Can Glass Be Fireproof?

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.