulation that has been tested and approved by Intertek or UL per ASTM E 2307. There are variations in the chemical makeup and density of mineral wool insulation products for various applications. There are mineral wool insulation products manufactured specifically for industrial applications. Some products are made for their acoustical or thermal properties. However, just because they are mineral wool insulation does not mean that they will necessarily provide the level of fire resistance that is required in the rigorous fire-exposure tests. Manufacturers develop proprietary formulations that have been tested and certified by the third-party laboratories evaluation and have the Intertek or UL classification mark that identifies that the material was approved for use in perimeter fire-containment systems.
   

   Image courtesy of Owens Corning

   While perimeter fire-containment systems vary in the details, they all seek to create an effective seal in the joint between the unrated curtain wall and the fire-rated floor slab.

2. Provide mechanical attachment of the mineral wool insulation. Mechanical attachment is required to keep the curtain-wall insulation securely in the place. If the curtain-wall insulation falls out of place, it will result in an early failure of the joint protection. A range of fasteners may be used to attach mineral wool insulation to the curtain wall. However, the fasteners must be installed per the Intertek or UL tested system referenced as the basis of design. These systems are listed in their respective fire-resistance directories and assure that the system functions as it was designed in the event of a fire.
   

   Image courtesy of Owens Corning

   Mechanical fasteners: Mechanical attachment is required to keep the curtain-wall insulation securely in the place. If the curtain-wall insulation falls out of place, it will result in an early failure of the joint protection. A range of fasteners are available for attaching mineral wool insulation to the curtain wall. See specific UL or Intertek design for fastener requirements.

3. Provide backer reinforcement at the safe-off line. All systems require some form of reinforcement of the mineral wool insulation at the safe-off line. This helps prevent the spandrel insulation from bowing due to the compression force at the safing joint. Most listed systems reference either a 20-gauge galvanized steel T-bar, L-angle, or hat channel, but other systems may use different components to reinforce the curtain-wall insulation. Some systems use the location of the window sill transom in combination with mechanical fasteners to provide support at the safing line.

   The reinforcement also ensures a tight seal at the interior joint; if the joint is not sealed properly, the spandrel insulation will flex, creating gaps or seams where flames and gases may penetrate and potentially ignite combustibles on the floor above.

   Another common misconception is that metal panels such as aluminum or steel-back pans will provide the necessary reinforcement. However, testing has proven these panels to be a failure point at the safing line if not properly reinforced, no matter what the material.

   

   Photo courtesy of Owens Corning

   Installing backer/reinforcement: All systems require some form of reinforcement for the mineral wool insulation at the safe-off line.

4. Compression-fit mineral wool safing insulation must be installed within the void between the floor assembly and exterior curtain-wall insulation. The insulation must have the correct density and compression to create a proper seal at the interior joint. Again, the safing insulation must be tested per ASTM E 2307 and classified for use in perimeter fire-containment systems as listed in the fire-resistance directories.
   

   Photo courtesy of Owens Corning

   Installing safing: The insulation must have the correct density and compression, as well as UL or Intertek approval, to create a proper seal at the interior joint.

5. Exposed vertical aluminum framing must be protected with mineral wool insulation mullion covers. Because this detail is seen as contributing little to the performance of the assembly, this component is often removed from the system, especially if it obstructs aesthetic elements such as interior finishes or window shade pockets.
   However, these covers play a critical role by protecting the mechanical fasteners that keep the spandrel insulation in place and helping keep the exterior wall in position so that the safing joint materials continue to block fire and smoke. If this component is eliminated, it results in a shorter fail rate of the exterior curtain wall—in other words, the curtain wall that supports the fire-barrier insulation system will block fire and smoke for less time than if the proper mullion cover protection were in place.
   

   Image courtesy of Owens Corning

   Mineral wool insulation is the best choice for providing protection in perimeter fire-containment systems, floor and wall penetrations, construction joints, and other firestopping applications.

   

   Image courtesy of Owens Corning

   Mechanical wool mullion cover: These covers play a critical role by protecting the mechanical fasteners that keep the spandrel insulation in place and helping keep the exterior wall in position so that the safing joint materials continue to block fire and smoke.

6. Smoke must be prevented from passing through the safe-off area. To prevent smoke from entering the safe-off area, systems include a smoke sealant applied on top of the safing insulation on the nonexposed side of the fire-containment system.
   

   Image courtesy of Owens Corning

   Smoke barrier: To prevent smoke from entering through the safe-off area, systems include a smoke sealant applied on top of the safing insulation on the nonexposed side of the fire-containment system.

   In December 2004, faulty wiring sparked a fire on the 29th floor of the LaSalle Bank building in Chicago. The fire burned for 6 hours, but due to the presence of a perimeter fire-containment system, the fire was contained to the 29th and 30th floors.

The Importance of Engineering JUDGMENTS (EJs)

There are a multitude of possible variations in curtain-wall systems, from the mullion and transom spacing, the number of transoms, spandrel heights, floor location with respect to the sill height, and type of mounting brackets used. Design professionals have access to hundreds of tested perimeter fire-containment systems listed in third-party laboratory fire-resistance directories. These systems consist of all elements of a tested and listed perimeter fire-containment system, including the assembly into which the system is installed. Together, the assembly with the firestop system constitutes a specific and inseparable engineered unit. Firestop system designs are tested and listed by independent testing agencies such as UL and Intertek. The specific elements of each design become integral to the listing.

In reality, architectural designs rarely match these systems perfectly. Consequently, when it comes to firestopping, the design professional will almost always need to seek an engineering analysis or judgment to address any deviations in the designed system from a tested system.

An engineering judgement, or EJ, is an evaluation of the anticipated performance of a proposed firestop assembly that has not itself been fire tested. The evaluation is conducted by comparing the proposed system to listed and tested systems. The part of the building code that sanctions the use of EJs to evaluate unlisted firestop system is Section 104.11 of the International Building Code. Often referred to as “Alternative Means and Methods Request,” or AMMR, this section states that “An alternative material, design, or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, not less than the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability, and safety.”

In many cases, securing an EJ is a very common occurrence in the submittal process. The architect should be familiar with the six design criteria of perimeter fire-containment systems outlined in the previous section. But just as important as making sure that these design components are incorporated, the architect should confirm that the EJ addresses every detail of the curtain-wall construction to support the hourly fire-resistance judgment rendered. Failure to address or substantiate the variances in the actual construction as compared to the design assembly could prove disastrous in the event of a fire. We will explore how to compare the EJ to the tested and listed system in more detail later in this article. For now, let’s consider the critical components to look for in a quality EJ:

1. The EJ must be project specific and represent the project conditions being evaluated.
2. At least one third-party-tested system (evaluated to test standard ASTM E 2307 or appropriate standard based on requirement of the applicable jurisdiction) that most closely represents the project construction details must be referenced as the basis of design in order to properly evaluate the hourly fire-rating.
3. EJs must provide a complete description of the critical elements of the system and must include the tested and listed system’s design criteria that are required to make the system work. The EJ must be based on interpolation of previously tested perimeter fire-barrier systems that are similar to the conditions upon which the judgment is given.
4. An EJ should outline the critical variations from the tested assembly versus the project conditions and how each of the variables will be addressed to support the hourly performance in which the EJ has been rendered.
5. An EJ is not to be used as a way to circumvent testing new fire-containment assemblies. EJs that do not have data to interpolate and/or extrapolate, within the boundaries of good design practices of the condition in question, should initiate the need for fire testing.
6. An EJ must state that it is such and is not a tested and listed system.

In addition to the critical components highlighted above, the International Firestop Council (IFC) provides guidance on EJs in a document titled “Recommended IFC Guidelines for Evaluating Firestop Systems in Engineering Judgments.”

The Chain of Responsibility

As an architect or builder, you must be confident that your building will be as safe as possible in the event of a fire. The design professional is one link in a chain of responsibility that also includes the curtain-wall manufacturer, firestop installer, general contractor, issuer of the EJ, and firestop building inspector. Together, these professionals are responsible for making sure the perimeter fire-containment system is designed, manufactured, and installed correctly. Let’s take a closer look at these roles.

Architect

While architects are responsible for a structure’s design, oftentimes they do not specify all construction materials, let alone ensure that the specified materials are actually used in construction. Even if they do specify the materials, they may not be responsible for choosing the manufacturer. The distance between the architectural drawings and the finished building can be vast. With large-scale projects where budget is a constant concern, developers, contractors, or subcontractors may opt for less-expensive products that still meet the required performance specifications. Often, less-expensive products carry with them the potential of unintended consequences or impacts.

Architects must prepare a bid for curtain-wall manufactures. Obtaining an EJ on the designed perimeter fire-containment system from a trusted provider can help the architect and associated firm ensure that their design—and ultimately, the structure that is built according to their design—is protected in the best possible and most project-specific way. It also provides them with documentation to back up their designs.

Curtain-Wall Manufacturer

As key stakeholders, curtain-wall manufacturers should be an integral part of the complex process of determining an appropriate firestopping system for projects where their products are used. Sometimes, curtain-wall manufacturers actually install a portion of the perimeter fire-containment system within their unitized curtain-wall panels. In this instance, their responsibilities go beyond just the safing detail.

By working closely with firestop manufacturers, third-party testing labs, and fire-protection engineering firms (FPEs), curtain-wall manufacturers can help inform the decision-making process by verifying fire test data for their own products.

Curtain-wall manufacturers need to know that when their wall system is installed, any fire risks have been properly addressed with tested and approved fire-containment systems. They also need to be consulted when something unexpected comes up during installation to help ensure that the materials and products used for the firestop are appropriate for their curtain-wall systems. There are a many variables to consider, and firestopping in general is a highly challenging task, and collaboration by all stakeholders is key to designing and installing a successful firestop. However, by being an active part of the process, curtain-wall manufacturers can help whomever issues the EJ make sure that the perimeter fire-barrier systems are as safe as possible. In turn, they can be more confident about the overall fire safety of the building and thus their liability, having done their due diligence by working closely with the firestop team.

EJ Provider

It is critical to obtain an EJ from a reputable source; after all, it is this evaluation that will confirm or deny that the proposed system will perform as well as a listed and tested system. There are three entities that may provide EJs: independent laboratories such as UL and Intertek; FPEs; and firestop manufacturers. Each of these comes with benefits and limitations, which will be discussed in the next section.

General Contractor

The general contractor manages overall coordination of subcontractors and must also make sure that nothing has been improperly substituted: if a code-approved system is required, it cannot be replaced with something else.

Firestop Manufacturer

Manufacturers are experts on their products and systems, as they have invested millions of dollars in testing and often are at the leading edge of innovation in firestopping applications. Consequently, a manufacturer can and should be a key part of the team that ensures a successful and code-compliant perimeter fire-containment system. Manufacturers usually have technical experts who can consult on projects and help guide the design and installation. Manufactures can also issue EJs. Since mineral wool is the integral component and ultimately provides the fire protection, it is recommended to collaborate with the mineral wool insulation manufacturers to ensure proper installment of the curtain wall and safing insulation. Also, the mineral wool manufacturers have the most knowledge when it comes to selecting the correct mineral wool products and the performance of insulation itself.

Firestop Installer

Firestopping contractors are tasked with installing firestopping correctly so that it performs as designed. When they install a firestop, contractors typically do so to address a construction joint between two rated assemblies, or a penetration through a rated wall. They are also responsible for installing perimeter fire-containment systems. Every situation is different, and more often than not, there is not a tested and approved system that fits the unique elements of the situation. As the professionals who install a firestop, they must trust that the specifications for the system have been tested, that the materials have been approved, and that the solution is code-compliant.

One of the most effective ways for a firestop installer to gain that confidence is to work closely with the firestop manufacturer. This partnership can help ensure that a technical specialist from the manufacturer can draw on past experiences and analyze the data specific to the situation and produce a high-quality EJ.

Building Inspector

The system must be properly installed for the specific space. In the case of a perimeter fire-containment system, even the smallest gap can provide enough space for flame or hot gases to penetrate, which could mean the floor above is not protected. The building inspector must verify that the perimeter fire system has been installed properly, with all design criteria implemented into the assembly and that it meets the requirements of the building code.

There are many critical details to a successful perimeter fire-containment system. Given the important role these systems play in helping to protect buildings and allowing more time for occupants to escape, it should be apparent that the process of designing, procuring, installing, and inspecting these system must be a team effort that includes everyone from the project’s architects and construction team to the component manufacturers, installers, and inspectors. It should also be apparent that a quality EJ can help ensure that the assembly is appropriate for the project, especially when a contractor encounters unanticipated problems, or when the conditions in the field differ from the original design.

Who Can Issue EJs?

You have now learned about the critical elements that a good EJ must possess. Recall that high-quality EJs are project specific, reference a third-party tested system, comprehensively describe the variables from the referenced tested assembly, and clearly identify that they are not a tested and listed system.

Given the stakes of a noncompliant perimeter fire-containment system, it should be obvious why the EJ must be specific to the project in question. In spite of this, some might be tempted to refer to a judgment from a similar project. To avoid this dangerous possibility, be sure to verify that the EJ has been provided by one of the three parties permitted to issue an EJ. The three parties include third-party testing laboratories, FPEs, and manufacturers of firestopping systems. Though there are benefits and drawbacks to each of these, they represent the best option for a quality EJ that will accurately evaluate the proposed system.

Third-Party Fire-Testing Laboratories

Laboratories that conduct the fire testing per ASTM E 2307 test standard can provide EJs for project conditions based on the performance of the assembly of materials in a specific tested and listed system from the Fire Resistance Directories. These directories provide critical information, from firestop design and installation to guidance during inspection.

One of the primary benefits of having a third-party fire-testing laboratory provide the requested EJs is that the labs are independent and objective; their analysis is purely based on the actual test data. The labs witness the fire testing first hand; consequently, they have a solid understanding of how specific curtain-wall components and configurations perform when exposed to the fire conditions of ASTM E 2307.

While these labs can offer unbiased, data-based recommendations, they often have limited knowledge about specific product performance characteristics. This means that they can only base their EJs on their interpolation of data from specific tested and listed designs. Labs are aware of this limitation, and they often prefer that the manufacturers provide the EJ for this very reason. As we shall see, the manufacturers have more test data on the fire performance and mechanical properties of their materials. In addition to the limitations on data, third-party labs charge a fee for their engineering services, which can be a limiting factor on some projects.

Fire-Protection Engineering Firms (FPEs)

FPEs employ professional engineers who can address situations where a firestop design does not match the listed assembly or cases where an installation is different from the approved design. Engineers in this field are well versed in the relevant code requirements and use this to justify how they expect an assembly or design to perform in the event of a fire.

There are three key benefits that an FPE brings to an EJ. First, as with third-party laboratories, it can offer an independent and objective analysis that is based on the actual tested and listed assemblies. Second, it will look at the entire project from a holistic life-safety perspective, rather than just the specific fire-containment system conditions. That is, it will review and evaluate the installation of passive fire-containment features, automatic sprinkler systems, the overall design of the building, and the means of egress for building occupant safety, among many other fire-safety aspects of the project. Third, these firms typically provide EJs based on professional engineering (PE) review and approval for municipalities requiring a PE stamp on EJ letters and drawings.

There are some drawbacks to utilizing FPEs for EJs, most of which stem from their general lack of testing experience. First, they tend to have a limited knowledge of specific product performance characteristics, and therefore they can only base EJs on interpolation of data from specific listed designs. Second, as mentioned, FPE firms do not conduct the actual fire testing; this means that they may not have access to the actual fire-performance data of the tested assembly being used as the basis of design. Third, FPE firms may not be necessarily be experienced or knowledgeable about evaluating and providing EJs for specialized firestopping applications. Finally, as with third-party laboratories, FPEs charge a fee for their engineering services.

Firestop System Manufacturers

Firestop system manufacturers also can issue EJs on perimeter fire-containment systems. These companies are often at the leading edge of innovative firestopping solutions, and their work requires working closely with third-party testing laboratories to test designs, materials, and systems in different situations. They employ highly trained technical experts who often have extensive testing experience and are qualified to provide EJs for challenging situations. These experts can also provide detailed technical assistance to architects and building professionals about the manufacturer’s products and how they will perform under certain situations. Perimeter fire-containment manufacturers also work closely with code development and other relevant organizations to ensure that their products (and the information they provide for how to use them) are based in the most up-to-date evidence available. Consequently, technical representatives from a manufacturer can provide architects and builders a highly credible judgment about their product in just about any situation.

Mineral wool manufacturers offer a long list of benefits when it comes to providing EJs. For one, they manufacture the actual products that are the integral components to the fire-containment assemblies. For example, mineral wool is the key component of penetration, construction joint, and perimeter fire-containment systems. A company that manufacturers mineral wool will be experts on the material and have invested significant financial resources into the development of its firestopping products and systems. Consequently, it will have an extensive test data set (both internal and third-party tested) to reference and support its EJs. Finally, as a manufacturer, it will have detailed knowledge about its products’ durability, performance, and safety as installed in the field.

A somewhat unique benefit that manufacturers who sponsor the tested and listed systems have is that they own and have access to the fire test report. This is particularly important because the actual fire test report, rather than just the listing from the labs’ fire-resistance directory, provides all the details of the assembly and fire performance (including thermocouple data and visual observations) made throughout the duration of the test. With this information, manufacturers can identify points of failure and potential weaknesses that can be applied to project specific conditions. An EJ provider who knows the failure points of a system can in turn provide safer recommendations for the design and installation of its fire-containment products and systems.

Yet another benefit is that manufacturers also tend to have an extensive archive of test data from past years (and even past decades), along with access to third-party and internal tests that they can draw on for the special conditions of existing buildings. And finally, most manufacturers do not charge for EJs.

While the list of benefits for having a firestop manufacturer provide an EJ are many, there are some limitations to consider. First, manufacturers who have promulgated designs based off another manufacturer’s base system will not have access to the fire test report that contains the critical fire performance data needed to provide a superior quality EJ. A design without the fire test report and included data means that they may know the “what” but not the “why” about a design decision. This missing information can negatively impact an EJ.

Second, most manufacturers do not provide PE-stamped EJs and drawings. However, they can collaborate with FPEs by providing testing and product performance data so that an FPE can develop the EJ. Often, reputable manufacturers simply conduct all the engineering analysis work and submit to FPEs, on behalf of their customers, and the FPEs signs off on the manufacturers’ EJs.

Unfortunately, because of a small percentage of manufacturers providing inferior-quality EJs, certain municipalities are reluctant to accept manufacturers’ EJs. Therefore, it is critical for designers, curtain-wall manufacturers, firestopping contractors, and firestopping inspectors to have a basic understanding of fire containment and how to evaluate and identify manufacturers who produce EJs based on actual testing and sound engineering principles.

Collaboration Is Key

A key takeaway from the benefits and limitations of the various EJ providers is that in many cases, the best judgment comes from a team of specialists drawn from two or even three of the above groups. Many of the providers work together to help fill in the gaps in knowledge or experience, and stakeholders requesting an EJ can certainly request the insights of more than one provider in order to ensure that the recommendation results in the safest option for building occupants.

CODES AND STANDARDS RELEVANT TO PERIMETER FIRE-CONTAINMENT SYSTEMS

Architects and construction professionals need to know the local code requirements, and their specifications must meet those requirements. Key to achieving this is understanding the fire-performance analysis reports provided by various manufacturers.

There are specific codes and standards that are relevant to perimeter fire-containment systems. It is important to understand these requirements when designing perimeter fire-containment systems and seeking and evaluating EJs.

The 2018 IBC, Section 715.4: Exterior Curtain Wall/Floor Intersection states that, where fire resistance-rated floor or floor/ceiling assemblies are required, voids created at the intersection of the exterior curtain-wall assemblies and such floor assemblies shall be sealed with an approved system to prevent the interior spread of fire. Such systems shall be securely installed and tested in accordance with ASTM E2307 to provide an F rating for a time period not less than the fire- resistance rating of the floor assembly. Although local codes may vary, generally fire-resistance-rated floor/ceiling assemblies are required in construction types I-A, I-B, II-A, III-A, and V-A. It is important to note that even when the floor/ceiling assembly is not required to be fire-resistance rated, Section 715.4.1 still requires that the joint be sealed with an approved material or system—typically mineral wool safing insulation—to prevent or slow the interior spread of fire and hot gases between stories.

This section of the code sets forth the two principles that form the basis of effective perimeter fire-containment systems, and the criteria by which any non-tested and listed system shall be judged: that the void between the curtain wall and floor slab is properly sealed, and that the firestopping system achieves a fire rating at least as high as the rated floor. Now we will take a look at the test standards used to evaluate perimeter fire-containment systems.

ASTM Test Standards

Section 715.4 of the 2015 IBC requires that only approved perimeter fire-containment systems be used. Such systems are specifically designed and constructed to protect the perimeter of an aluminum-framed curtain wall in accordance with ASTM E2307 and the IBC. However, the IBC recognizes that every building differs in its design details, and so EJs may be required to help the project team adjust the design for the containment system to function as needed for the specific site.

Perimeter fire-containment systems are tested differently than other rated construction. ASTM E2307: Standard Test Method for Determining Fire Resistance of Perimeter Fire Barriers Using Intermediate-Scale, Multistory Test Apparatus (ISMA) is the standard designed to test and measure how well a perimeter fire-barrier system can maintain a seal and prevent interior fire from spreading as the exterior wall assembly deflects and deforms when exposed to fire. The goal is to determine how long the perimeter fire barrier will prevent the flame from penetrating through the opening between the wall assembly and the floor assembly.

The ISMA structure is a two-story furnace that subjects a perimeter fire-barrier system to fire exposure from two sides at once. It is designed to simulate a building fire in which the fire causes the windows to break, allowing the flames to escape the room of origin and impinge directly on the exterior of the curtain wall. The test focuses on the joint, which is protected by the perimeter fire-barrier system. ASTM E2307 exposes the joint from the room of origin, and the exterior wall to fire from both interior and exterior as the fire plume exits the room through a window opening.

The fire originates on the first floor, or “burner room.” A second floor is located directly above the burner and is called the observation room. An interior burner is used to start a fire in the first floor room. Soon the room fills with flame and hot gasses. Approximately 5 minutes later, the exterior burner is ignited to simulate glass breakage on the first floor, allowing for fire exposure on the outside of the building. When the vision glass on the first floor breaks, flames and hot gasses spread up the exterior face of the exterior wall, while fire and heat attach the underside of the interior joint between the floor slab and perimeter curtain wall. The objective is to prevent flames and hot gasses from entering into the room above via the interior joint. If the fire breaks through the interior joint and fire is allowed to spread to the upper story (observation room) during the test, the system will have failed to provide a fire barrier.

Although the ISMA structure cannot represent a real-life situation—the floors are approximately 7 feet tall, for example—the test does provide a reasonable expectation of how the system will perform in an actual fire.

Tested systems receive two ratings: The “F” rating is the time in hours that a firestop system will prevent passage of flames through an opening.

Although not a pass/fail criteria, the “T” rating is recorded and listed on the tested design and represents the time period, that the firestop system limits the maximum temperature rise to 325 degrees Fahrenheit (163 degrees Celsius) above its initial temperature on the non-fire side. The ratings are established for the entire assembly, including the floor, safing joint, and exterior wall system, rather than just the safing joint alone. It should be noted that the F rating performance of the safing joint is what is required in the codes. The insulation rating is comparable to the T rating.

The UL testing laboratory provides two alternative ratings. The integrity rating is comparable to the F rating, but it reflects total compartmentation evaluating the performance of both the interior joint and the ability of the system to prevent the exterior spread of fire through the vision glass openings in the curtain wall above the perimeter fire-barrier system.

The Role of the International Firestop Council (IFC)

The International Firestop Council (IFC) is a non-profit association of manufacturers and users of fire-protective materials and systems. The organization’s mission is “to promote the technology of fire containment in modern building construction through research, education programs, and the development of safety standards and code provisions.” The IFC has developed guidelines to help design professionals, construction, professionals, building inspectors and officials, and firestop contractors evaluate and use EJs.

Perimeter fire-barrier system EJs should:

1. Not be used in lieu of tested systems when tested systems are available;
2. Be issued only by a firestop manufacturer’s qualified technical personnel or in concert with the manufacturer by a knowledgeable registered professional engineer, fire-protection engineer, or independent testing agency that provides listing services for firestop systems;
3. Be based upon interpolation of previously tested firestop systems that are either sufficiently similar in nature or clearly bracket the conditions upon which the judgment is to be given. Additional knowledge and technical interpretations based upon accepted engineering principles, fire science, and fire testing guidelines (e.g., ASTM E 2032: Standard Guide for Extension of Data from Fire Endurance Tests, ULC Subject C263E: Criteria for Use in Extension of Data from Fire Endurance Tests, or ASTM E2750: Standard Guide for Extensions of Data for Penetration Seals) also may be used as further support data;
4. Be based upon full knowledge of the elements of the construction to be protected and the understanding of the probable behavior of that construction and the recommended firestop system protecting that construction if it was subjected to the appropriate standard fire test method for firestops for the rating indicated on the EJ;
5. Be limited only to specific conditions and configurations upon which the EJ was rendered and should be based upon reasonable performance expectations for the recommended firestop system under those conditions; and
6. Be accepted only for a single, specific job and project location and should not be transferred to any other job or project location without thorough and appropriate review of all aspects of the next job or location’s circumstances.

The IFC also provides basic information on how the EJ should be written and presented.

Proper perimeter fire-barrier system EJs should:

1. Be presented in appropriately descriptive written form with or without detail drawings where appropriate;
2. Clearly indicate that the recommended firestop system is an EJ;
3. Include clear directions for the installation of the recommended firestop system;
4. Include dates of issue and authorization signature as well as the issuer’s name, address, and telephone number;
5. Reference tested system(s) upon which design (EJ) is based on;
6. Identify the job name, project location, and firm EJ is issued to along with the non-standard conditions and rating supported by the EJ;
7. Have proper justification (i.e., UL, ULC, Intertek, SWRI, or other independent laboratory system(s) and or opinions); and
8. Provide complete descriptions of critical elements for the firestop configuration. These should include, but are not limited to, the type of assembly, the required fire rating, and a detailed description of the perimeter fire-containment system, including details which demonstrate its compliance with the six design principles outlined earlier in this course.

Conclusion

The design professional has the sobering responsibility of designing buildings that comply with today’s rigorous building codes and, to the greatest extent possible, protect the life safety of the occupants within. The fire risk associated with curtain-wall systems is a serious issue that must be addressed, and although tested perimeter fire-containment systems can mitigate the problem, designed systems rarely match these perfectly. Most of the time, an EJ is required to compare the designed system to a listed and tested one. The design professional must be able to obtain a high-quality EJ to ensure the safety and code compliance of the systems they design. Having a foundational understanding of what makes effective perimeter fire containment and what to look for in a quality EJ is key. Fortunately, the architect is not alone, but is part of a team for the proper design, evaluation, and installation of the perimeter fire-containment system, and, ultimately, the life safety of the buildings they collaboratively create.