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Fire 411: The Information You Need about Fire-Related Glass and Framing

The information you need about fire-rated glass and framing

By Jerry Razwick

It could be argued that no other segment of the glass industry has evolved as dramatically as fire-rated glass and framing. In the not-too-distant past, there was only one product that even classified as fire-rated: polished wired glass. The codes were simple, and the solution was straightforward.

Things have changed. Today there are many different products, codes, and applications that make installing the correct product more challenging. New developments continue to emerge on a regular basis, making it sometimes difficult to keep up with all the changes. Yet with issues of fire and life safety on the line, the need to "get it right" couldn't be more critical. And although memorizing all the options may not be feasible, gaining a basic understanding of fire-rated glass and framing is fairly straightforward.

Just what is fire-rated glass? As the name suggests, it is glass that has proven to offer a certain degree of protection when exposed to fire. That may sound like a strange task for glass to perform. Obviously, glass can't extinguish a fire or warn a building's occupants that there's any danger. But fire-rated glass can keep flames and smoke from spreading from one room to another. The official term for this is compartmentation, and it means that glass can play a vital role in restricting fire damage to a limited area.

To the casual observer, it would seem that any glass could do this. 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 understand.

To earn its stripes, fire-rated glass must pass a battery of tests established by national test standards. Independent laboratories (such as Underwriters Laboratories-U.L.) run the tests, then assign an appropriate rating based on the results. The ratings are time increments, reflecting the duration of time the glass should perform reliably in a fire. If a product has a test rating of 45 minutes, it should contain flames and smoke for at least the first 45 minutes of a fire.

The fire test is conducted in two parts. First, several pieces of the glass are installed in the wall of a large furnace. The wall might contain doors, sidelites, transoms, windows, etc. Following a strict time/temperature curve, flames and heat in the furnace are raised to an intense level, simulating conditions in a burning building. In order to successfully pass the test, the glass must remain in the frame. Cracking is allowed, provided the glass can still act as a barrier to flames and smoke.

Assuming the glass survived this portion of the test, there is a second phase required in the United States 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 known as thermal shock. A fire hose with a high-pressure nozzle is brought in to douse the hot glass and frame system with water at a pressure of at least 30 psi. Most glass will shatter because it cannot tolerate the stress of having one area hot and the other cool at the same time.

Why require the hose stream test? Because if sprinklers activate during a fire, or if fire fighters arrive with extinguishers and hoses, it is quite probable the hot glass will be exposed to water. The last thing anyone would want, at that point, would be for the glass to vacate an opening, allowing flames and smoke to spread. The hose stream thus tests the integrity of the glass, framing system, and surrounding materials.

Once a product has completed the rigorous test process, it is assigned a fire rating. Ratings generally run anywhere from 20 minutes to three hours. Building codes then dictate where those differently rated products would be allowed in a building. In general, the codes are designed to take into account how long it will take people to exit a building in the event of a fire.

As you might suspect, many of the locations (such as doors and sidelites) requiring fire-rated glass are also locations where impact safety is a concern. This used to pose a real dilemma, because product options were very limited. None of the glass that had high impact ratings could pass the fire tests, and the fire-rated glass (typically wired glass) wasn't strong enough for more than the minimum impact testing. So there often had to be a compromise. Today, however, there are several wireless glass products available that offer high levels of both fire and impact safety.

Impact ratings indicate what can be expected if someone (or something) runs into the glass. To test for impact, a 100-pound bag of lead shot is dropped against a vertically mounted piece of glass. The bag is raised to various heights for the different ratings to approximate the impact of individuals coming in contact with the glass. Afterwards, the breakage pattern of the glass is closely examined to determine whether or not it would be considered a hazard.

If you see a piece of wired glass with a label that says ANSI Z97.1, this means the glass has been tested to withstand 100 ft.-lb., similar to the impact of a small child. On the other hand, glass labeled as meeting CPSC 16 CFR 1201 (Category II) withstands 400 ft.-lb. This is similar to the impact of a fast-moving, fully-grown adult.

When you multiply the number of fire ratings with the different safety ratings, you can see that the possible combinations are impressive. But ratings alone do not distinguish the various types of fire-rated glass on the market today. Each product has its own unique characteristics, making the decision process even more complex.

The Options
Despite the variety, all fire-rated glazing falls into the following four primary categories.

Polished wired glass is far and away the most well-known product in the industry. Used for more than a century, it has a solid track record. Most codes were originally written around wired glass, because for many years it was the only glass that could pass the fire testing. Wired glass is able to pass the hose stream test, and has earned a 45-minute rating (even higher in very small doorlite sizes). Code and fire officials have been able to instantly recognize the wire mesh as a sign that glass is fire-rated.

In some instances, however, that same wire mesh has presented an undesirable "institutional" image. And people frequently and mistakenly assume the wire mesh makes the glass highly impact resistant. Truth be told, wired glass is a relatively weak glass that only meets minimal 100 ft.-lb. impact standards. With that in mind, even though wired glass is readily available and easily affordable, great care should be taken if it is installed in areas where impact safety is a concern, such as schools and other high traffic areas. Some schools, with liability cost issues in mind, use alternative high impact fire-rated glass-even if initial costs are higher.

Ceramic glass is a category of fire-rated glazing that has entered the market during the past 12 years. Ceramic has long been known for its ability to withstand heat and thermal shock. That's why today you find ceramic in everything from cook tops to car engines. Once the technology was developed to form a clear ceramic product, it didn't take long to see the potential for its use as a fire-rated glazing material.

Transparent and wireless, ceramic glass offers a distinct aesthetic advantage over wired glass. It comes in a range of make-ups that can provide many different characteristics: fire ratings up to three hours, large sizes, high impact safety ratings, sound reduction, etc. It can also be beveled, etched, or sandblasted without affecting the fire rating. It is even available in insulating glass unit make-ups that comply with energy codes for use in exterior applications.

Specially tempered glass has become a popular alternative for low-level fire safety. It is clear, wireless, and has a fairly moderate initial investment. High impact ratings make it suitable for some door applications. However, it does have some serious drawbacks that are important to note.

Unlike other fire-rated glazing products, specially tempered glass doesn't pass the hose stream test. In an actual fire, if sprinklers activate nearby and even a small amount of water hits the hot glass, it will likely fall out of its frame-quite possibly within just a few minutes. That's why it has only been able to comply with standards for a 20-minute rating. Many times this type of material has been inappropriately substituted for wired glass or other higher performance fire-rated glass, when in fact it does not carry the same fire rating. If sprinklers are anywhere near the opening, for life-safety purposes, this product should not be considered.

Transparent wall units make up the final category of fire-rated glass, and, in reality, they are in a class by themselves. They are tested and classified as "walls," even though they are made of glass. Their claim to fame is their resistance to heat transfer. Transparent wall units can actually block significant amounts of heat from transferring through the glass. A fire could be raging on one side of the glass and you could literally still place your hand on the other side. For areas such as stairwells where people could be trapped for long periods of time, or in sensitive computer areas, or where large expanses of glass are used, transparent wall panels serve a genuine need.

There are different kinds of these products on the market. Some are insulating units filled with a clear gel that turns to opaque foam during a fire. Others are made of multiple layers of glass (similar to bullet resistant glass) with in-tumescent interlayers that turn opaque during a fire. Both styles of products have ratings of up to two hours, withstand the fire hose stream test, and offer high impact safety ratings. Architects can create full glass walls incorporating these transparent wall and door units, while still retaining two-hour fire protection.

Most recently, new fire-rated framing has also entered the North American market. In contrast to the bulky wrap-around style of traditional hollow metal steel frames, the new frames offer sleek narrow profiles. Similar in appearance to aluminum storefront framing, these narrow profiles are created from steel tubes that undergo a modified extrusion process. A typical 45-minute hollow metal steel window frame section has a profile of approximately 3 by 6 inches, compared to the new framing's profile of just 3 by 2 inches for the same rating. Full-lite doors also use these profiles. As thin as they appear, the new framing systems retain tremendous strength because the profiles are formed rather than bent steel. To ensure that the best fire-rated glass and framing is chosen, it is important to have a clear picture in mind of the unique needs of a particular application. Before quoting any products, ask the following questions:

1. What is the required fire rating?
What level of fire rating is required by the building code? Does the glazing material you are considering offer that rating without special "limitations?" Architects and specifiers may not have all the facts on a particular product they request, as they do not specialize in glass. If you're concerned that a product is being specified improperly, take the initiative to investigate the product thoroughly. Too much is at risk to ignore any red flags.

2. Will the glass be subject to frequent human contact?
If so, you may be required by building codes to meet an impact safety rating in addition to your fire rating. Not all product options can offer both types of protection.

3. Are there sprinklers near the glass?
As beneficial as sprinklers are in fire protection, they can cause more harm than good if they are installed near non-rated glass, or glass that cannot pass the hose stream test. Even if it is technically correct to install a 20-minute product in a particular location, nearby sprinklers may make it advisable to choose a product that can resist thermal shock. The project drawings show where sprinkler heads are located, and a quick glance at them could help avoid serious trouble in a real fire.

4. Will heat transfer through the glass be an issue?
Where a barrier to heat is required, you will need a product that is tested as a wall unit.

5. Does the framing carry an appropriate rating?
If the glass is not installed in the appropriate frame, with an approved sealant, the fire rating will not be valid.

6. What are the size limitations?
Often a product with an adequate fire rating is selected, but in a size that exceeds the product listing. Know the specific limitations of a product.

7. Are there any unusual design requirements?
Do you want beveled glass? An etched surface? Some degree of opacity for privacy? How about energy efficiency in exterior applications? What about a security or bullet resistant product that also offers fire resistance? There are now enough specialized products on the market to meet a variety of unique situations, so don't settle for less than what you really want.

Jerry Razwick is president of Technical Glass Products, a national distributor of fire-rated glazing and framing materials such as the FireLite family of products, Pyrostop, Fireglass20, and Fireframes. A glass factory agent for the last 20 years in both foreign and domestic markets, he has served as a member of the Industry Advisory Committee for Underwriters Laboratories, Inc., and he is an active member of CSI and NGA. Considered an expert in the area of fire-rated glass and framing, he has written frequently on the subject, and he also is regularly asked to speak for architectural glass, government, and fire protection association meetings nationwide, including the annual conventions of AIA, CSI, GANA, ICBO, and NGA.

Source: Guide to Glass Codes, Glass Magazine, September 2001.