Explosive dust extraction - ATEX - DIY downdraft... etc

[samfish]

Hi,
I am looking for a bit of advice/experience please.

I have spend a long time looking into the extraction of aluminium dust (lots of DA sanding/grinding). It seems everything needs to be ATEX approvesd, as the airborne dust is explosive - most places say that to do it properly would cost around £10k, even on a small scale.
I have been sanding aluminium ALOT for a long time in a nother workshop with no extraction, and have not exploded yet - but I want to do things properly in my own premises.

Fume extraction is already sorted by an arm and fan.

There are a few methods of extraction:
- on the tool - Festool do an ATEX approved mobile extractor @ £1800
- downdraft / side extraction - cyclone/spun, wet collector, dry filters

Extraction on the tool is a good one, but in theory all tools should be air powered (sparks) - which can be restrictive, and the compressor logistics are complicated. I don't think they would remove enough airborne dust either.

Downdraft tables look great and should tick all the boxes - but they are quite expensive. The airbench ones look fantastic and relatively cheap (approx £2500) compared to the competition, but still too expensive for me.... http://www.airbench.com/en/?gclid=CL-58deAmrwCFUsOwwodMCwA7g
...they are not ATEX approved, but hold the dust on filters so it is not airborne/explosive.

I would prefer to make my own, like the weldingtipsandtricks chap:

This means I can attach the extraction arm to a fabricated table when I need it to draw air down... but then I need an ATEX fan (?) - £1000+++

I have two questions (broken down into many!):
- How can I make a downdraft table with filters like the airbench version (I can send the extracted air outside, but would want to filter it briefly first
Airflow required for a 1x1m table top?
upside down Hood shape, to produce an even draw over the table surface?
Were to mount the filters?
What filters?
Does the air circulating through the table cause a threat of explosion, how can I minimise this?
Do I need to paint it in anti-static paint?

- Do I need an ATEX approved fan?
The fan is mounted outside, so the actual motor would not have dust passing over it, but can the turbine produce static, or risk of sparks?

It would be pretty straight forward to produce a table like the weldingtipsandtricks guy, but there are added complications with aluminium - as above.

What do you reckon? All help is much appreciated
Sam

 

[madkayaker]

Aluminium dust is explosive but so is any dust! (Flour and suger very much so) I guess it's down to a risk assessment and how fine the dust is/ needs to be to go bang. Atex gear is very expensive but that's down to the high level of testing and quality control I do work in battery rooms that have extraction and we don't use ex fans but have simple things like sealed light fitting, switch out side that sort of thing.

 

[samfish]

Thanks. Yeah, my brother works on a farm, and was telling me about the risks associated from the grain dust etc.
I am hoping that the rest of the room will be ok with electrical items, if the pull from the downdraft table is strong enough. Hopefully all (most) of the dust will go down the chute, and not into the air.
.... Maybe I need on-tool and downdraft... but it starts getting a bit crazy.

 

[madkayaker]

I would say earth everything to reduce static. I would also think an aluminum impeller on the fan would be best as less risk of sparks. The other good thing about effective dust collection is you can them weigh it in

 

[500e]

ATEX approval cover a wide range, remember your insurance will also be not to happy if you go bang, we supply radios for high risk work eg refinery's\aerosol fillers\flour mills the decision making process can be a nightmare, some Co. do a good impression of an Ostrich
This May help
http://www.hse.gov.uk/fireandexplosion/atex.htm

 

[AndyStobbs]

Between what concentrations is the dust explosive then? Just curious

 

[MattF]

I would say earth everything to reduce static. I would also think an aluminum impeller on the fan would be best as less risk of sparks. The other good thing about effective dust collection is you can them weigh it in

There's the motor too, which needs to be a specific type.

 

[samfish]

Cheers for the replies.
I read the HSE documents, and that is what prompted me to do all this properly. Ha.

Does the motor need to be a specific type if it is going outside, away from any dust? Only the impeller will be in the dust flow.....

Any idea on downdraft table designs, including filters?

I have some basic ideas, but can't really think what is best!
cheers
Sam

 

[samfish]

This is quite helpful:

http://www.delta-neu.co.uk/pdf/Dust-extraction-ATEX.pdf

 

[samfish]

And on another suppliers website (http://www.surtech.co.uk/info/documents/Easy Guide Dust 210113.pdf)
"
These dry, fabric filter extractors are not recommended for hazardous
dusts which can present a fire or explosion risk. They can, however, be
used for aluminium as long as they are fitted with an explosion panel and
a blast barrier of the correct size and design."

 

[Wedg1e]

There was a factory southeast of Peterborough that manufactured aluminium pipeline components. The building was a former spud store, essentially a metal-clad portal frame jobbie lined with sprayed-on foam insulation.
When they had a fire, all the aluminium particles trapped in the foam helped to cause a huge blaze in which two men died.

 

[samfish]

And More from Surtech.co.uk:

Here is a resumé of the Aluminium Federation’s leaflet:-
Aluminium dust can give rise to fire and explosion hazards. For this
to occur there must be a means of ignition, which can be a spark from
ferrous tools, an arc from a static electricity discharge, smoking, or
sparks from grinding ferrous materials on the same equipment.
Do not mix aluminium dust with any other dust.
Do not mix dust from the grinding or brushing of aluminium, with dust
from the polishing of aluminium.
Grinding, linishing and brushing
of aluminium on a large scale
should be used with wet dust
collectors of a prescribed
specification.
Ducting for aluminium dust
extraction equipment must be
constructed from a minimum
2mm thick steel, should be as
short as possible, and be flanged
at all joints, each flange being
earth-linked.
Wet dust should be weathered
in the open air and should not
be stored inside or in closed
containers.
Disposal of aluminium dust must
be carried out in accordance with
local authority regulations.
Machines and ducts must be
cleaned at the end of each shift.
All metal parts of the plant should
be earthed to prevent discharge of static electricity. Smoking must not be
allowed in areas where aluminium is being ground.
Aluminium dust fires must not be fought with water, vaporising liquid
foam, CO2 or any form of pressurised extinguisher. Dry sand applied with
long handled shovels is an effective extinguishant. Class D dry powder
special purpose extinguishers can be used. Avoid the generation of dust
clouds when fighting such fires.

 

[samfish]

There was a factory southeast of Peterborough that manufactured aluminium pipeline components. The building was a former spud store, essentially a metal-clad portal frame jobbie lined with sprayed-on foam insulation.
When they had a fire, all the aluminium particles trapped in the foam helped to cause a huge blaze in which two men died.

Oh dear, that's awful.

That surtec article is very good. They say that over 90% of the dust created by 180 grit paper is too big to actually ignite.
I am going alot finer than that though.

They also say a wet-collector is the proper way of doing it, but I got a price for a small one (decent - fabricated from GRP and stainless) and it was over £3.5k

I may have to fork out for an ATEX approved fan, and build a table with blast panels/valves, anti-static everything.... but that is going to cost a couple of thousand!

 

[samfish]

What do you think about using a commercial oven hood extractor, but upside down? Simply mounted to an ATEX approved fan and anti static ducting....
Like: http://www.ebay.co.uk/itm/1200mm-St...UK_BOI_Restaurant_RL&var=&hash=item43bac56714

Would it be an issue, being stainless?