My hi-tech DC system for my TS consists of a shop-vac connected to a 30
gallon plastic dust bin. The dust bin is then connected to the bottom
of my contractor saw with a flexible aluminum 4" dryer vent. I
normally have the back of the saw closed off with 1/4" plywood and this
system works fairly well.
Yesterday I needed to clean out the inside of the saw, so I unplugged
the saw and turned on the shop vac. I then bent over and pushed the
sawdust into the chute on the bottom of the saw. While I was doing
this everytime my hand partially blocked the hole leading to the dryer
vent it would compress slighty and touch the frame of the saw. That is
where I saw the spark.
A tiny spark between the leg of the saw and the aluminum vent connected
between the plastic dust bin and the plastice adapter on the saw. In
theory, static can ignite fuel vapors or gases, but wood dust?
Both the shop-vac and TS are plugged into properly wired 3-prong
outlets but this is only really grounding them in case of a motor
failure. Should I somehow ground this DC system or just ignore the
static?
In article <[email protected]>,
Edwin Pawlowski <[email protected]> wrote:
>
><[email protected]> wrote in message >
>> I've thrown hanfulls of sawdust into a fire.
>>
>> That's pretty much the same thing as dumping a load of dust on
>> the floor next to a gas water heater with a pilot light, right?
>>
>
>Did the room explode?
>
>
Not to diminish any dangers or recommend against any safety practices,
but it's often difficult to get a lit match to light a flammable
liquid, let alone a handful of dust.
--
Larry Wasserman Baltimore, Maryland
[email protected]
dnoyeB wrote:
> Upscale wrote:
> > "RayV" <[email protected]> wrote in message
> >
> >>theory, static can ignite fuel vapors or gases, but wood dust?
> >
> >
> > Wood dust in the right proportions can be explosive. You can probably find
> > more information on it in the rec archives, but I'm sure quite a few people
> > will respond with additional information.
> >
> >
>
> I'd like to see that one on myth busters.
http://www.ydr.com/newsfull/ci_3604224
Rick M wrote:
> "Gus" <[email protected]> wrote
> >
> > Myth Busters is pseudo-science at BEST.
> >
> > They raise more questions than they answer.
> >
>
> But this group is solidly science-based, aren't we? After all, we've a
> wealth of experience ... umm make that a large vocal group that believes
> they have solid factual data, with a minority that provides verifiable data,
> sound data analysis and (usually) a well written presentation of that
> analysis.
>
>
>
> Read the FAQ. The MYTH of static-induced home dust collection system
> explosions is well documented.
>
So, by your logic, if it's in the FAQ, it MUST be true.
Remind me to contact you next time I have swamp land for sale.
I've searched the wreck archives, osha site, googled the web... all I
can find are anecdotal statements.
"sawdust can explode..."
"any combustible material in dust form is explosive..."
"PVC cannot be effectively grounded..."
What I can't find are any specs or hard facts. If I rub my feet on the
carpet and touch a doorknob with a handful of sawdust will my hand
explode? Without any facts I'm extremely unlikely to believe that a
home shop DC system can explode. Didn't one of Adolf's boys say,
"if you repeat it often enough it will become true"?
Case in point:
Just about every driver's manual I have read (ok, two) states that
for a car with a manual transmission...you should put the car in
reverse when parked facing downhill and in first when parked facing
uphill. This is totally idiotic! That advice is based on the false
assumption that the engine can only rotate in one direction. But still
it is part of driver's ed training.
Doesn't anyone beLIEve in facts anymore?
How much dust in what concentration is required for an explosion?
How much of a static charge would be required to ignite that dust?
I only found one link that supposedly had data available but the link
is now dead.
Doug Payne wrote:
> On 28/03/2006 3:56 PM, RayV wrote:
> > I've searched the wreck archives, osha site, googled the web... all I
> > can find are anecdotal statements.
> >
> > "sawdust can explode..."
> > "any combustible material in dust form is explosive..."
>
> When I was younger, I worked a couple of summers on Great Lakes boats
> carrying wheat. That dust can definitely explode:
>
> http://www.fireworld.com/magazine/grainperil.html
> http://osuextra.okstate.edu/pdfs/CR-1737web.pdf
>
> Under the right conditions and in the right amounts, sawdust is no
> different:
>
> http://www.cep.ca/health_safety/files/wooddust_e.html
> http://www.hse.gov.uk/pubns/wis1.pdf
> http://www.healthandsafety.co.uk/hswd.html
> http://www.dol.state.nc.us/osha/etta/hazard_alerts/CombDust.pdf
>
> And on and on...
sure, in big industrial facilities with dust systems moving tons of
material per hour the risk is real, and the measures taken to control
static discharge are vital. in the home shop with probably a maximum
5hp collector sucking dust from at most a few machines at once through
probably 6" maximum pipe you aren't going to make a big enough static
spark to get ignition.
if you can present evidence to the contrary I'll nominate you king of
the wreck.
todd wrote:
> "Dhakala" <[email protected]> wrote in message
> news:[email protected]...
> >
> > dnoyeB wrote:
> >> Upscale wrote:
> >> > "RayV" <[email protected]> wrote in message
> >> >
> >> >>theory, static can ignite fuel vapors or gases, but wood dust?
> >> >
> >> >
> >> > Wood dust in the right proportions can be explosive. You can probably
> >> > find
> >> > more information on it in the rec archives, but I'm sure quite a few
> >> > people
> >> > will respond with additional information.
> >> >
> >> >
> >>
> >> I'd like to see that one on myth busters.
> >
> > http://www.ydr.com/newsfull/ci_3604224
>
> No one says it can't happen in an industrial situation. To my knowledge, no
> one has ever documented a case of a dust explosion in a home workshop. If
> there is such documentation, I'm open to seeing it, but AFAIK, it has never
> been produced here when this topic has surfaced.
>
Most of the theoretical calculations posted here indicate
such an explosion is unlikely under stady-state conditions.
Maybe if a clump of dust gets thrown into the air all at
once, like when changing dust collector bags or filters
and there is a pilot light nearby.
A few years back here in rec.woodorking someone
posted that the Ann Arbor, Michigan Fire Department
had documented an average one such accident per year,
over the past 25 years, in home workshops, with the
most common ignition source being a spark from an
older open-frame electircal motor.
I've not been able to find the article in the Google Archives.
That's not at all the same as a static spark. One supposes
these may have actually been vapor explosions though the
topic of the thread was dust explostions.
If you throw a handful of sawdust onto a fire you can get a nice
fireball. So there is no question that sawdust and air can
be ixed and ignited. That's a far cry from your garage suddenly
exploding while sanding down a coffee table.
--
FF
WConner wrote:
> 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.
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
at once.
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.
--
FF
Andy Dingley wrote:
> On Sat, 01 Apr 2006 14:16:34 -0000, [email protected] (Robert
> Bonomi) wrote:
>
> >I guarantee you that static electricity _does_ have enough energy. Under
> >the _right_ circumstances.
>
> I (and every professional electrostatics expert I've spoken to)
> disagree.
>
> Got the numbers ? What's the discharge mechanism ?
Ever hear of lightning?
If a lightning bolt strikes your dust collection system, duck!
--
FF
Ray,
This topic has been hashed since I was a regular over 6 years ago on
the wreck. I can tell you that I had a similar occurrence with my
original setup (which is similar to yours). I grounded everything and
never took the chance. Could it happen? Under the right circumstances
- sure. Do you have the right circumstances for it to happen? Why
take the chance. $10 for the ground wire and attach it to your TS or
whatever and it's done. I had a sanding table that created some
extremely "fine" dust and never had a problem. The $10 was just an
insurance policy that gave me that added peace of mind. Lew Hodgett is
a very well read and versed guy who give can you probably all the stats
you'd ever need. I've read some of his responses and he's correct in
his writings. If there's a doubt - remove it and ground them. Best of
luck to you.
Jim
Edwin Pawlowski wrote:
> <[email protected]> wrote in message
> > 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
> > at once.
> >
> > 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.
>
> Any documented cases of that happening?
Yes.
I've thrown hanfulls of sawdust into a fire.
That's pretty much the same thing as dumping a load of dust on
the floor next to a gas water heater with a pilot light, right?
--
FF
George wrote:
> <[email protected]> wrote in message
> news:[email protected]..
>>.
> > 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
> > at once.
> >
> > 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.
> >
>
> 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.
--
FF
Mark & Juanita wrote:
> ...
> 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.
>
Sure it will.
I've seen some impressive sparks generated by a prototype
pneumatic conveyer using PVC pipe. A dust collector is
a pneumatic conveyor. A foot long spark means hundreds of
thousands of volts. But I don't know how much current.
No one was hurt and no fires or explosions resulted so I
expect the current was miniscule.
As others have noted, grounding the system is a good idea to
prevent being zapped by the sparks. They won't kill kill you,
but they might shock you into doing something that will.
--
FF
Edwin Pawlowski wrote:
> <[email protected]> wrote in message >
egarding dumping a dust colector:
> > 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.
And later wrote:
> > I've thrown hanfulls of sawdust into a fire.
> >
> > That's pretty much the same thing as dumping a load of dust on
> > the floor next to a gas water heater with a pilot light, right?
> >
>
> Did the room explode?
Yes. In fact I was killed.
Seriously, I did it outdoors.
--
FF
[email protected] wrote:
> In article <[email protected]>,
> Edwin Pawlowski <[email protected]> wrote:
> >
> ><[email protected]> wrote in message >
> >> I've thrown hanfulls of sawdust into a fire.
> >>
> >> That's pretty much the same thing as dumping a load of dust on
> >> the floor next to a gas water heater with a pilot light, right?
> >>
> >
> >Did the room explode?
> >
> >
>
> Not to diminish any dangers or recommend against any safety practices,
> but it's often difficult to get a lit match to light a flammable
> liquid, let alone a handful of dust.
>
Dead wrong!
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
will ignite.
--
FF
"Flammable, nonflammable, inflammable--why are there three?"
-- George Carlin
George wrote:
> <[email protected]> wrote in message
> news:[email protected]...
> >>
> >> Not to diminish any dangers or recommend against any safety practices,
> >> but it's often difficult to get a lit match to light a flammable
> >> liquid, let alone a handful of dust.
> >>
> >
> > Dead wrong!
> >
> > 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
> > will ignite.
> >
>
> Which of course demonstrates that it's not the liquid, but the gas which
> ignites....
Precisely.
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.
--
FF
In article <[email protected]>,
Mark & Juanita <[email protected]> wrote:
>On 27 Mar 2006 09:15:12 -0800, "Dhakala" <[email protected]>
>wrote:
>
>>
>>dnoyeB wrote:
>>> Upscale wrote:
>>> > "RayV" <[email protected]> wrote in message
>>> >
>>> >>theory, static can ignite fuel vapors or gases, but wood dust?
>>> >
>>> >
>>> > Wood dust in the right proportions can be explosive. You can probably find
>>> > more information on it in the rec archives, but I'm sure quite a few people
>>> > will respond with additional information.
>>> >
>>> >
>>>
>>> I'd like to see that one on myth busters.
>>
>>http://www.ydr.com/newsfull/ci_3604224
>
> At the time the article was written, static electricity as a cause was
>purely speculation. They also indicated a hot ember could have started the
>fire.
>
> Mythbusters would be a good venue for testing this theory. I seriously
>doubt that static electricity has enough energy to ignite a dust explosion.
I guarantee you that static electricity _does_ have enough energy. Under
the _right_ circumstances.
Now, as for sawdust, in a home/hobby shop setting, it is *EXTREMELY*UNLIKELY*
that the 'right circumstances' will occur.
Look ... if you think it could be a problem, grab some wire and connect the
two together. You only get the spark where there is a difference between the
two conductors. Wire keeps them roughly equal.
If you then blow a breaker (or fry the wire) when you turn the saw on, that
aint static ... that's 'real' juice and you need to find out where it's
coming from and fix it.
This issue is a perpetual football here on the wreck and the simple answer
is the complete one. Ground it. The cost is small, the effort relatively
trivial, the peace of mind immeasurable. (My plastic pipe lays on a cement
basement floor and stays drained.)
The person who said that kits for bleeding the static from plastic pipe were
hokum doesn't understand capacitance. They do work ... but they are solving
a non-problem.
But the whole issue is probably moot since 1) you probably don't have dry
enough circumstances to allow you to build up sufficient static charges to
matter 2) you don't deal in a dense enough cloud of fine enough dust
particles to matter even if there was a spark plug every six inches in your
ducting and 3) your machines are not running long enough to build up those
charges even under Arizona humidity / worst case scenario.
Relax, cut some lumber. Have fun.
Bill
In article <[email protected]>,
Andy Dingley <[email protected]> wrote:
>On Sat, 01 Apr 2006 14:16:34 -0000, [email protected] (Robert
>Bonomi) wrote:
>
>>I guarantee you that static electricity _does_ have enough energy. Under
>>the _right_ circumstances.
>
>I (and every professional electrostatics expert I've spoken to)
>disagree.
Well, *that's* the problem. you listened to the experts. <grin>
Me, I just _did_ it. reliably and repeatably. around 35 years ago.
It was a high school 'science fair' project.
Plexiglas 5-sided cube, about 8" on a side, with a circa 3" spike
through the middle of one face, the outside of which was connected to
a fair-sized grounding cable (heavy-duty automotive jumper cables).
Then I had a fairly hefty Van de Graff generator -- one which could pull a
'spark' somewhere around 9". Agreed, this is getting well towards
'artificial lightning', but it _is_ still just static electricity.
Throw some cake flour in the box, hold a cover piece over it and 'shake well',
set it back down, slide the cover off, and promptly take the 'wand' connected
to the top of the Van de Graff and bring it across the box, from the edge
opposite where the spike was. ***KA-BOOOOM***!!!!
At around minimum explosive density it was merely "_really_ loud".
And it got more so, as the dust density increased.
Even without any dust, the static discharge alone made a pretty fair amount
of noise.
Note: then there were they guys building the *big* (as in 8-foot-plus tall)
Tesla coils. _Those_ things were dangerous! While admittedly not 'static'
machines, *anything* that can maintain and sustain an atmospheric arc (a
"Jacob's ladder") in excess of 4 _feet_ is deserving of some serious
respect. :)
In article <[email protected]>, todd <[email protected]> wrote:
>"Robert Bonomi" <[email protected]> wrote in message
>news:[email protected]...
>>
>> Note: then there were they guys building the *big* (as in 8-foot-plus
>> tall)
>> Tesla coils. _Those_ things were dangerous! While admittedly not
>> 'static'
>> machines, *anything* that can maintain and sustain an atmospheric arc (a
>> "Jacob's ladder") in excess of 4 _feet_ is deserving of some serious
>> respect. :)
>
>Sounds like they had a nice little toy there. In a previous career, I
>designed and tested high-voltage insulators. I tested using an AC set that
>could generate 1000kV and create an arc over 15 feet long.
That jibes w/ my recollections -- vague memories say they were playing
with circa 250KV.
> We also used an
>impulse generator which simulated lightning and switching surges that could
>go up to about 2500kV. All of that was very interesting.
>
>If you want even more fun, do high *current* testing and run 20kA through
>some hardware. Ka-boom!
Shall I mention the time I saw somebody swing a crane boom in to the
_feeder_ lines to an operating sub-station, and only about 500 ft away
from the sub-station. The _flame_ front was merely a couple of =hundred=
feet *wide*. It went away fairly quickly -- like a second or so -- but
there were also several 'booms' and small clouds of smoke from the station
itself -- apparently 'protective' disconnects when the three-phase feed
went *that* unbalanced.
I've heard _one_ louder noise than that -- a lightning strike on a telephone
pole about 50' outside our back door. I *saw* the glass patio-doors I
was sitting not 10' away from bulge (about 3 inches!!) from the pressure
wave.
"Dhakala" <[email protected]> wrote in message
news:[email protected]...
>
> dnoyeB wrote:
>> Upscale wrote:
>> > "RayV" <[email protected]> wrote in message
>> >
>> >>theory, static can ignite fuel vapors or gases, but wood dust?
>> >
>> >
>> > Wood dust in the right proportions can be explosive. You can probably
>> > find
>> > more information on it in the rec archives, but I'm sure quite a few
>> > people
>> > will respond with additional information.
>> >
>> >
>>
>> I'd like to see that one on myth busters.
>
> http://www.ydr.com/newsfull/ci_3604224
No one says it can't happen in an industrial situation. To my knowledge, no
one has ever documented a case of a dust explosion in a home workshop. If
there is such documentation, I'm open to seeing it, but AFAIK, it has never
been produced here when this topic has surfaced.
todd
"RayV" <[email protected]> wrote in message
news:[email protected]...
>
> A tiny spark between the leg of the saw and the aluminum vent connected
> between the plastic dust bin and the plastice adapter on the saw. In
> theory, static can ignite fuel vapors or gases, but wood dust?
>
> Both the shop-vac and TS are plugged into properly wired 3-prong
> outlets but this is only really grounding them in case of a motor
> failure. Should I somehow ground this DC system or just ignore the
> static?
>
A while back an engineer, MIT I think, wrote an article on the subject for
one of the ww mags (sorry, don't remember which one). He essensially
concluded (supported by formulas & math) that you can't move enough air thru
a 4" pipe with a dust collector (let alone a shopvac) to generate enough
static charge to sustain a spark of sufficient duration to ignite wood dust.
But urban legends die hard. Anyway, the spark you saw is the same as the
one you see when you slide out of your car and touch the key to the door.
And if you touch the door with your finger instead of the key you'll feel
it. If you find that discharge thru your finger annoying, that's about the
only reason to ground non-metalic dust collection pipe. You can ground the
metal dryer pipe if it makes you feel better but you will still be building
static charge in the non-metalic shop vac hose. And I'll bet you never
worried about that when you were using the shopvac for other things.
In article <[email protected]>, Michael Daly
<[email protected]> wrote:
> While I doubt that an explosion in a home DC will occur - how about a fire?
From static electricity? Bwahahahahahaha!
"Woodhead" <[email protected]> wrote in message
news:[email protected]...
> There is a possibility that one of the two machines has a faulty ground
> connection and you are seeing the connection of an ungrounded
> machine to a grounded one. Check to ensure there is zero-5 ohms
> resistance between the saw chassis and the shop-vac motor frame
> when they are plugged in...... or....There are kits available to
> ground plastic 4" hose to discharge static. Guess it could
> happen in aluminum pipe too. Wrap a copper ground wire
> around the pipe and screw the ends of the wire to the saw and
> DC frame.
>
I'd have a whole lot more confidence in your method if they didn't put
(insu/iso)lation on conductors to keep them from grounding.
Testing for stray voltage or bad ground is a good idea in the conducting
saw.
Andy Dingley <[email protected]> wrote:
>On Sat, 01 Apr 2006 14:16:34 -0000, [email protected] (Robert
>Bonomi) wrote:
>
>>I guarantee you that static electricity _does_ have enough energy. Under
>>the _right_ circumstances.
>
>I (and every professional electrostatics expert I've spoken to)
>disagree.
>
>Got the numbers ?
~10^10 joules
>What's the discharge mechanism ?
Thunderstorm.
;-)
Ken Muldrew
[email protected]
(remove all letters after y in the alphabet)
<[email protected]> wrote in message
news:[email protected]...
> 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.
>
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....
<[email protected]> wrote in message
news:[email protected]...
>>
>> Not to diminish any dangers or recommend against any safety practices,
>> but it's often difficult to get a lit match to light a flammable
>> liquid, let alone a handful of dust.
>>
>
> Dead wrong!
>
> 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
> will ignite.
>
Which of course demonstrates that it's not the liquid, but the gas which
ignites....
Oleg Lego wrote:
> The RayV entity posted thusly:
>
>
>>I've searched the wreck archives, osha site, googled the web... all I
>>can find are anecdotal statements.
>>
>>"sawdust can explode..."
>>"any combustible material in dust form is explosive..."
>>"PVC cannot be effectively grounded..."
>
>
> <snippage>
>
>>Doesn't anyone beLIEve in facts anymore?
>>How much dust in what concentration is required for an explosion?
>>How much of a static charge would be required to ignite that dust?
>
>
> Yes, I do believe in facts.
>
> No idea of the concentrations or how hot a spark it would take to set
> it off.
>
> 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.
er
--
email not valid
In article <[email protected]>,
Enoch Root <[email protected]> wrote:
<...snipped...>
>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.
>
>er
>--
>email not valid
That must have been fun, but how many times were you successful
igniting it with a static discharge?
--
Larry Wasserman Baltimore, Maryland
[email protected]
In article <[email protected]>,
Lew Hodgett <[email protected]> wrote:
>RE: Subject
>
>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.
>
>Lew
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.
--
Larry Wasserman Baltimore, Maryland
[email protected]
I should have so much dust and that big of a collector!!
"Dhakala" <[email protected]> wrote in message
news:[email protected]...
>
> dnoyeB wrote:
> > Upscale wrote:
> > > "RayV" <[email protected]> wrote in message
> > >
> > >>theory, static can ignite fuel vapors or gases, but wood dust?
> > >
> > >
> > > Wood dust in the right proportions can be explosive. You can probably
find
> > > more information on it in the rec archives, but I'm sure quite a few
people
> > > will respond with additional information.
> > >
> > >
> >
> > I'd like to see that one on myth busters.
>
> http://www.ydr.com/newsfull/ci_3604224
>
There is a possibility that one of the two machines has a faulty ground
connection and you are seeing the connection of an ungrounded
machine to a grounded one. Check to ensure there is zero-5 ohms
resistance between the saw chassis and the shop-vac motor frame
when they are plugged in...... or....There are kits available to
ground plastic 4" hose to discharge static. Guess it could
happen in aluminum pipe too. Wrap a copper ground wire
around the pipe and screw the ends of the wire to the saw and
DC frame.
Jim
"RayV" <[email protected]> wrote in message
news:[email protected]...
> My hi-tech DC system for my TS consists of a shop-vac connected to a 30
> gallon plastic dust bin. The dust bin is then connected to the bottom
> of my contractor saw with a flexible aluminum 4" dryer vent. I
> normally have the back of the saw closed off with 1/4" plywood and this
> system works fairly well.
>
> Yesterday I needed to clean out the inside of the saw, so I unplugged
> the saw and turned on the shop vac. I then bent over and pushed the
> sawdust into the chute on the bottom of the saw. While I was doing
> this everytime my hand partially blocked the hole leading to the dryer
> vent it would compress slighty and touch the frame of the saw. That is
> where I saw the spark.
>
> A tiny spark between the leg of the saw and the aluminum vent connected
> between the plastic dust bin and the plastice adapter on the saw. In
> theory, static can ignite fuel vapors or gases, but wood dust?
>
> Both the shop-vac and TS are plugged into properly wired 3-prong
> outlets but this is only really grounding them in case of a motor
> failure. Should I somehow ground this DC system or just ignore the
> static?
>
On Wed, 29 Mar 2006 00:20:55 GMT, Lew Hodgett <[email protected]>
wrote:
>What everybody is dancing around is "LEL"
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.
>or "Lower Explosive Limit".
>
>It is that point where the dust volume in the air WILL explode.
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"
comment.
On Sat, 01 Apr 2006 09:47:58 -0700, Mark & Juanita
<[email protected]> wrote:
This might help:
http://www.chemeng.ed.ac.uk/~emju49/SP2001/webpage/deh/deh4.html
>>I guarantee you that static electricity _does_ have enough energy. Under
>>the _right_ circumstances.
>>
>
> I should have been more specific. My sentence above should have read, "I
>seriously doubt that static electricity has enough energy to ignite a wood
>dust explosion from the dust that would be generated in a typical home
>woodshop."
>
>>Now, as for sawdust, in a home/hobby shop setting, it is *EXTREMELY*UNLIKELY*
>>that the 'right circumstances' will occur.
"Robert Bonomi" <[email protected]> wrote in message
news:[email protected]...
>
> Note: then there were they guys building the *big* (as in 8-foot-plus
> tall)
> Tesla coils. _Those_ things were dangerous! While admittedly not
> 'static'
> machines, *anything* that can maintain and sustain an atmospheric arc (a
> "Jacob's ladder") in excess of 4 _feet_ is deserving of some serious
> respect. :)
Sounds like they had a nice little toy there. In a previous career, I
designed and tested high-voltage insulators. I tested using an AC set that
could generate 1000kV and create an arc over 15 feet long. We also used an
impulse generator which simulated lightning and switching surges that could
go up to about 2500kV. All of that was very interesting.
If you want even more fun, do high *current* testing and run 20kA through
some hardware. Ka-boom!
todd
"Gus" <[email protected]> wrote
>
> Myth Busters is pseudo-science at BEST.
>
> They raise more questions than they answer.
>
But this group is solidly science-based, aren't we? After all, we've a
wealth of experience ... umm make that a large vocal group that believes
they have solid factual data, with a minority that provides verifiable data,
sound data analysis and (usually) a well written presentation of that
analysis.
Read the FAQ. The MYTH of static-induced home dust collection system
explosions is well documented.
Get to know Google ... in fact, make Google your friend. The MYTH of
static-induced home dust collection system explosions is well documented.
Especially important is to read the rec.woodworking archives, searching for
dust + explosion.
Rick
<[email protected]> wrote in message
> 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
> at once.
>
> 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.
Any documented cases of that happening?
In article <[email protected]>,
Andy Dingley <[email protected]> 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.
--
Larry Wasserman Baltimore, Maryland
[email protected]
RE: Subject
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.
Lew
[email protected] wrote:
> 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.
True, which is why dust is such a bugger.
Just ask the grain operator.
Lew
On 27-Mar-2006, Mark & Juanita <[email protected]> wrote:
> I seriously
> doubt that static electricity has enough energy to ignite a dust explosion.
That depends on how much static and how fine the dust. While I doubt
that walking across a carpet and then touching a dust collector would do it,
the kind of dusts that can be found in silos of anything (and bulk carriers being
loaded etc) in conjuction with a significant static source could do it.
Continuously running equipment can continuously generate static.
Mike
<[email protected]> wrote in message >
> I've thrown hanfulls of sawdust into a fire.
>
> That's pretty much the same thing as dumping a load of dust on
> the floor next to a gas water heater with a pilot light, right?
>
Did the room explode?
Bill Pentz has done a lot of research into dust collectors:
http://billpentz.com/woodworking/cyclone/index.cfm
and has some info on static concerns:
http://billpentz.com/woodworking/cyclone/Ducting.cfm#StaticElectricity
After reading much on the subject my feeling is that a shop system will
not be a problem. A dust explosion is a rapid burning. The static spark
will have to produce enough BTUs to start a spec of dust burning then
(almost instantaneously) the spec of dust must be close enough to
another speck and produce enough BTUs to get that burning, and so on and
so on. Impossible, no but not very likely.
The real danger in a shop situation is what happened when YOU feel the
shock from a static discharge. Does your hand suddenly and involuntarily
jump into that spinning saw blade? Do you best to eliminate static for
this reason.
RayV wrote:
> My hi-tech DC system for my TS consists of a shop-vac connected to a 30
> gallon plastic dust bin. The dust bin is then connected to the bottom
> of my contractor saw with a flexible aluminum 4" dryer vent. I
> normally have the back of the saw closed off with 1/4" plywood and this
> system works fairly well.
>
> Yesterday I needed to clean out the inside of the saw, so I unplugged
> the saw and turned on the shop vac. I then bent over and pushed the
> sawdust into the chute on the bottom of the saw. While I was doing
> this everytime my hand partially blocked the hole leading to the dryer
> vent it would compress slighty and touch the frame of the saw. That is
> where I saw the spark.
>
> A tiny spark between the leg of the saw and the aluminum vent connected
> between the plastic dust bin and the plastice adapter on the saw. In
> theory, static can ignite fuel vapors or gases, but wood dust?
>
> Both the shop-vac and TS are plugged into properly wired 3-prong
> outlets but this is only really grounding them in case of a motor
> failure. Should I somehow ground this DC system or just ignore the
> static?
>
"Doug Payne" <[email protected]> wrote in message
news:[email protected]...
> On 28/03/2006 3:56 PM, RayV wrote:
>> I've searched the wreck archives, osha site, googled the web... all I
>> can find are anecdotal statements.
>>
>> "sawdust can explode..."
>> "any combustible material in dust form is explosive..."
>
> When I was younger, I worked a couple of summers on Great Lakes boats
> carrying wheat. That dust can definitely explode:
>
> http://www.fireworld.com/magazine/grainperil.html
> http://osuextra.okstate.edu/pdfs/CR-1737web.pdf
>
> Under the right conditions and in the right amounts, sawdust is no
> different:
>
> http://www.cep.ca/health_safety/files/wooddust_e.html
> http://www.hse.gov.uk/pubns/wis1.pdf
> http://www.healthandsafety.co.uk/hswd.html
> http://www.dol.state.nc.us/osha/etta/hazard_alerts/CombDust.pdf
>
> And on and on...
Flour would be another prime example. I'm sure we're all familiar with the
many reports of kitchen dust explosions when flour particles became airborne
and explosively ignited from a lit burner on the stove.
todd
On 28/03/2006 3:56 PM, RayV wrote:
> I've searched the wreck archives, osha site, googled the web... all I
> can find are anecdotal statements.
>
> "sawdust can explode..."
> "any combustible material in dust form is explosive..."
When I was younger, I worked a couple of summers on Great Lakes boats
carrying wheat. That dust can definitely explode:
http://www.fireworld.com/magazine/grainperil.html
http://osuextra.okstate.edu/pdfs/CR-1737web.pdf
Under the right conditions and in the right amounts, sawdust is no
different:
http://www.cep.ca/health_safety/files/wooddust_e.html
http://www.hse.gov.uk/pubns/wis1.pdf
http://www.healthandsafety.co.uk/hswd.html
http://www.dol.state.nc.us/osha/etta/hazard_alerts/CombDust.pdf
And on and on...
On Sat, 01 Apr 2006 14:16:34 -0000, [email protected] (Robert
Bonomi) wrote:
>In article <[email protected]>,
>Mark & Juanita <[email protected]> wrote:
>>On 27 Mar 2006 09:15:12 -0800, "Dhakala" <[email protected]>
>>wrote:
>>
>>>
>>>dnoyeB wrote:
>>>> Upscale wrote:
>>>> > "RayV" <[email protected]> wrote in message
>>>> >
>>>> >>theory, static can ignite fuel vapors or gases, but wood dust?
>>>> >
>>>> >
>>>> > Wood dust in the right proportions can be explosive. You can probably find
>>>> > more information on it in the rec archives, but I'm sure quite a few people
>>>> > will respond with additional information.
>>>> >
>>>> >
>>>>
>>>> I'd like to see that one on myth busters.
>>>
>>>http://www.ydr.com/newsfull/ci_3604224
>>
>> At the time the article was written, static electricity as a cause was
>>purely speculation. They also indicated a hot ember could have started the
>>fire.
>>
>> Mythbusters would be a good venue for testing this theory. I seriously
>>doubt that static electricity has enough energy to ignite a dust explosion.
>
>I guarantee you that static electricity _does_ have enough energy. Under
>the _right_ circumstances.
>
I should have been more specific. My sentence above should have read, "I
seriously doubt that static electricity has enough energy to ignite a wood
dust explosion from the dust that would be generated in a typical home
woodshop."
>Now, as for sawdust, in a home/hobby shop setting, it is *EXTREMELY*UNLIKELY*
>that the 'right circumstances' will occur.
>
+--------------------------------------------------------------------------------+
If you're gonna be dumb, you better be tough
+--------------------------------------------------------------------------------+
On 27 Mar 2006 09:15:12 -0800, "Dhakala" <[email protected]>
wrote:
>
>dnoyeB wrote:
>> Upscale wrote:
>> > "RayV" <[email protected]> wrote in message
>> >
>> >>theory, static can ignite fuel vapors or gases, but wood dust?
>> >
>> >
>> > Wood dust in the right proportions can be explosive. You can probably find
>> > more information on it in the rec archives, but I'm sure quite a few people
>> > will respond with additional information.
>> >
>> >
>>
>> I'd like to see that one on myth busters.
>
>http://www.ydr.com/newsfull/ci_3604224
At the time the article was written, static electricity as a cause was
purely speculation. They also indicated a hot ember could have started the
fire.
Mythbusters would be a good venue for testing this theory. I seriously
doubt that static electricity has enough energy to ignite a dust explosion.
An electric arc or hot piece of metal contains significantly more energy to
start the required reaction.
+--------------------------------------------------------------------------------+
If you're gonna be dumb, you better be tough
+--------------------------------------------------------------------------------+
<[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>,
> Andy Dingley <[email protected]> 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.
>
>
> --
>
> Larry Wasserman Baltimore, Maryland
> [email protected]
>
Agreed, but ... still don't throw a box of sanding dust into the
wood stove if there's still a small fire in there. Took a LONG
time to grow back eyebrows!
Woof!
Pop
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.
Walt Conner
Robert Bonomi wrote:
> In article <[email protected]>, todd <[email protected]> wrote:
>
>>"Robert Bonomi" <[email protected]> wrote in message
>>news:[email protected]...
>>
>>>Note: then there were they guys building the *big* (as in 8-foot-plus
>>>tall)
>>>Tesla coils. _Those_ things were dangerous! While admittedly not
>>>'static'
>>>machines, *anything* that can maintain and sustain an atmospheric arc (a
>>>"Jacob's ladder") in excess of 4 _feet_ is deserving of some serious
>>>respect. :)
>>
>>Sounds like they had a nice little toy there. In a previous career, I
>>designed and tested high-voltage insulators. I tested using an AC set that
>>could generate 1000kV and create an arc over 15 feet long.
>
>
> That jibes w/ my recollections -- vague memories say they were playing
> with circa 250KV.
>
>
>> We also used an
>>impulse generator which simulated lightning and switching surges that could
>>go up to about 2500kV. All of that was very interesting.
>>
>>If you want even more fun, do high *current* testing and run 20kA through
>>some hardware. Ka-boom!
>
>
> Shall I mention the time I saw somebody swing a crane boom in to the
> _feeder_ lines to an operating sub-station, and only about 500 ft away
> from the sub-station. The _flame_ front was merely a couple of =hundred=
> feet *wide*. It went away fairly quickly -- like a second or so -- but
> there were also several 'booms' and small clouds of smoke from the station
> itself -- apparently 'protective' disconnects when the three-phase feed
> went *that* unbalanced.
>
> I've heard _one_ louder noise than that -- a lightning strike on a telephone
> pole about 50' outside our back door. I *saw* the glass patio-doors I
> was sitting not 10' away from bulge (about 3 inches!!) from the pressure
> wave.
Fun. When I was a kid I was tossing a javelin (dead and desiccated
hemlock plant with the root still on the tip) over the powerlines.
Was. On the last vault over, the back struck the near-side powerline on
the top, and the front settled down on the far side. Smoke, and when it
started flaming I turned to run inside and plead my case, when I saw the
front side of the house light up in a bright blue light. I ducked and
turned to see remnants of my javelin spiraling down in flame.
Couple minutes later and a PG&E truck came tooling by...
er
--
email not valid
"Gus" <[email protected]> wrote >
> So, by your logic, if it's in the FAQ, it MUST be true.
Factual evidence supports the FAQ entry in question. The absence of any
contrary data presented as a counterpoint by you simply illustrates your
emotional denial, rather than supporting your opinion.
If you have factual evidence, kindly present it. If not, feel free to
believe what you will, but don't take offense if I don't share your beliefs.
Rick
"RayV" <[email protected]> wrote in message
> theory, static can ignite fuel vapors or gases, but wood dust?
Wood dust in the right proportions can be explosive. You can probably find
more information on it in the rec archives, but I'm sure quite a few people
will respond with additional information.
On 29-Mar-2006, Mark & Juanita <[email protected]> wrote:
> 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.
But that wimpy little wire will bleed off the charge before it can get as big as
a lightning discharge.
While I doubt that an explosion in a home DC will occur - how about a fire?
The only difference between a fire and an explosion is the rate of combustion.
Mike
The RayV entity posted thusly:
>I've searched the wreck archives, osha site, googled the web... all I
>can find are anecdotal statements.
>
>"sawdust can explode..."
>"any combustible material in dust form is explosive..."
>"PVC cannot be effectively grounded..."
<snippage>
>Doesn't anyone beLIEve in facts anymore?
>How much dust in what concentration is required for an explosion?
>How much of a static charge would be required to ignite that dust?
Yes, I do believe in facts.
No idea of the concentrations or how hot a spark it would take to set
it off.
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.
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
happen.
On 28 Mar 2006 12:56:03 -0800, "RayV" <[email protected]> wrote:
>I've searched the wreck archives, osha site, googled the web... all I
>can find are anecdotal statements.
>
>"sawdust can explode..."
>"any combustible material in dust form is explosive..."
>"PVC cannot be effectively grounded..."
>
>What I can't find are any specs or hard facts. If I rub my feet on the
>carpet and touch a doorknob with a handful of sawdust will my hand
>explode? Without any facts I'm extremely unlikely to believe that a
>home shop DC system can explode. Didn't one of Adolf's boys say,
>"if you repeat it often enough it will become true"?
>
>Case in point:
>Just about every driver's manual I have read (ok, two) states that
>for a car with a manual transmission...you should put the car in
>reverse when parked facing downhill and in first when parked facing
>uphill. This is totally idiotic! That advice is based on the false
>assumption that the engine can only rotate in one direction. But still
>it is part of driver's ed training.
>
>Doesn't anyone beLIEve in facts anymore?
>How much dust in what concentration is required for an explosion?
>How much of a static charge would be required to ignite that dust?
>
>I only found one link that supposedly had data available but the link
>is now dead.
On 28 Mar 2006 15:50:40 -0800, [email protected] wrote:
>sure, in big industrial facilities with dust systems moving tons of
>material per hour the risk is real, and the measures taken to control
>static discharge are vital.
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.
Upscale wrote:
> "RayV" <[email protected]> wrote in message
>
>>theory, static can ignite fuel vapors or gases, but wood dust?
>
>
> Wood dust in the right proportions can be explosive. You can probably find
> more information on it in the rec archives, but I'm sure quite a few people
> will respond with additional information.
>
>
I'd like to see that one on myth busters.
--
Thank you,
"Then said I, Wisdom [is] better than strength: nevertheless the poor
man's wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16
On Wed, 29 Mar 2006 00:03:52 -0600, [email protected] () wrote:
>In article <[email protected]>,
>Andy Dingley <[email protected]> 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.
+--------------------------------------------------------------------------------+
If you're gonna be dumb, you better be tough
+--------------------------------------------------------------------------------+
On Sat, 01 Apr 2006 14:16:34 -0000, [email protected] (Robert
Bonomi) wrote:
>I guarantee you that static electricity _does_ have enough energy. Under
>the _right_ circumstances.
I (and every professional electrostatics expert I've spoken to)
disagree.
Got the numbers ? What's the discharge mechanism ?
On Wed, 29 Mar 2006 00:03:52 -0600, [email protected] () wrote:
>Can you support that statement?
Any standard industrial handbook of safety electrostatics. I'd suggest
Luttgens & Wilson's "Electrostatic Hazards" for readability, although
it's expensive and light on some tables of hard figures that you need to
do real work.
>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.
"Discharges" are categorised into different causes, of which "sparks"
are only one.
The non-spark discharges occur around insulators and it's a relatively
easy matter to calculate their maximum energy. Put simply, the fact that
it's an insulator allows charge to build up, but it also limits the area
that can contribute to the discharge when it happens. Maximum energy is
a function of the materials, not the dust flow.
Sparks are discharges between conductors. These are rarer, as only an
insulated conductor builds up charge. However the whole conductor can
contribute, so there's no intrinsic limit on the discharge energy.
However we just don't build dust collectors this way.