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Problems with our air cleaner article

Asa Christiana, editor, Fine Woodworking magazine

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We have reworked the online version of the article to correct our mistakes and clarify the conclusions drawn from our testing.

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Update: Free download of the corrected article available here.

We made some missteps in our recent review of air filters in FWW #213, and since then we have published a number of letters critical of the article. We've also reworked the online version of the article (a free for download here). This recent letter from Robert Witter, the president of Oneida Air Systems, was too long to fit in the Letters section of the magazine, and Witter preferred that we not edit it, so here it is in its entirety. We are running a correction in the next issue (FWW 216). That correction also appears below, under Witter's letter:

"September, 4th 2010

FWW’s July/August “Air Filters” is a dangerously misleading article and it is not at all on the caliber of what is expected from this publication.

Only a fraction of the personal exposure level of total inhalable airborne dust in the test room was reported, personal exposures of airborne dust in the FWW test room were significantly higher than reported, approved industry air sampling methods were not adhered to and threshold limit values (TLVs) for wood dust were not mentioned.  The author lists the air filters as a third line of defense only to be used in addition to dust collection and a dust mask, but the tests performed are without dust collection.  There was no mention of the hazards of fugitive dust in the shop. 
The author’s comments that,” air filters capture dust quickly” and  “ air filters get the job done”  lead people to think that they are effective as a standalone device for dust control but this isn’t supported by the data presented in the article or by those knowledgeable about industrial hygiene.  

As verified by FWW’s editor, the “Air Filter” test reported only on airborne particulate 0.1 - 10 microns in size and all dust larger than 10 microns was ignored.  This size range (0.1 – 10 microns) constitutes only a fraction of the total suspended and inhalable dust (typically 0.1 - 100 microns) produced by woodworking tools.  The reported dust levels from this test were only 5 – 25% by mass of total dust levels depending on the WW tool operated.  Based on this alone the actual personal exposure levels in this test would have been 4 to 20 times higher than reported or 12 – 60 mg/m3, not 3 mg/m3.  By not reporting the total inhalable dust level the readership was misled as to the total amount of dust they are exposed to when woodworking and false conclusions are drawn.  

In the FWW Air Filters test, dust producing machines were only run for 7 minutes.  The graph correctly measured the dust loading in the shop air rising rapidly.  This was because the emissions of the source machines far exceed the ability of the air cleaner to remove dust.  In the FFW test, the total suspended dust exceeded the threshold limit value in only a few minutes and continued to rise until the offending source machines were shut down.   Only then the dust level started to drop over an extended time period.  In the meantime the operators are breathing the dust, despite the cheap face masks, before it reaches the ceiling mounted air filter.  A woodworking dust emission test done at UK Health and Safety Executive laboratory where a saw and sander were operated for 30 minutes (more than 7 min as in the FWW test) reported personal exposures levels on average between 50 and 120 mg/m3.  Peak values were between 95 and 231 mg/m3. 

Industrial hygienists are principally concerned with how much dust machine operators breathe because they are located in the high dust concentration zone by proximity to the dust source.  Without source collection tool operators are working in the effluent produced by the machine.   NIOSH and OSHA personal sampling methods provide that air sample probes are located in the operators breathing zone to measure personal exposure levels (air probes are typically clipped to the operator’s shirt pocket).   The FWW test was conducted with the sampling probe located on the wall away from the source machine.  This in nearly all cases understates the operator’s actual exposure level.
Not reported is that NIOSH, and ACGIH threshold limit values (TLVs) for hardwood dust is one milligram per meter cubed (1 mg/m3).  These values were established by industrial hygienists and schools of medicine on the expectation that chronic exposures at or below this level would not lead to adverse health effects.  Actual exposure levels in the test far exceed the TLVs. 

Dust control is not only about respiratory health.   Fugitive (free) dust that is not collected is a fire and deflagration (explosion) hazard. This is why OSHA will issue citations for wood dust layers more than 1/32nd of an inch deep.   Fugitive dust not collected at the source of emissions settles everywhere in the work area the shop and when disturbed becomes airborne again and again.  Air filters do little or nothing to prevent fugitive dust.   The recent BP oil well leak is an example of this.  What we have all seen is that the collection of fugitive oil released into the Gulf of Mexico by a runaway well becomes nearly impossible to reclaim.  The damage is done.  Control at the source is the only remedy.

Air filters are not considered effective or a best practice control in industry.  Air quality and safety standards cannot be met.  Unless fine dust is entrained, captured at the source of emission and filtered down to the smallest particle much of it becomes airborne.   Once contaminates are airborne they cause illness and safety risks, recapture becomes futile.  If your shop air is contaminated to the point where dust can be collected by an overhead air filter device you are already breathing too much dust.

Sincerely,
Robert Witter
Oneida Air Systems, Inc."

And here's the correction we are running in the next issue:

"Correction
In a chart in “Tool Test: Air Filters” (FWW #213) we gave misleading information about the total amount of dust in the air, and thus the overall performance of the units. Our meter measured only the dust from 0.1 to 10 microns in size, nothing larger. So after using the tablesaw, router and sander with no dust collection in place, it stands to reason that there was much more dust in the air than the 3 to 5 mg/m3 shown in the chart. In retrospect, we should have tested for the total amount of dust, in order to give a more complete assessment of these units.
Bottom line: While these units reduced the levels of airborne dust in our tests, they did not bring it down to safe levels. So labels and headlines in the article that read “Clear the air and protect your lungs” and Air filters get the job done” were misleading. Proper dust collection at the source is the only way to reduce airborne dust to a safe level, and we regret giving any other impression. We have reworked the online version of the article to correct these mistakes."

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Comments (16)

BowAndFiddle writes: A while ago I attended a wood turning class with 6 lathes in action i a small shop. The shop had a Jet filter installed and as soon as the filter was turned on the air just got so much easier to breathe. I have no idea of the dust levels before and after the filter was turned on and thus no idea if they were safe or not. It seems however an air filter is a good supplement to any existing dust collection system. Personally I'm considering the JET for my little hobby shop.
Posted: 4:29 pm on October 25th

MikeMT writes: In case I was not clear in my long-winded comment, I certainly am not advocating sole use of an air filter to control dust in a shop, but the possibility that an air filter along with a dust collector might meaningfully improve shop air quality. Here is my situation: I use a 1.5 HP bag-type dust collector with my stationary power tools, most of which are 20-25 years old and not well-designed for dust collection. I know that this setup is not nearly 100% efficient (never mind using a hand held router, even with a shop vac) in collecting dust. So I am looking for ways to further reduce dust in my shop without installing a new, top-shelf dust collection system and buying all new tools that are better-designed for dust collection.
Posted: 7:40 am on October 21st

MikeMT writes: The letter by Mr. Witter of Oneida Air Systems and the comments and correction above have provided for a very interesting and worthwhile discussion. However, I believe that some important details have been left out of the discussion on worker exposure levels by Mr. Whitter. Furthermore, I am distressed to see that FWW has published a correction to the article which prominently features speculation about the non-effectiveness of air filters (“some have challenged the effectiveness of these units...[claiming] that the filters don't catch the smallest and most dangerous dust particles...”). Who claims this? Perhaps people trying to sell dust collection systems? Because we don't know, this isn't very useful information. Although it may have been flawed in some ways, at least the initial article was based on systematically collected data.

Before addressing a few points about worker exposure levels, I should first say that I do not dispute the fact that complete source dust collection (zero free dust in the shop) is a worthy goal, but I recognize that a common reason that many of us do not achieve this goal is a simple matter of how we allocate our very limited financial resources. I am interested in learning about cost-effective ways that I can reduce my exposure to dust in the wood shop—and I still suspect that air filters have a place, along with standard dust collection systems, in achieving this goal.

Regarding exposure limits: As birchwoodguy notes, the standards Mr. Whitter refers to standards are designed with full-time workers in mind. Specifically, the NIOSH and ACGIH recommended exposure levels are designed to provide adequate protection to a worker who is exposed to 1 mg/m3 of wood dust for 10 hours (8 in the case of ACGIH) per day over a 40 hour work week—hardly the conditions that most hobbyist wood workers find themselves in. In addition to the NIOSH and ACGIH standards, OSHA also publishes its own permissible exposure limit for total wood dust (15 mg/m3) and a separate limit for respirable wood dust (5 mg/m3), both of which are published as time weighted averages (8 hours per day over a 40 hour work week). To imply that any of the above mentioned worker exposure limits are instantly voilated if the concentration of dust temporarily exceeds the limit is simply incorrect. As explained above, these are average concentrations, not to be exceeded over a 40 hour work week. Temporary spikes in concentrations (depending on the magnitude), can at times be acceptable.

To address the issue of temporary spikes, enter another measure used to quantify worker exposure to hazardous compounds: the short term exposure limit (STEL), which generally corresponds to the maximum 15 minute average concentration of a compound considered acceptable for worker exposure (unfortunately, I have been unable to locate a published STEL for hardwood dust). STELs are often used in concert with 40 hour time weighted averages. As long as your short term exposure stays below the STEL and your 40 hour time weighted average stays below the TWA limit, in the industrial hygiene world, you are doing okay. (Although I always operate under a “less exposure is better” frame of mind).

With all of this in mind, I have to ask, how could air filters (assuming they are effective in removing dangerous dust from the air) not help to reduce your time-weighted exposure to airborne dust? Perhaps air filtration is part of a low(er) cost solution to reducing our exposure to wood dust in the shop after all? I am not sure yet, but I would like to see FWW consult actual experts in this field (e.g. people without a vested interest in selling something) and perhaps conduct additional air quality testing under more realistic conditions to give us all a better idea. In any case, I applaud the original author for taking on this tricky issue and I appreciate the discussion it has generated. - Mike
Posted: 8:29 pm on October 20th

paulvino writes: Thanks to the editors for publishing the correction to the article.
Dust collection at source is the way to go!
Over the years, as a part-time woodworker, I have added dust collection to all my stationary machines.
I must say, thought, that collecting a reasonable amount of dust and chips from the chop saw is a huge challenge. I own a Bosch 12" sliding miter saw and that machine is the single largest headache to a clean environment.
If anyone can direct me to a simple (!?) system, it would be much appreciated.
Posted: 8:30 am on October 19th

KOAMAN writes: I have a two car garage shop with an Oneida cyclone and a Jet overhead ambient dust colector, and both of them have done a great job in helping me to manage the dust. It's still a chore to collect all of the dust, so whenever I'm in the shop creating dust, I still wear my personal dust protection.
Posted: 6:09 pm on October 12th

GEide writes: rpeowen2, Good suggestion. Sorry we didn't think of that. Here it is: http://www.finewoodworking.com/fwnpdfFREE/011213054.pdf

Gina, FineWoodworking.com
Posted: 2:42 pm on October 6th

BingoBoy writes: I am so very glad that the magazine has published a retraction & corrected the article. I thought something was fishy when I skimmed the original article after getting the magazine, but I didn’t think too much about it at the time. I jus shrugged it off and thought “c'est la vie”, “caveat emptor”, “a fool and his money” etc.
Now I’m a novice woodworker to say the least, but I have a reasonably well equipped shop. Before I buy equipment I research on the web which specific products are best or the best value. In this process I rely most on the comparative tool tests you find in the woodworking magazine’s archives.
I did this kind of research on dust collection about a year ago & as a result bought a Delta dust collector & a Fein shop vac, each of which I converted to two-stage operation. [See the P.S. below for more info on what I did, if you’re interested.] I purposely did not purchase a ceiling mounted filter, since my research suggested, in short, that you can’t fight gravity and ceiling mounted filters just can’t do that much to clean the air in a shop if that is all you use.
But the article made me wonder whether the author knew what he was doing, how the editors of the magazine allowed such information to be published & whether manufacturers may have influenced the outcome.
So, as I said, I am very glad that the magazine has published a retraction & corrected the article.

P.S.
If you’re interested in what I bought for dust collection purposes, and how I modified the items, see the following:
1. For larger machines I use a Delta vertical bag dust collector # 50-760 (1.5 hp, 1,200 cfm, 4" hose). My research indicated it is one of the best of this type and size of dust collector, and it can be easily converted to function as a two-stage unit without increasing the “footprint” size of the dust collector. I did this by adding a 30-gallon metal garbage can (the first stage) connected to the Delta unit (the second stage) by a Delta quick connect fitting # 50-196. I also replaced the stock fabric filter with a Wynn cartridge filter # 35A. This is not necessary to convert the Delta unit to two-stage operation, but it reduces the height of the Delta unit, which is what I wanted.
The total cost was $300 for the dust collector (a real steal at Amazon at the time, with free shipping no less), $20 for the garbage can and $25 for the connector. The optional cartridge filter was $150.
You can see photos of how I converted the Delta unit to two-stage unit at Amazon, along with photos of similar conversions by others. Mine are the photos referenced “GAT.” Just search for the part number.
2. For smaller machines or tools I use an old style Fein # 9-55-13 Turbo II 9-gallon shop vac. Similar vacs by a variety of manufacturers will work just as well. I liked the old style Fein because it is very compact. The vac was converted to two-stage function with an Oneida Dust Deputy and the combination was mounted to a Seville Classics utility cart # SHE18304, so it can be rolled around easily to wherever needed. The Seville cart is very sturdy, has nice big wheels and is reasonably priced at Amazon with free shipping.
The cost was: $ 300 for the vac, $100 for the Dust Deputy and $60 for the cart.

Posted: 1:36 pm on October 6th

birchwoodguy writes: I think the readers have a lot of good points. And lets remember that as hobbists we are not exposed 8 hours a day 5 days a week as assumed by the industry regulators. And if we had to maintain less than 1/32" of accumulated dust at all times, well I can't think of any hobby shop like that. So I think the idea of the ideal shop dust collection capturing at source is a great target for all of us but in knowing our systems are no-where near that level, the ceiling mount filters seem like a great improvement to the alternative - breathing all that dust for hours instead of minutes, allowing dust to accumulate on surfaces to be re-disturbed again later rather than having a filter system collect a portion, albeit not 100%.
Posted: 10:45 am on October 5th

Zecarle writes: I am a hobbyist in a small shop using older woodworking machinery that is not dust collection efficient. The one thing that I want to mention is that proper air ventilation is key. I installed an industrial fan at the window by my dust collector and that thing sucks out all the dusted air to the outside. The difference in my small shop is considerable.

The letter from Oneida assumes that dust collection at the source of emission is controlled. That goes only for newer machines. A lot of hobbyists which are 2/3 perhaps of the audience of this magazine might not have modern tools designed around proper dust collection. but ventilation to the outside with a 1000 lfm fan will go a long way. In fact from memory that was in the end the #1 recommendation of Bill Pentz in his famed article
Posted: 7:56 pm on October 4th

Zecarle writes: I am a hobbyist in a small shop using older woodworking machinery that is not dust collection efficient. The one thing that I want to mention is that proper air ventilation is key. I installed an industrial fan at the window by my dust collector and that thing sucks out all the dusted air to the outside. The difference in my small shop is considerable.

The letter from Oneida assumes that dust collection at the source of emission is controlled. That goes only for newer machines. A lot of hobbyists which are 2/3 perhaps of the audience of this magazine might not have modern tools designed around proper dust collection. but ventilation to the outside with a 1000 lfm fan will go a long way. In fact from memory that was in the end the #1 recommendation of Bill Pentz in his famed article
Posted: 7:56 pm on October 4th

Zecarle writes: I am a hobbyist in a small shop using older woodworking machinery that is not dust collection efficient. The one thing that I want to mention is that proper air ventilation is key. I installed an industrial fan at the window by my dust collector and that thing sucks out all the dusted air to the outside. The difference in my small shop is considerable.

The letter from Oneida assumes that dust collection at the source of emission is controlled. That goes only for newer machines. A lot of hobbyists which are 2/3 perhaps of the audience of this magazine might not have modern tools designed aroudn proper dust collection. but ventilation to the outside with a 1000 lfm fan wil go a long way. In fact from memory that was in the end the #1 recommendation of Bill Pentz in his famed article
Posted: 7:55 pm on October 4th

Zecarle writes: I am a hobbyist in a small shop using older woodworking machinery that is not dust collection efficient. The one thing that I want to mention is that proper air ventilation is key. I installed an industrial fan at the window by my dust collector and that thing sucks out all the dusted air to the outside. The difference in my small shop is considerable.

The letter from Oneida assumes that dust collection at the source of emission is controlled. That goes only for newer machines. A lot of hobbyists which are 2/3 perhaps of the audience of this magazine might not have modern tools designed aroudn proper dust collection. but ventilation to the outside with a 1000 lfm fan wil go a long way. In fact from memory that was in the end the #1 recommendation of Bill Pentz in his famed article
Posted: 7:55 pm on October 4th

Zecarle writes: I am a hobbyist in a small shop using older woodworking machinery that is not dust collection efficient. The one thing that I want to mention is that proper air ventilation is key. I installed an industrial fan at the window by my dust collector and that thing sucks out all the dusted air to the outside. The difference in my small shop is considerable.

The letter from Oneida assumes that dust collection at the source of emission is controlled. That goes only for newer machines. A lot of hobbyists which are 2/3 perhaps of the audience of this magazine might not have modern tools designed aroudn proper dust collection. but ventilation to the outside with a 1000 lfm fan wil go a long way. In fact from memory that was in the end the #1 recommendation of Bill Pentz in his famed article
Posted: 7:55 pm on October 4th

rpeowen2 writes: Given the errors in the print version of the article, shouldn't the corrected version be available to all Fine Woodworking readers not just members?
Posted: 12:26 pm on October 4th

9michael9 writes: I considered My new Jet air filter a supplement rather than the main source of dust removal. I own an Odeina dust collector and was amazed at its efficient removal of fine dust. My vacuum has never collected hardly any sawdust since incorporating the Odeina into my dust collecting system. The article was remiss in mentioning this and I happy to see the correction.
~~Michael Griffin
Posted: 2:18 pm on October 2nd

ondablade writes: Good going FWW for refocusing this piece - it caught my attention too in that it seemed to go against my limited understanding of the reality of the situation regarding safety and wood dust.

It's important, because it's not unusual to see people talk of these units as though they are a stand alone dust solution.

There are major issues with DIY/hobby level woodworking dust control practices anyway as a result of the gap between common perceptions/received wisdom, and the realities of wood dust safety.

This it would appear is in part the result of the sale for many years of low performing dust collection systems to the DIY and hobbyist market. Another factor is the fact that the truly dangerous sub 10 micron dust particles are invisible, and the consequences cumulative and usually medium to long term.

The result is that people struggle to understand why they should spend large amounts of money on high spec and high flow fine filter systems when they are not the norm.

'If THEY let it be sold/let us use it, then it must be OK....' - the classic disbelief that arises when realities conflict with perceived norms.

Following the uphill struggle waged by the likes of Bill Pentz http://billpentz.com/woodworking/cyclone/index.cfm (Bill's pages are a goldmine of information - but never a model of concise writing :-)) to bring these issues to consciousness and provide an alternative some manufacturers are responding - we're for example starting to see optional fine cartridge filters and the like offered as (sticking plaster?) options by some, and properly sized cyclone based systems by a few others.

There's also a sizable number of people out there who have taken control of their own situations and are running DIY and/or part purchased (http://www.clearvuecyclones.com/Order_Page.htm) installations based on Bill's data.

I'm part way through a DIY installation of a Pentz system, and chose this route as a result of the compelling safety argument, and excellent feedback.

I'd be much happier to see an end end to the fuzzy and qualitative 'gets the job done' style of magazine review of dust collection equipment - to be replaced with hard data based performance testing (in realistic situations) against TLVs.

In the case of the ducted dust systems that so far are the norm, and in keeping with the thrust of Bill's writing there are perhaps three basic questions that often get overlooked:

1. Presuming reasonable guarding and hooding arrangements - is enough airflow/depression generated around the point of work to prevent dust getting into circulation in the room? (the issue of duct and fan sizing)

2. Is the filter system fitted capable of preventing the recycling of the highly dangerous (and invisible) 10 micron and below dust particles into the room? (the issue of filtration capability)

3. Can the system hope to maintain this level of performance over a reasonable period of time in use? (the issue of the rapid filter blinding that seems to occur unless a cyclone or similar device is used to separate most of the dust and reduce the load on the filter)

The ability to test systems adequately does not come cheaply without considerable ingenuity and expertise, this must be a major consideration for the mags.

It seems to me though that this is pretty much a moral obligation for any publication that purports to serve its readership.

There's other reasons too. We're already all aware of the threat posed by heavy handed regulation to DIY and hobby woodworking. Wouldn't it be infinitely preferable to get the information out there on what comprises and adequate dust system so that market forces can sort this out in a much more finely nuanced way that leaves freedom of choice intact??



Posted: 8:15 am on October 2nd

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