FIRE-RATED GLASS & FRAMING SYSTEMS: New developments may change the way you specify them
By Jerry Razwick, Technical Glass Products
Not too long ago, there wouldn't have been any need for an article about specifying fire-rated glass. There was really only one choice: polished wired glass. In fact, building codes and standards created their performance criteria around the capabilities of wired glass, as no other glass product at that early time offered an acceptable level of fire protection.
Today, the situation has changed dramatically. Not only do several products perform as well as wired glass in fire situations, most substantially surpass it. Taking advantage of the latest technologies and production methods, manufacturers have introduced wireless glass products and framing systems that combine a variety of features to meet a wide range of needs.
It opens up an entirely new way of thinking about fire-rated products. Design and performance considerations can now drive the decision, along with code compliance. The challenge for specifiers in this new environment is how to stay informed about the numerous options available. With issues of life safety and liability on the line, specifying the correct glass and framing system is essential.
Defining Fire-Rated Glass
Generally speaking, glass classified as fire-rated has two primary functions. First, it must provide reliable "compartmentation" during a fire. In other words, the glass must act as a barrier to the deadly flames and smoke so they do not spread to other areas of a building.
A second function of fire-rated glass is to allow visibility. A solid wall might provide compartmentation, but it also prevents people from seeing what is on the other side. Fire-rated glass opens up an area for lighting, security and aesthetic reasons.
Meeting those job descriptions is easier said than done. Ordinary window glass will shatter, explode or melt out of the frame within only a few minutes of direct exposure to a fire. In contrast, fire-rated glass products have a different composition or make-up that help them remain in place under the stresses of a fire.
For glass to be considered fire-rated, it must undergo rigorous testing in an independent laboratory (such as Underwriters Laboratories). The testing consists of two parts. In the first phase, large pieces of the glass are installed in a test furnace. Following a strict time/temperature curve, the heat of the furnace is steadily raised above 1600� F, with flames directly on the glass surface, to simulate actual fire conditions in a building. As a point of comparison, ordinary window glass breaks at approximately 250� F. The furnace burns for a set duration of time, which is then used to determine the rating the glass will be given. Depending on the type of glass product, fire ratings from 20 minutes to 3 hours may be achieved.
For a rating of 45 minutes or greater, glass must endure a second trial, called the fire "hose stream test." This exercise measures how well the hot glass withstands the thermal shock of being hit by water. Most hot glass cannot survive this test and will break as soon as any amount of water hits it. (That's why the use of sprinkler "deluge" systems with non-rated glass may be very risky. Further, if drapes or blinds are used in the window openings, as is often the case, the sprinkler water may never reach the glass it is supposed to protect.) The hose stream test is critical, because if water from a sprinkler, fire extinguisher or fire hose causes glass to vacate an opening during a fire, compartmentation is lost - nothing is left to prevent the spread of flames and smoke. Using fire-rated glazing materials in conjunction with sprinkler systems may offer the best possible protection. If the sprinklers fail for any reason, as is sometimes the case, the fire-rated glass will still perform its vital function.
In some applications, glass may need to act as a barrier to heat transfer in addition to flames and smoke. For instance, in areas such as stairwells, where people might become trapped for a long period of time during a fire, it is important to keep the temperature at a tolerable level until they can escape or be rescued. The same need may exist in rooms where intense heat would cause serious property damage, such as computer labs. Sometimes design considerations call for glass to fill more than 25% of the rated wall area. These special situations require a glass and frame system that is actually tested as a solid barrier wall.
Multi-Talented Products
Specifying fire-rated glazing becomes more complex when considerations in addition to fire become a factor. Since fires are relatively rare occurrences, fire-rated glass spends most of its time functioning as any "normal" window glass would. As such, there may be additional performance criteria that are equally important.
For example, in a school hallway, it is more likely that glass will need to resist the physical impact of fast moving bodies than it will a fire. Accordingly, some manufacturers have developed fire-rated glass that offers impact safety protection at the same high levels of tempered or laminated glass. These products typically offer at least four times the impact resistance of the comparatively fragile wired glass, and may substantially reduce liability in high activity areas such as schools and hospitals.
Although such high performance products initially cost more than wired glass, some architects and designers are willing to pay for increased life safety considerations and reduced exposure to litigation over the life of the building - which may be 50 years or more.
Beyond that, design considerations may call for large glass lites, beveled edges, obscured surfaces or glass that can be etched with a corporate logo. Other locations may require a product that meets energy codes, or glass that offers one-way viewing. Today's fire-rated glass products can provide you with any of the above, and more. Whatever the specific requirements of a given application, chances are you no longer need to compromise to achieve an end result that is aesthetically pleasing and compliant with all relevant codes.
Categorizing the Options
Despite the array of choices and characteristics, all the products currently available in North America can be grouped into four basic categories: Specially tempered glass, polished wired glass, ceramics and transparent wall units.
Specially tempered glass offers a limited degree of fire protection: It carries a 20 minute fire rating and meets the impact safety standard CPSC 16CFR1201 (Cat. II). However, specially tempered glass products cannot withstand the hose stream test. As a result, specially tempered glass is not recommended for locations near sprinklers. Most building codes restrict the use of 20 minute fire-rated glass to doors in a 60 minute corridor. The present draft of the ICC adopts a similar stance, which means that the applications for specially tempered glass may continue to diminish in the future.
As already mentioned, polished wired glass was the first fire-rated glazing material, and it has been the "workhorse" of the industry. As a 45 minute rated product, wired glass can pass the hose stream test. However, contrary to popular belief, wired glass is not a particularly strong product, typically offering only 25% of the impact resistance of standard tempered or laminated glass. Historically it has been given an "exemption" from meeting certain impact safety standards due to its position as a fire rated glass. With the move toward a national building code and the introduction of high performance fire and impact rated products, the exemption may be removed in the future. In the meantime, caution should be used to avoid specifying wired glass in settings where human impact is a concern.
One of the more versatile fire-rated glass product categories is technically not even glass. Transparent ceramics have been developed to take advantage of that material's extremely high resistance to heat and thermal shock. Ceramic products in large sizes now offer high impact and fire safety, and can be incorporated into IGU's (insulated glass units). The IGU's can be used in exterior windows to meet fire and energy codes; or in any window and door location to reduce sound transmission. Visually, ceramics offer the advantage of being clear and wireless for high profile locations such as lobbies and corporate offices. With fire ratings from 20 minutes to 3 hours, ceramics offer great flexibility and performance.
Transparent wall units make up the final classification of fire-rated glass. Tested and listed as "walls," these units carry fire ratings up to 2 hours and make it possible to have floor-to-ceiling and wall-to-wall glass. They pass the fire hose stream test as well as high impact safety tests. The primary characteristic of transparent wall units is the ability to block the transfer of conductive and radiant heat. While there are different product make-ups to achieve this effect, all utilize an inert material which turns to foam during a fire. Remarkably, even when an intense fire is on one side of the glass, the opposite surface stays cool enough to touch. Because it is tested as a barrier wall, designers are no longer restricted to using glass in only 25% of a fire rated wall.
New Choices in Framing
As rapidly as changes have come in fire-rated glazing, fire-rated framing has remained relatively static. The vast majority of applications have utilized standard hollow metal steel frames that carry ratings limited to the listing of the traditional glazing products. However, as demand has increased for more aesthetic choices and larger glass surfaces, new options have emerged.
For years, European architects have been able to utilize framing with much narrower profiles. Similar in appearance to aluminum storefront framing, these steel profiles are nearly "extruded" from steel tubes. By way of comparison, a typical hollow metal steel window frame section, with a 45 minute rating, has a profile of approximately 3" x 6". A comparable European frame may have a profile of 3" x 3". This provides a much narrower sightline for the architect. In spite of the sleek appearance, tremendous strength is retained in these new systems as the profiles are formed rather than bent steel. Now that these narrow profile systems have been tested to North American standards, they are beginning to be fabricated in the United States. To date, at least two new frame systems are available.
One line carries ratings of 20 and 45 minutes and, similar to hollow metal steel frames, is not a barrier to heat transfer. It is typically used with "thin" fire rated products such as wired glass or ceramics, or insulated glass units. Because the narrow profile systems are so visually appealing, they are sometimes used throughout a building, in fire and non-fire rated areas alike, to achieve a consistent appearance.
The other system, making use of an insulated steel unitized profile, has achieved ratings from 60 minutes to 2 hours. Acting as a barrier to heat transfer, these frames and tested transparent panels allow an unrestricted amount of glass in walls.
Both systems allow for full lite doors, opening new possibilities for designers who wish to use large expanses of glass in a project where walls required ratings from 20 minutes up to 2 hours.
This is a far cry from the days when fire-rated glass meant settling for the institutional look of wired glass. Now, with so many new options and so few restrictions, choices can actually be driven by what the architect or designer visualizes.
Questions to Ask
There are a number of key questions that can help make the specification process go more smoothly:
1. What is the fire rating required?
20, 45, 60, 90 minutes or 2 hours? This rating applies to both the glass and framing. For a "system" to meet building code requirements, all components must have been tested and satisfy the appropriate rating. It is a good idea to check a product's test listings carefully, because sometimes there are restrictions. For example, if you see a "listing" or product literature for 60 minute rated glazing material that states, "...does not meet the hose stream test requirements of the test standards," that should be a big warning flag. Such a "provisional" listing will shift liability to your shoulders for using a non-complying product.
2. Is impact safety a concern?
Building codes require glass installed in "hazardous locations" (doors, sidelites, glass near the floor, etc.) to meet impact safety test requirements. Fire-rated glass used in those locations should also meet impact standards. If the glazed opening is in a high traffic area, you may want to use products that offer higher impact resistance than the minimal levels of wired glass.
3. What about heat transfer?
If the location needs to be protected from heat transfer as well as flames and smoke, look for glass and frame "systems" that have been tested as a barrier wall.
4. In addition to a fire rating, what other performance needs do you require?
Do you need large glass sizes, energy code compliance, one-way viewing? What about beveled, sandblasted or pattern glass? Painted or stainless steel frames? Nearly any appearance is possible in fire-rated glass and frames, so there are few reasons to change your design based on limited products availability.
5. Is my product information current?
The field of fire-rated glass and framing continues to change rapidly. Even during the preparation of this article, one manufacturer successfully tested a fire and security rated glass and frame system. This will open up design possibilities that previously sacrificed fire safety in order to assure security - and vice versa. Now, both critical issues can be addressed at one time. Because these products continue to evolve, make sure you talk with your supplier prior to specifying any fire-rated glass or framing to ensure that you are basing your decision on the most current data.
Fire-rated glazing systems have gone from being a nuisance to being a positive design enhancement. Rather than simply specifying fire-rated glass and framing to satisfy code requirements, today you can hand-pick the performance level and aesthetic characteristics that best suit your project. The future of fire safety is looking better all the time.
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