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?

"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.

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.

--
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

dnoyeB wrote:



I'd like to see that one on myth busters.



Myth Busters is pseudo-science at BEST.

They raise more questions than they answer.

"Gus" 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

Rick M wrote:
"Gus" 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.

"RayV" wrote in message
oups.com...

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.

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

Ray,

You might want to run a wire between the aluminum flex hose and the
metal leg of your table saw.

- MB

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" wrote in message
oups.com...
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?

"Woodhead" wrote in message
...
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.

Woodhead wrote:
....There are kits available to
ground plastic 4" hose to discharge static.


you cannot ground plastic pipe. plastic is an insulator. the kits are
strictly for suckers.

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 28/03/2006 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...s/CombDust.pdf

And on and on...

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...s/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.

On 28 Mar 2006 15:50:40 -0800, 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.

In article ,
Andy Dingley 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

"Doug Payne" wrote in message
...
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...s/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

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" 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.

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

On Wed, 29 Mar 2006 00:20:55 GMT, Lew Hodgett
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.

I previously wrote:

It is that point where the dust volume in the air WILL explode.

As written, not true.

It should have read: It is that point where the dust volume in the air
WILL explode IF an ignition source is provided.

Blame it on a lazy typist, ME.

Lew

In article . net,
Lew Hodgett wrote:
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

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

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.

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 ,
Enoch Root 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

OK, dust can explode! But I'm not putting a candle in my DC anytime
soon.

http://jchemed.chem.wisc.edu/JCEsoft...cca7dust1.html

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?

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