• Field Notes 13.09.2011

    Hurricane Irene roared up the East Coast, an earthquake struck Virginia, and it’s the 10-year anniversary of 9/11 – all within two weeks! One thing you can say about natural and man-made disasters is they teach us how to make buildings safer. The glass industry has certainly been one to get smarter from when things go wrong.

    In ’83, Hurricane Alicia struck Houston. A couple of curtainwall pioneers, Jack Stevens and Bob Johnston, waited out the storm in some of the city’s recently completed 70-story towers. They wanted to see if code changes made over the years really made the walls better.

    After the storm blew through, there was a lot of broken glass in the mid-20th to mid-40th floor areas of the curtainwalls, but little damage above that, where one would think the highest wind loads would be. But lower down, there was a lot more damage than expected. It turns out much glass was broken by pea gravel used on the roofs of lower buildings. The wind picked it up and made it into buckshot. Lesson learned, and the code changed. We got smarter about how to build buildings.

    Likewise, codes in NYC changed after 9/11. Due to exiting difficulties from the Towers, stairs are now made wider, and reinforced concrete (materials other than sheetrock and studs) is now used for fire stair walls. This offers a greater degree of protection for occupants going down and firefighters going up – both of which may be happening at the same time. Again, we got smarter.

    And earthquakes have taught us a lesson or two. Ask a structural engineer in Southern California how much seismic codes have changed in the last 20-30 years. Are buildings safer? You bet. Is something being overlooked? Possibly. We’re human, we’re not perfect. But I like our chances because we learn from past disasters.

    Man-made mistakes also can – or should – lead to improvements. For example, there have been a lot of write-ups lately about broken glass in tempered glass handrails in condominiums. Some of the causes might be nickel-sulfide inclusions, which is small debris trapped in the glass that doesn’t melt in the furnace. Small cracks can develop around the inclusions due to thermal expansion/contraction differences between them and the pure glass. Once the cracks reach the tension zone of the glass, the entire lite can shatter.

    In the U.S., the primary glass manufacturers have made a great deal of improvement to weed out nickel sulfide inclusions. Glass can be heat soaked, exposing it to extreme temperatures over a short time so that any nickel sulfide inclusions present cause the glass to break before leaving the tempering facility. It’s thought that heat soaking catches 90% of inclusions. We got smarter about how to catch most of this problem sooner rather than later.

    Then we got dumb again. A lot of glass companies no longer are including heat soaking in the price of tempered glass. Specifications may require heat soaking, but the supplier or subs put it out there as an “Add” or “Deduct” in a quote, which is another way of saying, “we really don’t want to do this, and we can show you how much it costs, and let you, Mr. Owner, decide if it’s really needed.” When the owner sees how much it is, the heat soaking often gets left on the “value engineering” table because they figure they’ll just replace it during the warranty period if it breaks.

    A suggestion here for a possible change in the codes for exterior hand rail applications: eliminate tempered monolithic glass that evacuates the opening when it breaks and replace it with laminated glass that stays in place, but doesn’t fall onto the pedestrians below. You get the transparency of the glass without losing the lite or fragments if it breaks. It may cost a little more, but wouldn’t it be worth it?

    Let’s keep getting smarter. We owe it to those whose lives may have been sacrificed on the alter of “we didn’t think or know that could happen.” That’s not to say more problems won’t arise. But as humans, the reason we reason is hopefully to make it better the next time.

    As has been said many times before, “Those who do not study the past are condemned to live it.” Sage advice, especially for us in the construction and glazing industry.

    Posted by Blogger @ 6:13 pm

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USGlass Magazine

USGlass Magazine