Well this nonsense comes up two or three times a year so didn't even bother
to read most. A research done 3 - 4 years ago found that according to Gov.
specs. you would have to reduce something like a 6" x 6" x 1 ft. pc. of Oak
to dust in one minute to get enough concentration of dust to support an
explosion. Anyone got one of these machines in their shop? Anyone actually
have FIRST HAND evidence of a home wood shop explosion?
Wheat dust, bean dust, corn dust in grain elevators, etc, is not wood dust
in home workshop.
Why would that work with oak and not pine?
Of course it would and this is my point:
That is plainly not plainly not the ONLY way
to get a wood dust explosion.
Suppose you sand away with your ROS or belt sander and
collect a nice large volume of dust. Then when you are
emptying your dust collector you drop it and the dust you
created over the course of several hours all goes airborne
Now, that could make a nice impressive fireball--but only if
there is an ignition source like a pilot light or a spark from
an electric motor. A static spark may not be enough, but
static sparks are not the only ignition sources.
One should be careful not ot give an overly broad answer
to a rather specific question.
It is easy to light a _flammable_ liquid (e.g. gasoline) with a match,
that follows from the formal definition of 'flammable'.
It is not easy to light a _combustible_ liquid (e.g. kerosine)
with a match as you have to heat it to the flashpoint before it
"Flammable, nonflammable, inflammable--why are there three?"
-- George Carlin
The flashpoint for a liquid is approximately the temperature a which
the partial pressure of the vapor over the liquid reaches the LEL.
In theory, I suppose they are exactly the same but in practice
flashpoint is determined in a laboratory and there are at least
two methods used that can give slightly different results--open
cup and closed cup.
Once again, the big picture. If your ignition source is continuous, it will
burn away the smaller amounts as they come within range, preventing an
explosive situation. You've got a ways to go to figure out how to get a
bolus of properly dispersed dust to duplicate that in a tube....
What is to stop the flame front from progessing through the dust
cloud after the edge of the cloud reaches the ignition source?
The answer is nothing.
So don't dump your dust collector out near a continuous ignition
source. Seems straightforward enough for me.
But it is wrong to make an overbroad statement implying that
you cannot light a cloud of sawdust on fire. I've done it.
Best person to ask is your local fire department. They might have
some good stories to tell.
Fuel + Oxygen + Heat (spark) = Fire
I think a DC can catch fire, although I'm not sure how likely it is to
What everybody is dancing around is "LEL" or "Lower Explosive Limit".
It is that point where the dust volume in the air WILL explode.
An entire industry exists to provide instrumentation to measure "LEL"
for various products.
There are published tables of LEL values and are usually available from
the instrumentation manufacturer.
Been there, done that, but that was a while ago.
No, not at all. Fill a reasonable router extractor hose with typical
levels of fine larch dust, initiate it pyrotechnically and I have no
doubt at all that you can have your very own wood dust explosion.
You'll not do it from static though. That's the demonstrable case where
you can't initiate it.
No, far from it. It's the lower limit for where the mixture _can_
explode. Below this it's impossible to explode, at this limit it's
barely possible. It isn't especially likely (depending on other
conditions regarding ignition sources) and it certainly isn't any sort
of spontaneous ignition as suggested by your emphatic "WILL explode"
I previously wrote:
>>It is that point where the dust volume in the air WILL explode.
As written, not true.
It should have read: It is that point where the dust volume in the air
WILL explode IF an ignition source is provided.
Blame it on a lazy typist, ME.
No disrepect intended, but I've read dozens if not hundreds of MSDS
and had some training as well, and I have never seen a reference to
LEL/UEL that was not for gas or vapor concentration in air. In fact,
for dust any LEL would vary with the particle size.
Yes, I do believe in facts.
No idea of the concentrations or how hot a spark it would take to set
I was, however, rudely awakened one Sunday morning in North Vancouver
when a grain elevator about 5 miles from me was subject to a grain
dust explosion. That was in the mid-70s or so, if you feel like
looking it up.
I also participated in several experiments in which we ignited clouds
of flour, cornstarch, and sawdust. No real explosion, because it was a
small and unconfined cloud, but it was, nonetheless, spectacular.
My mother couldn't explain the seemingly rapid disappearance of her
cache of corn starch when I, unbeknownst to her, would sneak baggies of
it down to the creek bed to huff it out my mouth at a candle held before
my face--much to my inner pyromaniac's delight.
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