Static electricity with dust collector

[BobL]

So why is there so much static outside?

It's all the same charge on the duct, (the opposite charge is carried along in the air/dust) and like charges repel so they like to be as far apart as possible so they head for the outside of the container hence they appear on the outside.

The reason that the risk of fire inside a home shop DC is very low is that the amount of charge made inside the ducting is small and over a long enough period so it has plenty of time of time to move to outside the ducting. In commercial/industrial DCs the charge generation is much greater and the ducting is much thicker. Some also use sheets of a wear plastic to line deflection areas inside the ducting, if these wear plates are not earthed or mounted correctly they can build us a charge and discharge to the ducting inside the dust flow and whammo.

[Dengue]

Thanks Claw, willl be fitting the bare wire this weekend. But I still don't understand why the static on the outside of the hose

regards,
Jill

[glenn k]

I had a dust explosion once, they are not easy to ignite. I was sanding my floors and decided to run a ventilation system, I lit the open fire in the room (big roaring fire) and opened the windows a little. It worked reasonably well and I poured the dust on the fire to get rid of it on tipping the last of about the 6th bag the room caught fire flames everywhere the windows shook and I had burnt eyebrows and hair felt rather stupid afterwards.

[Claw Hama]

I think the static is formed on the inside of the hose but the whole flex becomes staticly charged by earthing the length of the flex it doesn't allow the charge to build up. Like when you scuff your feet on nylon carpet in an air conditioned room (dry air/ lack of moisture in the air makes it worse, air conditioning removes moisture like a fridge) and then zap someone on the nose (great fun) if you had an earth strap/wire on connected to an earth point it just wouldn't build up.
That is the other thing, normaly with moderate relative humidity say 30% plus you may not get an explosion but if the conditions were right you might, who knows could be 1/100000 chance. Ifyou get low humidity like we had in Newcastle the other day which I measured in my workshop at 18% and if you had a hot day say 35C or up and some the static in your flex will be a lot worse than normal, add some nice fine dust and
The bush as we know goes up with spontanious combustion, hell, throw in a nice big 1000 volt plus static zap.
All government dust extraction systems have always had to have earthing systems and having worked in wheat silos etc static is a big concern.

[Enfield Guy]

Hmmmmm. Petrol tankers, wheat silos and commercial/ government installs all do it. Low humidity and high temps. Might not be so expensive and time consuming after all, to err on the side of caution.

[Claw Hama]

My greatest expense was about 8 cable ties.

[Groggy]

Hmmmmm. Petrol tankers, wheat silos and commercial/ government installs all do it. Low humidity and high temps. Might not be so expensive and time consuming after all, to err on the side of caution.

This logic is just wrong, sorry. With petrol tankers you are talking about highly flammable fumes and with silos you are talking different materials and larger volumes. Government and commercial installations deal with much higher volumes and flows. I understand the caution (always a good thing) but it is not required. There has never been a verified instance of it happening.

I'll say again, use it to help stop the static from zapping you but if you buy a kit to avoid a dust explosion you are wasting your money. An equivalent amount would be much more wisely spent on a smoke detector as fires DO occur.

[robbo266317]

I found that spraying a line of zinc paint down the length of the pipe did the trick.
No mucking about attaching wires.

[rrobor]

The answer to "beer is good" with the petrol tanker is not static but another effect pressure. Falling fron the top or if it was one big tank without baffles there is a chance that a bubble of fumes could be compressed enough to ignite like happens in a diesel engine.

[glenn k]

I used to work for a transport company and we carried petrol as well many other liquids. It was always poured in from the top it would take too long to load through a 100mm pipe at the bottom, not to mention the spillage when you disconected. This is 35 tonne in 5 compartments. A static line was conected to earth the tanker.

[BobL]

I'll say again, use it to help stop the static from zapping you but if you buy a kit to avoid a dust explosion you are wasting your money. An equivalent amount would be much more wisely spent on a smoke detector as fires DO occur.

As well as a detector how about a fire extinguisher?

[Groggy]

As well as a detector how about a fire extinguisher?

I don't think I would use an extinguisher on a dust collector as the pressure would blow the burning dust all over the place and maybe make it worse. I'd use water after killing the power - any firies out there can say what would work best for a dust collector fire?

[issatree]

Hi JillB,
What Enfield Guy said is what I also think.Don't be fooled by those who believe in myths. It is a fact, but it will only Explode.
The easiest way to stop all this is to use Metal pipes, what I mean is
Household Downpipe, then you don't have to Earth anything to my knowledge.
Where do you get it ?, at the local tip, or recycle dump. Probably a fraction of the cost of buying plastic pipe, & maybe you might be able to use plastic joints, but then that separates the metal.
You can cut short pieces off, cut & split the band to use as a join, & pop rivet them together.
The Plastic must be earthed to a spike in the ground.
So how do I know this, easy, I was Employed by The State Electricity Commission of Victoria for 33 yrs.
Had I said I worked for them, there would be a barrage of comments.
Well that's my bit, & let us all know how it worked out.
Regards,
issatree.

[BobL]

I don't think I would use an extinguisher on a dust collector as the pressure would blow the burning dust all over the place and maybe make it worse. I'd use water after killing the power - any firies out there can say what would work best for a dust collector fire?

I wasn't referring to the 1:100000 chance of fire in a DC but the much greater risk of fire in a shed from other causes which is what we should really be worrying about.

[Groggy]

I wasn't referring to the 1:100000 chance of fire in a DC but the much greater risk of fire in a shed from other causes which is what we should really be worrying about.

Agreed