Exploding Kegs and Bob McKenzie

Sorry for the lack of posts of late, my brain has been occupied with researchy stuff.
All I feel like posting today is this link to a story on exploding beer kegs that stopped traffic. The most interesting part? The driver was a guy named Bob McKenzie.

On a more technical note, why did the kegs explode? The police said "carbon dioxide in the kegs"... well that doesn't help, all beer ought to have carbon dioxide in it. Kegs are rated to take more than 60 psig in pressure, but a filled keg really ought to not have more than 30 psig pressure, even in hot weather. Unless, of course, the temperature was very very hot. Or the beer was very over carbonated. Seems weird... the only time I've heard of kegs exploding are from drunken idiots throwing them on the fire or somebody hooking up an un-regulated beergas line to the gas-in (which would be like 2000-8000 psi instantly).

Anyway, that was a lame post. Cheers!