There is an art/science video clip on youtube, by Simon Faithful, called Escape Vehicle no.6 (chair in space). It shows a simple steel office chair, tied to a weather balloon, ascending into the upper reaches of the atmosphere. Apparently it reaches about 30km above sea level. It's quite a beautiful clip.
At the start, the chair rises quite violently, as it is buffetted by surface turbulence, as would be expected. After a while (2:07-2:33, I suppose once it gets above the planetary boundary layer), the ascent becomes fairly smooth - there is still a lot of movement, but it's not so violent. Then at 2:45, when the chair is near the top of it's ascent (~30km), suddenly things start getting really violent again, and the chair looses a leg, then half the back is torn off, and then the chair is apparently torn from the rope, and disappears.
What forces would cause such a violent disintegration of what is a reasonably strong object, in such a thin atmosphere?