I’ve heard many accounts of people being killed and wounded by glass falling from the World Trade Center on 9/11. I’m wondering, why didn’t they use the kind of safety glass that shatters into those tiny cubes, instead of huge, deadly sheets?
Because they didn’t expect airplanes to fly into them.
Seriously, it’s a good question. The best answer that I can think of is that if a bunch of little glass pieces will kill you just as surely after dropping several tens of stories as a big piece. Saftey glass costs; if it makes no difference, might as well go with the cheaper stuff.
The WTC held up for a surprisingly long time, however, given that it wasn’t built in expectation of high-velocity impacts from large objects. The impact and explosion didn’t faze the structure at all, and for that I priase the builders. It’s the heat from the fire that did it in - the steel softened slightly under the intense heat of the burning fuel and other materials of the building, and the weight of the above floors killed everyone.
Because they don’t WANT the windows to break; the thick plate glass used in buildings is incredibly difficult to break, so that any scenario requiring safety glass is just too unlikely to plan for.
Doesn’t safety glass simply shatter into small, blunt pieces rather than sharp shards?
I wouldn’t fancy my chances being hit on the head by a piece of glass from 100 storeys up, no matter how blunt it is.
The Pentagon, which was expecting such a possibility, employed some. Their rebuild has used it extensively. But for the average building, considering the exhorbant cost… why?
TheLoadedDog: I’ve had some experience with broken safety glass, a glass roof over a hot tub at my house was destroyed by a falling tree. It shattered into into cubes the width of the glass, which while sharp on the edges, are easy to clean up in bare hands without cutting yourself. I wouldn’t want to be hit by falling glass, but the pieces would be small thus not moving too fast, and I’d think at worst they’d give you a little cut. It’s better than being killed by a huge sheet of glass…
Nametag: I suppose that makes sence. Couldn’t they make thick sheets of Safety glass, though? Maybe 2 panes stuck together so they would shatter independently, but be strong enough?
The New York City building code, which is available on line, has a long section of glass. The subject is pretty complex and various kinds of glass are approved for various uses. Laminated or tempered safety glass is mandated for certain uses but not everywhere. Probably to hold down expense because modern buildings have a lot of windows.
Windows have long been a pain in the neck. In Boston the John Hancock Tower was beset by the problem of whole windows falling out and crashing to the street. The unusual story is in the cite.
No cite but…
Having worked with tempered glass on pinball machines and video game monitor covers. Tempered glass is VERY brittle and most likely the wind pushing against large windows under the kinds of conditions found in hirise buildings would be enough to shatter tempered glass.
Also IIRC tempered glass is mainly used in situations where breaking the glass can cause injury. If you smash through a window 40 stories up glass cuts are the least of your problems…
I’m not sure what “safty glass” is. There are plate glass windows which are pretty think and strong. There is also laminated car-windshield glass that has layers of plastic to keep the small blunt pieces from going into your face. I sort of assumed that all comercial glass was designed to either not break or break as blunt pieces.
But, as you say, if it falls from 50 stories up, it could be as blunt as a baseball for all the good it will do.
I wonder what they’re doing in Houston these days. I remember several years ago a hurricane came through and broke a truly amazing amount of glass on all the big, shiny skyscrapers they have downtown. Does anyone know if that’s been replaced with something different since then?
Simple: COST:D