Sliding Glass Doors Shatter Spontaneously?

Help! Two years ago I had sliding glass doors (6 panes total) installed to enclose a covered lanai on my condo. Today, one of the doors spontaneously shattered. It is a door I have rarely opened, and haven't been near it in weeks.
The contractor that installed them said it is not unprecedented for this to happen, as the building may have settled (building is 30+ years old) or an event that happened weeks ago may have triggered this. Is this bull? I find it hard to believe this can happen without apparent incident.
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You could try to determine whether the door frame is out of square or distorted. If you never open the door you would not be aware of shifting. Sliding doors are among the first things to break when framing shifts because they have such large glass areas.

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installed wrong, or something hit it. I lost a panel a couple weeks ago to an idiot lawn crew that doesn't bother to clear debris first. That safety tempering really works- whole panel was spiderwebbed, but it didn't seperate or fall out of the frame. With a/c on, or if you had the drapes closed, you likely wouldn't even hear the rock or whatever hit it. The glass tells the tale- the impact point or stress point should have been obvious, as long as it didn't all fall out of the frame into a pile of gravel.
aem sends....
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