yup. he bought the whole load of BS too. it's a shame, 'cause he's a
pretty good teacher.
let's make a clear distinction between production shops and home shops
in production shops there are large machines, multiples of them,
running continuously, each making lots of dust. this is an environment
where plastic piping is a hazard and AFAIK illegal.
in home shops this is not the case.
there are plenty of non-static discharge hazards associated with dust
collectors in home shops. big bags of sawdust are a ready source of
fuel just waiting for a source of ignition. vacuum up a cigarette butt
or a nail that sparks off of some metal part inside the DC and you
could have a smouldering fire inside the DC that erupts into full
ignition hours after you've shut off the lights and gone to bed.
I fail to see how a pilot light could do this short of sucking big
piles of dust through the piloted device, but someone somewhere might
be able to pull it off ; ^ ) more likely is that the DC would blow
out the pilot...
On Mon, 15 Nov 2004 12:57:49 -0700, firstname.lastname@example.org wrote:
Why ? The physics is the same.
If plastic piping is a no-no for commercial workshops in your
jurisdiction, then that's to reduce the _consequences_ of a fire (and
they do happen, for many reasons). Plastic piping, and unearthed too,
is in regular use for the flexible sections of DC hookups.
If I had a roof mounted central DC system, I'd want steel pipe too.
home shops never involve anywhere near the volume of dust needed to
generate a hot static discharge into a dust cloud dense enough to
sustain it. that takes a dust collector in the 40 HP range pulling
from multiple high volume dust producing machines at once. while in
theory a home shop could create the right conditions, in practice it's
never happened and never will.
not just to reduce the conscequences- also to reduce the sources.
that's ABS flex, not long straight sections of PVC
steel pipe is the preferred installation. for home shops, PVC is very
You're right that it's not the volume, it's the concentration. To get an
explosion you need x quantity of suspended particles per unit volume and
you need an ignition source. If the concentration is high enough for an
explosion to occur, then it is not a good idea to rely on the hope that any
discharge will be of too little energy to cause ignition. In a home shop
it's not likely that you'll get that kind of concentration. In a
commercial shop it might be a different story.
Reply to jclarke at ae tee tee global dot net
It's the concentration and the energy. If there's inadequate energy
in the discharge, it won't ignite. If the concentration is inadequate,
it won't propagate.
However, even low concentration is not a guarantee of safety for wood
dust handling. There's a problem with smouldering and a burning
particle _may_ settle out in a dead-air zone where there's likely to
be a build up of other dust. In forensic examinations of many dust
collector fires, they began not in the filter or the collecting bin,
but at stagnant corners and sudden pipe expansions.
For a real treatment of this problem, read Luttgens & Wilson's
"Electrostatic Hazards" or a similar industry-standard handbook. I
still haven't found one that has evidence of static discharge caused
fires in wood dust.
dust volume *and* the speed that dust is travelling do have a bearing
on the static charges built up in plastic pipe. high volume + high
speed = large static energy being generated. in systems handling tons
per day like grain silos and millwork factories the risk of static
discharge becomes real. in home shops it's pure unadulterated urban
and that one machine is unlikely to make enough dust to be a problem.
it's the main trunk lines that do.
On Tue, 16 Nov 2004 10:03:07 -0700, email@example.com wrote:
In the grain elevator explosions with which I am familiar, static was not
the cause of the explosion, it is usually either a faulty electric motor
that generates a spark (much longer duration and thus more energy supplied
to start the ignition), or an open flame.
On Mon, 15 Nov 2004 21:36:38 -0700, firstname.lastname@example.org wrote:
And MUCH less expensive. I just bought a bunch of the PVC for installing a
cyclone currently on order from Bill Pentz.
Comparitive pricing between a local plumbing supply house for 6" ASTM-D2729 S&D
PVC and the web prices from a well-known woodworking supply house:
Pipe: PVC $8.50 for 10 ft length, Steel $28.00 (+ shipping) for 2 x 5 ft
Wye: PVC $12.00 each, Steel $60.00 (+ shipping)
Well, you get the idea. Comparative costs for other fittings are similar. But,
there is a wider variety of fittings available in the steel.
Wichita, KS USA
But the volume of dust handled by the collector may be different. CWG has a
planer that is bigger than my truck. Somehow I think that when it's
turning a piece of 8/4 lapacho into 5/4 it produces a little more in the
way of shavings and dust and whatnot than my 13" Delta.
Whether the volume is high enough to constitute an explosion hazard in the
event of a static discharge in the system, I have no idea.
Reply to jclarke at ae tee tee global dot net
I could be that Sandor Nagyszalanczy is referring to a commercial wood shop and
avoiding a law suit.. The book is not just written for the hobbyist.
Buffalo, NY - USA
(Remove "SPAM" from email address to reply)
As I said,
To date none of the experts have come up with a single
itty-bitty bit of evidence that PVC piping will lead to a
dust collector explosion.
And this includes Sandor.
UA100, who is mentioned by name on the acknowledgements page
of Sandor's book Power Tools...
Very unlikely. The research I've seen (Sorry, I don't have a cite immediately
available) indicates that in order for a dust cloud to support a flame front,
the visibility in the cloud would be on the order of a meter. That's a pretty
thick dust cloud. Based on that, the rule of thumb I use is - If I can still see
the far wall of the shop through the dust, an explosion is the least of my
Wichita, KS USA
The myth is that a construction worker finds a really nice piece of large
diameter, about 8-10 inch, plastic pipe and wants to use it but it's all
dirty so he sandblasts it at the site and builds up such a huge static
charge on it that when he walks around its end, it shoots a lightning
bolt out of it and blows him across the compound.
They tried everything. Couldn't even make the thing spark. They had a
voltmeter on it, and it kept building up a little charge and then
As someone else has said, the stuff is an insulator. Grounding the
outside grounds only the outside. Don't need a resistor, you're only
sending a few volts to the ground. But any charge inside the pipe is
I've also seen articles on attempts to duplicate a shop explosion. They
found that the dust particles have to be a certain size, and be dispersed
in the air in such a way that each ignited particle ignites the particle
next to it, and in such a manner that it creates an explosion-like
combustion. They found that when they finally got the conditions correct
for a dust explosion, the air was so full of fine-particle dust they
could barely see. And any air currents in the area screwed it up. The
dust particles weren't close enough together. Their conclusion was, if
you have the correct conditions to create a dust explosion, you should be
more worried about breathing than an explosion.
Want me to hunt around for the article? I think it might have been posted
to this very newsgroup.
So the general word is that there's no safety hazard involved - saw
dust is obviously different to flour, for example.
That's what I was looking to be sure about! My new shop will be in a
building that doesn't belong to me and as the lawyers here in europe
are starting to get almost as trigger happy as in the USA I wanted to
be sure I wasn't not making myself negligent through ignorance.
Thanks people ....
I read somewhere on-line (the dust collection info site?) about a factory
using PVC and how everyone would get nasty static shocks from it. They tried
the usual tricks of wire, etc but none really worked. What finally did work
was a strip of the metal (aluminum ?) duct tape in a strip along the inside
of the PVC and another strip along the outside. The two strips were then
connected together with several holes drilled through the pipe wall and
fastened with a bolt and washers. This was then earth grounded. Something
about the greater surface area of the conductor in the pipe doing a better
job of collecting those pesky extra electrons....
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