Volume 39, Issue 3,
The Turning Kaleidoscope
Fire-Rated Glazing Continues to Evolve
by Jerry Razwick
In 1816, physicist Sir David Brewster produced a small hand-held tube that housed
mirrors and small bits of loose colored glass. As the tube was turned, the position of the glass shifted, resulting in changing patterns of color and light. The kaleidoscope was born.
Overnight, it became a favorite pastime of the masses. People were fascinated by this new marvel. It was like nothing they had ever seen before. As they looked into the tube, the images could be both beautiful and disorienting, since the reflections changed constantly and made it impossible to know what one was really looking at.
In many ways, the field of fire-rated glass and framing has become a kaleidoscope of sorts. An explosion of innovative new products has created a dazzling array of options that are a wonder to behold.
At the same time, that array can be somewhat disorienting. As wonderful as it is to have more alternatives, making sense of the choices now available is challenging.
Of course, anyone who has taken apart a kaleidoscope can tell you that it isn’t nearly as mysterious when you examine the pieces individually. Similarly, by breaking down the pieces that have shaped the growth of the fire-rated glass and framing market, we can gain new clarity and understanding of what is happening in the industry.
There’s an old saying that goes “We did then what we knew how. Now that we know better, we’ll do better.” As an industry, we know a great deal more now about the relationship of fire and glass than we did when the topic first became an issue. And we’re producing much better materials as a result.
It was more than a century ago that wired glass was developed, offering the first type of fire protection in glazing. The idea of incorporating wire mesh into glass was ingenious. In those days, no glass product could withstand the intense heat of a fire. Even the glass in wired glass couldn’t, but the network of wires served to hold the glass in place as it slumped, maintaining a barrier to flames and smoke.
When testing became formalized, the limits of wired glass were clearly identified. The size of the glass typically has to be kept less than 9 square feet (1,296 square inches) in order for the wires to work. And although it gives an appearance of security and strength, wired glass cannot resist much in the way of impact. When broken, the wires can create dangerous snags that could cause injury.
Unfortunately, for many years, no other glass could offer any type of fire protection. Architects had to make a decision as to which type of performance they needed most from their glass. Code standards made compromises to allow wired glass in situations where fire safety was an issue in what would normally be areas that required impact safety products.
Clearly, there was room for improvement. But it would need to come from non-traditional thinking about glass. If the standard glazing materials being produced were incapable of delivering the desired capabilities, new avenues would need to be explored.
It was at this point that ceramics were introduced. Long known for their ability to tolerate extremely high temperatures, ceramics had begun to be used in everything from cook tops to car engines. Ceramics don’t expand and contract the way glass does, making it an extremely stable material in a fire. And, as technology made it possible to have transparent and clear ceramics, the potential applications were apparent.
What’s more, ceramics can be specified in much larger sizes than wired glass (up to 23 square feet). They also can endure the heat for longer periods of time, earning fire ratings up to three hours in doors (90 minutes in other applications). In its laminated form, ceramics also offer high impact safety protection, meeting CPSC 16CFR1201 (Category II).
Another category of glazing that changed the landscape can be classified as glass firewalls. Again, these products take an entirely different direction than ordinary glass to achieve greater results. While there are several different make-ups available, these products operate on essentially the same principle. Multiple layers of glass sandwich an interlayer or thick gel. During a fire, the interlayer or gel turns to foam, blocking heat as well as the spread of fire.
These glass firewalls are such tremendous performers that they carry the same type of rating as a solid barrier wall. A fire can be raging on one side and someone can walk up and touch the opposite surface of the glass without being burned. This heat-blocking characteristic enables glass firewalls to be used without size restrictions, offering the design possibility of wall-to-wall and floor-to-ceiling glass.
Framing has also evolved. Hollow metal steel framing used to be the nearly universal choice when fire ratings were required. The bulky, wrap-around look wasn’t always desirable, but it was functional. Today, a new wave of framing gives the choice of narrow profile steel that is similar in appearance to aluminum storefront material. And when steel is not appropriate, genuine hardwood framing now comes with fire ratings of 45 minutes or more.
Another factor that has added color to the fire-rated kaleidoscope has been a changing market. Needs have evolved significantly over the past few decades. In many applications today, architects are looking for a product that is not just fire-rated. Most often they want a product that is fire-rated and _________.
That blank could be filled with any variety of requirements. For example, in high-density areas where construction is close to property lines codes may require glazing that is fire-rated. However, that same glass will also need to comply with energy codes. It may also need special tinting or coatings to be consistent with other faces of the building. Such complex demands are now common. Products have to cross-train and function on multiple levels.
One area of renewed interest has been security. Concerns about terrorism, vandalism and burglary have focused attention on the need for safer glass. In the past, glass-clad polycarbonate has been the frontrunner for these types of jobs. However, some bullet-resistant glazing is highly flammable. Providing protection from one threat can create a new problem altogether.
Recent testing of glass firewalls now makes it possible to specify a fire-rated material with a bullet resistance rating of level III (capable of stopping a .44 magnum bullet). Even higher ratings are available when the glass firewall is made into an insulating glass unit (IGU).
IGUs have opened up the floodgates in fire-rated glazing, since they allow nearly any type of glass to be used as the second layer in the unit. And fire-rated IGUs have even been tested with blinds in the middle, adding one more option to the mix. Add to that the availability of curtainwall construction with ratings up to two hours, and you can see the performance capabilities are becoming endless.
If product technology and market changes have fueled innovation, code changes have capitalized on that innovation, incorporating it into new standards to make buildings safer. Now that more options are available, the codes can raise the bar and require a higher level of performance.
For example, the 2003 International Building Code (IBC) has reversed the long-held exemption for wired glass in K-12 schools, day care centers and athletic facilities. All glass products now used in hazardous fire-rated areas of those facilities must meet CPSC 16CFR1201—something traditional wired glass cannot do. Since fire-rated ceramics can be stocked and cut in the field and are available with high fire- and impact-ratings, they are becoming a ready substitute.
One drawback to the new IBC code is that it allows more sprinkler trade-offs than in the past. In other words, in locations that would normally require fire-rated glass, walls and ceilings, architects are sometimes allowed to substitute unrated products when sprinklers are installed in an area.
This may be setting a dangerous precedent. Dr. Gene Corley, the team leader for the WTC Building Performance study, came to the conclusion that sprinklers in the World Trade Center failed to activate, but that fire-resistant construction delayed the collapse of the towers and allowed occupants to escape. He stated, “Fire safety cannot be an either/or proposition. Buildings for which sprinklers are appropriate should also have fire-resistant construction for better fire protection. Anything less puts occupants and emergency responders at risk and is unacceptable.” (Building Design & Construction, January 2004)
The new kaleidoscope of options available can make it more challenging to select the appropriate product. Yet getting it right is critical, particularly with life-safety issues on the line.
There have never been more exciting opportunities in the area of fire-rated glass and framing. As the market continues to evolve, we can look forward to even greater product advances to meet the ever-increasing needs of a changing world.
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