Given the highly technical nature of fire-rated glass, building teams may sometimes be unsure about what type of glass can withstand fire and high heat. Read below to find out more about the specifics of fire-rated glass.

Fire-proof vs. Fire-rated

Not all glass is fireproof. In fact, some might argue that there is no such thing as fireproof glass because “fireproof” is not a term the glazing and architecture industry use to categorize glass. To refer generally to glass that can withstand fire and high heat, glaziers and designers use the term “fire-rated.”

When designers specify fire-rated glass, they will choose between fire-protective and fire-resistive glass. Both options will provide varying levels and durations of protection and have specific applications where they can be used as prescribed by building codes. Fire-protective glass is a thin glazing and will defend against the spread of flames and smoke for a designated period of time and is limited to less than 25% of the aggregate length of the wall. Fire-protective materials do not meet ASTM E119 standards and so are not allowed for 2-hour applications.

Thicker than fire-protective glass, fire-resistive glass will provide the same protection in addition to blocking radiant and conductive heat and is actually classified as a “wall” rather than an opening (or window). Fire-resistive assemblies have unlimited opening sizes. Each classification of glass can offer fire protection for times that range from 20 to 180 minutes.

Types of glass that can withstand high heat

Fire-protective and fire-resistive glass may bear a deceptive similarity to non-rated glass (either standard window or tempered glass), but they can withstand much higher temperatures. Standard window glass will shatter at about 250 degrees Fahrenheit (F), and tempered glass can last to about 500 degrees F. Fire-rated glass, on the other hand, can typically survive heat over 1600 degrees F.

Fire-rated glass can withstand such high heat because it is engineered differently than non-rated glass. There are three main types of fire-protective glass: polished wired glass, specially tempered glass and glass ceramic.

• Polished wired glass has been, historically, the most well-known type of fire-protective glass. It is made by embedding a metal wire mesh into softened glass. The wire mesh helps the glass withstand heat and thermal shock but leaves an institutional appearance, is relatively weak and only meets 100ft/lb impact safety standards.
• Specially tempered glass is clear with high impact ratings but does not pass the hose stream test required for fire-ratings over 20 minutes.
• Glass ceramics are a relatively recent development in the fire-rated glass world. This type of glass shares many properties with glass and ceramic due to the controlled crystallization process that toughens it. In addition to withstanding heat and thermal shock, it can come in a variety of make-ups, can be laminated or filmed to achieve higher impact safety ratings and passes the required hose stream test. It can also achieve fire-ratings up to 3 hours. Further, glass ceramics do not have a wire mesh and support a less “institutional” feel than their wired counterparts and can be used in a wide variety of applications due to their ability to offer substantial fire protection.

There is only one type of fire-resistant glass—transparent wall units. These clear glass panels are tested as “walls” and protect against flames, smoke and heat transfer. Their glazing area can exceed 25% of the wall.

For a more detailed explanation of fire-rated glass options, please click the link to visit our FAQ page.

Receiving a fire rating

To receive its rating, fire-rated glass must pass rigorous tests conducted by an independent laboratory. The initial test is the fire test. During this test, the glass is placed in a furnace, and the temperature is raised to simulate a real fire. Test success is indicated in the length of time that the glass can withstand the fire.

In the United States, glazing rated for more than 20 minutes must also pass the hose stream test. In Canada, all glass must pass the hose stream test. Immediately following the fire test, while the glass is still hot, laboratory technicians spray the glass with a fire hose to test the integrity of the glass from the thermal shock.

Because both tests are durational and cannot possibly account for every factor of an actual fire, they cannot be used to determine if the glass is fireproof. Instead, they provide architects and glaziers distinct information about how the glass will meet fire codes and protect building occupants in the event of a fire.

The term “fire-rated glass” refers to the complete set of fire-rated glazing products available in the market. Within that wide category, designers can choose from both “fire-protective” and “fire-resistive” glazing products, depending on their project’s requirements. Fire ratings for glass, which are noted on a product’s label, range from 20 minutes to 3 hours, with the specified number corresponding to testing by independent laboratories (in accordance with fire test standards). The rating reflects the amount of time the material is anticipated to remain in place to help stop the spread of fire and smoke.

Fire-rated framing works with fire-rated glass to protect openings from the spread of fire and smoke, and in some cases, radiant and conductive heat. Because fire-rated framing and fire-rated glass work in tandem to provide compartmentation, the frames and glass must carry the same fire rating and classification (fire protective or fire resistive) in accordance with the International Building Code (IBC).

When specifying fire-rated glazing, it is crucial to understand the difference between fire-protective vs. fire-resistive glazing products (technically referred to as fire-protection rated and fire-resistance rated):

Fire protective: Fire protective means the glazing defends against the spread of flames and smoke for its designated fire rating. Such materials include traditional wired glass, glass ceramics, and specially tempered glass. Fire-protective glazing typically is suitable where building codes allow “opening-protective” assemblies, including doors, sidelites, and windows. Such glazing is available with fire ratings ranging from 20 to 180 minutes, with varying impact safety ratings. Since it does not block the transfer of radiant and conductive heat, it is subject to area and size limitations under the applicable building code (typically the International Building Code – IBC, in the U.S.) and/or authority having jurisdiction.

Fire resistive: Fire resistive glass provides the same defense against flames and smoke as fire-protective glazing, but adds further protection by blocking the transfer of radiant and conductive heat. It is tested to the stringent fire-resistance test standards for walls, including ASTM E119: Standard Test Methods for Fire Tests of Building Construction and Materials and Underwriters Laboratories (UL) 263: Fire-resistance Ratings.

Given these performance benefits, fire-resistive glazing assemblies are typically suitable where building codes require an assembly designated “fire resistant” to enclose a space. Examples include wall applications requiring a 60-minute or greater fire rating that must meet temperature-rise criteria, such as stairwells, exit access corridors, or other fire barriers dividing interior construction. Due to its heat-blocking characteristics and classification as fire-resistive wall construction, it is not restricted to 25 percent of the wall area. This provides design teams with greater flexibility when working to create light-filled and inviting spaces that meet strict fire and life safety criteria.