FAQ - Frequently Asked Questions about fire-rated glass & framing
Frequently Asked Questions
1. What are my primary options in fire-rated glass?
2. Why is the "fire hose stream" (thermal shock) test so important?
3. If 20-minute rated specially tempered glass cannot pass the fire hose stream test, are there special issues I should address?
4. My area of the country is now requiring fire-rated glazing materials to have a permanent label. That seems like a bother. Is it important?
5. I recently received product information for a fire-rated glass that indicated several limitations on use. Should this be of concern?
6. Is fire-rated glass really necessary if I use sprinklers? Can't I just use tempered or heat strengthened glass with a water "deluge" system?
7. Generally speaking, the "wireless" fire-rated glazing materials are more expensive than polished wired glass. How can I persuade my building owner that those products are worth the extra cost?
8. What are some of the latest developments that could enhance building designs?
9. Who is responsible if I've specified the wrong glass or framing, and it gets installed?
1. What are my primary options in fire-rated glass?
The glass product most often associated with fire rating is polished wired glass. It has provided fire protection for more than 100 years. In North America, wired glass is typically rated for 45 minutes in light sizes up to 9 square feet (1,296 square inches), with a 90 minute rating restricted to 100 square inches for use in fire doors. The biggest advantage of wired glass may be its low cost. However, because wired glass has low impact resistance, the 2003 International Building Code (IBC) now prohibits th use of wired glass in schools and athletic facilties. Visit www.iccsafe.org for information on the IBC and your state.
A second type of fire-rated glazing is glass ceramic. Once installed, this wireless product looks similar to ordinary window glass. Glass ceramic products, such as those in the FireLite family, provide fire ratings from 20 minutes to 3 hours, and in sizes ranging up to 24 square feet per light. Like wired glass, the glass ceramics are able to withstand the thermal shock of water thrown by sprinklers or fire hose. Glass ceramic products offer great design flexibility. Where impact safety is required, products are available that offer at least four times the impact resistance of wired glass, thus meeting Federal Standards 16CFR1201 - Category II. Products can also have beveled edges and be sandblasted for artistic effect.
Glass ceramic is also available made into insulated glass units (IGU). The IGU are made of two layers of glass with an air space in between. They can incorporate many types of float glass - clear, tinted, Low-E, mirrored, etc. Depending on which components are used, they provide not only fire protection but comply with energy codes as well. The IGU's are sometimes used for interior applications where sound reduction is desired.
Another category of fire-rated glass is classified as glass fire walls. These units are special, multi-layer assemblies that block the transfer of heat. The thicker composition of the units allows them to perform similar to a fire-rated masonry wall. Having been tested as walls, products such as Pilkington Pyrostop could be installed with proper framing from wall to wall and floor to ceiling. Incredibly, these large expanses of glass have obtained fire ratings up to 2 hours. They are typically used where architects desire (or building codes require) the blockage of heat transfer through the glass. Designers can thus provide clear, fire-rated glass "walls" that allow visibility, light, and security. These products, like wired glass and glass ceramics, withstand thermal shock. In addition, they meet high levels of impact safety as well.
A final category of fire-rated glazing is specially tempered glass. Products such as Fireglass20 only carry 20 minute ratings and -- extremely important -- they cannot withstand the thermal shock of water thrown from sprinklers or fire hose. So applications for these products are limited.
2. Why is the "fire hose stream" (thermal shock) test so important?
The fire hose stream test shows how hot glass will react when hit by water from a fire hose, or perhaps from just a sprinkler. At the same time, the test proves the durability of the window frames and other components. Most types of glazing products are unable to withstand the thermal shock of fire and water. If nearby sprinklers activate during a fire, the "shocked" glass can shatter and vacate the frame within only a few minutes, thus allowing the spread of the deadly flames and smoke. For this reason, and others, national building standards require glass in fire-rated areas to have a fire rating. All glass having a fire listing for 45 minutes or more is required to pass the fire hose
stream test.
3. If 20-minute rated specially tempered glass cannot pass the fire hose stream test, are there special issues I should address?
While we supply such a product, we are concerned that such products are frequently misused, or used in a way that will not allow them to perform properly. One need only walk through a number of commercial building projects to see that fire sprinklers are widely used as a method to suppress fires. That is good. However, one can easily imagine what will happen if water from the sprinklers impacts hot glass (fire-rated or not), that cannot withstand the thermal shock of the fire hose stream test. According to NFPA-80 (Fire doors and windows) and the 2003 IBC Section 715.3.3 (Door assemblies in corridors and smoke barriers) and Section 715.4 (Fire protection rated glazing), all glass in locations other than the 20 min. door itself (transoms, sidelites, window assemblies, etc.) require at least 45-minute ratings that can withstand the hose stream test.
4. My area of the country is now requiring fire-rated glazing materials to have a permanent label. That seems like a bother. Is it important?
Most building codes in North America now require such a label, although enforcement of such requirements lags in some areas. Fire-rated glazing materials do not all perform in a similar manner. Thus, it is important that products be supplied to the jobsite in conditions covered by their test listings. With the newer "wireless" glazing products now available, it becomes more important than ever to identify the glass as a fire-rated product, even though it may appear to be regular window glass. Most manufacturers are not only labeling the fire-rated product, they are also including information as to their fire duration listing in minutes or hours, thier impact safety rating when appropriate, and so forth.
5. I recently received product information for a fire-rated glass that indicated several limitations on use. Should this be of concern?
Architects and designers should always be wary of product "listings" that carry what appear to be unusual limitations. For example, one fire-rated glazing material on the market indicates a fire rating of "60 minutes", but then goes on to say, "This product does not meet the hose stream requirements of the test standards". Further, "This product protects from fire from one direction only. The identified face MUST be installed facing the direction of expected fire attack." Such limitations should raise red flags, and prove how important it is to thoroughly read manufacturers literature. This clearly indicates how a laboratory "listed" product may not be exactly what you thought it may be.
6. Is fire-rated glass really necessary if I use sprinklers? Can't I just use tempered or heat strengthened glass with a water "deluge" system?
Theoretically, it is possible, and one sprinkler company even promotes such a special sprinkler product. However, the likelihood of such a system working properly is questionable and is not recommended. In order for a sprinkler system to protect non fire-rated glass, it would have to activate early, bathing every inch of the glass completely and continuously. While tests at Underwriters Labs showed this could be accomplished under very specific conditions (fire starts away from the glass surface, no horizontal frame members, etc), it also proved that when conditions were not perfect, the glass can shatter and fall from the frame in less than five minutes. There are additional "real world" issues that need to be addressed with such an installation. For example, the sprinkler manufacturer's literature indicates that drapes, blinds, shutters, etc., are not allowed in front of the glass as that would prevent water from the sprinkler covering the glass. However, a stroll through most commercial structures clearly shows the use of such window covering materials is widespread.
An additional problem with the "deluge" system is that it totally relies on the perfect operation of the sprinkler system. In fact, there have been several stories in the news the last few years regarding sprinkler failures; one brand had to recall several million sprinkler heads. While sprinklers do much to save lives, they are no substitute for the use of fire-rated glazing materials. If sprinklers do not activate due to faulty manufacture, loss of water pressure, or other reasons, fire-rated glass will perform its critical function of compartmentation - with or without water from the sprinklers.
7. Generally speaking, the "wireless" fire-rated glazing materials are more expensive than polished wired glass. How can I persuade my building owner that those products are worth the extra cost?
We generally see architects and designers using the more expensive products for reasons of aesthetics and/or higher performance. The manufacturing process for the high performance wireless products are complicated, and frequently make use of expensive materials. While costs are coming down as production volumes increase, we suspect they will never reach the levels of wired glass. Interestingly, we often find the wireless products are in line with the architectural construction costs - they are just more expensive than traditional wired glass. In addition, the amount of fire-rated glazing used in most projects is rather small. Increasingly, we see architects and designers willing to use the newer products for aesthetics reasons, such as opening up entire glass walls that have high performance ratings. Characteristics such as higher fire ratings, larger glass sizes, higher impact ratings, meeting energy codes, etching and beveling, etc., are also issues. As our parents told us, "...you get what you pay for...".
8. What are some of the latest developments that could enhance building designs?
The new, wireless fire-rated products allow great flexibility in design and performance. However, as mentioned earlier, they must be installed in the appropriate fire rated framing systems. Typically, those frames are made of hollow metal steel. For many years, Europe has been using frame designs with different steel extrusions that are much more aesthetically pleasing, and in some cases, have much higher performance. Look for the introduction of narrow line fire-rated window and door frames.
9. Who is responsible if I've specified the wrong glass or framing, and it gets installed?
Potentially, everyone involved in the selection, specification, approval, or installation of products may be held liable. The building owner may look to the architect, who might point to the code officials and the glazing contractor. Code officials will say their approval has the disclaimer that it is "subject to errors and omissions". Glaziers are the glass experts, and architects rely on them for advice. If a glazier sees a problem, he needs to alert the architect about suitable alternatives. Using the excuse, "I just bid what the architect specified...", may not go far in a court of law.
When it comes to life safety in a building, everyone involved bears some responsibility to avoid making costly or dangerous mistakes. After examining the application and narrowing the option for glazing and framing materials, review an individuals product's literature in detail. Look for any special requirements, limitations or exclusions. It is important to gather all the details.