Commercial and Residential Glass Installer and Manufacturer Resource

Fire-Rated Glass: Fire-Protective Vs. Fire-Resistant Glass

Oct 31, 2022 8:45:00 AM / by Greg Martell


While often used in projects for functionality and appearance, glass is also a material that keeps your property and those inside safe. 

In the event of a fire, fire-protective glass can be one of the top defenses against a quickly moving blaze. 

While providing an additional layer of protection from smoke and flames, not all fire-rated glass serves the same purpose. That’s why it’s critical to select the right fire glass when designing a project. 

Types of Fire-Rated Glass

Fire-rated glazing acts as a barrier to the spread of fire and smoke, allowing more time for occupants to escape to safety while limiting structural and property damage.

There are two types of fire-rated glass:

  • Fire-protective glass
  • Fire-resistant glass 

Fire-Protective Glass

This type of glass blocks the spread of fire and smoke and is most often ceramic, traditional wired glass, or some specially tempered glass. 

Depending on local building codes, it usually applies to “opening protective” assemblies. It can inhibit fire elements for up to 90 minutes, depending on area and size limitations.

Fire-protective glass is typically used for:

  • Windows
  • Sidelights 
  • Door windows
  • Cases
  • Fireplaces 

Fire-Resistant Glass

The main distinction with this glass is that it inhibits radiant heat in addition to containing the spread of fire and smoke. This extra protection is achieved by creating multi-laminates, which incorporate layers of glass and fire-resistant interlayers. 

It’s suitable when local building codes require a fire-resistant assembly to enclose a particular space. This might include stairwells and exit corridors that require a 60-plus-minute restraint time. The temperature on the non-fire side should not exceed 250° F above the surrounding temperature.

Fire-resistant glass is installed in:

  • Doors
  • Windows
  • Walls 
  • Stairwell enclosures
  • Elevator cores
  • Exit access corridors

Testing and Ratings for Fire Glazing

Fire-rated glass goes through a rigorous testing process to receive its designation.  

Based on the results, the glass is assigned a rating that reflects the length of time the glass is expected to reliably perform during a fire. Typical ratings are:  

  • 20 minutes
  • 45 minutes
  • 60 minutes
  • 90 minutes
  • 120 minutes

A glass with a 60-minute rating, for example, would be expected to withstand a blaze for an hour without breaking. In extreme cases, glass might be able to achieve a 3-hour rating. Testing to achieve these ratings is conducted in two parts:

  • Fire Testing: The glass is heated inside a furnace at temperatures of up to 1,700° F to simulate actual fire conditions. It’s tested for how long it can stay intact without breaking. Cracking is acceptable as long as glass can still act as a barrier to the flames and smoke.
  • Hose Stream Test: A second test is required to achieve a rating of 45 minutes or more. This test gauges the ability of glass to withstand the thermal shock of having one side exposed to the fire and the other to water from a fire hose with a pressure of at least 20 psi.

Is Tempered Glass Heat-Proof?

For certain applications, commercial tempered glass does provide low levels of fire protection. It’s not ideal for heavy-duty applications.

Standard window glass might break at a temperature of around 250° F, while tempered glass can last until 500° F or so. While these temperatures are nowhere near the intensity of a full-blown fire, tempered glass is a cost-effective alternative for lower-temperature applications such as fireplace hearths or wood stove doors.

Ceramic glass also provides a greater level of heat resistance when used in a fireplace hearth or a wood stove door. It’s important to note while ceramic glass may be used as a barrier against heat, it does not undergo the same testing or receive the same labeling as true fire-rated glass.

Choosing the Right Fire-Rated Glass

The choice of which high heat resistant glass to use for your project comes down to the Three A’s:

  • Aesthetics
  • Application
  • Authenticity 

But the most important requirement for your fire-rated glass is to ensure it’s in compliance with local fire codes. 

A high level of communication is needed between the architect, designer, engineer, and glass manufacturer regarding glass specifications. A skilled glass vendor can then create high-quality glass that provides the ultimate peace of mind.

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Topics: Fire Rated Glass

Written by Greg Martell