Friend of mine worked at Goo-yer (or something like that) factory.  Man
showed up with a tire in shreds, he had been stuck in snow, spinning the
wheel when it blew up, major type.  The damage was more than an overspeed
would cause, total destruction had occured.  He was given another tire, and
sent home.  It blew up under the same circumstances, so Goo-yer sent Dave to
check it out.

The guy had topped up the tire at a local garage.  The garage had recently
cleaned up its air compressor with some flammable solvent which had been
sucked into its tank and then on to the guys tire, in vapour form.  Seems
that when he got stuck and was spinning, the tire built up a large static
electricity charge.  Somehow this static discharged via the brass valve stem
onto the rim inside and ignited the gas inside the tire.  Dave was able to
do this back at Goo-yer with a tire he pumped up at the garage and an
ignition coil.  Little scary.  Goes along with the Icelandic 4x4 drivers who
remount tires that have popped off the rim by using starting fluid and a
match =:O.  tim