Everything You Always Wanted To Know About Fire-Rated Glass (But Were Afraid To Ask...)
Reprinted from Glass Digest
By Jerry Razwick, Technical Glass Products
A state glass association chapter recently held a panel discussion on fire-rated glass. Three leading distributors of fire-rated glass products were invited to participate and share with the membership some information about the field of fire rated glass and framing.
After each of the speakers had given a brief presentation, the discussion was opened up to questions from the floor. It soon became clear that the question and answer time would be very brief, because the room was filled with blank stares. Finally, one honest individual said, "I really don't know anything about fire-rated glass. Is there a good source where I can get some basic, unbiased information?"
It was a very revealing event. Unless fire-rated glass is your specialty, it's difficult for most glaziers to stay up to speed with the rapid changes in the industry, let alone have a firm grasp on the basics of fire-rated glass. Terms such as "thermal shock," and "transparent wall units" have no meaning unless someone takes the time to explain them.
And they are important terms for any glazier involved in commercial projects. With litigation at an all-time high, becoming more familiar with fire-rated glass is one way to protect yourself and your customers from the liability of installing the wrong product.
Here, then, is a brief overview of the basics of fire-rated glazing - a primer of the most essential information. While not comprehensive in the details, the following material provides the "big picture" and can help you build a solid foundation of understanding.
Fire-Rated Glass: What It Does
So the project specs call for fire-rated glass. That�s clear enough. But just exactly what does glass have to do with fire safety?
There are three primary methods of ensuring fire safety in a building. The first way is through detection systems, such as smoke alarms. Sprinklers and fire extinguishers fall into the second category, suppression. Finally, there are building components, such as fire-rated glass, that offer compartmentation.
Compartmentation is simply dividing the space of a building into smaller units and providing barriers that prevent the fire and smoke from moving from one area into another. There�s no question that smoke detectors and sprinklers are needed. But they are also systems that require activation to function properly.
That means that if the right sequence of events does not occur, those products will not be able to offer any fire protection. For instance, if someone accidentally turns off a water supply or paints over sprinkler heads during a remodel, the system breaks down. However, compartmentation products such as fire-rated glass perform their role 24 hours a day. They offer an additional line of defense regardless of how well other components may function.
That means, of course, it is absolutely critical to make sure the fire-rated glass installed meets the necessary requirements for the job. The question to ask is: If the glass is the only protection standing between you and the fire, are you sure you can trust your life to it?
Making Sure It Works: Testing for Fire-Rated Glass
It's comforting to know that the process for obtaining a fire rating is rigorous. Products are put through their paces before being assigned any kind of listing. As with other rating scales, there are varying levels that can be achieved. In the world of fire ratings, everything is measured in terms of time. A piece of glass could earn anywhere from a 20 minute rating to a 3 hour rating, depending on how it performs. The minutes or hours indicate how long that piece of glass can be expected to perform reliably in an actual fire.
Structural fires can rapidly reach intense temperatures, so one of the most important criteria for fire-rated glass is that it can withstand extreme heat. During testing, glass is installed in a wall that is placed in front of a giant furnace. Following a strict time/temperature curve, the heat is turned up to more than 1600° F. To give it some perspective, ordinary glass breaks at 250° F and tempered breaks at about 500° F. For a successful test, the glass must remain in the frame for the entire duration of the rating desired (20 minutes, 60 minutes, etc.).
U.S. standards require a second test before glass can earn a fire rating of 45 minutes or more. This is commonly called "the hose stream test." Immediately after the furnace test, an actual fire hose is brought in to blast the hot glass with water. Some glass cannot tolerate this kind of "thermal shock," and will shatter as soon as the cool water hits it. If that happened in real life, there would be nothing left in the opening to stop the flames and smoke from spreading. So glass that can't pass the hose stream test isn't considered appropriate for locations that require anything more than a 20 minute rating. In fact, some jurisdictions in North America restrict 20 minute glass to doors, while other jurisdictions won�t allow it at all. Because sprinklers are used so extensively in the U.S. and Canada, thermal shock is a real concern.
Understanding the testing process may seem irrelevant to glaziers, but it can be a great help when it comes time to evaluate whether or not a product is correctly specified. For example, one manufacturer has introduced a product with a 60 minute label that has not been through the required hose stream test. A small disclaimer has been placed on the label and in the product literature, but for all intents and purposes, the glass appears to have a regular 60 minute listing. Unless you're aware of the value of the hose stream test, such a disclaimer could easily be overlooked.
In addition to fire ratings, there are many times when a glass product will need to offer some level of impact safety as well. Essentially, any hazardous location (as defined by building codes) that would normally require an impact safety rated product will still need to offer that same protection when it is in a fire-rated corridor.
So there are many fire-rated products today that have also gone through the necessary steps to obtain impact safety ratings. Some glass (such as polished wired glass) can offer a limited degree of protection by meeting minimum levels of the ANSI Z97.1 test. The rule of thumb comparison would say that a child could run into that glass without being injured. In contrast, other impact safety products could withstand the impact of a full-grown adult. These products are typically labeled as meeting CPSC 16 CFR 1201 (Category II).
Choices, Choices: The Expanding Options
While the fire rating test criteria are standard across the industry, the products available today are anything but uniform. When you cross multiple levels of fire protection with multiple levels of impact safety, there is a staggering number of potential combinations. And since no two products are exactly alike, it can be a challenge to keep them all straight.
For all the variety, however, there are still only four main categories of fire-rated glass on the market today.
Polished wired glass represents the lion's share of fire-rated products. With a 100 year track record worldwide, it has proven itself to be reliable. Typically rated for 45 minutes, wired glass passes the hose stream test. It continues to be an affordable choice for many applications. But wired glass does have some disadvantages. The average person on the street sees the wires and assumes they make the glass more resistant to impact, when in fact they are really there to keep the glass in the frame during a fire. Wired glass only offers limited impact protection, so it shouldn�t be used in areas where the threat of breakage is a concern. And from an aesthetic viewpoint, the wires can convey an undesirable image.
Glass Ceramics have brought new performance capabilities and continue to expand. The high tolerance for heat that characterizes ceramic makes it an ideal material for fire situations. Ceramics have taken full advantage of the latest technological advancements, so that today there are a number of different options available. Fire ratings range from 20 minutes to 3 hours, and the additional choice of high impact safety ratings and IGU make-ups make ceramics a viable option for a broad range of applications. Designers also appreciate having the ability to incorporate innovative features such as beveling, etching, sandblasting, sound reduction, energy savings, etc.
Specially Tempered Glass has become quite common in the American market as well. Unfortunately, it is often specified inappropriately, because it has sometimes been positioned as an "alternative to wired glass," when it cannot pass the hose stream test. In other words, a product with a 20 minute rating sometimes is substituted for a product with a 45 minute rating, on the assumption that the two are equal. Specially tempered glass should only be used in 20 minute applications, which the UBC restricts to doors in a 1-hour corridor. And if sprinklers are located in the area, you should consider this product's inability to withstand thermal shock. If water from the sprinklers hits the hot glass, the glass is likely to explode from the opening -- even less than five minutes into the fire.
Transparent Wall Units may represent the trend of the future. These glass products are thicker and heavier than wired glass or ceramics. However, their outstanding feature is their ability to stop heat from transferring through the glass. In fact, they're actually classified as walls. (, because they are able to stop heat from transferring through the glass. ) Architects can now design with glass (going) from floor to ceiling, with ratings from 60 minutes to 2 hours. In addition, new narrow profile door and framing options are becoming available which can replace the rather bulky systems that have been the norm.
Back to Basics: Asking the Right Questions
In broad terms, those are some of the key points to keep in mind about fire-rated glass. When it comes to a specific project, that informational grid can help you work through the following checklist to arrive at the right product solution.
1. Check the required rating.
What is the required glass rating? Does the specified glazing material meet these ratings without special "limitations"? Sometimes a specifier may not have all the facts about the proposed product. If you have concerns that an improper product is being specified, check into the matter thoroughly. The risks of human injury and potential liability make it well worth the effort. Begin by making sure that the listing of the glass matches the required rating. Framing and other components will also need to have matching ratings in order for the system as a whole to truly be up to code.
This emphasis on double checking the listings would hold true for any safety ratings, energy requirements, heat transfer concerns or other performance criteria that might be considered important.
2. Look for sprinklers.
Sprinklers can pose a genuine threat to glass if the glass doesn't pass the hose stream test. So even if it would be technically correct to install a 20 minute product, but sprinklers are nearby, it may be advisable to use products that can resist thermal shock. A quick check of the drawings for where sprinkler heads are located could prevent disastrous results.
3. Keep in touch.
One of the best ways to ensure that you are utilizing the right product is to connect directly with someone working in fire-rated glazing. Most distributors and manufacturers value the opportunity to hear from people "in the field," and they would be happy to take the time to direct you to the most suitable alternatives. Sometimes a five minute phone call can save you a great deal of grief down the road.
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