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Advanced fire-rated glass floor systems are afoot

Photos © Virginia Hamrick Photography/Glavé & Holmes Architecture

by Jeff Razwick
In 2001, the first recognized fire-rated glass floor system made headlines for its ability to expand glazing in a variety of building types, from increasing admissible daylight to supporting structural loads while defending against the spread of fire. (For more, read Michael Rae and Greg Butler’s “The Design and Installation of Glass Flooring and Fire-rated Glass Flooring,” a 2003 paper obtained from the Centre for Window and Cladding Technology. Visit www.bath.ac.uk/cwct/cladding_org/fdp/paper27.pdf.) Today, such assemblies are generating a second wave of interest for their ability to enhance performance and design goals in areas requiring a code-approved fire barrier exist between floors.

Fire-rated glass floor systems are distinguished by an ability to provide fire resistance. As defined by the 2015 International Building Code (IBC), fire resistance is, “that property of materials or their assemblies that prevents or retards the passage of excessive heat, hot gases, or flames under conditions of use.” This capability allows tested and approved fire-resistance-rated glass floor systems to satisfy codes requiring a fire barrier between floors, helping provide building occupants with a period of safe passage during a fire.

To earn a fire-resistance designation, the entire glass floor system, including the frames, glass, and component parts, must undergo and pass the fire test. During this process, the entire floor system is placed in a large furnace, loaded, and exposed to heat and flames for a given time period. The furnace’s temperature is then raised in accordance with a time-temperature curve per national standards. To pass the fire test, the system must:

  • remain intact for its given period (fire rating);
  • be free of flames on the non-fire side of the glass floor system;
  • ensure the temperature rise on the non-fire side
    of the floor system does not exceed an average of 121 C (250 F) above the ambient room temperature; and
  • bear loads up to 732 kg/m2 (150 psf) for the given time (fire rating).

Glass floor systems meeting these qualifications ensure the assembly provides both structural integrity and fire safety. Independent testing agencies, such
as Underwriters Laboratories (UL), verify these standards are upheld by evaluating and testing glass floor systems in accordance with:

  • ASTM E119, Standard Methods for Fire Tests of Building Construction and Materials;
  • National Fire Protection Association (NFPA) 251, Standard Methods of Tests of Fire Resistance of Building Construction and Materials; or
  • UL 263, Fire Tests of Building Construction and Materials.

Today, a small, but growing number of glass floor systems in the United States meet such standards. They are listed and classified with independent testing agencies with fire-resistance ratings up to two hours, and are available for both interior and exterior applications. Examples include lobby floors, atriums, corridors near exits, and other public egress areas at risk for fire progression.

Design teams initially specified these high-performing systems as a way to reclaim unusable daylighting space in areas requiring a fire barrier between floors. Increasingly, they are using it to push the limits of what is possible in areas with stringent fire and life safety requirements. Multiple projects found across the United States are already showcasing this type of assembly’s value. From coast to coast, the following installations demonstrate how design teams are using the multifunctional assembly to combine form and function in a powerful way.

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