What Is A Fire-Rated Window

A Fire-Rated Window is a tested window assembly that has proven to offer a certain degree of protection in the face of fire. That may sound like a strange task for a window and it's glass to perform.

Obviously, neither can extinguish a fire or warn a building's occupants that there's any danger. But a tested fire-rated window assembly can keep flames and smoke from spreading from one room to another. The official term for this is compartmentation, and it means that a window and it's glazing can play a vital role in restricting fire damage to a limited area.

To the casual observer, it would seem that any glazed assembly could potentially do that.. After all, fire-rated glass looks deceptively similar to its non-rated counterparts. However, in reality, most glass offers little, if any, fire protection. For instance, standard window glass will break when the temperature reaches approximately 250° F.

Tempered glass can last until about 500°F. In contrast, fire-rated glass can typically survive heat in excess of 1600° F. That's a marked difference in performance. With structural fires capable of reaching extremely high temperatures very quickly, the need for this specialty glass is easy to recognize.

To earn its stripes, fire-rated glass must pass a battery of tests established by national test standards. Independent laboratories (such as U.L.) run the tests, then assign an appropriate rating based on the results.

The ratings are time increments, reflecting the duration of testing the product endured. That duration is intended to correspond to the length of time the glass should be expected to perform reliably in a fire. So if a product has a 45 minute rating, theoretically you could count on it containing flames and smoke for the first 45 minutes of a fire.

The testing is conducted in two parts. First, our full window assembly is installed into the wall of a large furnace. Following a strict time/temperature curve, the heat in the furnace is raised to an intense level, simulating conditions in a burning building. In order to successfully pass the test, the frame, sash if applicable and glass must remain intact for the duration of the test. Cracking is allowed, provided the glass can still act as a barrier to flames and smoke.

Assuming the glass survived that portion of the test, there is a second phase required in the U.S. for a rating of 45 minutes or more. This is called the hose stream test, and it demonstrates the ability of the glass to withstand what is know as thermal shock. A fire hose with a high pressure nozzle is brought in to douse the hot glass with water at a pressure of at least 30 psi.