On Sat, 01 Apr 2006 14:16:34 -0000, (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 ?

Andy Dingley wrote:

On Sat, 01 Apr 2006 14:16:34 -0000, (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

(remove all letters after y in the alphabet)

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

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/cyc...ticElectricity

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?

todd wrote:
"Dhakala" wrote in message
oups.com...

dnoyeB wrote:
Upscale wrote:
"RayV" 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, (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

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?

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

wrote in message
oups.com...
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....

Edwin Pawlowski wrote:
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

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

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?

It was in Fine Woodworking. Search their archives for the
article. Pretty much said, as I remember it, that running a grounding
wire is not needed.

MJ Wallace

In article ,
Andy Dingley wrote:
On Sat, 01 Apr 2006 14:16:34 -0000, (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.

"Robert Bonomi" wrote in message
...

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

In article ,
Edwin Pawlowski wrote:

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

wrote:
In article ,
Edwin Pawlowski wrote:

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

wrote in message
oups.com...

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....

George wrote:
wrote in message
oups.com...

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 , todd wrote:
"Robert Bonomi" wrote in message
...

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.

Robert Bonomi wrote:
In article , todd wrote:

"Robert Bonomi" wrote in message
...

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
--
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