The Importance of Engineering Judgments for Perimeter Fire-Containment Systems

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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.”

Image courtesy of Owens Corning

IFC guidelines for engineering judgements: In addition to the critical components highlighted above, the International Firestop Council (IFC) provides guidance on engineering judgments (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.

 

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Originally published in Architectural Record

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