Dust extraction system - PVC versus Acrylic ducting

[Thedog]

Hello,

I am about to add 100mm solid pipe ducting to my Camvac extractor to service a few tools (Table saw, thicknesser and band saw).
It seems that most 100mm solid clear ducting used for this is PVC and not acrylic or polycarbonate.
I am no expert in this but from I thought PVC would cause a lot more static build up compared to acrylic or polycarbonate ducting.

Why is most standard available ducting for woodworking made from PVC? Or is still the best option when added with some earthing straps for static discharge?

Any views or advice would be good.

Cheers

 

[Sideways]

Acrylic has rotten static as I recall.
Polycarb for impact resistance but it's more expensive and soft.
Have you looked at metal ? It's the best functional choice.

 

[Thedog]

Yeah, metal is readily available and around a 3rd of the price. But, I would like to see my Wood chips whizzing along. Mainly so I can see blockages and any segments that may have poor performance or buildups

I don't mind pvc but just thought another plastic material may be more suitable. Got this wrong by the looks so will go with PVC I think. Not cheap for what it is though. About £22 for 900mm

Thanks anyway. I least l now know. Thanks

 

[gcusick]

As regards static electricity, there’s little or no difference - they are all insulators. I agree that it’s nice to be able to see where dust or chips are building up (mostly on the far side of 90 degree T-junctions in my experience). Otherwise, i’d suggest 102mm UPVC waste pipe.

 

[XTiffy]

It used to be standard routine to run an earth wire inside plastic dust ducting. Wood dust is a real explosion risk.

 

[Mike Jordan]

For pity’s sake use the purpose made metal ducting! The static risk is real and using plastic materials may give your insurers a great excuse if the worst happens. Now please think in terms of safety rather than an imaginary saving.

 

[Jake]

I don't believe the static / explosion risk is real in a domestic workshop. HSE guidance notes that the concentration of dust (and it is only very fine dust - 'wood flour') needed to create an explosive risk looks like a dense fog. I don't believe any small wood workshop generates that much dust. I've certainly never seen anything even approaching a visible fog in the final clear flexi leg of my ducting.

I'd be interested to hear of any example of the worst happening with this real risk.

 

[Delaney]

I don't believe the static / explosion risk is real in a domestic workshop. HSE guidance notes that the concentration of dust (and it is only very fine dust - 'wood flour') needed to create an explosive risk looks like a dense fog. I don't believe any small wood workshop generates that much dust. I've certainly never seen anything even approaching a visible fog in the final clear flexi leg of my ducting.

I'd be interested to hear of any example of the worst happening with this real risk.

I’m all over the place on this one.
I would never use plastic but domestic explosions are very rare. You’re right that there needs to be a lot of very fine dust in the air for it to happen but it’s also true that most DIYers don’t take extraction very seriously and do lots of sanding with the ‘door open’.
I also know fitters in the industrial side who’ve never known one happen in over 10 years in the industry; likely because standards around extraction are so much better.

That being said, do you want to be the exception? Not if it’s a garage attached to your home, with your children in it.

In a side note I now buy permanently antistatic flexi hose to attach the metal ducting to the machines. Saves having to do the wire connecting.

 

[Jake]

I would never use plastic but domestic explosions are very rare.

Are you aware of any at all? I've never seen an example cited with any evidence of it ever having happened to anyone (outside of an industrial setting).

 

[Delaney]

As regards static electricity, there’s little or no difference - they are all insulators. I agree that it’s nice to be able to see where dust or chips are building up (mostly on the far side of 90 degree T-junctions in my experience). Otherwise, i’d suggest 102mm UPVC waste pipe.

One way to sort that is to use 45’s and to have the correct flow rate to carry the dust.
I find most blockages happen due to the saw not having a 0 table insert, so thin strips of wood get sucked up the ducting and bridge the 90 bend.
Unfortunately working out the required flow rate and velocity requires a phd in astro physics.

 

[Delaney]

Are you aware of any at all? I've never seen an example cited with any evidence of it ever having happened to anyone (outside of an industrial setting).

Agreed.

 

[Inspector]

The minimum concentration of wood dust (flour size) is 60mg/m3 for a dust explosion. Since 100mm ducts can only flow about 12 m3/per minute you would need to be sucking up 720g of dust every minute to have that concentration in the ducts to explode if there was a hot enough spark to set it off. I don't know of any home shop machine that makes 750g of fine dust a minute. Also a home shop can't generate a spark of sufficient intensity to serve as an ignition source. You need to get in the 300mm+ sizes of ducts to get in that range. That's why there are no home shop fires in dust collectors from static.

The way fires happen in small systems is friction of blades or bits making embers when cutting or sparks from metal, screws or nails sucked up and hitting an impeller. Those sparks or embers smouldering in the collected dust cause the shop fire.

The other reasons for preventing sparks from static are the nuisance factor of getting zapped which can hurt or distract you when you need to be concentrating and now with more electronics in the shop the possibility of the spark discharging through a circuit board, damaging it.

Pete

 

[imageel]

The minimum concentration of wood dust (flour size) is 60mg/m3 for a dust explosion. Since 100mm ducts can only flow about 12 m3/per minute you would need to be sucking up 720g of dust every minute to have that concentration in the ducts to explode if there was a hot enough spark to set it off. I don't know of any home shop machine that makes 750g of fine dust a minute. Also a home shop can't generate a spark of sufficient intensity to serve as an ignition source. You need to get in the 300mm+ sizes of ducts to get in that range. That's why there are no home shop fires in dust collectors from static.

The way fires happen in small systems is friction of blades or bits making embers when cutting or sparks from metal, screws or nails sucked up and hitting an impeller. Those sparks or embers smouldering in the collected dust cause the shop fire.

The other reasons for preventing sparks from static are the nuisance factor of getting zapped which can hurt or distract you when you need to be concentrating and now with more electronics in the shop the possibility of the spark discharging through a circuit board, damaging it.

Pete

Whilst I have no experience of static induced fires I certainly do from a carbide tipped saw blade hitting concrete oversite particles embedded in bitumen encrusted parquet blocks
I can thoroughly recommend taking steps to minimise the risks of such an event be it static or as in my experience, the consequences can be catastrophic for your workshop and also the risk to yourself too, it certainly was a brown-trouser moment for me....
I consider myself lucky in both surviving my incident and also minimising the resultant collateral damage - living as I did in a rural location with my workshop at the end of a 50m garden if a fire had taken hold I doubt much would have been left by the time the fire services would have arrived and doused it down...

I'd agree that metal ducting would be my preferred choice, bonded at machine and impeller end so as to mitigate potential breaks in continuity from blast-gates and the like. I'm sure that using swept bends would minimise risks of blockages..