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Thread: Whole-shop Air Filtration Units Bad?

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  1. #1
    Join Date
    Mar 2005
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    Ontario, Canada
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    Whole-shop Air Filtration Units Bad?

    I was discussing the idea of making a whole-shop air filtration unit with the Oneida rep and engineer. They were very adamant that this was *not* a good idea. The following is an article forwarded to me in support of this argument....

    Steve Aiken
    Belleville, Ontario

    Overhead Shop Air Cleaners Can Increase Airborne Health Hazards in the Woodshop








    The ubiquitous air cleaners that hang on shop ceilings do not 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 do not improve shop air or in the worst-case scenario increase the fine airborne particulate in suspension. Recently a national wood working magazine published 3<SUP>rd</SUP> party filter efficiency tests of these units using a 1-100 micron test material dust. The results were misunderstood.

    The test data actually 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 filter efficiency by measuring and counting all the particles that migrate through 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 predominant 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" then 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 is 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.

    Another 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 would only be 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 woodworkers 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 is 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.



    Sincerely,

    Robert Witter

    Oneida Air Systems Inc

  2. #2
    Join Date
    Mar 2003
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    SE PA - Central Bucks County
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    I have always found this to be more of a mixed message. It is true that air filtration systems have limited or no value in improving air quality...you really do need to catch it at the source. But I also love my air filter for it's ability to help keep my shop a little cleaner from settling dust...you know, the stuff that doesn't get caught when you are hand-sanding or even spraying water-bourne finishes. It does bubkus for your health, but the layer of fines on those shelves is at least a little bit less. Mine also serves to circulate air around when I'm heating in the cold months for a more comfortable shop in a faster time frame.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  3. #3
    I agree with Jim. When I am sanding, I still wear a filter mask. Also, I don't have any facts to back it up, but I used to use my sander with no vacuum attached and without the dust bag. (I know...I know!!). From the time I quit sanding until the time the air "looked" clean was about 5-6 minutes. Now this was sanding at the other side of the shop from the air filter.

    I use my filter to keep my shop cleaner.
    Jeff Sudmeier

    "It's not the quality of the tool being used, it's the skills of the craftsman using the tool that really matter. Unfortunately, I don't have high quality in either"

  4. #4
    Join Date
    Feb 2003
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    Huntsville, AL (The Sun and Fun Capital of The South)
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    I can tell you that the air in my shop can be clouded with dust and within minutes of turning on my air cleaner it is very noticeably cleaner.
    If less particles are visable, it must be better air.

    The source of the article is not identified - only the fact that Oneida is using it to promote their own products. So that makes me somewhat suspicious.


    Like Jim said: "But I also love my air filter for it's ability to help keep my shop a little cleaner from settling dust...you know, the stuff that doesn't get caught when you are hand-sanding or even spraying water-bourne finishes."
    "If you believe in yourself and have dedication and pride - and never quit, you'll be a winner. The price of victory is high - but so are the rewards" - - Coach Paul "Bear" Bryant
    Ken Salisbury Passed away on May 1st, 2008 and will forever be in our hearts.

  5. #5
    Join Date
    Feb 2003
    Location
    Charlottesville, VA
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    26

    So, should one leave their Onieda cyclone running...

    ... with an open blast gate to let it filter the air. While its a little noisy, it certainly is moving lots of CFM and exhasting (Onieda certified) filtered air.

  6. #6
    I've heard other people say the same thing about air filters and wondered why there would be less dust on everything if the air cleaner wasn't doing something. I guess the best bet would be to have it exhaust outside, that way the fine dust wouldn't be recirculated. BTW aren't 1 micron dust filters available for the air cleaners?
    Dennis

  7. #7
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    Feb 2003
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    Southern MD
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    I always use mine when finishing. The amount of dust nibs at the end is definitely less. As already mentioned, the dust layer is also noticeably less after a day with the router or cutting up a bunch of MDF on the table saw.

    Jay
    Jay St. Peter

  8. #8
    Join Date
    Jul 2004
    Location
    Tacoma, WA
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    519
    When I first saw this it seemed to me that it was comparing the efficacy of a whole shop filter and a point source cyclone system. I would agree that a shop filter does not replace a cyclone but it just doesn't make sense that it wouldn't help along with a cyclone. Not everything can be hooked to my cyclone. This includes some sanders, routing operations, drill press, etc.

  9. #9
    Join Date
    May 2004
    Location
    Meridianville, AL
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    345

    filters

    I too have read these writeup's from the DC companies and have gotten the impression that they are talking using air filters alone to take care of the dust problem. While it makes perfect sense that removing the dust at it's source is the best way to keep the dust down I also believe that one can't have enough of "all types" of dust removal. One of the themes that they keep repeating is how a ceiling mounted unit only gets what is at the upper levels and not at the floor level, that's why I use a large 220v whole house blower in a 25x25 box that sits on the floor using 3 normal filters as prefilters and a hepa type final filter. In the other corner of the shop is a ceiling mounted 16x20 filter using a 1750cfm attic fan, a regular filter and a filtrete final. I now have air movement at all levels of my shop and I use a 2 HP DC that vents to the outside of my shop. In addition if I'm cutting or sanding I wear a quality face mask (not one of those paper types). I have done all of this for around $500 bucks versus the $1500 to 3000 that one of the DC companies wanted to sell me for my 24x20 shop. DC companies are in the business to sell you DC systems and anything that will cut into that is going to be painted as "bad". So bottom line is you have to have a comprehensive plan to attack the dust threat, limiting your self to just one way or the other is short cutting your health.

    Last edited by Jack Wood; 05-03-2005 at 8:28 AM.

  10. #10
    Quote Originally Posted by Ken Salisbury
    I can tell you that the air in my shop can be clouded with dust and within minutes of turning on my air cleaner it is very noticeably cleaner.
    If less particles are visable, it must be better air.

    The source of the article is not identified - only the fact that Oneida is using it to promote their own products. So that makes me somewhat suspicious.


    Like Jim said: "But I also love my air filter for it's ability to help keep my shop a little cleaner from settling dust...you know, the stuff that doesn't get caught when you are hand-sanding or even spraying water-bourne finishes."
    Good points! The cleaner may not get the very fine, possibly cancer-causing dust, but the big stuff it catches would drive my allergies crazy! (And, I hate to clean the shop.)

    Bob
    Spinning is good on a lathe, not good in a Miata.

  11. #11
    Join Date
    May 2004
    Location
    Oakland, MI
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    492
    Quote Originally Posted by Bob Hovde
    Good points! The cleaner may not get the very fine, possibly cancer-causing dust, but the big stuff it catches would drive my allergies crazy! (And, I hate to clean the shop.)

    Bob
    I like my shop surfaces clean as well, but, in the process of taking out the bigger stuff, are we re-circulating the invisible stuff by constantly moving air without filtration adequate to get out the really harmful stuff? I'm not saying I know the answer, but I think that is the most important question here. When we say that it must be working because the shop is cleaner, we have met one goal. I don't think it necessarily follows that it is still healthier than letting the dust settle.

    Greg

  12. #12
    Here are two interesting web pages:

    http://www.tinworks.com/tw/airfil1.htm
    http://www.tinworks.com/tw/filtest1.htm

    The second link re-iterates my critique of one of the conclusions reached in the Oneida article:

    "However, it is open to criticism because weight measurements give predominantly the weight of the largest particles in the sample. This is generally true of filter test samples regardless of the absolute size of the largest particles. Little credit is given for the removal of very small particles because they contribute insignificantly to the total weight of the sample...

    If all airborne particles were of uniform, filterable size, measuring filter efficiency by weight evaluation might prove satisfactory. Obviously, particles are not of uniform size."

  13. #13
    Join Date
    May 2005
    Location
    Cleveland, OH
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    14
    Quote Originally Posted by Ken Salisbury
    I can tell you that the air in my shop can be clouded with dust and within minutes of turning on my air cleaner it is very noticeably cleaner.
    If less particles are visable, it must be better air.

    The source of the article is not identified - only the fact that Oneida is using it to promote their own products. So that makes me somewhat suspicious.


    Like Jim said: "But I also love my air filter for it's ability to help keep my shop a little cleaner from settling dust...you know, the stuff that doesn't get caught when you are hand-sanding or even spraying water-bourne finishes."
    Ken & Jim....I'm not picking on either of you...really. I'm using these two quotes as examples of a string of opinions running throughout this thread. Oneida, if I'm not mistaken, isn't talking about the dust that you or I can actually see. They are saying that the dust which we cannot see...the dust that is the harmful dust...is being recirculated throughout your shop when you run these cleaners. If I read their statements further, they say that if I use a system (presumably theirs) at the source, I can mostly eliminate the harmful dust, and the air filtration unit is not necessary for anything other than controlling the dust that I can see.

    On the other hand, I could be completely wrong, and they're just pissed that they don't have the market cornered on filtration units.

  14. #14
    Join Date
    Mar 2003
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    SE PA - Central Bucks County
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    42,358
    Doug, you make good observations. Oneida isn't "wrong" at all...they just are not acknowledging all the reasons one might use an air filter in the shop. I think that jives with what many folks are saying as you point out.

    BTW, welcome to the Creek!!!!
    --

    The most expensive tool is the one you buy "cheaply" and often...

  15. #15
    Join Date
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    Quote Originally Posted by DougButterfield
    Ken & Jim....I'm not picking on either of you...really. I'm using these two quotes as examples of a string of opinions running throughout this thread. Oneida, if I'm not mistaken, isn't talking about the dust that you or I can actually see. They are saying that the dust which we cannot see...the dust that is the harmful dust...is being recirculated throughout your shop when you run these cleaners. If I read their statements further, they say that if I use a system (presumably theirs) at the source, I can mostly eliminate the harmful dust, and the air filtration unit is not necessary for anything other than controlling the dust that I can see.

    On the other hand, I could be completely wrong, and they're just pissed that they don't have the market cornered on filtration units.
    Doug,

    All I can say is when I run my air filter my breathing is noticeably better. I will let that be the judge as to the worth of the unit.
    "If you believe in yourself and have dedication and pride - and never quit, you'll be a winner. The price of victory is high - but so are the rewards" - - Coach Paul "Bear" Bryant
    Ken Salisbury Passed away on May 1st, 2008 and will forever be in our hearts.

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