Fire-Rated Glazing

By Jeff Razwick

Today, there are more options than ever for building materials that can help block the spread of flames and smoke. Fire-rated glass, in particular, has advanced greatly in recent years. These materials play a critical role in building compartmentation, providing additional time for firefighters to arrive and helping to protect building occupants and fire service personnel until extinguishment. Understanding modern types of fire-rated glass and the tests they are required to pass can help departments work with building officials to ensure appropriate materials are installed.


No one knows better than the fire service that state and local codes increasingly allow trade-offs between fire-resistant construction assemblies and active suppression systems. While sprinklers and similar technologies are an important part of a comprehensive fire protection plan, they can, and do, fail. In the report “Reliability of Automatic Sprinkler Systems” by William E. Koffel, P.E., an analysis of National Fire Protection Association (NFPA) data found that “sprinklers fail to operate in 1 in every 6 fires that are large enough to activate a sprinkler.”

Fire-rated ceramic glazing looks like ordinary window glass but blocks flames and smoke and offers impact safety resistance. [Photo courtesy of Technical Glass Products (TGP).]

Fire-resistant materials and systems that make up compartmentation provide essential backup protection if anything goes wrong with fire detection and suppression systems. But even if the sprinklers and alarms operate perfectly, good compartmentation is a must, with fire-rated glass playing a key role. Specifically, nonfire-rated window glass that becomes hot from a fire and is impacted by water from a sprinkler or fire hose may shatter. In contrast, fire-rated glass is not susceptible to thermal shock, so sprinklers pose little problem. The glass remains intact and aids in compartmentation while the sprinklers do their work.


For decades, polished wired glass was the only fire-rated glazing product available. Although it is well suited for blocking flames and smoke, it can be broken relatively easily in the course of everyday use. Because of the potential for injury when broken, building codes in recent years have eliminated the use of wired glass in locations such as doors, glass panels next to doors (sidelites), and openings near the floor. Fortunately, advances in materials have created new options that not only resist fire but also provide other life and property safety benefits.

For example, transparent and wireless fire-rated ceramic glass comes in a range of makeups that can provide many different characteristics including fire ratings up to three hours and the highest glass impact safety ratings—CPSC 16 CFR 1201, Category II. In addition to withstanding heat from fires, ceramics can also endure thermal shock from sprinklers and fire hoses.

Transparent wall units are another advanced type of fire-rated glazing. They are tested and classified as walls and can block significant amounts of radiant and conductive heat. For areas where people could be trapped for long periods of time, such units provide critical protection. These products include insulated units filled with a clear gel that turns to an opaque foam during a fire and products using newer technology that incorporate multiple layers of glass with intumescent interlayers. Both styles offer fire ratings up to two hours, withstand thermal shock, and provide high-impact safety ratings.


To earn a fire rating, independent testing facilities, such as Underwriters Laboratories, subject samples of glass and framing to a fire test, followed by a required hose stream test. For the fire portion of the test, the lab constructs a wall assembly that contains window frames or doors holding the subject glass and then places it in a large furnace. Multiple burners simulate an intense fire on one side of the glass, and the furnace is heated in accordance with a standard time-temperature curve per NFPA test standards. The window or door assembly must remain in the wall for the duration of the test and have no flaming on the unexposed surface of the assembly and no openings.

For fire ratings of 45 minutes or longer in the United States (and for all fire ratings in Canada), the glazing must also pass a required hose stream test. Immediately after the fire test, the hot glass and framing assembly is sprayed with water from a fire hose using a standard hose size and pressure. To successfully pass the test, the glass and framing must remain intact.

Understanding fire-glass testing is especially critical since some glazing materials are labeled as having 45- and 60-minute fire ratings “without hose stream.” Although NFPA test standards and building codes are clear that the hose stream test is mandatory, building owners and architects unaware of mandatory testing requirements can be misled by conditional product listings. As mentioned in the NFPA test standards, the required hose stream test is critical to eliminating inadequate materials or constructions.

Jeff Razwick is the vice president of business development for Technical Glass Products (TGP), a supplier of fire-rated glass and framing systems. He writes frequently about the design and specification of glazing for commercial buildings.

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