Hot Topic: Fire-Rated Glass

The topic of fire safety is never far from mind. For Californians, especially, wildfires are a very real occurrence, and are becoming increasingly common and severe as summers get hotter, and drier, and as “fire seasons” extend for longer periods of time.

Giroux Glass is based in California and has several offices within the state. We know that every California-based construction project includes precautions to mitigate the spread of fire, from building codes to construction materials, to regulations that dictate site locations and distances between buildings.

For glass and glazing, precautionary measures often require the use of “fire-rated” products—glazing materials designed to withstand ultra-high temperatures and extreme conditions to help contain the spread of fire. In this post, we break down the ins-and-outs of fire-rated glass: what it is, how it’s tested, how it’s used, and what different options are available on the market.

What is Fire-Rated Glass?

Fire-rated glass is specifically engineered to keep a fire as contained as possible—a fire-fighting technique known as compartmentation. It is made to withstand flames and smoke, and in certain cases, also radiant and/or conductive heat to keep harmful conditions from spreading within a building, or leaping to another structure.

There are many different kinds of fire-rated glass and glazing products on the market, and many degrees of distinction. In general, what they have in common is the ability to remain intact at much higher heat levels than their standard glass counterparts. For example, regular glass will break or shatter at 250°F. Tempered glass fares a bit better, with a limit of 500°F. Fire-rated glass, however, is typically able to withstand temperatures upwards of 1600°F before breaking to a point at which it can no longer perform its compartmentation function. Given that fires are known to reach 1,000°F in as little as five minutes, fire-rated glass can play a huge role in slowing the spread of a fire—reducing potential structural damage and allowing more time for people inside the building to evacuate safely.

Municipal codes generally require the use of fire-rated glass in large institutional buildings designed to house many people at a time. It is most commonly installed in schools and healthcare facilities, but also courthouses, public transit stations, libraries, office buildings, prisons, and certain residential buildings. Some may elect to install fire-rated glass in private residences, but this is much less common, and rarely required by code.

How it’s Evaluated

Testing involves two phases. The first phase tests for temperature endurance. First, the glass is placed in a setting that replicates its function in real life—i.e. if it will be used in a door frame, it will be installed in the same type of door during testing. Then, the entire installation is placed inside a large furnace to simulate potential real situations. The heat of the furnace is set to accelerate at the same rate and to the same degree that a room would during a large fire. If the glass remains intact with no major damage (cracks and fissures are allowed, provided fire and smoke cannot get through), it passes the test.

To secure a rating of 45 minutes or higher, glass is required to undergo a second phase of testing that measures its ability to withstand drastic temperature changes (thermal shock) and pressure. As soon as the glass reaches its time limit in the furnace, it is sprayed with cold water from a high-pressure fire hose, similar to what it would encounter in firefighting efforts. If the glass does not shatter at this point, it passes the second test and qualifies as fire-rated glass.

Impact Safety Glass

Separate from fire-rated glass, but related, is impact safety glass. Building code often requires this type of glass to be installed at areas of transit, such as doors and structural support.

There are two impact safety glass distinctions: Category 1, which can withstand 150 lbs. of force—the average force a child exerts while running, and Category 2, which holds up under 400 lbs. of force— the average amount exerted by a fast-moving adult.

Impact safety is tested by swinging a 100-lb. lead weight from various heights to test the degree of force it can withstand. As one can imagine, only an extremely durable product can withstand heat testing, pressure/thermal shock testing, and impact testing in succession. For this reason, it’s rare to see building codes require glass that is both impact-safe and fire-rated in one installation. However, a handful of glass technologies have been able to merge fire-rating with impact safety. We may see policy change as these products become more prevalent and affordable.

Categories of Fire-Rated Glass

There are two categories of fire-rated glass: fire-protective and fire resistive. Fire protective glass can contain smoke and fire, but does not prevent radiant heat from passing through its surface. Fire-resistive glass, on the other hand, can contain smoke, fire, and radiant heat emitted from a fire. Building code dictates which type of glass should be used and where.

In general, fire-protective glass is used in smaller installations, and those that do not serve any supportive or barrier functions. Fire-resistive glass is becoming more common in building codes, and is required in installations that provide support to walls or other barriers, as well as doors, large interior windows, and more. For an installation to be considered fire-resistive, both the glass and the frame it is installed in must meet fire, smoke, and heat-containing requirements.

Makes and Models

There are many different types of fire-rated glass. Here are some of the most common types on the market:

Polished Wired Glass

This is the original and most widely recognized type of fire-rated glass, though it may no longer be the strongest. Developed over a hundred years ago, it features glass with a wire mesh inset, creating a distinctive diamond pattern. Generally used for smaller applications — doors, smaller windows, glass partitions, and the like — it typically has a fire rating of 45 minutes, though smaller pieces earn higher ratings. Certain models of this glass also meet Category 1 impact safety requirements.

Ceramic Glass

Ceramic glass is the more versatile and dynamic option. The glass itself is available in ratings as high as 3 hours, and additional film applications can be added to make it meet either degree of impact safety as well. It’s clear, it’s wireless, and it can be manufactured at much larger sizes than its wired counterparts. It can also be adapted to meet a number of LEED requirements like light conservation, insulation, and more. For these features, it’s also a more expensive option.

Transparent Wall Units

These large, thick panels of layered glass are structurally strong enough to act as walls. They are available with ratings up to 2 hours, and are extremely effective in blocking the transfer of heat from one side of the panel to the other. With their heat-shielding abilities, transparent wall units are commonly installed in areas that house valuable equipment or especially sensitive materials: computer server rooms, storage facilities, archival collections in museums and libraries, etc. They also provide extra protection in areas of a facility that might be used to move or shelter large groups during emergencies: fire exit stairwells, school gyms, hospital waiting rooms, and the like.

Next Evolution

The variety of fire-rated glass products in today’s market is very different from the limited and “institutional”-looking options of the past. Each year, new products emerge that offer improved clarity, larger size capabilities, more dynamic functionality, and increased system integration than before. Such new products take fire-rated glass beyond code requirements, into a new realm of aesthetic possibilities. As it becomes more versatile and attractive, this functional glass becomes increasingly viable for a wide array of architectural applications. The result? Safer, more protected buildings all-around.