Passive Fire Resistance for Buildings

By Mike Hannan, UL LLC

How do I choose the right fire-rated design for a building's walls, beams, columns, floors or roof? Passive systems might not always fit your design parameters, but must be accordance with the test procedures set forth in ASTM E119 (The American Society for Testing Materials) or UL 263 (Underwriters Laboratories). Let us first define a passive fire resistance element. 
Passive fire resistance results from the use of construction materials and assemblies that can be expected to withstand exposure to fire without collapsing or exceeding a certain temperature on the side facing away from a fire. The codification of fire resistance in buildings really begins to take shape in the "Uniform Building Code 1927 Edition," which focuses on the fire resistance of buildings based on occupancy and the type of construction we are familar with today.

These days, we have a large database of tested floor assemblies that are composed of mass-produced materials. The path of least resistance is, of course, to specify a tested assembly, without any modification, for a project. Since not every combination of products and materials has been tested, invariably the architect may have to apply one of Hamathy's 10 Rules of Fire Endurance Rating and obtain approval from the code authority or enlist the aid of a recognized fire resistance engineer and obtain a detailed analysis commonly called an engineering judgment. Most often an engineering judgment is issued by the manufacturer of the product involved, a testing laboratory, a professional engineer or a fire protection engineer. The evaluator must be acceptable to the code authority. 

When should the architect begin the process of picking fire resistant materials for the passive building elements? The schematic design phase, where an architect researches zoning and building codes applicable to the project to determine the major building elements' fire rating requirements and cost implications.  

There are different approaches an architect can take when researching fire rated designs. You can go directly to the manufacturer and determine if the product is included in a tested fire rated design. In addition, testing labs have online resources to search for fire-rated designs by the name of the manufacturer.

Often, an architect won't know which manufacturer is chosen for a particular material, as many materials can be generic in nature and tested as such. In this case, some of the options include researching the tested fire resistance of the combination of these materials at a testing company like UL; reviewing IBC chapter 7, "Prescriptive Fire Resistance," or, in the case of gypsum board, checking out the Gypsum Association's "Fire Resistance Design Manual." 

What about an existing building that no longer conforms to today's passive fire resistance requirements? In some cases, previously-tested designs are retested with new products. If the products are no longer available or the manufacturer is no longer in business, the architect can work with the code authority and testing lab, perhaps via an engineering judgment. For historic buildings, researching historical records and consulting tests on archaic materials might be possible avenues to code compliance. 

After the passive fire resistance designs are identified, the information must be documented to ensure a safe and code-compliant building. It should enable a code official to easily perform a plan review. One way would be to call out each wall type with a lettered tag on the floor plans with an accompanying wall legend that describes the basic materials along with a cross reference to the testing lab data. For more complex walls, floors, roofs, columns or beams, a detail illustrating the many elements dimensionally would be the proper method of documentation. 

Click here for the full article with test questions and the form to earn 1.0 LU in HSW. 


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