explosive situation?

Page 2 of 4  

Rick M wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ray,
You might want to run a wire between the aluminum flex hose and the metal leg of your table saw.
- MB
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Woodhead wrote:

you cannot ground plastic pipe. plastic is an insulator. the kits are strictly for suckers.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 28/03/2006 3:56 PM, RayV wrote:

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...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Doug Payne 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. 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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 28 Mar 2006 15:50:40 -0800, snipped-for-privacy@yahoo.com wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<...snipped...>

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
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 29 Mar 2006 00:03:52 -0600, snipped-for-privacy@fellspt.charm.net () wrote:

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 +--------------------------------------------------------------------------------+
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
From static electricity? Bwahahahahahaha!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Mark & Juanita wrote:

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


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 29 Mar 2006 00:03:52 -0600, snipped-for-privacy@fellspt.charm.net () wrote:

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.

"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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.