I've been diddling with maybe  doing a DC system for years.  To eliminate the whine and howl of the DC I've contemplated building my own Impeller from ply and making it a  squirrel cage type   about 4-feet in diameter  and  two  feet across to give me high delta P while not causing the high speed interruption of the air stream which latter fact is why sirens and impellers howl.

But I have yet to even purchase the wood the pillow block bearings or the shafts.

I have considered the ducting. I'll prolly build mine from 1/4" Luan.   Paint the insides and nail and glue it together nice and cheap and I can make it whatever geometry and size I want so it fits in my low  ceiling shop. 

I have dithered around with location and  decided that outside is best.  I can put the motor, filtration system, storage, and cyclone in a little out building  I'd make attached to gb the back of my shop.

 

OK Great I'll need a nice 4 or 5 H P motor to do a decent job and I'll have to filter down to sub micron particle sizes.

But recently I've learned a few things:

Wood dust contains silica.  I was unaware of this just recently.  In my business there is a saying: Silica is the Next Asbestos. Silica causes silicosis and it’s as deadly as asbestos maybe more so.

Nobody sells decent  effective and safe DC filtration to small scale shops.  I mean nobody.   They are all nothing but dust pumps.

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 Some facts

Drawing in Insurance industry files a researcher I know learned the following:

7% of all woodworker professionals end up with such bad allergic reactions they have to stop doing woodworking. This is not a statistically insignificant number. 

 The high silica content in wood is killing woodworkers at an alarming rate.  In the large commercial shops where all gets vented outside, the average woodworker loses more than 1% of their respiratory capacity per year of work.   Between the allergic reactions and silica exposure roughly 14% of commercial workers in sites that only maintain OSHA air quality levels end up forced into an early medical retirement. The medical research is clear this is a dose response relationship, meaning the more dust the more damage.  

Most home and small  shop woodworkers vent inside  causing higher levels of exposure  than commercial workers get in months of full time work.

 Small scale and especially hobby class DC systems do not move enough air to get good collection and with almost no exceptions the  vendors sell filters that freely pass the fine dust for a year or more until their fine filters “seasonâ€.  The bottom line is the average small shop airborne dust level stays at least a thousand times higher than the commercial shops that vent outside.

This  fellow  also paid to have Cal-OSHA’s senior inspector  test his home and attached garage based shop three months after he had  quit woodworking (from silica and allergies). The fugitive dust that escaped his filters and DC collection had built up so high that just walking around in his immaculately clean shop stirred up enough dust that his shop failed its air quality test.  His shop and home both pegged the inspector’s meters.   The inspector told him that if the site had been a commercial building that the inspector would have to shut it down until it was cleaned up.

 

A typical 2-car garage sized shop holds about 100 cubic meters of air. The EPA, European Union, and medical standards all call for no more than 0.1 milligrams of airborne dust per cubic meter. Multiply 0.1 milligrams per cubic meter times 100 cubic meters   equals  10 milligrams of fine airborne dust as enough to cause a shop to fail air quality tests.  In ounces this is 0.00035 ounces or about two tiny thimblefuls of the light dust.

 

The peer reviewed medical research is clear that every exposure to any fine particulate under 10-micron dust causes a measurable loss in FEV (FEV1 is the volume exhaled during the first second of a forced expiratory maneuver started from the level of total lung capacity).

 With wood dust some of this FEV loss is permanent.  This is from silicosis, plus the chemicals found in and on wood.

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I'm going to have to learn a fair bit about getting the very small particles out of the air.

 

Have you visited the Bill Pentz site? You'll find his life's work was about capturing the finest particles. I don't remember silica ever being a specific focus, but he's done some great work.

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No Ref

He is my source. 

A dust mask won't filter down to the micron size. 

Here is an electron microscope  image of the silica in walnut:

The PDF on that product

http://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSu7zK1fslxtUnx_ePvTSev7qe17zHvTSevTSeSSSSSS%96%96

Says not to use it for sandblasting which possibly might mean it's not good for  fine silica. Alternatively it might  mean that it is not robust enough to take a shot from the sand blast nozzle.  One has to  know what Micron or Angstrom size it filters out. 

What to do?  I use a carbon filter  with a NIOSH MSA stamp on it, but I've never checked into the particle size filtration  it handles

The last item on this page says it's for silica dust

http://www.icscompany.net/Respirators.htm

Still no statement of particulate size.

Looks like you are golden Joe

I wrote to 3-M and asked about silica from wood dust.  This is the reply I got:

Thank you for contacting 3M regarding respiratory protection. A P95 or higher class of particulate filter (2071, 2091) can be used to reduce your airborne exposure to silica dust concentrations up to 10 times the Occupational Exposure Limit when worn with a half facepiece respirator (6000 or 7500 series). These filters can be viewed on our website using the link below.

http://solutions.3m.com/wps/portal/3M/en_US/PPESafetySolutions/PPES...

Becky
Occupational Health & Environmental Safety Technical Service

sure looks like it to me.

All good info! Thanks for posting