Photo © Robert Brayton
Fire-protective versus fire-resistive
Along with the general categories outlined above, it is important to understand the differences between the two classifications of fire-rated glass—fire-protective and fire-resistive—to ensure each system meets codes and properly addresses the unique safety aspects of each area of the building.
Fire-protective glass
Also known as ‘filmed ceramics,’ fire-protective glass is designed to block (or compartmentalize) smoke and flames, but not radiant heat. This means the glass will help keep the fire from spreading, but will not prevent heat-related injury to occupants. Examples of fire-protective-rated products are polished wired glass, specialty tempered glass, some intumescent laminates, and glass ceramic.
While there are fire-protective-rated products available from 60 to 180 minutes, their application is limited to door vision panels, and size limitations may apply. For 180-minute doors, fire-protective-rated products may be listed for 64,516 mm2 (100 si), although IBC does not permit any vision panel in a three-hour rated fire door. For 60- and 90-minute doors in exit enclosures and passageways, fire-protective-rated products are limited to 64,516 mm2, whether or not the building is fully sprinklered.
Additionally, fire-protective-rated glass has limited use in one-hour walls, and is not permitted altogether as sidelites, transoms, and windows in two-hour interior walls because it cannot block radiant heat. These limitations are recognized in IBC, and recent revisions to the 2012 IBC give end-users clear guidance in applying those limits.
Many fire-protective-rated glass types can provide a CPSC Category II high-impact safety rating as well.
Fire-resistive glass
Fire-resistive glass is made with multiple layers of laminated glass with an intumescent liquid in between, providing an insulative layer to not only block smoke and flames, but also provide a barrier to radiant heat. This allows building occupants to exit the building without being subjected to radiant heat burns, making it suitable for egress applications such as stairwells designed with glass walls to encourage more frequent use. The glass conforms to non-loadbearing wall requirements under ASTM E119, Standard Test Method for Fire Tests of Building Construction and Materials. Its limits in application and size only depend on the product limitations of each manufacturer.
Fire-resistive glass is required for glazed assembly openings, door vision panels, and sidelites and transoms comprising greater than 25 percent of the common wall; these areas are classified as a ‘transparent wall’ and must comply with ASTM E119. Fire-resistive glass is also required for one- and two-hour walls, 60- to 90-minute door vision panels, and 60- to 120-minute sidelites and transoms when not in exit enclosures and passageways. Examples of fire-resistive products are intumescent multilayer laminated and intumescent multilayer gel glass.
It is imperative only a tested and approved system of fire-rated glass and frame be used as a fire-resistive-rated assembly.
Additional safety features
Along with fire resistance, glass options are expanding to include protection against intrusion while maintaining the cost-effectiveness required for traditional schools and buildings. One challenge with bullet-resistant glass is it is too expensive for widespread use. One new fire-protective-rated ceramic glazing product combines protection against fire, accidental impact, ballistics, and intruders.
As an intrusion barrier, this type of material deters or delays an active shooter to help prevent an attack or slow it until first responders arrive. In bullet-resistance tests, such glazing should not shatter; in threatening situations, it should protect occupants from injuries that can result from shattered glass. More importantly, the fact the glass does not shatter will help prevent intruders from potentially gaining access through the opening. In the event of fire, the glass will also contain smoke and flames, allowing more time for occupants to escape.
In addition, the glass features a patent-pending surface polishing technology with advanced composition to create sharper, more accurate color-viewing. It has a color-rendering index (CRI) of 97.1 (out of 100), a high R96a value, and a low haze value at 0.5 percent. It is comparable to float glass in quality and lacks the orange peel effect often seen in standard fire-rated glass.
