This report describes a problem on the ISS that happened the other day. Apparently potassium hydroxide was leaking from an oxygen vent. This was only the second time that an emergency was declared on the ISS, and the first time was a false alarm.
Here's a great picuture (from a very cool site) of the ISS (visit the page):

And here's a even cooler one of the shuttle and the ISS in front of the sun (visit the page):
