On Wed, 29 Mar 2006 00:03:52 -0600, () wrote:

In article ,
Andy Dingley wrote:
...snipped...

No, the situation is exactly the same. It's a question of max possible
discharge energy vs. minimum energy needed to initiate a dust explosion.
These don't change for industrial scale wood dust collectors - the
volumes get bigger, the densities don't.


Can you support that statement? At any rate, in an industrial
setting the greater volume of air and dust being moved would have
the potential to create a more powerful static discharge.

And all the comparison to grain silos; The dust that creates the
danger of an explosion in them is MUCH finer than the sawdust created
in the typical wood shop operation, except perhaps for sanding dust.



One of the things that people seem to keep missing here when citing
grain silo explosions is the difference between spark sources. In all of
the grain elevator explosions that I have read about, yes, a spark caused
the explosion, but the spark was not a static spark, it was an electrical
spark from a faulty connection or exposed electric motor. An electrical
spark carries a much larger amount of energy than a static spark. The only
static-caused explosions I have read about have been those which ignite
gasoline fumes. Gasoline fumes are significantly more volatile than an
air/dust mixture.

Even in the cites given,
"The third major factor is the ignition source. Sparks from welding and
cutting equipment, or cigarettes, can ignite dust. If a bolt, or some
other piece of metal, located on moving equipment rubs or scrapes against
another metal surface, sparks again could result, leading to an explosion.
A choked bucket elevator, a conveyor belt slipping, an electrical
malfunction, or lightning could also start a fire leading to an explosion."
OK, lightning is static electricity. If your dust collector can generate a
static spark with equivalent energy to a lightning bolt, some wimpy little
wire wrapped around the pipe isn't going to help you anyway.

The OSU article, and a couple of the other sources, cite static as a
possible ignition source, but provide no information to back up that
assertion.



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