Safety Warning - Sanding Aluminum & Rusty Steel

Fisher, Scott Scott_Fisher at
Fri Feb 8 09:04:24 EST 2002

Fred Munro points out:

>     First of all, thermite is a mixture of aluminium powder
> and iron oxide (rust). When ignited, it burns fiercely, [...]

PBS ran a fabulous series not long ago in which various historic events were
analyzed by forensic scientists -- sort of "History's Mysteries" meets
"CSI," but for real.  Every episode was fascinating (I think my favorite was
the one about Islandhwana), but the one that comes to mind was the analysis
of the crash of the Hindenburg.

Turns out that the worst problem in the doomed zeppelin was not the hydrogen
fuel as much as it was the aluminium oxide used to paint the fabric silver.
Ignition occurred when the Hindenburg touched off a massive static-electric
charge on a very windy day in Lakehurst, NJ; the rapid disappearance of the
zeppelin's skin was not due to the hydrogen igniting per se, but to the
aluminum-impregnated fabric essentially turning into a rapid-fire fuse.
Reconstructions of the event were fairly convincing, particularly the
observation that hydrogen combustion is a faint bluish color, while the
flames from the Hindenburg were described by onlookers (and captured on the
B&W newsreel footage that has since been famous) as very bright yellow, and
the burn rate was another key -- it doesn't so much explode from within as
the skin burns incredibly rapidly, from the tail forward.

The episode not only mentioned thermite, but listed another application for
aluminum powder -- solid-fuel rocket boosters.  And since the Challenger
explosion *used* to be the most horrible news footage I'd seen live (or
tape-delay, anyway), that put it in perspective for me.

So anybody who's doing a little bodywork on an A8 with an angle grinder (or
porting a cylinder head, for that matter)... be careful out there.

--Scott Fisher
  Tualatin, Oregon

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