electrostatic discharge

[ELMARTO]

Hi all - I'm a newbie I've been lurking about reading & learning - very impressed with Mr Thien's concepts & everyone's combined knowledge on dust extraction - two questions if I may

1)When I was a lad I worked in a flour mill & learned about dust explosions (& witnessed a dust fire) - Is there any risk of such with the wood dust in these systems being caused by an electrostatic buildup??? Is there a need for grounding for electrostatic discharging - I have acquired a plastic drum & plastic sewer piping, can it be grounded???

2) Now for the dumb question - I vaguely remember something from my school-boy science about the "Corolis(?) Effect" - I live in the southern hemisphere "DownUnder" & I'wondered whether the air in the baffle system should be spinning clockwise (or is it anti-clockwise???) for me & if so should the inlet on a Thien baffle or top-hat design be reversed ??? - or maybe it just doesn't matter - don't laugh but i was studying the bathwater going down the drain last night to find the Effect

in anticipation thanks

[retired2]

1)  A lot of people will tell you it is necessary, especially if they are selling grounding wire, or if they are concerned about liability.  However, if you search the web you will find numerous articles stating that the risk of a dust explosion from a static discharge in a home shop is a myth.   The greatest likelihood of a DC fire comes from sending a piece of hot metal into the chip collection bag or drum.  Even then the risk is not dust explosion, it is a smoldering fire the breaks into an open flame long after you've left the shop.  So, pay very close attention to what you are sucking into the dc system. 

2) The motive force here is not gravity or the rotation of the earth, so forget the Coriolis effect.  However, there is an issue on rotation if you have a top hat separator close coupled to the DC.  For more information on that issue read the thread on my top hat build.   It has scrolled off to the second page of the index now.

Update

Here's some links:
http://www.workshopaholic.net/articles/dustExplosion.html
http://www.sacramentoareawoodworkers.com/Articles/DustCollectionandPVCPipeDangersDebunked.pdf

[WayTooLate]

Retired -
Thanks for re-stating the realities of our systems. 
Dust explosions are spectacular events for the MythBusters, but they won't happen in our workshops. 
Even the 'grain elevator explosions' that everyone fears had an external ignition source. 

Fire is a possible risk in any woodworking shop - you have lots and lots of combustible material.  Dust and chips and shavings can flare up in seconds.  But they all require an external ignition source.  Spontaneous explosions are for the movies 
and special effects. 

I recently built a burner system with several 200,000btu propane torches for charring wood.  Trying to install a BBQ spark igniter to a 'weed-burner' torch is NOT simple.  I had continuous sparking and lots of propane flooding the area - but it is amazing how difficult it is to get ignition.  Fuel-air and exact positioning is critical. 

If it is that hard to ignite propane, I will never worry about dust flying by a spark at 4000fps. 

Sleep easy, woodworkers.  Your DC will not explode from static!
- Jim

[ELMARTO]

Fellas thanks for input - gives peace of mind so I'll continue with the project - all the best for Xmas & NY

[Loren]

I am new to this great site and just wanted to relate my experience with electrostatic discharge. I have started using a ground wire or metal tape on my dust collector. One evening I was running a lot of MDF on my table saw set up with a molding head cutter. After about 20 minutes of running, I heard a woof sound and smelled a burning odor. I shut off the saw and looked everything over. There was no damage or fire but something definitely happened. The plastic tube in my dust collector had a lot of static buildup. When I put my hand inside, it would snap and pop. I can't say for sure that the cause was electrostatic discharge; it could have been heat buildup from the molding head. The very fine dust from the MDF was probably a factor too. All I know is that since I have grounded the components of my system, I have not had any issues and no longer get a shock from the plastic hoses.

My DC system does not have a Thien baffle yet but I plan to build one as soon as I can.

[retired2]

I am new to this great site and just wanted to relate my experience with electrostatic discharge. I have started using a ground wire or metal tape on my dust collector. One evening I was running a lot of MDF on my table saw set up with a molding head cutter. After about 20 minutes of running, I heard a woof sound and smelled a burning odor. I shut off the saw and looked everything over. There was no damage or fire but something definitely happened. The plastic tube in my dust collector had a lot of static buildup. When I put my hand inside, it would snap and pop. I can't say for sure that the cause was electrostatic discharge; it could have been heat buildup from the molding head. The very fine dust from the MDF was probably a factor too. All I know is that since I have grounded the components of my system, I have not had any issues and no longer get a shock from the plastic hoses.

My DC system does not have a Thien baffle yet but I plan to build one as soon as I can.

Tools should be grounded for reasons other than static build-up.  The helical wire inside flex hose can be attached to the tool in a way that it is also grounded, but most likely it won't prevent static build-up inside the plastic pipe.

Here is one of the better articles on this subject.  It also discusses the realities of trying to ground PVC or other plastic pipes since they are insulators. 

http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

In the end, you will have to do whatever makes you feel comfortable.

[RCOX]

I have to kick in my .02 cents worth here.

You can connect the helical wire in flex duct to whatever is on either end but IMHO the only thing you have done is ground whatever it is connected to, on either end. YOU can still receive a static shock if you get next to the flex. The wire is completely enclosed in the rubber/plastic the flex is made of, which is an insulator. If the flex is long enough it will still build up a small charge. This charge probably is not enough to do any damage but can be a surprise to you, which may cause you to hurt yourself when you reactively jump.

Just saying, wire encased in rubber/plastic can not be grounded.

Raymond

Merry Christmas to all.

[phil (admin)]

There was a thread on Woodnet about a year or so ago.  A guy was getting awful shocks from a hose he had connected to his vac.  He was able to wrap it in some wire and reduce the shocks substantially.

I know, hardly definitive.

What I really want to say is, Merry Christmas.

[retired2]

What I really want to say is, Merry Christmas.

Merry Christmas and Happy New Year to you too Phil, and thanks for all you've given to the woodworking community.

[Loren]

Thank you for the link to the very informative article. I do not want to perpetuate something that is not true but I wanted to relate my experience. I also realize stating I grounded the components for my DC system is not correct. I have wrapped the hose with a ground wire, wrapped a ground wire around the outside of the plastic DC inlet pipe and put a ground wire inside the DC inlet pipe.

I am not sure what happened when I was using a molding head on MDF to make baseboard. All I know is that there was a sound that seemed to be a very small explosion and then there was an odor of burnt wood. I finished running the baseboard without the dust collector without any issues.
I have also been using a ground wire wrapped around the hose from my orbital sander. This has made long sanding sessions much more comfortable.

Again, I apologize for drawing a conclusion that is not correct. I am more comfortable, both mentally and physically, since adding the ground wires.

-Loren

[RCOX]

If it feels good, do it.

Raymond

[WayTooLate]

I think it is important to distinguish between the recent comments about getting shocked and the thread's original topic of a dust explosion. 

Any grounding of ductwork, tools, benches, etc. can make immediate and significant reductions of the nasty jolt from static charges.  Although you cannot ground your PVC ducts, grounding the wires inside the flex tubing allows a path to dissipate the charges generated at either end.  They don't eliminate the static generation, but it can greatly reduce its toll on me when I touch them.

I have had fun replicating some of the Myth-Buster events - igniting sawdust, flour, even non-dairy creamers.  Even one package of creamer and a Bunsen burner is surprisingly 'big'.  If you contained it within a 4" PCV pipe, it would make a decent flame-thrower.  However, ignition still becomes the tricky part. 

I can't speak for Loren's experience.  There are lots of chances for combustion.  Loren's description of a 'woof' instead of a 'bang' is accurate for sawdust combustion.  However, a real dust explosion would have scorched bags and filters at one end and spewed a few flames out the tool ports.  My hunch is that is was not a spark induced explosion, but possibly some other source/form of combustion.   

I would definitely recommend all practical forms of grounding the DC and ductwork.  However, the purpose is our own increased protection from static shocks - NOT safety from explosions. 

Hope this helps!
Jim