THE DOOR IS O.P.E.N. - Today's fire-rated glass expands the possibilities
Reprinted from Doors & Hardware Magazine
By Jerry Razwick, Technical Glass Products
Not that long ago, any article about glass in fire-rated doors would have been extremely short. There just was not a whole lot that could be said. Typical fire doors were slabs of steel. If there was any glass at all, it was polished wired glass in rather small sizes, perhaps only 100 square inches or less.
You'll still find that type of door being installed in many locations. But the trend is definitely toward incorporating more glass in new ways. And there are many new product options available in addition to wired glass. Ceramics, specially tempered glass and transparent wall units have transformed the way architects think about fire doors. To understand what is happening in the world of fire-rated glass, it is helpful to categorize the changes by using the word "OPEN" as an acronym.
O - Overall Size Increases
Virtually all of the "wireless" fire-rated glass products introduced in recent years offer a distinct advantage over polished wired glass: They all carry listings in much larger sizes. That means that the maximum dimensions for glass in a door have been greatly expanded.
For example, wired glass has typically been restricted to 1,296 square inches in a 45 minute door (9 square feet). This was the maximum size at which wired glass would remain in the frame during fire testing. Since for many years wired glass was the only product on the market, many building codes made 1,296 square inches the maximum allowable size for fire-rated glass in doors.
When the new products came onto the scene, they quickly posed a challenge for the codes, because they were capable of exceeding the existing size limits. Today, depending on the application, a 45 minute door may now have as much as 3,204 square inches of glass (over 22 square feet) - or more.
In 90 minute doors, the changes in overall size of glass have been even more dramatic. Non-temperature rise 90 minute doors have historically had a limit of 100 square inches of glass. New fire-rated ceramics have pushed the limit to 1,296 square inches. And in temperature rise doors, the new transparent wall units can provide as much as 3,724 square inches of vision area. In other words, full-lite 90 minute doors are now a reality.
P - Performance, performance, performance
Wired glass is really the benchmark in the industry when it comes to performance. Everything else is compared to this product that has been around for more than a century. It is a tried and true work horse that has proved itself to be reliable and effective in real-life fire situations. Even today, it is still the most widely used fire-rated glazing material in the world. The wire mesh embedded in the glass provides a net that holds the glass in place during a fire, when ordinary glass would shatter or explode due to the intense heat.
But wired glass has its limitations, since it is a relatively weak product that can have dangerous break patterns due to the wire. In high traffic areas, the risk of breakage can often exceed the risk of fire, pitting two safety concerns against each other. Since wired glass was historically the only material on the market that could pass the fire testing, a compromise had to be made that allowed the use of wired glass in spite of its inability to earn high impact ratings.
Obviously, such a compromise could not suffice for long. The demand for safer facilities continued to fuel increasingly stringent code requirements, making it more and more difficult to ignore one safety need in favor of another. Manufacturers saw the opportunity for innovation, and began developing a number of advanced fire-rated glazing materials that could perform a dual role. The majority of fire-rated glass products on the market today satisfy the highest standard of impact safety for window glass - CPSC 16CFR1201 (Category II). In other words, impact safety no longer needs to be sacrificed when fire is an issue.
Not only have these newer products outperformed wired glass in terms of impact - they have also surpassed it in fire protection. This means that the amount of glass allowed in doors, sidelites, transoms and windows has increased dramatically.
Wired glass typically carries a fire rating of 45 minutes. This means wired glass can be expected to contain the spread of flames and smoke for 45 minutes. In contrast, the newer products can last much longer in the event of a fire.
The new ceramic products are a case in point. Ceramic is well known for its ability to withstand heat. It can be found in everything from car engines to cooktops, because ceramic has a very low coefficient of expansion when it gets hot. That is why fire-rated glass composed of transparent ceramic has been able to earn fire ratings up to 3 hours.
Quite often, the need for the higher fire ratings is accompanied by the need to block the passage of heat (in addition to flames and smoke). In stairwells, computer rooms and other heat-sensitive areas, extremely high temperatures transferring through the glass could be just as devastating as the fire itself.
Products called "transparent wall units" address this issue directly. Composed of multiple layers of glass with an intumescent material in between, transparent wall units are actually tested to the same standards as barrier walls. These products greatly reduce heat transfer and therefore can be used in applications where other types of fire-rated glass would not be sufficient. Transparent wall units allow for an unlimited amount of glazing in a wall, making it possible to design with floor-to-ceiling glass.
E - Everything but the kitchen sink
One trend that has been growing in recent years has been to think outside the normal definitions of fire-rated glass. Hybrid materials that combine multiple characteristics in one product are quickly becoming the norm.
Today's building materials have to function on multiple levels. Whether a project dictates accommodating for energy conservation, acoustic control, hurricane resistance or security needs, chances are good there's a fire-rated glass product available that can pull "double duty" and provide the additional features that are needed.
One way this has been accomplished has been through the introduction of fire-rated insulated glass units (IGUs). This enables a tremendous amount of flexibility, since the second piece of glass in the IGU can be virtually any type of product - tinted, mirrored, etc. The IGUs offer energy code compliance and sound control, which again expands the capacity of fire-rated glass beyond simply containing flames and smoke.
Other testing is also underway to develop fire-rated glazing for exterior applications in "extreme weather" locales. Various counties in the Southeast now have hurricane resistance requirements for glass used in the building envelope. Projects such as airports often have fire concerns in addition to weather, and so new work is being done to test products that can meet both rigorous demands.
N - Narrow profile framing
Glass isn't the only component in fire-rated systems that has changed: Fire-rated framing has been developing as well. For a number of years, architects in Europe have had the option of specifying framing with much narrower profiles than their American counterparts. Similar in appearance to aluminum storefront framing, these narrow profiles are nearly "extruded" from steel tubes. Whereas a typical hollow metal steel window frame section with a 45 minute rating has a profile of approximately 3" x 6", a comparable European style frame could have a profile of just 3" x 2". 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 being fabricated in the United States. To date, at least two new door and frame systems are available.
One line of doors and frames carries ratings of 20 to 60 minutes. As with hollow metal steel, these frames do not provide a barrier to heat transfer. They are most commonly used with "thin" fire rated products such as wired glass or the FireLite family of products. Due to their visual appeal, the narrow profile doors and frames 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 profile, has achieved ratings up to 90 minutes in doors, and 60 minutes to 2 hours for other applications. Acting as a barrier to heat transfer, these frames and transparent panels allow an unrestricted amount of glass in walls and doors.
Both systems allow for full lite doors, opening new possibilities for designers who wish to use large expanses of glass in a project with fire ratings from 20 minutes to 2 hours. That means that in a door that is 48" x 96", you can now have a single piece of glass measuring up to 41-5/8" x 89-3/4".
Such innovations in glass and framing are more than aesthetic. They quite often can mean a higher level of safety, thereby minimizing the exposure to legal risks. The threat of expensive litigation can be a powerful motivation to take added precautions.
For example, public school district officials are highly sensitive to the safety of their students. So when injuries involving wired glass began resulting in lawsuits against school districts, administrators in other districts began to take notice. After all, wired glass is a common commodity in schools across the nation. Today, districts in cities such as Las Vegas and Chicago have sometimes opted to eliminate wired glass entirely from their new construction specifications in favor of high impact, wireless fire-rated glazing products. In the face of potential liability, they felt that the use of wired glass wasn't worth the risk.
Safety, performance, flexibility, aesthetics...the list of benefits continues to grow. Developments in fire-rated glass and framing are expanding the horizons of design, with no end in sight. The future is a wide open door.
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