http://www.cpsc.gov/cpscpub/prerel/prhtml08/08594.html
Propane Storage Tanks Recalled By American Welding & Tank Due to Risk of Gas Leak; Can Pose Fire and Burn Hazard
Apparently these tanks become rusty, and the rust causes the mercaptan (the chemical that adds the smell to propane) to come out of solution, so you won't know that you have a gas leak.

The following article is about a restaurant that blew up under these circumstances.  People died and were horribly injured. "Fire and burn hazard" seems rather weak to me.  How about violent explosion hazard that could kill you, your family, your pets, and destroy all your worldly possessions?
http://www.brucegoldfarb.com/propane.htm