Dust Collector Really Need PVC Grounding?
RS0...@rohvm1.rohmhaas.com
I recently installed a 610 CFM Grizzly dust collector in my basement shop.
I use 4 inch PVC pipe to carry the dust (about 30 feet of it tops).
The Catalog say ' PVC must be grounded to the intake of the dust collector'.
Is this *really* necessary? Does it only happen in places with ulta-low
humidity? My shop is never less that 25% humid and usually is about 50-60%
humid alto the tools never rust...
Then again I'd rather not blow-up the house..
G. Paul Houtz
ALL plastic pipe in a dust collection system should be grounded, both
to the frame of the dust collector AND to the grounded frames of the
machines the hoods are connected to. Without exception. Not just
PVC.
Even metal duct pipe must be grounded to the dust collector and to
the grounded frames of the machines the pipe is connected to. Without
exception. You just don't have to run a copper wire inside the tubing,
as the metal pipe itself is a conductor.
Otherwise you take a serious risk of blowing up your system and burning
down your house.
Bruno Bienenfeld
As far as I know, PVC is an insulator and as such is not conductiv, meaning
once charged you can not discharged it by """ connecting """???? to anything.
The only way to eliminate buildup of electrostatic and or discharge of it
in insulators is by Ionizers.
So if you are concerned about ESD ( Electrostatic Discharge ) and in the case
of Dust collecting devices you should be, use galvanized and or any metalic/
conductiv pipe - and it CAN and should be grounded at Dust collector.
from the log of AA6AD
Keith L
been getting zapped pretty badly when I touched the flexhoses that connected my machines to the dust system.
The static discharge was most powerful during low humidity conditions but occured even during the
"Dog Days" of August. I kinda miss the long pretty sparks though. They sure did wake you up on those
lazy Saturday mornings.
I used uncoated 1/16' cable which I found in the rope and cable section of my local home center. It was
less expensive than uninsulated braided copper wire . I drilled 1/16" hole at each end of the pipes and
threaded the cable through these holes so that the cable ran along the inside of the pipe and the ends of
the cable were outside the pipe. The holes were sealed with a bit of hot melt glue. In this manner, cable
interconnects can be made outside the ducting thereby minimizing the possibilities for snags within.
I used crimp-on terminals to connect the cables together and to the dust-collector. Spade-type
terminals were used on one-to-one connections. Ring terminals were used on three-way
connections and the ring terminals were fastened together using one of the screws that connect the pipe
to the coupling. The idea is that each piece of the duct system has its own cable built into it so that things
can be taken apart and put back together easily in kind of a modular set-up. This should be useful for
a move planned in the near future. (New house = New (larger) shop. I can't wait!)
Another safety device I added was a smoke detector near the collector. The collector had sucked smoldering
bits of hard maple out of table saw in the past (Thick maple can be extremely troublesome in this regard) and
I want to make sure that I'm notified if there is a fire in the hole! It is a good idea to check the collector any time
you happen to get a bad burn mark on the wood you are cutting. Sawdust and shavings only smolder when I throw
them on a bonfire but you blast some air past the smoldering debris and you get instant flameage. (and not the
net kind) Better to be safe than to have toasted tools, I say.- :^)
Keith L.
Touting safety and eschewing fancy .sigs
Tibor Polgar
> RS0...@rohvm1.rohmhaas.com> writes:
> >Dear Woodworkers.
> >
> >I recently installed a 610 CFM Grizzly dust collector in my basement shop.
> >I use 4 inch PVC pipe to carry the dust (about 30 feet of it tops).
> >The Catalog say ' PVC must be grounded to the intake of the dust collector'.
> >
> >Is this *really* necessary? Does it only happen in places with ulta-low
> >humidity? My shop is never less that 25% humid and usually is about 50-60%
> >humid alto the tools never rust...
> >
> >Then again I'd rather not blow-up the house..
> >----------
>
> ALL plastic pipe in a dust collection system should be grounded, both
> to the frame of the dust collector AND to the grounded frames of the
> machines the hoods are connected to. Without exception. Not just
> PVC.
I'd like to "third" the statement of grounding everything. When i first got
my dust collector, the last 10ft section to my planer was not properly
gounded. I got lucky and only got a shock so strong it knocked by back a few
feet. Everything along the dust collector's path must be gounded... unless
of course you may like shocks and fires.
--
-------------------------------------------------------------------------------
| Tibor L. Polgar | (408) 746-8649 | tl...@climb.ras.amdahl.com
| Amdahl Corporation
| 1250 East Arques Avenue (M/S 281)
| P.O. Box 3470
| Sunnyvale, CA 94088-3470
|
| The opinions expressed above are mine, solely, and do not in any way
| shape or form reflect the opinions or policies of Amdahl Corp.
-------------------------------------------------------------------------------
(Michael Gerhard aka Elmo P. Suggins)
> to the frame of the dust collector AND to the grounded frames of the
> machines the hoods are connected to. Without exception. Not just
> PVC.
>
> Even metal duct pipe must be grounded to the dust collector and to
> the grounded frames of the machines the pipe is connected to. Without
> exception. You just don't have to run a copper wire inside the tubing,
> as the metal pipe itself is a conductor.
>
> Otherwise you take a serious risk of blowing up your system and burning
> down your house.
I'm going to use PVC and good flex hose. I've thought of using light,
braided aircraft cable as the gound wire in the tubing. Everyone talks
about copper. Any thoughts on whether aircraft cable would work (its
cheaper and easier to find). Alternately, where might I find braided copper
wire?
+----------------------------------------------------------------+
| Michael Gerhard ger...@mikas.llnl.gov |
| aka Elmo P. Suggins |
+----------------------------------------------------------------+
la...@duphy4.physics.drexel.edu
>
> I'm going to use PVC and good flex hose. I've thought of using light,
> braided aircraft cable as the gound wire in the tubing. Everyone talks
> about copper. Any thoughts on whether aircraft cable would work (its
> cheaper and easier to find). Alternately, where might I find braided copper
> wire?
>
The main point of copper is that it's resistance is low, but the currents
are so low (& voltages so high!) in static electricity that even a lousy
conductor is fine. Steel cable should work well, as long as it is not
jacketed with an insulator.
--
Drexel University \V --Chuck Lane
----------------->--------*------------<------...@duphy4.hepnet
(215) 895-1545 / \ Particle Physics la...@duphy1.bitnet
FAX: (215) 895-5934 /~~~~~~~~~~~ la...@duphy4.physics.drexel.edu
Stuart Friedberg
>The only way to eliminate buildup of electrostatic and or discharge of it
>in insulators is by Ionizers.
No, there is a simple way. Run a wire though the plastic piping (on
the inside) and ground the wire.
Stu Friedberg (stu...@sequent.com)
Shaw Moldauer
> bits of hard maple out of table saw in the past (Thick maple can be extremely troublesome in this regard) and
> I want to make sure that I'm notified if there is a fire in the hole! It is a good idea to check the collector any time
> you happen to get a bad burn mark on the wood you are cutting. Sawdust and shavings only smolder when I throw
> them on a bonfire but you blast some air past the smoldering debris and you get instant flameage. (and not the
> net kind) Better to be safe than to have toasted tools, I say.- :^)
>
>
>
> Keith L.
> Touting safety and eschewing fancy .sigs
I bought a smoke detector for my shop. Before installing it, I
read the instructions. They indicate that the detector will not work
in a dusty environment. Does this mean I would get false triggers, or
would it not notify me of a fire, or would it burn down my shop. How
did you address this?
-Shaw
G. Paul Houtz
>Am I missing something.....?????
>As far as I know, PVC is an insulator and as such is not conductiv, meaning
>once charged you can not discharged it by """ connecting """???? to anything.
>in insulators is by Ionizers.
>of Dust collecting devices you should be, use galvanized and or any metalic/
>conductiv pipe - and it CAN and should be grounded at Dust collector.
>
>from the log of AA6AD
Actually, you are missing something. If you re-read my postings,
you will see that I said if you use *metal* pipe, that pipe must be
grounded.
If you use plastic (pvc, other) pipe, experts recommend that you run
a length of bare 16 or 18 awg copper wire the length of the pipe to
conduct away any static discharges.
I am not an electrical engineer. I am not an expert in dust collection
systems.
But everything I have read on the subject agrees that use of plastic
pipe in wood dust collection requires running a cooper ground throughout
the inside and outside of pipe.
G. Paul Houtz
>
> I bought a smoke detector for my shop. Before installing it, I
>read the instructions. They indicate that the detector will not work
>in a dusty environment. Does this mean I would get false triggers, or
>would it not notify me of a fire, or would it burn down my shop. How
>did you address this?
>
If you have a dust control system, the idea is that this will
remove most of the dust in your air.
Actually, this gives rise to an idea. Could the smoke detector
serve dual purpose, telling you either when there is smoke, or
when there is too much dust for safety?
Mike Huber
: I bought a smoke detector for my shop. Before installing it, I
: read the instructions. They indicate that the detector will not work
: in a dusty environment. Does this mean I would get false triggers, or
: would it not notify me of a fire, or would it burn down my shop. How
: did you address this?
:
: -Shaw
Mine goes off all the time. I don't know if it's the dust or the smoke
from the occasional rough cut. I suspect the dust, because there realy
isn't much smoke involved (at least since I checked the alignement on my
table saw...)
As for grounding the dust collector tubing (I'm installing one now), there
are two possibilities:
1) Static discharge is a real hazard and might blow my house off the
foundation with no warning, so I had better run the wire.
2) Static discharge is merely annoying, and running a wire is an easy
way to stop it.
The cost/benefit analysis of running a wire through the tube is quite
simple. It's an easy, cheap, non-intrusive safety measure that may prevent
massive death and destruction. It also makes your work environment more
pleasant.
Bill Ross
Has anyone on this group:
1. Had a dust collector catch-fire or explode due to static?
2. Known a friend/relative who has had this happen?
3. Read or heard about an incident where this happened?
I know that a static discharge can cause a fire, they are
very careful about static during the handling of certain
types of explosives. I also know that very finely divided
powders can cause tremendous explosions -- grain silo
explosions are not uncommon. But can anyone document an
actual incident of this type in a dust-collection system?
Just curious.
Bill
Anthony DeBoer
> I bought a smoke detector for my shop. Before installing it, I
>read the instructions. They indicate that the detector will not work
>in a dusty environment. Does this mean I would get false triggers, or
>would it not notify me of a fire, or would it burn down my shop. How
>did you address this?
Fine dust (such as the fine particles that do get through the dust
collector bags) could mimic smoke particles, perhaps well enough to cause
a false alarm. Also, if they crud up the detector's air vents over the
years, they could ultimately prevent real smoke from getting in.
What I'd worry about, though, is the possibility of a false alarm while
I'm ripping a board on the tablesaw or some such activity where I DON'T
want to jump suddenly due to the loud siren.
--
Anthony DeBoer < a...@herboid.uucp | uunet!geac!herboid!adb | a...@geac.com >
Mike Huber
I have had false alarms while ripping on my table saw. Actualy, that
used to happen a lot (then I bought some decent blades and invested
the time to get the machine properly aligned). I can't hear the alarm
while ripping.
<<< Mike Huber >>>
: --
G. Paul Houtz
I read about a cabinet shop in San Jose several years ago that had a
fire that did some major damage. Seems like it was on the order of
$100,000.00 of damage, and the article did say it was a dust collector
fire.
You probably won't hear about commercial stuff more recent than this since
the new OSHA regulations went in a while back.
We have already had people post to this newsgroup in the last week that
indicated they found smoldering chips in the dust collector bag.
Michael D. Myjak x7-3286
>
> Has anyone on this group:
>
> 1. Had a dust collector catch-fire or explode due to static?
>
> 2. Known a friend/relative who has had this happen?
>
> 3. Read or heard about an incident where this happened?
to which G. Paul Houtz (g...@hpcc01.corp.hp.com) writes:
I read about a cabinet shop in San Jose several years ago that had
a fire that did some major damage. Seems like it was on the order
of $100,000.00 of damage, and the article did say it was a dust
collector fire.
You probably won't hear about commercial stuff more recent than
this since the new OSHA regulations went in a while back.
I wonder what those reg's were..
We have already had people post to this newsgroup in the last week that
indicated they found smoldering chips in the dust collector bag.
Well yes, but smoldering chips are not caused by the build-up of
static charges from dust collector system piping.
When this question came up 8 or 9 months ago, no one on the net has
had nor knew of anyone who had a dust collector induced explosion. I
believe that the lack of any quick and immediate posting to that
affect indicate that this is still the case.
(now for the flame inducing, opinionated, discussion generating statement... ?^)
IMHO (a general disclaimer) the volume of airborne "dust" (i.e. not
counting particles, shavings, and in general non-combustible although
flammable chunks of wood) being collected by a residential dust
collection system is *no where near the density level* necessary to
induce a (spark generated) spontaneous explosion.
Now, why would I say such an outlandish thing? After all, this is
Rec.Woodworking... isn't it? And this goes completely against
rec.woodworking folklore!
No, I have not run an empirical analysis... just a "back of the
envelop" sketch. Am I saying that its not a good idea to statically
ground your system? No I am not... However, I am saying that with a
high degree of probability it is not absolutely necessary. I believe
that the netScareTactic of "you'd better ground that thing before your
house (like Dorothy's) lands somewhere outside of Kansas" is just
*way* off base and (almost) completely without justification.
Yes, this is just my opinion. Note that I am talking about
combustibles and not flammables; there is significant between the two.
When one (me) thinks about a grain silo going off in a puff of
chemical logic, its because the density of the combined airborne
particulates generated by the filling, draining, etc. of the silo were
high enough at standard temp. and pressure to sustain the RedOx
(reduction/oxidation) reaction necessary to induce combustion. In
other words, the density was extremely high.
The dense airborne matter in the grain silo system is trapped in a
confined space and the particles are allowed to float freely
therein... much like a gas in a confined chamber. Keep in mind that
dust as fuel is simply not as efficient as say gasoline or lacquer
thinner, although it is effective enough. The silo system explodes in
situations much like that of an internal combustion engine... where
the fuel is dense enough, and is at a specific pressure (in this case
probably 1+ atm) and temperature, and with the aide of a spark all
combine to ignite dust as a fuel. The confinement chamber also helps
to keep the fuel together for a more complete burn... and an explosion
results.
Simply put, these are not the conditions in a residential dust
collector system. In the collector system, low density dust and
chunks are collected/moved through the system (yes, picking up a small
static charge) and land harmlessly at the end of the line. Here the
larger particles fall to the bottom and the smaller ones are
immediately pressed against (or through) the filtering bag by the
force of flowing air. I simply cannot see where the density of
airborne matter in this system is ever given the chance to build to
sufficient combustible levels. IMHO.
--
- Michael D. Myjak
Principal Design Engineer, Network Planning & Design
McDonnell Douglas Space Systems Company
Kennedy Space Center, Fl., 32815
MY...@TITAN.KSC.NASA.GOV
Gravity. It's not just a good idea. Its the LAW!
PAUL HETHMON
A few years back when I was working for Philips Consusmer Electronics,
the plant which makes cabinets for console tv's had a fire in their
dust collection system. I don't remember the specifics very well, but
I think in this instance most of the damage was contained to the dust
collection system. But you have to realize that it was a commmercial
building with sprinklers, fire alarms, etc.
About 10 years back, here in Knoxville, we had a grain silo facility
explode killing several people also. I believe it was a ConAgra facility.
It leveled it completely.
My opinion is that a ground wire is pretty cheap insurance for me and
my family.
--
/* Paul Hethmon |
* het...@cs.utk.edu | for the OS/2 faq: ftp to ftp-os2.nmsu.edu
* 615/974-6433 | for brewing info: ftp to sierra.stanford.edu
*/ |
Roger Hoover
|> A few years back when I was working for Philips Consusmer Electronics,
|> the plant which makes cabinets for console tv's had a fire in their
|> dust collection system. I don't remember the specifics very well, but
|> I think in this instance most of the damage was contained to the dust
|> collection system. But you have to realize that it was a commmercial
|> building with sprinklers, fire alarms, etc.
|>
|> About 10 years back, here in Knoxville, we had a grain silo facility
|> explode killing several people also. I believe it was a ConAgra facility.
|> It leveled it completely.
|>
|> My opinion is that a ground wire is pretty cheap insurance for me and
|> my family.
There are two different dangers being discussed here.
1) dust explosion
2) fires in the dust collection bag
Clearly, if there is a dense enough dust/air mixture in the collector,
any ignition could cause a dust explosion. This includes static
electricity as well as burning wood chips. I suspect that since the
explosion of home dust collectors seems to be completely unknown in
rec.woodworking or woodworking magazine land, I would suggest that the
ground wire's "cheap insurance" policy does not cover the primary
danger.
What is this danger? Well, the shavings in a dust collector do burn.
In fact, they burn quite well--I use them in my woodstove. While I've
never been able to ignite them with static electricity (or even a torch
spark generator), a match works well. However, if they are already
burning when they enter the dust collection system, you might have a
nice fire. Thus, I'd recommend the "insurance policy" of keeping bits
and blades pitch free and keeping tools in tune so that they don't burn
the wood in the first place.
Marc F Pucci
> I bought a smoke detector for my shop. Before installing it, I
>read the instructions. They indicate that the detector will not work
>in a dusty environment. Does this mean I would get false triggers, or
>would it not notify me of a fire, or would it burn down my shop. How
>did you address this?
>
> -Shaw
I put a smoke detector in my shop when I did some renovation in my home.
The Fire inspector suggested covering it when I work in the shop, else
it would just clog up from the dust and become ineffective. I put
a plastic bag over it with a rubber band and remove it when I'm done
for the day. Only problem is I occasionally forget and leave it covered.
BTW: the detector is connected to all the other detectors in the house.
If any one goes off, they all go off. Ask yourself if you had a fire
in your shop, how long would it burn before you realized that a
distant smoke alarm was chirping.
Marc Pucci
ma...@bellcore.com
Keith L
(Bill Ross) writes:
:^O___>
:^O___> Has anyone on this group:
:^O___>
:^O___> 1. Had a dust collector catch-fire or explode due to static?
:^O___>
:^O___> 2. Known a friend/relative who has had this happen?
:^O___>
:^O___> 3. Read or heard about an incident where this happened?
:^O___>
:^O___> I know that a static discharge can cause a fire, they are
:^O___> very careful about static during the handling of certain
:^O___> types of explosives. I also know that very finely divided
:^O___> powders can cause tremendous explosions -- grain silo
:^O___> explosions are not uncommon. But can anyone document an
:^O___> actual incident of this type in a dust-collection system?
:^O___>
:^O___> Just curious.
:^O___> Bill
I've never had a fire or explosion but I installed the ground wires
to prevent getting zapped by rather powerful discharge sparks
that occur under low-humidity conditions. These sparks were
impressive enough (on the order of 1/2" inch or so) that I became
concerned about them igniting sawdust or shavings. The static charge
builds up on the surface of the PVC pipe and flex-hoses
and just waits for a way to be discharged. The ground wire conducts
the charge away preventing its build-up.
Jake the Cat didn't appreciate them either when he brushed up
against a hose while I was cleaning sawdust off the floor.
I'd never seen him run quite that fast!
Stavros Macrakis
because they "perceive" them as smoke, and because they clog them up.
In fact, most will probably detect some kinds of chemical fumes (e.g.
solvents for finishes) as smoke as well.
Thus the best solution in a shop (as in a kitchen) is a _heat_ rather
than a smoke detector. It should be installed directly over where a
fire is most likely to start, e.g. over the dust collector or over the
pile of linseed-oil-soaked rags :-) . As usual, it should not be too
close to the ceiling/wall interface or other places where it might be
isolated from convection currents. The same people who make smoke
detectors make heat detectors.
It should also be hard-wired to 120v, and not battery powered (the
most common cause of alarm failure is dead batteries; the risk is
greater in parts of the house which are not continuously inhabited);
and it should be hard-wired to other alarms in the house, so there is
a good chance of hearing it even in deep sleep at the other end of the
house.
-s
Michael D. Myjak x7-3286
>
> There are two different dangers being discussed here.
>
> 1) dust explosion
> 2) fires in the dust collection bag
>
> Clearly, if there is a dense enough dust/air mixture in the collector,
> any ignition could cause a dust explosion. This includes static
> electricity as well as burning wood chips. I suspect that since the
> explosion of home dust collectors seems to be completely unknown in
> rec.woodworking or woodworking magazine land, I would suggest that the
> ground wire's "cheap insurance" policy does not cover the primary
> danger.
>
> What is this danger? Well, the shavings in a dust collector do burn.
> In fact, they burn quite well--I use them in my woodstove. While I've
> never been able to ignite them with static electricity (or even a torch
> spark generator), a match works well. However, if they are already
> burning when they enter the dust collection system, you might have a
> nice fire. Thus, I'd recommend the "insurance policy" of keeping bits
> and blades pitch free and keeping tools in tune so that they don't burn
> the wood in the first place.
I would also add a fire extinguisher to the "cheap insurance" list.
G. Paul Houtz
> b...@cs.cmu.edu (Bill Ross) writes:
> >
> >
> >
> >
>
> a fire that did some major damage. Seems like it was on the order
> of $100,000.00 of damage, and the article did say it was a dust
> collector fire.
>
> You probably won't hear about commercial stuff more recent than
> this since the new OSHA regulations went in a while back.
>
>
> indicated they found smoldering chips in the dust collector bag.
>
>static charges from dust collector system piping.
You state unequivacably that smoldering chips are not caused by build-up
of static charges from dust collecotr piping.
How do you know? What is your proof?
I ask, because:
1. Every major authority I have read on dust collection systems,
from Fine Woodworking, to books specifically about designing
dust collection systems, ALL indicate that there is a danger
of static discharge igniting the fine particles of dust
in the system.
2. It makes sense to me from my physics background. Extremely tiny
particles of flammable wood, and static discharges created by
fast moving wood chips against a plastic insulator. I seems
quite likely that a spark could ignite a particle of dust,
and that said particles could smolder and eventually start a fire.
>When this question came up 8 or 9 months ago, no one on the net has
>had nor knew of anyone who had a dust collector induced explosion. I
>believe that the lack of any quick and immediate posting to that
>affect indicate that this is still the case.
>IMHO (a general disclaimer) the volume of airborne "dust" (i.e. not
>counting particles, shavings, and in general non-combustible although
>flammable chunks of wood) being collected by a residential dust
>collection system is *no where near the density level* necessary to
>induce a (spark generated) spontaneous explosion.
> . . .
>No, I have not run an empirical analysis... just a "back of the
>envelop" sketch. Am I saying that its not a good idea to statically
>ground your system? No I am not... However, I am saying that with a
>high degree of probability it is not absolutely necessary. I believe
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
As I see it, There are two dangers from static discharge in a dust
collector:
1. Dust Explosion
2. Fire
The odds of the first one, are of course, extremely low. I would say
that you are right, that a dust explosion is unlikely.
However, you apply this conclusion to both dangers, which I believe
is a mistake. In fact, you do not even mention the fire aspect for
the rest of your posting. You concentrate instead on the dust explosion
aspect for the entire rest of your posting.
The danger from fire, is, I believe, quite high. While I cannot give
you a number, what if it were 1 in 100? Then, every 100th time you
turned on the dust collector, you would get a fire. For me, this would
take about a week.
What if it were 1 in 10,000? Then I would get a fire every two years.
What is the result? I don't think anyone would take the risk that
every two years their dust collector was going to catch fire. I won't.
Not with kids in the house. In fact, I grounded my DC, AND I empty
both bags, every night, without fail, because I don't want to take
ANY risk of fire with my system.
Let's not muddle the issue. It may cause people to decide that "the
whole dust collection grounding issue is up in the air, so I don't need
to ground mine", which is not true.
As I said before, authorities and experts all agree that dust collection
systems must be grounded. To advise otherwise, it seems to me, is to
advise a dangerous course which is contrary to expert opinion. I would
not want to be responsible for any tragedies.
Tom Gilstrap
> I know that a static discharge can cause a fire, they are
> very careful about static during the handling of certain
>
> ... Stuff deleted ...
>
> explosions are not uncommon. But can anyone document an
> actual incident of this type in a dust-collection system?
I don't know about fire, but from personal experience I can say
DON'T TOUCH YOUR TABLE SAW after you clean up a pile of sawdust
whether from a dust-collection system or a plain shopvac! The
other day I sucked up the 6" deep pile under my table saw and
noticed the sawdust was standing on-end around the tip of the
suction hose. When I reached up and grabbed the edge of the
table saw I got a static shock that left my arm numb for a
few minutes. Nothing serious, but I'll pay attention to not
touching anything metal (grounded) after bulk cleanup.
--
Tom Gilstrap
Northeastern State University
Tahlequah, Oklahoma
gils...@cherokee.nsuok.edu
Ken Colasuonno
> IMHO (a general disclaimer) the volume of airborne "dust" (i.e. not
> counting particles, shavings, and in general non-combustible although
> flammable chunks of wood) being collected by a residential dust
> collection system is *no where near the density level* necessary to
> induce a (spark generated) spontaneous explosion.
OK I will bite. Here is what I have read from the booklet titled
"Dust Collection Basics. Recommendations for Home Shop Systems". Put
out by Woodstock International Inc. Ordered from Grizzly ($5.95+sh).
Here are some interesting passages. (CAPS means bold face).
Pg 10. "WARNING: THERE IS RISK OF EXPLOSION DUE TO DUST DISPERAL INTO
THE AIR IF A COLLECTION OR FILTER BAG ACCIDENTALLY BECOMES LOOSE
DURING OPERATOIN OR DURING NORMAL CLEANING PROCEDURES."
Nothing to due with static really, but it means that you can generate
enough dust to make your house go boom.
Pg. 17 "WARNING: There is a fire or explosion hazard if plastic piping
material is used for dust collection without being grounded against
static electrical charge build-up".
Pg. 19 "It is important to note again that nonconduction plastic
piping and flexible hose, no matter what type (including wire
reinforced), must be completely grounded against static electrical
charge build-up."
Pg. 20. "It is very important when using insulating-type materials in
a dust collection system, that no matter what the type, they must be
grounded."
Pg 25. "If you elect to use plastic pipe or flex-hose, your system
MUST BE grounded."
And finally:
Pg 28. "WARNING: There is a fire or explosion hazard if all duct work
is not properly grounded."
Seems to say pretty clearly that you should ground your systems.
Right? And the $25 or so for all the ham radio wire that you might
use is pretty cheap insurance in light of all the other money you
poured into your dust system. And shop. And house. etc.
Ken
Chris Lewis
>(now for the flame inducing, opinionated, discussion generating statement... ?^)
Not this one again.
>IMHO (a general disclaimer) the volume of airborne "dust" (i.e. not
>counting particles, shavings, and in general non-combustible although
>flammable chunks of wood) being collected by a residential dust
>collection system is *no where near the density level* necessary to
>induce a (spark generated) spontaneous explosion.
Perform the following experiment:
- take a candle, light it, and place it in the centre
of a table.
- take a half teaspoon or so of fine dry sawdust. Ie: the
dust produced by a orbital or belt sander with relatively
fine grit.
- place the sawdust in the centre of a sheet of paper.
- roll the sheet of paper into a cylinder.
- "puff" thru the cylinder, blowing the sawdust into the
upper edge of the candle flame.
Provided that the dust is dry enough, and you puff sharply enough,
you will generate a fireball as big as a basketball. If you throw in some
fine aluminum dust too, it'll be even better. You'll probably lose
some facial hair too.
You've gotten stuck on it having to be an "explosion". It won't
do that unless there's LOTS of it, or it's tightly contained (paint
cans make great "dust cannons"...). But that's beside the point.
A teaspoon or so of fine sawdust dust can cause a pretty spectacular
flash, which may ignite something else. Like the can of paint thinner
sitting nearby, or the solvent soaked rags you were finishing your
wood with. It might not blow your shop off its foundations, but
a flash fire is close enough not to matter.
Certainly, a properly running dust collector without grounding may
not quite have a spark coincide with a sufficiently high concentration
of dust. But a teaspoon ain't much dust, and a static discharge is
hotter than a candle flame. It's too marginal to trust for long-term
safety.
Incidentally, the instructions for my dust collector state very
clearly that the highest hazard is when you're pulling the bag
off the blower. That's when the really fine dust will fly around,
and provides a good opportunity for a spark discharge while fiddling
with tubing or simply touching the bag.
>No, I have not run an empirical analysis... just a "back of the
>envelop" sketch.
All you've done is some handwaving. "Back of the envelope sketches"
have rough numbers and calculations. I've not seen any in your posting.
--
Chris Lewis; cle...@ferret.ocunix.on.ca; Phone: Canada 613 832-0541
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