Air Borne Dust Hazzard, for your consideration and comments

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Reprinted Material. All credit to -Robert Witter Oneida Air Systems Inc.
What do you guys think. I have one of these systems. Am I hurting myself and my shop by running it.
Ovrhead Shop Air Cleaners Can Increase Airborne Health Hazards in the Woodshop
The ubiquitous air cleaners that hang on shop ceilings don’t improve shop air quality. A scientific look at how they work and the percent of fine material actually filtered indicate that in the best case they don’t improve shop air or in the worst-case scenario increase the fine airborne particulate in suspension.
Recently a national wood working magazine published 3rd party filter efficiency tests of these units using a 1-100 micron test material dust. The results were misunderstood. Actually, the data presents a strong argument as to the ineffectiveness of these units. ASHRAE and other recognized tests use a test powder between 0.3 – 10 microns in size. The ASHRAE test measures the efficiency of filter by measuring and counting all the particles that migrate the filter. It is the 1-10 micron particle size range industrial hygienists consider the most damaging to human health. This size has the ability to lodge into the deepest recesses of the lung, and is very difficult for the body to excrete. It is also the predominate size range floating for hours in your shop air. The test results indicate that even the best machine tested did not filter the finest and most lung damaging material. If a one-micron particle is the size of a BB than a 100-micron is a bowling ball. The best filtering machine tested allowed 0.1 grams out of 80 grams through the filter. This might sound good on the surface, but assuming a fairly even size distribution of the test dust, no size break down was given, the 0.1 grams represents the entire weight of all of the 1- 15 micron dust in the sample. Actually, calculating by average weights of the size distribution, it’s possible that none of the material in the 1-15 micron range was filtered on the most efficient unit tested. It is precisely this range that constitutes the worst health hazard. A 100-micron particle, assuming stoke equivalent or roughly spherical, is one million times heavier than a one-micron particle, and has a settling velocity of about 10 inches a second, about the same as a falling cotton ball. Large particles this size are far too heavy to float up to the ceiling where the units are typically positioned.
The second misconception in the same article is the idea that the proper size air cleaner will filter all the air in your shop in 6 minutes. The example given: a 15 x 20 x 8 ft shop contains 2,400 cubic feet of air, divide this by 6 to get the minimum CFM required, which would be a 400 CFM air unit. Ventilation engineers use a factor for incomplete mixing which in this case would be a factor of somewhere between 7- 10. In other words, based on this formula the real length of time to filter all the air in the shop would be between 42 to 60 minutes, and this is only valid if the offending external source of dust emission is shut down. Even assuming an ideal 100% filtration the removal process is much slower than the dust generation process. Meanwhile, you are in the shop breathing contaminated air. Commonly woodworker’s will comment,” when I look in the filter I see trapped dust, isn’t it beneficial to collect at least some dust?” In this case the answer is no. Not with the machines tested here. The dust accumulated on the filter is only a fraction of the total dust drawn into the unit. The remaining dust is passed through the filter and exhausted. The circulating fan keeps this dust suspended and aloft in the air you are breathing. The dust on that filter is evidence that too much dust is in your shop air to begin with. Quoting American Governmental Industrial Hygienists,” when toxic contaminants are evolved in the workroom, recirculation must be avoided.” This is why these units are not used in industry.
A properly designed dust collection system lowers airborne particulate to safer levels no higher than 5mg/M3. It does this by entraining the dust with air near the source of dust emission and then filtering the air to near 100%. Air quality testing in industry is performed routinely where workers wear dust monitors on their collar. It’s not uncommon for well-designed dust collection systems to lower airborne dust levels by 10 to 30 times over uncontrolled environments. Get the facts and protect your health.
-Robert Witter Oneida Air Systems Inc.
ScRaPleR
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ScRaPLeR wrote:

I'm no scientist, but my common sense says the safest course of action is to use the best dust collection method you can afford and implement, and wear a suitable mask, and skip spending money on an air filter unless it's just an additional measure of protection. It doesn't make sense that dust created across the room from a small air filter is going to make it's way into the filter any time soon. Small particulates will make their way into your unprotected lungs just as readily as they will to the air filter. bottom line: wear a mask as the last line of defense.
Dave
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All the dust filters I've seen advertised list their capabilities with multi-micron-size dust particles. Irrelevant according to USCG research. (Think overhauling ship engineering spaces.) Okay, they reduce explosion hazard.
Gore-Tex filter in Shop-Vac alleges capability of removing 99+% of .3 micron particles. Over the years, I've been impressed at how they trap extremely fine dust, like wood ash and drywall dust.
J
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As the article points out, the heavy stuff never makes it up to the air cleaner. Yet my filters get plenty dirty. They must be filtering something out, and since only the light stuff goes up, it must be the light stuff! I am satisfied.
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Toller wrote:

at all the gunk in your hanky and I don't mean snot.
Dave
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With my HF dust collector running along with my home built dust filter, my snot is nice and clean. Without, it comes out in chunks! Good enough for me! Greg
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hours in the shop if you don't wear a mask. Look

I think the only way to resolve this is for everyone to post their snot photos for comparison. The cleanest snot by a majority vote is the method the wRec will endorse.
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Edwin Pawlowski wrote:

dave
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But then we need a judge (I'm thinking Ed) to go onsite with the finalist and get current samples after witnessing dust being produced..
How else can we know that the snot samples were not a "before" when they were alleged to be an "after"?
mac
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Greg O wrote:

Dave
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A very valid point, maybe: In my experience neander techniques like planing, scraping produce do dust but shavings, only sawing makes dust in my shop, but I have no idea about the particle size distribution...
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Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
mailto: snipped-for-privacy@physik.uni-bonn.de Phone: +49 228 73 2447 FAX ... 7869
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Toller wrote:

Your unit is about 7 to 10 feet above the ground and your nose is about 5 to 6 feet above the ground, so you get all dust in the nose first and the unit get the rest, so wear a mask while sanding or sawing. Maxen
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But is it just while sanding and sawing? Doesn't this stuff hang around in the air long after you have finished the offending operation...
Roy
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RzB wrote:

dave
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snipped-for-privacy@hotmail.com wrote:

Umm... my 'unit' is more in the 2 to 3 foot off the ground range. ;)
-John in NH
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Doesn't that depend on angle and gravity, or something like that?
mac
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wrote:

I wear a dust even with both my high effeciecy cyclone dust collector and an ambient air filter but I feel that my tool and surfaces in the shop benefit at least a little from the air filter. I also use three phase filtering on the ambient air system. 1. a 3M type furnace filter, the 2. 5-20 micron filter then 3. the Hepa sheet and all three get dirty after about 12 hours of contineous use. So I guess what still have me puzzled is the fact that I AM capturing a lot of dust to get out of the shop and is this not a good thing in the long run?
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I think they are just saying it gives a false sense of security; rather than that it is doing harm.
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I'm not qualified to assess the technical merits, but what it says is that you might be doing more harm by continuously circulating improperly-filtered air and keeping it stirred up vs. letting it (eventually) settle to the floor.
todd
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Todd Fatheree wrote:

This is only a factor if it won't be stirred up anyways. I have a poorly-insulated garage shop, and keeping it warm in -40 weather circulates the air pretty well...
Chris
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