Perimeter Fire Containment and Engineering Judgments  

On June 14, 2017, just before 1 in the morning, a fire started in a kitchen on the fourth-floor apartment of the 23-story Grenfell Tower in the North Kensington neighborhood of West London. Within half an hour, the fire had traveled up the building’s exterior, and within the hour it had consumed all four sides of the structure. By 3 in the morning, all of the upper floors were engulfed in flames. According to a fire-safety engineer who reported on the event to the Grenfell Public Inquiry, the fire spread vertically and then took a lateral path along the cladding above and below the window lines and the panels between the windows.¹ Photos from the night confirm this claim.

All images courtesy of Thermafiber

Curtain wall, joint, and floor slab

Seventy-two people died in that fire. Many died because of how rapidly the blaze spread and because of the property’s “stay put” policy. This policy was in place because the building was designed to contain a fire in a single flat until firefighters could extinguish the fire, thus keeping everyone else in the building safe. Fortunately, some residents ignored the policy and evacuated the building. Others did so only after the fire commander ordered people to “make efforts to leave the building.”²

Over the course of the following day, the building continued to burn, finally dying out nearly 24 hours after it had first started, with more than 100 flats destroyed.

Nearly a year and a half later, an ongoing independent public inquiry is still looking into how and why the fire spread, as well as other aspects of the tragedy. The window and exterior cladding design and a lack of sprinklers are believed to be the primary causes of the rapid fire spread, with the continuous insulation application and cladding not being tested to NFPA 285.

The Grenfell Tower fire made issues of fire safety in newer and renovated high-rise buildings a priority; the rate at which the tower burned and the lives lost hit home for everyone in the building and fire-safety professions. And this tragedy has meant that a lot of people are looking at these buildings differently than they had before and focusing on ways to improve fire safety. This is a good thing, but it also can be extremely complicated, and it requires that everyone involved in the design and construction process—including inspections—work together and communicate their concerns to ensure that nothing gets overlooked.

One challenge has been that when it comes to high-rise fire safety, most people assume that the building has been designed and built to meet all fire codes and that the structure is safe. Architects assume this, building owners assume this, and building occupants assume that their safety is a priority. In some cases, however, where the building has been signed off as being safe, it actually is not, resulting from a feature common in buildings with curtain walls. This feature is a void, located between the fire-rated floor slabs and the edge of the nonrated curtain wall, and it is frequently overlooked in fire-safety design. Sometimes, since the void space is hidden from view after construction, it is not protected with the proper system that seals the joint or protects a portion of the exterior curtain wall in order to keep the joint material in place. Other times, a curtain wall is attached as part of a building renovation. Regardless of the situation, a building that does not have an appropriately designed and properly tested system is a serious fire risk. That unprotected space at the edge of the slab immediately acts as a chimney for fire and hot gases, and that means that the fire will easily spread from floor to floor.

Perimeter fire-barrier systems, also called perimeter containment systems or “firestops,” are designed to protect buildings from having fire, hot gases, and toxic smoke travel upward into other levels through the floor-slab edge and the exterior assembly, or curtain wall. By blocking openings and properly protecting a portion of the exterior curtain wall with tested and rated fire-resistant materials, they can help contain the fire to the room of origin and give building occupants time to escape. The tricky part is making sure that the fire-ratings of the firestop systems and sealants match the fire-ratings of other building components.

The void between the floor slab and the curtain wall tends to be anywhere from 1 to 8 inches, although in some buildings it can be more. While that space may seem insignificant in comparison to the size of the overall building, it’s important to realize that in fact is quite the opposite, especially when the building as a whole is taken into account. Take, for example, a building with a floor plate size of 200 by 200 feet, or 800 lineal feet. An unprotected joint that is 3 feet wide will create 200 square feet of open area (i.e., a “chimney”) just on one floor. The square footage of open air will be multiplied by the number of floors on the building.³ That open space not only puts the floors above at risk, but it also makes the curtain wall vulnerable from the heat of the fire, which can degrade curtain wall components. It is also important to note that smoke will travel through a small space very quickly, and so the system also must be properly sealed against smoke.

Let’s consider what may happen in a high-rise fire. As an example, a small fire starts in the kitchen in a unit on the fifth floor. If that fire is not immediately suppressed, the fire inside the building will begin to burn the interior surfaces, including the interior details of the curtain wall and perimeter fire-barrier materials. If the barrier does not hold, the flames will make their way outside of the building through broken glazing or other openings caused by the fire. Fire and hot gases will continue to travel upward, with the fire igniting any combustible components in its path. Any flames that escape through broken glazing or windows will radiate heat to other openings, which will ignite the contents and furnishings inside other building units. Exterior flames can extend as high as 15 to 20 feet above an open window, putting the floors above at risk. The gases and smoke also pose potentially lethal threats to building occupants.

On the most basic level, the 2015 International Building Code (IBC) requires the interior joint to be controlled by sealing the void between the fire-rated floor and the non-rated curtain wall so that it has a fire resistance equal to the rating of the floor. That is, a perimeter fire-containment system must be designed and tested to ensure not only that it functions properly but also that its fire rating is the same as the floor.

As we have noted, firestop insulation systems have several important functions, such as protecting the interior joint between a nonrated curtain wall and rated floor assembly from vertical fire spread and sealing against smoke. However, 95 percent of the time-tested and listed perimeter fire-containment systems don’t match the special conditions encountered on a project. Any variation from tested and listed systems has to be evaluated. This is where the engineering judgment (EJ) comes into the picture. EJs are typically short documents that include detailed drawings of a proposed firestop system for a given situation. They are the result of highly specialized review and analysis of the project conditions, and are written by specialists who work with relevant stakeholders who use new and existing fire test data to evaluate the real-world conditions of the situation and assess the fire performance of the proposed firestop assembly.

However, as Angie M. Ogino, technical services leader for Thermafiber, explains, “just having an engineering judgment in hand does not mean that the system is code compliant or would actually provide the level of performance necessary to prevent vertical fire spread and keep the occupants of the building safe. The difference is between a quality engineering judgment and a judgment that is questionable in terms of effectiveness.”

Between innovative and evolving architectural design trends and design changes during construction, projects often must be reevaluated in order to ensure that they are code compliant and that the firestop system is appropriate. This often requires close collaboration between the architect, specifiers, curtain wall manufacturer, contractor, firestop installer, and firestop inspector. This is a team effort.

Active versus Passive Fire-Containment Systems

There are three main ways to protect a building from fire and smoke, and they must be used together for optimal safety. First, there are detection systems—typically for smoke and heat/fire. Second, there are suppression systems, such as sprinklers, which will automatically turn on if a fire is detected in the space. Suppression systems are considered to be “active” because they can be turned on and off as needed, but a system needs to turn on for it to work. Third, there are compartmentation systems, or systems that help contain a fire and prevent it from spreading. These systems are considered to be a “passive ” approach in the sense that once they are properly installed, nothing else has to be done—they should be guaranteed to contain the fire to the room it originated, giving building occupants the necessary time to evacuate the building. Perimeter fire-barrier systems are part of this passive approach.

One of the most effective ways to ensure that a proposed perimeter fire-containment solution system is appropriate, particularly when there is no tested and listed system available for a particular design—and to reduce the risk of potentially catastrophic fire—is to secure an EJ that addresses every aspect of the curtain wall construction and installation. The perimeter fire-barrier manufacturer, a fire engineering firm, or an independent third party such as UL or Intertek can evaluate the design and issue an EJ, which is an expert’s interpolation of the design in reference to similar previously tested systems. The International Firestop Council (IFC) has published recommended guidelines for evaluating and providing EJs for firestopping systems. We will look at these issues more in depth in the next section.

Curtain wall with callouts

Perimeter Fire-Containment Engineering Judgments

As we noted in the previous section, a curtain wall is a complex type of a facade that does not provide any structural support and does not support any load other than its own weight. The curtain wall itself is supported by an anchor that is attached to the floor slab. Depending on the building design, a curtain wall system may include a combination of different components, such as spandrel panels of metal, glass, or stone, aluminum frames, or spandrel glass. These major components then are combined with attachment elements such as anchors and connectors, and they must be sealed with gaskets and sealants. The systems are highly complex and vary from project to project, so when it comes to fire protection, there are many different possible points of failure, and the proper protection of the spandrel and anchor that connects the curtain wall to the floor slab is often overlooked. However, fire tests and photographs of controlled burns show that insulation around these anchors is in fact very important.⁴

Curtain wall and glass on the Hearst Tower

Passive fire prevention such as perimeter fire-barrier systems rely heavily on how well the interface of the spandrel and the joint system is protected. That is, every part of the barrier system must be tested together as a system, and it must meet the ASTM E2307 standards while remaining intact and in place for the same time as the fire-rated floor assembly. The perimeter barrier system cannot be the weak link, and yet if it is installed without being properly tested, it very well may be.

Required Perimeter Fire-Barrier System Components to Successfully Achieve Hourly Rating

Fire-resistance directories, published by third-party testing laboratories such as UL and Intertek, provide details on more than 250 listed systems. However, every building has its own unique design challenges. While a listed system is a good place to start, architects, contractors, and firestop installers all need to be sure that the system used for a project includes the following required components.

1. Mineral wool insulation. 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 mineral wool have extremely high melting temperatures (upward of 2,000 degrees Fahrenheit).⁵ Components protected by mineral wool insulation are less likely to fail than components protected by insulation with a considerably lower melting point. A successful design will include mineral wool installed at the required densities and thicknesses both within the curtain wall spandrel and in the interior joint; this is the only material that has been tested and proven to protect the spandrel and interior joint.
2. Manufacturer-approved installation of the mechanical attachment of mineral wool curtain wall insulation. Different projects will include different fasteners, which will require different fastening methods. The fasteners must be installed per the tested system that is being referenced as the basis of design to make sure that the system functions as it was designed in the event of a fire. That is, the system must be ASTM E2307 tested and approved for fire, thermal, and structural movement.
3. Backer reinforcement at the safe-off line. All systems require that the mineral wool have some form of reinforcement at the safe-off line to prevent the spandrel insulation from bowing from the compression force at the safing joint. The reinforcement is also used to ensure a tight seal at the interior joint; if the joint isn’t sealed properly, the spandrel insulation will flex, which will create gaps or seams where flames and gases can get through to the floor above. Most listed systems reference either a 20-gauge galvanized steel T-bar, L-angle, or hat channel. However, other systems use different components such as additional insulation or other tested and approved components to reinforce the curtain wall insulation. Testing has shown that even steel panels will be a failure point at the safing lining if they are not properly reinforced.
4. Compression-fit mineral wool safing insulation. This must be installed within the void between the floor assembly and the exterior curtain wall insulation. The insulation must have the correct density and compression in order to properly seal at the interior joint.
5. Mineral wool insulation mullion covers. Exposed vertical aluminum framing must be covered with mineral wool insulation. This component is often seen as not contributing much to the assembly performance—and sometimes is removed from the system if it gets in the way of aesthetic elements such as interior finish or a window shade pocket. However, the covering is an essential component in that it protects the mechanical fasteners that keep the spandrel insulation in place. Moreover, in the event of a fire, it helps retain the exterior wall in position so that the safing joint materials will block fire and smoke. Without this component in place, the exterior curtain wall element will fail in less time than if the framing is protected.
6. Firestopping sealant. The final required component for a perimeter fire-containment system is that smoke must not be able to pass into the safe-off area. To prevent smoke from entering the safe-off area, smoke sealant must be applied on top of the safing insulation on the non-exposed side of the fire-containment system.

Firespan installation

Safing installation

The number of required components for a perimeter barrier system and the overall diversity of building designs mean that specifying the perfect firestop system can be challenging. After all, a firestop system is only as strong as its weakest link. Architects need to be absolutely certain that the system they use will work for their specific construction details. A major part of the problem is that third-party laboratories such as UL and Intertek simply cannot provide a fire-resistance directory that covers all of the possible component combinations from different manufacturers or evaluate each possible system. Different projects may require different configurations and ultimately different component providers, and so there may be no simple way to test each and every system.

So, what’s the solution? As an architect or builder, you absolutely need to be confident that your building will be as safe as possible in the event of a fire. As Tony Crimi, PE, MASc, outlines in The Construction Specifier, there are five keys to effective perimeter fire barriers⁶:

1. Architects and construction professionals need to know the local code requirements.
2. They also need to specify to those requirements; this means understanding all of the fire-rating reports from each manufacturer.
3. The general contractor needs to make sure that nothing has been improperly substituted: if a code-approved material is required, it cannot be replaced with something else.
4. 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 gas to get through, which could mean the floor above is not protected.
5. A firestop inspector needs to verify that the installation was done properly. That is, an inspector must ensure that the system protecting the curtain wall from an interior fire meets code requirements and ASTM E 2307.

Between the required perimeter fire-barrier components and the above five key elements to have a successful system, two things stand out: first, this process must be a team effort that includes everyone from the project’s architects and construction team to the component manufacturers, installers, and inspectors. Second, 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.

Engineering Judgments for Perimeter Fire Barriers

Every so often, a project hits a point where the original design simply does not work in the construction phase. In the case of perimeter fire barriers or firestops, this can be a difficult and expensive problem because it is too late to redesign the original solution. In this case, the project requires an alternate protection solution that will maintain the system’s integrity. This alternative recommendation is communicated through an EJ. Here a trained technical specialist or engineer can help a project team by interpolating and analyzing information about the situation and recommending alternative methods that help ensure the perimeter fire-barrier system will perform as needed.

An EJ for perimeter fire containment should meet the following five criteria.⁷ The EJ:

1. Must be project specific in that it clearly addresses the precise project conditions that are being evaluated.
2. Must reference the third-party tested system that most closely represents the project construction details as the basis of design; this is to ensure that the hourly F-rating can be properly evaluated. If possible, other tested systems should be used for comparison.
3. Must provide a complete description of the critical elements of the system, including 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 fire-barrier systems that are similar to the condition upon which the judgment is given.
4. Must NOT be used to circumvent testing new fire-containment assemblies. EJs must have good data to interpolate/extrapolate within the boundaries of good design practices in question; if they do not, this should be a red flag that fire testing is needed.
5. Must state that it is an EJ and not a tested and listed system.

What Happens When a System Fails?

Testing reports and EJs are especially important when a tested system fails. Why? Because that test information can help assessors design appropriate, fire-safe recommendations. Let’s say, for example, that a manufacturer has tested a spandrel condition that was 24 inches tall, and in the project the spandrel is 20 inches tall. During the testing, the curtain wall attachment points deteriorated only 2 inches, but that was enough for the attachment points to be compromised. In the EJ, the manufacturer may recommend that the attachment points be moved to a higher point than where it deteriorated in the actual test. Through the test—and component failure—the manufacturer can make a better recommendation for a safer system.

Who Can Issue an Engineering Judgment and How to Know if It’s High Quality

In the previous section, we discussed the elements that a quality EJ must have—namely that they are project specific, based on data from third-party testing, comprehensively described, and that they clearly identify that they are not a tested and listed system.

In most senses, the issue that the judgment must be project specific and represent the project conditions under evaluation should be obvious. After all, the repercussions of relying on a judgment that doesn’t consider the precise project could be disastrous; however, it may be a tempting time saver to refer to a judgment for an analogous project. One way to avoid this is to ensure that the judgment is provided by one of the three parties permitted to issue an EJ. The three parties include a third-party testing laboratory, a fire-protection engineering firm, and a manufacturer of the firestopping system.

Third-Party Fire-Testing Laboratories

Laboratories that conduct the fire testing per ASTM E2307 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 for different phases of the project, from firestop design and installation to inspection.

The primary benefits of having a third-party fire-testing laboratory provide the requested EJs are 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, and so they have a solid understanding of how specific curtain wall components and configurations perform when exposed to the fire conditions of ASTM E2307.

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. 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, and that can be a limiting factor on some projects.

Fire-Protection Engineering Firms

Fire-protection engineering (FPE) firms will 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 to help them assess the unique situation and provide a solution that is based on solid, technical evidence to justify how they expect an assembly or design to perform in the event of a fire.

There are three key benefits that a FPE firm brings to an EJ. First, like 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.

The four main limitations that FPE firms have in providing an EJ stem from their general lack of testing experience. First, they tend to have a limited knowledge on specific product performance characteristics, and therefore they can only base EJs on interpolation of data from specific listed designs. Second, as we mentioned, FPE firms most often don’t 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 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 about relevant situations. These companies are often the leading designers of innovative solutions, and a primary part of their work involves working closely with third-party testing laboratories to test designs, materials, and systems in different situations. Highly trained technical experts within the company have extensive testing experience and are qualified to provide EJs for challenging situations. They also can provide detailed technical assistance to architects and building professionals in regard to the manufacturer’s products and how various products 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 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.

Firestop 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, as we discussed earlier, is the preferred material in most penetration, construction joint, and perimeter fire-containment systems. A company that manufacturers mineral wool will know a lot about it, and it will have also invested significant financial resources into the development of its firestopping products and systems. Both of these points mean that they have an extensive test data set (both internal and third-party tested) to reference and support their EJs. A third point is that as a manufacturer, it will have detailed knowledge about its products’ durability, performance, and safety when it comes to actual use.

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 their 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 often 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 several limitations of which to be aware. The three most pressing challenges are that 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. That 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 the FPE, on behalf of their customers, and the FPE signs off on the manufacturer’s EJ.

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.

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 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.

Engineering Judgments and the Design Community

We have looked at the role a quality EJ for a perimeter fire-barrier system plays in the design and construction process, but how does it affect the day-to-day practice of key stakeholders such as architects, curtain wall manufacturers, firestop installers, or firestop inspectors? Each stakeholder has critical roles in ensuring that building occupants are safe in the event of fire and that their health and welfare are considered in the project design.

Trends have shown that building and fire safety professionals are increasingly aware of a building’s fire performance and the potential liability for the design community given the unfortunate event of a fire. No one wants a repeat of the Grenfell Tower fire. Therefore, it is critical to understand that an EJ does not necessarily mean that one is indemnified from any liability. However, taking steps to understand how to identify a quality EJ, as well as partnering with manufacturers who have the testing and experience to provide engineering analysis and recommendations, are two steps that can equip the designer or installer with a solution that provides the highest level of fire safety to the occupants of a building. In this section, we will discuss how a good judgment can help stakeholders feel more confident in their decision-making process as well as in terms of liability.

In the event of a high-rise fire, one of the first questions is “who was responsible?” By their very nature, high-rise projects will include more than just one person or architecture firm responsible for the design, and other stakeholders have a duty to warn building occupants about potential fire hazards. If we go back to the case of the Grenfell Tower tragedy (as of late 2018, it is still under investigation and may take years to complete), we are reminded of how complex this kind of situation is and of how long it can take to conclusively determine what went wrong. Simply put, the more complex the system, the more challenging the investigation. And no one wants to be responsible, especially if lives were lost in a fire. Quality EJs for perimeter fire barriers can help all stakeholders avoid landing in such a position by helping ensure that a system is designed for the specific project and installed according to code requirements.

San Francisco’s Museum of Modern Art (SFMOMA)

Architects

This role of the architect is highly important in the case of fire safety, where it is critical that all of the specified materials in the building are fit for their intended purpose and are actually installed on the job, not value-engineered out or substituted during construction. As we have discussed throughout this course, perimeter fire-barrier systems are in and of themselves complex, as is their installation into an already challenging building design. Where an alternative product might be acceptable for another element of the project, it most certainly is not when it comes to anything related to fire protection. Joint insulation needs to be made of mineral wool, and smoke sealants need to maintain their seal when exposed to extreme heat, and thus should be specifically designed for this purpose. More importantly, it is absolutely critical that the safing insulation and the curtain wall insulation are made from the same material and that they have equal densities; otherwise the fire will find a path through the weakest part of the system. Alternative materials and last-minute substitutions are not acceptable.

An EJ concerning the barrier from a trusted provider can help the architect and associated firm be sure that their design and structure is protected in the best possible and most project-specific way—and they will have the documentation to prove it.

Curtain Wall Manufacturers

Curtain walls are vulnerable in fires in part because of their lightweight design; often, the aluminum framing, the attachment materials, or both will fail in the event of a high-rise fire. Moreover, the lack of proper protection of the joint and the spandrel area can act as a chimney for smoke, gases, and fire. With these issues in mind, it is understandable that curtain wall manufacturers want to be confident that their products (and their liability) are protected by project-appropriate firestop systems. And quality EJs are an important part of this process.

In the previous section, we outlined the benefits and limitations of the three parties authorized to provide EJs. As a key stakeholder, curtain wall manufacturers need to become an integral part of the complex process of determining an appropriate firestopping system for projects where their products are used. Curtain wall manufacturers can help inform the decision-making process by verifying fire test data for their own products when they work closely with firestop manufacturers, third-party fire-testing labs, and FPE firms—or any feasible combination of the three.

Curtain wall manufacturers need to know that when their wall systems are 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 lot of variables to consider, and firestopping in general is a highly challenging task. However, by being an active part of the process, curtain wall manufacturers can help whoever 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 after having done the due diligence of working closely with the firestop team.

Firestop Installers

Firestop installers have a tricky task. When they install a firestop, they typically do so to address a new penetration that has been made through a fire-rated assembly or the application of the fire safing, mullion covers, and firestopping sealant. 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, the materials have been approved, and 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.

Installers often consult EJs for projects where stick wall assemblies are used. In these cases, when the curtain wall frame (mullions) and panels are installed piece by piece, the installers benefit significantly from knowing that the materials they install are code compliant.

Firestop Inspectors

Firestop inspectors go through extensive training through the IFC and often do additional training with independent testing laboratories. Still, they rely heavily on having high-quality EJs available to ensure that everything is up to code and safe. In addition to high-rise projects, firestops are now required in health-care facilities, so inspectors need to understand the nuances of the EJ and know what to look for to ensure that buildings are code compliant.

Inspectors do far more than a just physical field inspection of the building and containment system; they also closely review the associated reports and other paperwork concerning the structure, and that includes any EJs. This level of document review is typically the first step of the inspection. In addition to consulting the International Firestop Council Recommended Guidelines for Evaluating Firestop Systems in Engineering Judgments (see sidebar), they will also verify that the system used as the basis of design was tested with a nationally recognized laboratory before it was installed. These documents will help during the field-inspection process, where inspectors will be required to make their own expert judgments about the systems and installation based on the sample sites that they can review. (There is simply no way that an inspector can visually inspect every single penetration or the length of every joint and ventilation duct.)

ASTM provides additional guidance that also addresses documentation issues. For example, construction documents detailing the firestop locations and systems must be kept on-site and made available for the inspection. ASTM also recommends that empty containers, wrappings, or boxes of specified materials are also kept on-site as a reference and that the materials are labeled with the approved testing agency marks.

THE SALESFORCE TOWER

Salesforce Tower (left) during construction

During its construction, the Salesforce Tower, currently the tallest building in San Francisco, required an evaluation of the curtain wall design so that a perimeter fire-containment system could be installed. The unique design meant that there were some variances in the project, including a curved curtain wall, a wider-than-standard spandrel opening, and radius details at the corner of the building. While even one of these variances would require an expert technical evaluation, the combination meant that this project was exceptionally challenging.

As is noted throughout this article, a firestop system—or a perimeter fire-containment system—serves as the first line of defense in the event of a fire by containing the fire to the room of origin. With a project as complex as the Salesforce Tower, the architect is responsible for designing and specifying the system, and then a firestop contractor will properly install it, ensuring that it complies with the relevant building and fire codes. This is most definitely not a one-person job.

The building itself, which opened in January of this year, consists of 61 floors and 1.4 million square feet. The curved curtain wall design helps it stand out in the San Francisco skyline. It should go without saying that fire protection would be a top priority in a new high-profile building such as this, especially in the seismically active San Francisco. And yet, the unique design features meant that a perimeter fire-containment system would require a true team effort from everyone involved in the project in order to make sure that the system was appropriate. Architects, designers, contractors, firestop installers—and manufacturers and inspectors—all needed to be consulted on the project.

The manufacturer of the perimeter fire-containment system played a critical role in providing the EJs, drawing on decades of test data from its own tests as well as third-party data. As per standard practice, it confirmed its evaluation by running a parallel engineering analysis through a third-party engineering firm.

This team effort meant that the designers could be confidant that perimeter fire-containment details and project variances had been reviewed by several independent parties and that the findings were well documented. More importantly, the collaborative work helped reduce any concerns about liability as well as the building design. When firestop contractors work closely with the manufacturer, they get the important benefit of working with people who perform the tests and can then provide the detailed technical support throughout the entire construction process. At no time is a firestop contractor left without support, and for critical aspects of the design, it has access to EJs that can provide guidance.

Conclusion and Assessment

As high-rise design and development become increasingly complex with curtain walls being a standard feature, architects, building professionals, and fire-prevention specialists are paying closer attention to ensure the safety of building occupants in the event of a fire. A balanced fire-protection system that detects, actively suppresses (e.g., with sprinklers), and compartmentalizes a fire is absolutely critical to the safety of building occupants. Given the diversity of building and curtain wall designs, the passive element of this system—perimeter fire containment—is often project specific. It can take a team effort to ensure that the firestop system is appropriate.

Architects and building professionals can benefit from working closely with the technical specialists who are authorized to issue EJs, whether they are from a testing laboratory, third-party engineering firm, or firestop manufacturer. The key is to ensure that the judgment is of high quality and appropriate for the specific project considerations. Issuing organizations should have extensive fire-testing experience, highly trained individuals, and deep knowledge of how the components work together. All the major players of a project team from the architects and specifiers to the contractors, installers, and inspectors should be on the same page when it comes to designing and installing perimeter fire-containment systems.

Rebecca A. Pinkus is an independent communication consultant, writer, and editor focusing on the intersection of technology, environment, and human health. She has contributed to more than 40 continuing education courses and publications through Confluence Communications. www.confluencec.com

References

¹“Grenfell Tower: What happened.” BBC News. 18 June 2018. Web. 7 Nov. 2018.

²Ibid

³Owens Corning. “Steel Stud Perimeter Fire Containment System – ASTM E2307.” Enclosure Solutions: Technical Bulletin SS-04. May 2016. Web. 7 Nov. 2018.

⁴James C. Shriver. “High-rise perimeter protection systems reviewed.” Web. 7 Nov. 2018.

⁵Tony Crimi. “Perimeter Fire Barrier Systems: Taking a team approach to fire-safe construction.” The Construction Specifier. September 2017. Web. 7 Nov. 2018.

⁶Ibid

⁷Owens Corning. “Aluminum-Framed Curtain Wall Perimeter Fire-Containment System: ASTM E2307.” Enclosure Solutions: Technical Bulletin CW-01. Web. 7 Nov. 2018.

⁸“Recommended IFC Guidelines for Evaluating Firestop Systems in Engineering Judgments (EJs).” International Firestop Council.

Owens Corning develops, manufactures, and markets insulation, roofing, and composites. The company’s businesses use their deep expertise in materials, manufacturing, and building science to develop products and systems that save energy and improve comfort in commercial and residential buildings.