PHYSICS 101 ---- What happen to a balloon when it rises up in the sky?

First of all, we'd better look at how balloons are released. When helium filled balloons are handed out at public events, they usually come with a piece of string or ribbon attached. The attachment is either tied into the knot, or secured with a plastic disk. Either way, if these balloons are accidentally (or purposely) released, the attachment becomes litter and that's bad. I've only spotted a few balloons in the amazing amount of litter I see surfing here in Sydney, but they all had ribbons attached.

The other argument is that helium balloons are claimed to reach a height of anywhere up to ten kilometres before shattering into tiny little pieces. These pieces, it is said, would be too small to pose a threat to animals. Now the shattering effect sounds reasonable for two reasons. One is that atmospheric pressure is dramatically reduced at high altitudes, so a helium balloon expands as it rises and eventually explodes.