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Until very recently very few woodworkers were willing to believe that woodworking creates much if dust particles that go right through normal home HVAC filters and even most air cleaners. When I shared the results of these tests with fellow woodworkers on these pages some listened, some agreed, and many did neither. In fact, it kind of became a game to see how far others could insult me and my web page efforts on some of the less well behaved Internet woodworking forums.

In late 2007 the began selling an inexpensive laser particle counter that people can buy for under $150. In speaking with Roger Unger owner and principal designer of this unit, it appears to be a good solid air quality test meter at an affordable price. Woodworking creates a huge amount of fine dust particles. Those sized under 10-microns are known by medical people as inhalable dust because they get right by our normal body protections and lodge deep in our tissues. These 10-micron and smaller particles are invisible without magnification. This test unit uses a laser and photocell system with software to count these particles. This unit should be very accurate at lower dust levels but as we reach the higher concentrations often found in enclosed shops that vent inside the larger particles are going to block the light which will impact accuracy at high dust levels. Regardless, when well over the scale this meter is still saying the dust level is bad news even if the counts are off at the higher levels. This unit can really open Pandora’s box on vendor’s selling dust collectors and cyclones that come with fine filters and just plain don’t do a good job at all. What it will not do is also address the huge number of chemicals found in wood dust that have all kinds of nasty health effects from being poisonous, strong irritants, sensitizers that create allergic reactions, carcinogens, and those that create the few serious woodworking related respiratory diseases. I think it is a great product and will work with this firm to setup an ongoing discounted price for those who want a meter to track the status of their own shops. I personally ordered the 0.5 accuracy unit with PC interface. I look forward to trying it out and comparing its results against my MetOne Aerocet 531 meter that cost over $5500.

Enough fuss has been raised about the dangers of fine wood dust that many small shop owners are now beginning to order these units. The little shop air quality testing already done with my and other meters so far has strongly validated what these web pages have been saying for years. I suspect we will learn a lot more about fine wood dust as others get, use and share their results from using this meter. I have already learned from one meter user that his upgraded home HVAC system that has a fine Honeywell 0.3-micron allergy filtration system rapidly reduces the airborne dust level in his basement shop. I also learned just moving around in a fairly clean looking shop stirs up a high amount of airborne invisible dust without doing any woodworking.

I think soon many will realize a number of things. Even just a little woodworking makes a huge amount of the most dangerous 10-micron and smaller invisible airborne dust particles. We get terrible dust collection unless our tool hoods to block the fast moving airstreams and control the fine dust. Even with upgraded hoods most basic tool designs still spew lots of dust so we have to provide higher airflows to pull in this dust. Festool and Fein have already shown that tools built from the ground up with good dust collection built in get great collection with a powerful small vacuum. Until we can buy tools with this kind of dust collection built in we still need to upgrade hoods and move a lot more air. My testing shows dust collectors need to be 3 hp and larger and cyclones 5 hp and larger to move enough air to pull in most of the fine dust. When we use these larger airflows we need good sized ducting as ducting under 6” or 7” in diameter depending upon the pressure our blowers can generate does not move enough air at our larger tools. I think these meters are going to most challenge the quality of our filters. Vendors have long known they can claim any level of filtering they want and prove their claims as long as they also don’t include the airflow at any given filtering level. We can load up a chicken wire grid with enough rocks and dirt to provide a 0.3 HEPA level filter but it won’t pass air. These meters give woodworkers two important tools. They can check the quality of their new filters and actually know when it is time to change out the filters because they have become worn out. I think these meters are also going to rapidly advance our knowledge of how to get rid of the fine dust and keep it from building up in our shops.

I’m not sure if these affordable laser test units are good or bad news for me personally. Since a few posts went up on some of the larger woodworking forums my email volumes and number of telephone calls have been overwhelming. Anyhow, after I get my meter from this firm and have a chance to test it out, I’ll try to update this test information a little to help use these meters.

A.    Caution

Unfortunately, knowing how much dust we take in misses one very important part of dust exposure. Knowing how much dust we are breathing does not tell us how dangerous this dust actually is. In addition to the fine particles causing damage, dust also contains many different chemicals. For wood dust we know trees produce many different strong chemicals to protect themselves from insects and other predators. Wood is also exposed to many other chemicals from the molds, fungi, yeasts, lichen, mosses, etc. that break wood and bark down, plus other chemicals such as insecticides, herbicides, preservatives glues, solvents, finishes, drying agents, fine metal filings, etc. As discussed in my pages even a good is still not going to warn us about these other chemicals commonly found in wood and other airborne dusts. When working with dangerous, unknown, treated, or moldy woods we should always wear a good NIOSH dual cartridge respirator and keep wearing our respirator until we thoroughly clean our shops.

The other serious problem with wood dust is taking in too much dust in a short period. Too much dust can clog our airways, sinuses, throats, and lead to chronic infections, pneumonia and a variety of respiratory diseases. This is why OSHA sets a maximum personal exposure limit of 15 milligrams of dust per cubic meter of air (mg/cm3) over any fifteen minute period.

B.     Magazine Testing

I had hoped that the magazine testing would take over the testing of dust collectors, cyclones and air quality. My keeping up that testing was too expensive and hard on my not so great health. I worked closely with one of the most respected small shop magazines to do another full and far more complete round of dust collector and cyclone testing. The dust collector test results were pretty amazing and the most accurate to date. Sadly, the magazine decided to not also test these units for how well they actually separated off and captured the fine invisible unhealthiest 10-micron and smaller particles.

The cyclone testing went well, but also failed to test to see just how well these units actually separated. Unfortunately, that testing found every small shop cyclone except my cyclone design gravely failed the last set of magazine tests that actually looked at real airflow under real shop conditions. A decision was made by the magazine senior editors to not share that last round of testing. I understand that no magazine would want to put out a review that showed their main advertisers as selling products with serious performance problems.

C.    My Testing

1.      Incentive

Seeing that no new testing is expected in the near future, I chose to spend the considerable money it cost to buy and do some testing on my own. Before making these purchases I did quite a bit of research and had help from a number of experts who advised me on what test equipment to buy and what they said would make the most sense in terms of testing. Although I was not looking for laboratory results, I did want real numbers that others could see, duplicate, and understand in terms of how this affected their own shops. I also wanted all tested under real world working conditions instead of the long time magazine tests that have become a vendor game of who can move the most air under the most unusual test conditions.

I bought an expensive test meter (See Test Equipment below) then tested many of my local friends’ shops to get my testing protocol refined. My friends surprised me as quite a few had excellent dust collection mostly due to lots of careful work on their systems and making excellent custom tool dust collection hoods. In fact, the only dust collector that passed the relatively easy OSHA air quality standards belongs to one of my friends who vented outside. Some of my other friends also did excellent work with their smaller cyclones that they had either made or put together from commercial parts, but they had also totally remade their tool hoods to provide very tight fitting collection that let almost no air escape their blades, bits and cutters.

I learned two importing things from testing my friends’ shops. Regardless of how powerful their dust collector or cyclone, not one single shop passed their air quality test unless they had an upgraded over blade guard hood with dust port with a strong airflow. They had to either use a shop vacuum if they had a smaller port or use at least a 3.5” port if they were going to connect to a cyclone. The cyclones and dust collectors just did not have ample pressure to collect through a 2.25” to 2.5” small opening on a blade guard hood and provide much fine dust collection at all. I also sadly learned that the eBay sold cyclones and the one cyclone that failed so dismally in the last published magazine cyclone test could not be made to provide good fine dust collection no matter what we did. The add on to your dust collector cyclones from eBay used the same early cyclone design that almost all abandoned before 2003 because it added so much resistance it all but killed our blower airflows. This design actually works worse for 2 hp and smaller dust collectors than simply using a $25 plastic trashcan separator lid. That other vendor cyclone does not work nearly as well as a trashcan separator lid and plugs its filter so quickly it was recommended as something to not buy at all. The second very important thing I learned is every shop that I tested that vented inside had huge amounts of fine dust that just walking around stirred up enough to fail the more sensitive dust level tests.

2.      Volunteers

An announcement was placed on two of the major woodworking forums asking for volunteers within the State of California willing to have their shop air quality tested. Quite a few volunteered to participate in this testing. Each was asked their brand, purchase date, and motor size of their cyclone. Each was asked if their cyclone supplier had advised them to upgrade any tool hoods or port sizes. Each was also asked if they had upgraded their table saw hoods with a dust collection port. Candidates were screened to omit all that had the eBay cyclones. None volunteered for testing that had cyclones from that vendor with such poor magazine test results. Candidates were further screened to ensure each different type of cyclone also included at least one shop with a table saw that used an upgraded blade guard with dust collection port. Each volunteer was advised of the test equipment to be used, asked for permission to make a small test hole in their main duct, and advised of what would be tested. Results would be shared with them after the testing and all people’s identities would be kept private. Each was asked to do a little preparation work in advance of the testing.

3.      Testing Protocol

  1. Each shop owner was asked to do a little preparation to settle any airborne dust in their shop. Each was asked to thoroughly blow or vacuum out their shops then do no woodworking or shop cleaning for at least 72 hours prior to the testing and do what they could to minimize airflow in their shops from any source during that settling time.
  2. A baseline was set by testing the outdoor air quality.
  3. The inside shop air quality was then tested with nothing running and compared to that baseline.
  4. The cyclone was then turned on with all blast gates open and another air quality test was run before doing any woodworking.
  5. All airflow except to their table saw was shut off with gates or plugs. While the cyclone ran collecting only from the table saw the owner cut 54 linear feet of ¾” MDF using their standard blade with 1/8” kerf followed by another air quality test of the shop air.
  6. We then turned on any exhaust fans, air cleaners, opened available doors and windows, and ran the cyclones while doing ongoing air quality checks with the meter to see how long it would take to clear the air to below 0.1 mg/cm3.
  7. While the shops purged a 1/8” diameter hole was drilled into the main duct 12” before the cyclone inlet. A stand was then secured to the duct to hold a pitot air velocity sensor tube centered in the main duct. After the shop air had recovered a Dwyer Instruments 166-12 model calibrated pitot tube was inserted and attached to that stand. A Dwyer Instruments digital differential pressure meter was then used to determine system air pressure and velocity. That velocity was then used with the main ducting size to compute maximum air volume. All blast gates were then closed to determine how much air was being leaked within the system. Airflow was directed to each individual tool and measured. The largest airflow and lowest airflows were recorded. The test hole in the duct was sealed and the shop owner was then given a summary of the results of their tests.

4.      Test Results

Twenty nine shops were tested in late 2005 and early 2006.

a.      Filter Test

Every cyclone that vented inside except for those that used top quality commercial filters (specifically tested Donaldson-Torit, Farr, and Wynn Environmental) immediately failed the first air quality test before doing any woodworking. Just turning on the cyclones without the good commercial filters instantly filled the shop air with huge amounts of fine dust. Every shop appeared to have been well cleaned prior to the testing. This very sensitive meter registers the fine dust stirred up by just walking around and would have shown if these shops had buildups of fine dust. This makes it apparent that almost all this fine dust came from or through the existing filters. The airborne dust levels without doing any woodworking all exceeded the EPA and medical recommended maximum of 0.1 mg/cm3 range. Most averaged around the 1 mg/cm3 recommended by ACGIH. The worst was over the OSHA 5.0 mg/cm3 range. And this bad news was before doing any woodworking at all, just turning on the cyclones in a clean shop. My particle counter showed all small shop vendor fine filters continued to freely pass the unhealthiest invisible under 10-micron particles as the particle counts for this very fine invisible dust did not appear to fall while just the cyclones ran. This indicates that in the up to a year that some of these shops had used their cyclones these filters had not “seasoned” enough to provide good fine dust filtering. Seasoning means building up a cake of fine dust in the filter pores that does not come out with normal cleaning.

b.      Dust Test

Proper Hoods – No shop with a 2.5″ or smaller port on their upgraded blade guard hood passed its air quality tests after cutting that 54 linear feet of MDF regardless of size or brand of cyclone. Just like those saws with no blade guard hoods, the best of these hoods with the smaller ports still allowed the air quality to go well over twice the maximum airborne dust levels allowed by OSHA. The worst went to nearly five times the maximum airborne dust level allowed by OSHA. Air will not even hold more than this much dust unless pretty strongly stirred. Those that worked best had 3.5” and 4” openings on their blade guard hoods. In conclusion these small ports either need connected directly to a powerful shop vacuum or need 3.5” or larger ports connected to cyclones or dust collectors.

Ample Blower & Filter – None of the 2 hp powered cyclones were able to maintain the air quality at or below the OSHA 5.0 mg/cm3 level. None of the 3 hp cyclones were able to maintain the air quality at or below the ACGIH 1.0 mg/cm3 level. Only the one 5 hp cyclone that directly vented outside and the six cyclones of my design actually maintained a shop air quality during and after cutting of the EPA and medical recommended 0.1 mg/cm3.

c.       Recovery

Only those shops that either used Farr, Wynn, and Donaldson-Torit filters or provided a strong air cleaning effort with fine filters and or blasts of air going outside recovered quickly. All shops that stayed sealed with lesser quality filters did not return to outside ambient air quality levels.

d.      Air Volume Testing

None of the 2 or 3 hp cyclones had a maximum airflow with all blast gates open much over 800 CFM. All 2 and 3 hp cyclones had a worst case airflow under 600 CFM to distant machines served by a 6” pipe. Every vendor supplied ducting design had air speeds in the main drop to well under the minimum 2800 FPM considered a minimum to avoid dangerous ducting piles. Some had vertical runs that fell well below the minimums needed to avoid ducts from plugging. Only the 5 hp cyclones actually moved maximum airflows in excess of 1000 CFM with all ducts open. Only my design and one other of the 5 hp cyclones actually moved a real 1000 CFM or better at the closest machine with a large duct and hood all others moved under 1000 CFM at their largest single airflow machine. The lowest airflow machines all used vendor supplied ducting plans with even some of the 5 hp cyclones moving airflows well under 400 CFM due to totally inappropriately small down drops. All small shop vendor provided ducting designs had problems using 4″ down drops for tools that require in excess of 800 CFM. No vendor recommended either replacing existing hoods or opening undersized tool ports.

e.       Testing Summary

Only the one other 5 hp cyclone vented outside and the six cyclones of my design with good commercial filters actually moved ample airflow and to pass any of the air quality tests including the easiest to achieve Department of Labor, Office of Health and Safety Administration (OSHA) air quality tests. All 2 and 3 hp cyclones lacked ample airflow for good fine dust collection. All small shop supplied vendor filters also provided very poor filtering of the 10-micron and finer particles, plus stored up this fine dust and launched it all over our shops when these units were first turned on. All small shop vendor ducting designs had serious problems with providing ample air to our machines and most had problems keeping ample air moving to keep the ducting clear. Recovery time to restore breathable air quality required strongly venting outside or a combination of large air cleaner and cyclone with very good quality fine filters. My attorney told me to not release the specific vendor name and model numbers because I don’t want the aggravation of another vendor threatened law suit.

I believe the issues are the same that I have been pushing hard since 1999. Over twenty years of air engineering and refinement by the dust collection firms whose customers must pass regular air quality testing shows that for good fine dust collection we must collect the fine dust at the source and keep our shops clear of the fugitive dust that escapes collection. To capture the fine dust at the source we must first fix our tool hoods to control the fine dust, move ample air to collect this dust, then get rid of that dust by either blowing it away outside or amply filtering the air before returning the air to our shops.

5.      Test Equipment


2000 – The Aerocet 531 was introduced to the market. The Aerocet 531 combines particulate and mass measurements in a single small hand-held instrument with easy to use data logging.

Particle Mass Profiler and Counter in a Single Handheld Unit
The Aerocet 531 is a small, handheld, battery operated, and completely portable unit. This unit provides both particle counts or mass PM measurements as stored data logged values, real-time networked data, or printed results.

Five Mass Ranges and Two Particle Sizes
All five important mass size ranges (PM1, PM2.5, PM7, PM10, and TSP) are displayed in mass mode as well as two popular cumulative particle sizes (> 0.5 and > 5.0 microns) in particle mode.

Tailored Mass Conversion
The particle counts from eight size ranges are converted to mass using a proprietary algorithm for typical-density aerosols. Accommodation for special particulate with different densities is provided through user-programmable “K-factors.”

6.      Data Collection Forms