Glass at the Extreme

Last week, I experienced firsthand the incredible abilities of glass at the extreme—specifically, a glass floor 1,353 feet in the air, and a fire-rated glass assembly quite literally maintaining its cool in the face of 2,000-degree temperatures.

Vetrotech Saint-Gobain hosted a group of building industry professionals and press for a two-day product launch and educational program, which I’m going to refer to simply as an “extreme glass” event. The event began at the top of the Willis Tower (formerly, the Sears Tower) in Chicago, with a Vetrotech product launch reception and a visit to “The Ledge,” all-glass boxes cantilevered about 4 feet from the building.

Willis Tower

The glass is comprised of three layers of ½-inch, low-iron, tempered and laminated glass. The floor also features a sacrificial tempered glass layer on the walking surface. The glass boxes of “The Ledge” are designed to retract into the building for cleaning and maintenance.

The original Sears Tower architect, SOM, designed the ledge, with structural glass designer Halcrow Yolles. MTH Industries completed the installation of the 1,500-pound glass panels.

On the second day of this “extreme glass” event, the group visited the Underwriters Laboratory fire testing location just outside of Chicago. We were given a tour of UL’s building materials lab that concluded with a viewing of the fire test for Vetrotech’s Contraflam 120 in a corner arrangement.

The fire test chamber starts at room temperature and reaches 1000 degrees within five minutes. At the conclusion of the 2-hour test, the temperature will be closer to 2100 degrees. The Contraflam product consists of two or more sheets of toughened safety glass with a transparent intumescent gel interlayer that reacts when exposed to fire.

As the interior of the test furnace rises, the interior tempered glass lite breaks. The interlayer begins to cloud and bubble as it is exposed to the fiery temperatures. But the exterior lite of glass remains safe to the touch—about 100 degrees in this case. Pictured above is the interior of the furnace and Vetrotech's Kevin Frisone, sales and marketing manager, North America, touching the exterior of the glass during the test.

Thanks to Vetrotech for the extreme glass tour. I continue to be amazed at the possibilities of glass products, particularly in these extreme situations.

Devlin is editor of Glass Magazine. Write her at


Katy, There is another exciting "extreme glass event" coming to Chicago soon........keep you posted!

Yes? I can't wait to hear more.

Wow! Many years ago when I was still a freshman glazier, we were asked to install a kidney bean shaped glass similar in composition to the floor you have shown. It went in the middle of a floor in an upper sunroom that had a large party patio underneath. This was to be the highlight of the local Homarama. Unfortunately it never caught on. It seems some young men were taking pleasure in watching the ladies walk and even dance over the glass during the festivities. A row ensued including some legal threats, and we had to remove the glass later. It was a local extreme glass event :)

Haha! Yes, that *is* quite extreme. I've heard about similar issues on glass stairs and walkways in retail applications.

Katy, Did you watch the Today Show and Kevin Tibbles' piece on the John Hancock Tilt? This is the other extreme glass event in Chicago from the March 5th post.

Oh wow! I guess I need to get back to Chicago! Just incredible.

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