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Friday, April 8, 2016

Dust Collection Basics - Blog

Updated: November 1, 2017


This blog provides an overview of dust collection. Although this blog targets woodworkers, it applies to all who work in dusty air such as those who work with stone, sand blasting, finishing, fiberglass, etc. This blog defines and explains the differences between the two main types of dust collection, chip collection and fine dust collection. It shares why there is so much small shop dust collection confusion. It also defines the different types of airborne dust and shares the risks associated with fine dust. This blog shares what hobbyists and small shop owners can do to better protect themselves with much better fine dust protection and collection.


The expensive top magazine rated cyclone system I installed to protect my health was a dangerous dust pump that created a bad false sense of security. It left a clean looking shop while it produced dangerously high invisible dust levels that caused me to develop a life threatening allergic reaction. I spent my recovery time figuring out what happened and came up with better solutions to protect my family and me. My respiratory doctor was so impressed he talked me into sharing both what I learned about dust collection and my solutions for good dust collection. We co-wrote three articles that generated tens of thousands of emails, so in self-defense in 2000 I created my Cyclone and Dust Collection Research web pages. Daily thousands read my pages and now, over 20,000 people worldwide use cyclones of my design to help with their dust collection. Hundreds have contributed even more growing my pages to huge. I was asked to build this blog as a quick way to get out the basic information.

Dust Collection

Different people mean totally different things when they say dust collection. Traditional dust collection collects the same dust and chips we would otherwise sweep up with a broom. We use traditional dust collection to keep our tools, work surfaces and floors clear of the dust that can lead to people falling, accidents, fires, and poor quality work because the dust obscures the work. Traditional dust collection has been a requirement in many areas since the 1920s, so is well understood and how to get good traditional dust collection is very well documented. Fine dust collection provides both good traditional dust collection plus collects amply to keep the airborne invisible unhealthiest particles down to a safe level. Fine dust collection got its start in the 1950s with worries about nuclear fallout and for some industries it has been a requirement since the 1960s, so is also well understood and documented. Now so many areas require good fine dust collection that many automatically assume that dust collection means both traditional and good fine dust collection. Conversely, so many other areas have no fine dust requirements that when they say dust collection, they only mean traditional dust collection. This blog and my Cyclone and Dust Collection Research web pages follow the convention of saying fine dust collection and chip collection to make clear which dust collection is meant.


The dangers of wood dust are confusing because until fairly recently most considered all wood dusts except Western red cedar only a nuisance that causes irritation. Solid verified medical research now shows fine invisible airborne dust of any type causes so much health damage that the EPA sets really tough indoor air quality standards. The peer reviewed medical research shows wood dust particles are one of the worst commonly found fine airborne dusts. Woodworking makes huge amounts of fine dust compared to how little it takes to harm our health. Fine wood dust particles are also covered in razor sharp edges and sharp extended points that cause scaring and trap fine wood dust deep in our respiratory tissues. These lodged fine wood dust particles also contain and carry toxic chemicals that cause additional health damage.


The experts who build the best dust collection equipment and guarantee customer air quality have long shared exactly what we need to do to get both good chip collection and good fine dust collection. They found our tools launch dust filled air streams at about twice the speed of the air moved by our dust collection systems, so there is zero chance of either good chip collection or fine dust collection unless we start with hoods that block, control, direct and deliver the fast moving dust filled air streams for collection.

Decades of experience show even with good hoods to get good traditional dust collection at most small shop stationary tools we need to move air at close to 4000 feet per minute (FPM) with a volume of about 350 cubic feet per minute (CFM) using at least four inch diameter ducting. Due to fire and explosion risks the experts, building codes, and even insurance companies require that the collected debris and dust should be stored in metal fire and explosion proof containers and storage bins, or the dust collection should be placed outside behind fire and explosion proof barriers.

Fine airborne dust is so light even the lightest breath or breeze can blow it around, so fine dust will be blown all over by our tools and even normal room air currents. The experts found that woodworking creates so much fine dust compared to how little it takes to harm our health, that exhaust fans and air cleaners will not clean the air fast enough to avoid failing air quality tests or keep our shop air safe to breathe. The experts found the only effective way to deal with fine airborne dust is to collect it as it gets made. The experts found that we only have to pull the air in at about 50 FPM airspeed to capture the fine dust, but we must maintain that air speed out to a considerable distance all around the working areas of our tools. That creates an interesting problem because unlike blown air, sucked air speed falls off very rapidly. We all know that a shop vacuum on blow will blow fine dust all over, but when sucking a vacuum will not collect until we get the nozzle right next to what we want to collect. This is because sucked air comes from all directions at once, so airspeed falls off at four times Pi times the distance squared. So, good fine dust collection requires even better hoods, plus requires moving an air volume of over 1000 CFM to get our needed 50 FPM air speed over a large enough area. Because air hardly compresses at all at dust collection pressures this means we also need all at least seven inch diameter ducting to carry this much air volume.

The experts also found the best ways to get rid of fine dust. Woodworking makes so much fine dust and filters require so much cleaning and expensive replacement that most commercial shops use cyclones or 30-micron filters to separate off the heavier dust then vent the fine dust outside. Fine dust lasts nearly forever when vented inside, but when vented outside it quickly dissipates and breaks down as soon as it gets wet. Venting outside works very well so long as ample make up is provided to keep from sucking toxic fumes backward through our vents. Most find they can vent outside and still be comfortable using infrared heat dishes. Air conditioners cannot keep up with the heat losses when venting outside. In some areas venting outside is illegal so filtering is required. The major vendors have found from decades of experience with filters it takes at least one square foot of fine filter area for every 4 CFM of airflow, but to last at least three months with less cleaning most vendors recommend use of twice as much filter area.


All the major industry experts agree that these are the workable solutions for good chip collection and good fine dust collection, but there is still huge amounts of dust collection confusion. In addition to not knowing if someone is talking about chip collection or good fine dust collection, there is considerable confusion about the danger of airborne dust and even more confusion about what it takes to get good fine dust collection. What adds even more to this confusion is a logical but very bad widespread assumption about what it takes to get good fine dust collection. Most small shop vendors, magazines, woodworkers, hobbyists and even experts wrongly assume a dust collector that can suck up a block of wood or heavy tool should do a great job collecting the fine dust that can be moved with the lightest breath


This faulty assumption about what it takes to get good fine dust collection has hobbyists and even professionals all over the world using shop vacuums, dust collectors, cyclones and air cleaners advertised to provide health protection that actually create dangerous air quality. The air volumes these units produce are too small to generate a big enough "bubble" with enough airspeed to pull in the fine dust before normal room air currents blow the fine dust all over. Our test equipment shows all shop vacuums, most under 3 hp dust collectors and most under 5 hp cyclones fail to move enough air for good fine dust collection, so much of the fine dust we make ends up getting blown into our shop air. Worse, our particle counters show almost all small shop air cleaners, shop vacuums, dust collectors, and even cyclones only come with filters fine enough to get rid of the visible dust. Getting rid of the visible dust makes very clean looking shops, but unlike this visible dust that builds up overnight and can ruin our finishes, the unhealthiest dust is the invisible dust that cannot be seen without magnification. This invisible dust stays airborne in normal room air currents and is so fine it slips right by our bodies' natural protections and goes deep into our respiratory tissues. The fine dust that escapes collection known as fugitive dust will last nearly forever unless it get wet. As a result, government testing shows almost all even very clean looking shops have so much built up fine dust that just walking around stirs enough fine invisible dust airborne to fail air quality tests without doing any more woodworking.


After a lifetime of teaching university engineering and woodworking I had a healthy respect and fine dust. When making dust I always followed what is still the safest advice. Always put on a good NIOSH certified dual cartridge respirator mask with open doors and windows plus a strong fan that moves fresh air through our shops. Our particle counters show the mask and fan should go on before we start making dust and stay on for about a half hour after we finish making dust. My woodworking shop used one bay of our garage that also holds two cars parked inside. Working with a fan running in my shop left me freezing during cold months and burning up during hot months. Adding IR heat dishes took care of being cold even in the coldest weather, but air conditioning could not keep up when venting outside. Tired of burning up I built a kit cyclone hoping for a better system for when I retired. It worked so poorly I built a better kit and even after making many positive changes shown on my cyclone modifications pages, I still had a cyclone that worked much worse that my dust collector with an identical blower. After wasting too much time on dust collection I stupidly threw money at the problem.

I was badly blindsided after installing the top small shop magazine rated cyclone dust collection system advertised to provide good health protection and provide ample airflow to collect from three large and one small tool working at once. My vendor sized and configured my system, designed my ducting plan, provided their ducting and supplied their best fine filter. This cyclone collected far worse than my prior cyclones or much smaller dust collector and it required me to spend more time clearing its clogged filter and cyclone cone than doing woodworking. Each cleaning left me and my shop covered in the dust I installed this unit to avoid. Thinking it at least protected my health I foolishly continued to use if to finish my Christmas projects and planned on replacing it with a commercial system in a few weeks. Instead, less than three months after installing that system I was rushed to the hospital with an apparent heart attack. My doctors found in just a few months I went from no allergy problems to such bad allergies that my lungs would not supply enough oxygen for my heart. This made no sense because recent allergy tests showed no problems, I used the best finest filters available, and consistently wore my fitted dual cartridge respirator mask when doing dusty work because no dust collection system can capture all the fine dust. Allergy tests confirmed with nasty welts and boils severe allergic reactions to a wide range of woods, many of which I never used. My respiratory doctor a fellow woodworker, said he has seen many develop bad allergies to cocobolo and rosewood in as little as a few hour exposure.

My health did not improve and the allergic reactions continued so my respiratory doctor asked me to pay for expensive air quality testing to see if my shop and home were still contaminated. I stalled not believing him. My shop should have been clear as no woodworking had been done for months and during that time our cars that share the garage were constantly going in and out, so the shop had to be well aired out. My home had a very expensive upgraded fine dust collection system built into the HVAC, so it should have gotten rid of the fine dust. After three months of not getting better I paid for expensive testing. My certified inspector gave me quite an education and shared the detail of what the major vendors found it takes for good fine dust collection, as follows.

Inspector: My inspector was the senior OSHA inspector for our area who has tested hundreds of shops. He said my shop was one of the cleanest he had ever seen, but then predicted my shop and home would both badly fail. He explained that I installed the same system that most buy before going pro and all have the same problems with their cyclone failing all the way around.

Fire Safety: My inspector said my indoor dust collection system was not certified as fire and explosion proof so unless it was placed outside behind a fire and explosion proof barrier it would fail building, fire marshal and home insurance inspections. He shared that most shop fires occur because a spark gets into the collection bin then smolders to later grow into a fire, often long after we have left our shops, so my system's cardboard collection bin was a fire just waiting to happen as were the plastic bag below my older dust collector and plastic tub below my shop vacuum. He said my impressive graduated sized ducting system was dead wrong for a small shop that only collected from one tool running at a time. Duct size determines air volume and speed, so my smaller down drops so limited the airflow that my mains would build up piles. That explained why piles kept forming in my mains and when I opened up larger down drop blast gates these piles would slam down the pipes so hard they blew the joints apart system and destroyed fine filters. He shared that if a spark lands in a duct pile it can quickly be blown into a nasty ducting fire. My only choice was to completely redesign my ducting. Trying to run my system with multiple gates open created enough airflow to avoid the piles but left too little air to even get good chip collection let alone good fine dust collection.

Proper Design: He said my vendor's advertising claims promising good fine dust collection from three large tools and one small tool working at once were nonsense. He said he tested many shops with this vendor's dust collection systems and none passed air quality tests. He explained that the experts who guarantee customer air quality found the only way to get good fine dust collection is to collect the fine dust at each source as it is made which requires upgraded hoods and higher airflow. This vendor's designs fail to move enough air for good chip collection, let alone good fine dust collection, plus they use wide open filters that freely pass the unhealthiest fine invisible dust. I explained that my system used the much more expensive upgraded finest filters. He said this is a common lie as vendors can claim any level of filtering they want unless they share that they test when the filters are clean and new. Even a road grate becomes an excellent fine filter if clogged enough that it no longer passes air. His particle counter proved my expensive upgraded fine filters freely passed the unhealthiest fine invisible dust. He looked at my expensive air cleaner and showed with his particle counter that it also freely passed the unhealthiest invisible dust, so was great for protecting finishes but useless for good health protection. He said even if I had good fine filters on both my cyclone and air cleaner, woodworking makes so much fine airborne dust and it spreads so rapidly that there is no chance that running both would get rid of enough airborne dust fast enough to avoid failing air quality tests. Clearing the air would be far too slow to protect my health and avoid contaminating my shop and attached home.

Proper Hoods: He said most dust collectors are optimized to move air at 4000 feet per minute (FPM) which is a little over 40 miles per hour. Most of our blades, bits, cutters, and sandpaper launch fine dust filled air streams at over 100 miles an hour, so we must start with upgraded hoods that contain, direct and enable capturing the fast moving air streams or there is no hope of good fine dust collection. None of my tools had the upgraded hoods required.

Dust Riddance: He explained the problem in my shop would be very bad. I vented inside so the fugitive dust that escaped collection would build to dangerously unhealthy levels. He said most large facilities choose to vent outside. Not only does all dust collection equipment have to be either fire and explosion certified or placed outside behind fire and explosion proof barriers, but also almost none choose to filter because filters constantly need cleaned, are expensive, typically need replaced every three months. Most large facilities find that venting outside is the most efficient, safest and least expensive way to get rid of the fine invisible unhealthiest fugitive dust that escapes collection.

Inspection: His gauges showed just walking around before doing any woodworking stirred up enough invisible dust to cause my shop to fail its air quality test. As soon as we turned on my cyclone without any woodworking my filter was such a dust store it blew so much fine dust all over the air quality got five times worse. My system collected so poorly a few minutes of woodworking pushed the airborne dust level as high as normal room air can carry. He said the fugitive dust that escapes collection builds so much that government testing shows in most small shops, including hobbyist shops, if we vent inside we get more fine dust exposure in two hours than most large facility wood workers get in months of full time work. His meters also showed my home badly contaminated and a chemical test showed the main contaminate was wood dust. He explained woodworking makes huge amounts of fine invisible dust, this dust is so light it behaves more like an odor so will rapidly contaminate any shared air space and this wood dust lasts nearly forever unless it gets wet. Going through the door that connects my garage shop to my home let the contaminated air into my home, plus I carried in more fine dust in on my hair, skin and clothes. His test gear showed even my fine home air filters freely passed the fine wood dust, so like my shop that kept recirculating the air, the contamination just continued to build with whatever more came in.

Ample Airflow: He said none of the under 3 hp dust collectors or under 5 hp cyclone systems move enough air for good fine dust collection. He verified what I previously read. He explained chip collection collects the same visible sawdust and chips that we would otherwise sweep up with a broom and has been a requirement in some areas since the 1920s, so is well understood. Good chip collection requires a real airflow at most small shop stationary tools of 350 cubic feet per minute (CFM). Good fine dust collection has been a requirement in some areas since the 1960s so is also well understood. Good fine dust collection keeps the amount of airborne dust below EPA maximums. Fine dust that can be blown around with the least breath will get blown all over our shops unless we have hoods to control the fast moving air streams, move enough air to surround the working areas of our tools and pull in the fine dust before it gets blown all over by normal room air currents. It takes moving lots of air to pull in the fine dust. In fact, good fine dust collection needs a full 1000 CFM to pull in the fine dust on the same tools that get good chip collection with 350 CFM. His test gauges showed even when collecting from just one tool at a time the airflows my system provided ranged from 30 CFM to less than 350 CFM regardless of my vendor advertising 1200 CFM maximum airflow. He explained most vendors cheat and publish maximum airflows which are measured without any ducting, no filters and often special bell shaped hoods that increase airflow, so maximum advertised airflows tends to be over double working airflows. My vendor made all worse by using all four inch diameter down drops and smaller when they needed all seven inch diameter down drops to carry the 1000 CFM needed for good fine dust collection. It moved far less when trying to collect from more than one tool at a time.

Ample Blower: He said a big part of the airflow problem was my undersized cyclone blower. Blower technology is mature meaning if we buy the same type, size, and speed of blower from any of the major industrial blower makers the performance will be near identical. This lets us use blower tables that let us see how much air a particular blower will move against different levels of resistance known as static pressure. The commercial blower tables show that dust collection blowers need at least 3 hp to move the 1000 CFM needed for good fine dust collection when using a dust collector and at least 5 hp when working with cyclones as cyclones take more overhead to force the air into a tight separation spiral. Sadly, most small shop blowers are not nearly as well made, so these blower tables show higher performance than most get from their small shop dust collectors and cyclones. He showed me that my blower had a very rough impeller, an uneven spiral that the air went into, a bad rough outlet that immediately compressed the air with a tight transition, and forced the air to make a tight turn. His gauges showed the effect of my cyclone vendor's much smaller than 5 hp blower and their poor blower design did not move enough air to even provide good chip collection let alone provide good fine dust collection.

Ample Ducting: He said another big part of my airflow problem was my impressive looking graduated ducting failed to move enough air. He said he tested many shops with ducting designs from this same vendor and all had the same problems because their ducting went from a 7" main to 1" diameter down drops. He said this looked impressive but was dead wrong. He asked if my system did a good job of chip collection. When I said no, he explained air at dust collection pressures air is like water and barely compresses so any small down drop or tool port acts like a closed water valve and kills our airflow. He shared good chip collection requires at least 350 CFM at most small shop stationary tools and it takes 4" diameter duct to carry this much air. My system was designed with 1", 2" and 3" diameter down drops that were too small to carry the needed 350 CFM. He said small shops should never attach anything but a shop vacuum to duct sized under 4". Large commercial shops collect from all tools working at once, so need ducting that increases in size ample to handle all down stream air. In a small shop with a blower only large enough to collect from just one machine at a time, blast gates direct the air to collect from a single tool, so in small shops all ducts and down drops should be the same size or just slightly larger for the horizontal main. He then asked if my system built up piles in the ducts that would break loose and knock the ducting joints apart plus ruin filters. When I said yes, he explained these same undersized down drops caused so limited airflow that the mains lacked enough air speed to keep vertical runs from plugging or prevent building piles in the horizontal runs. He said in addition to damage done when these piles break loose, any spark can land in a ducting pile and quickly get blown into a nasty ducting fire. Also, when these piles break loose they create one of the few times in small shop woodworking where we have a potentially explosive dust to air mixture. He also said this system would never be a good fine dust collector because that blower needed 7" diameter down drops to carry the 1000 CFM needed for good fine dust collection and no down drop was sized over 4".

Proper Filter: He asked if my filter clogged constantly. When I said yes he explained this was because it was far too small. The filter makers recommend a minimum of one square foot of fine filter area for every four cubic feet of air. For better filter life and less cleaning they recommend at least one square foot of fine filter for every two cubic feet of air. My system supposedly moved over 1200 CFM and came with only ninety square feet of filter area, roughly one sixth as much as recommended and less than one third the minimum.

Unsafe Impeller: I later learned the National Fire Protection Association (NFPA) that writes building inspector and fire marshal standards now strongly opposes use of aluminum impellers in dust collection systems as came with my cyclone. All dust collectors and cyclones with full bins put all right through the blower impeller. When an aluminum impeller gets hit by a piece of metal tiny slivers of metal come off that can burst into dangerous white hot flames. Burning aluminum is known as a thermite reaction and is exactly how 4th of July sparklers work. My vendor who continues to boast of their custom designed aluminum impellers forgets to mention this real risk.

Fine Dust Definition

Researchers call dust PM short for particle material. This graphic shows airborne dust particle sizes compared to an average human hair. There are  one million microns in a roughly 39 inch long meter and an average human hair is about 70-microns thick. By definition airborne wood dust consists of PM sized smaller than 30-microns. Airborne wood dust when vented outside falls so slowly it vanishes with no visible trace. By definition fine dust consists of PM sized under 10-microns and are invisible without magnification. Fine wood dust particles are so small and light they stay airborne in normal room air currents and rapidly spread to fill all shared air. Fine dust particles slip right past our bodies' natural protections, go deep into our respiratory systems then damage and scar our tissues. Fine dust is so heavily studied that researchers use PM10 as shorthand to describe fine dust meaning particle material (PM) sized under 10-microns.

Fine Dust Sources

Most small shop activities generate huge amounts of fine airborne dust particles. Activities that make any smoke are particularly bad, especially woodworking. An engineer friend said working wood is similar to working a stack of glass tubes with a rock ax. When viewed by an electron microscope we see wood looks like a big bunch of glued together glass tubes. Wood gets much of its strength from silica better known as glass. Every time our blades, bits, cutters and especially sand paper touch wood they shatter these fragile tubes and launch millions and millions of tiny dust particles airborne. Particle meters show even the sharpest hand plane that makes no visible dust launches millions of fine invisible particles as the blade smashes through wood.

Dust Pumps

As part of our research my professor and engineer friends tested hundreds of shops. We already knew that Cal-OSHA found almost all shops that vented inside badly failed their air quality tests. Almost every shop we tested looked very clean, but we found all but two shops had built up so much fine dust they failed their EPA air quality tests before doing any more woodworking. The only reason those two passed is both shop owners used a strong fan blowing the air through their shops. Our particle counters showed almost all stationary tools used hoods that sprayed huge amounts of fine dust all over. Our air meters showed almost all used way undersized shop vacuums, small dust collectors, or small cyclones that moved far less than the air needed to pull in the fine dust before normal room air currents spread it all over. Most used 4" diameter ducting that limits airflow to about one third what good fine dust collection requires. Almost all shop vacuums, dust collectors, cyclones, and air cleaners claimed they came with fine filters, but calibrated test dust showed almost all small shop fine filters freely pass the unhealthiest fine invisible dust particles. In short, just like mine most small shops had serious dust problems.

Our testing confirmed most small shop vendors sell equipment not based on how well it works, but instead on what it takes to be cost competitive. There are no standards or oversight on small shop equipment makers except what we choose to buy. Making informed choices is tough because most available advertising information is misleading. All vendors cite maximum airflows, but working airflows are consistently only about half maximums. Many vendors lie. Our truth in advertising laws permit vendors to say anything they can prove for an instant. For instance, I can claim my car gets 99.9 miles per gallon because my mileage gauge shows this reading when coasting down a steep hill. With filters so long as the vendor does not include flow, they can claim anything they want. Even a chicken wire screen with 1” openings when clogged enough will eventually become a 0.3-micron filter with almost no airflow. This is why ASHRAE who sets the filter standards requires that all indoor filters be tested when clean and new and measure both airflow and filtering.

Fine Dust Lifetime

My inspector said most small shop dust problems come not just from the dust we make while doing woodworking, but more from dust we made during prior woodworking. He explained that wood dust lasts until it gets wet. In fact, when one of the pyramids was opened they found considerable fine wood dust. One reason that wood dust lasts so long is wood gets most of its strength from silica better known as glass. As the soft organic portions of the wood cells break down what is left are glass shells embedded in very tough lignin fibers.

Fine Dust Behavior

Fine invisible dust particles are so small and light they stay airborne in normal room air currents, so like a bad odor fine dust quickly spreads to evenly fill all available air. Think about working with a skunk in your shop. If your shop is in your attached garage like mine, just opening the door can also contaminate your home. So, for those who vent inside unless we regularly blow out our shops the fine dust just keeps building. Just about any air movement will stir the residual dust back airborne again and again. Many report that their logging particle meters running at night show their dogs and cats going through their clean looking garage based shops stir up enough fine dust to create unhealthy air quality.

Fine Dust Health Risks

All fine dusts meaning PM10 are also known by medical people as inhalable particles because they slip by our natural protections then lodge stuck in different portions of our respiratory systems where their sharp edges and sharp often barbed points damage and scar our tissues. Most never notice any problems as this damage occurs, but over time the damage builds to cause many serious health problems and worsen other age related diseases. A Google search on PM health risks gives over one hundred million references. The credible medical information says, every fine dust exposure of any type dust causes a measurable loss in respiratory capacity, some of this loss becomes permanent, and the more and longer the exposure the worse the damage. This damage over time is so bad that the EPA, European Union, and medical experts set very tough limits on fine airborne dust. These standards only permit 0.1 milligrams per cubic meter of air which is near nothing compared to how much fine dust most shop operations create.

Wood Dust Health Risks

All fine airborne dusts are unhealthy, but wood dust is particularly bad. As shown in this electron microscope picture fine wood particles have razor sharp edges and sharp often barbed points that damage and scar our respiratory tissues similar to asbestos and lock this dust trapped lodged deep inside our respiratory systems where our bodies have a very tough time getting rid it. Wood dusts also carry toxic chemicals that can cause serious short and long term problems. Toxic chemicals found in and on wood can cause irritation, inflammation, respiratory problems, asthma, pneumonia, emphysema, rapidly worsening allergic reactions, poisoning, nerve damage, and even increase our risk of cancer. Many woods such as mimosa, yew, and oleander are so poisonous they can kill us. Most woods contain chemicals that over enough time will eventually cause allergic reactions, but a few woods such as cocobolo, rosewood, and walnut are so toxic they can cause us to build a nasty allergic reaction in just a few hours exposure. Before working any wood  always check a good  wood toxicity table then amply protect yourself. The fine particle damage and toxic chemicals often combine with other elderly health problems to significantly reduce our lifespans.

Large commercial facilities almost all vent their dust collection systems outside, so these firms rarely have any significant build up of fine dust. In 2000 when I first started doing research, the large health care insurance firms shared their data on-line. That data vanished when people started using it to sue employers and insurance firms, particularly over asbestos fine particle respiratory damage. The insurance data showed at typical large facility exposure levels where the fine dust is vented outside, one in seven workers develops such bad wood dust allergies they must stop woodworking. One in fourteen ends up being forced into an early wood dust triggered medical retirement. Almost all lose about 1%  of their respiratory capacity per year of woodworking. Most built such a significant loss in overall respiratory capacity that it ends up worsening other age related illnesses. Average life expectancy fell roughly ten years. Small shop and hobbyist woodworkers who vent their dust collection inside have much higher exposures in spite of spending less time in our shops.

Wood Dust Volumes

Wood dust volumes are huge compared to how little it takes to harm our health or fail an air quality check. An average two-car garage sized shop contains less than 100 cubic meters of air. All types of fine dust are so unhealthy that the EPA indoor air quality maximum is only 0.1 milligrams per cubic meter. Multiply that 100 cubic meters of air times the 0.1 milligram EPA limit and we see that a typical two-car garage sized shop with its under 100 cubic meters of air will fail an EPA air quality test as soon as 10 milligrams of fine dust goes airborne. This means a typical small shop exceeds EPA air quality limits when only a tiny thimbleful of dust goes airborne which is less fine dust than we get from slapping a dusty shop apron or hand sawing just over seven inches of 3/4 inch thick wood. OSHA testing shows with every twenty pounds of sawdust, woodworking makes on average 5 1/3 ounces of fine dust particles which is 151,191 milligrams. This means every twenty pounds of sawdust makes enough fine dust to cause 15,119 average two-car garage sized shops to fail an EPA air quality test. OSHA testing shows on average most small shop dust collectors and cyclones miss collecting at least 16% of the fine dust, yet every 1% of the dust we miss collecting from each 20 pounds of sawdust produced spreads enough extra fine dust in our shops to cause 151 typical shops to fail an EPA air quality test. Because wood dust lasts nearly forever unless it gets wet, most shops that vent inside build up such dangerously high amounts of fine invisible dust that just walking around without doing any woodworking will launch enough fine dust airborne to fail air quality tests. Clearly most small shop activities make huge amounts of very unhealthy fine invisible dust compared to how little it takes to cause serious health problems.

Risk Analysis

A risk analysis compares how bad things can be against the chances of that happening then tries to make a measured response. Unless you are the one in seven who develops an allergy, you get poisoned or develop cancer, the odds are you will never be aware of or inconvenienced by the long term damage caused by wood dust until your later years. Because this damage builds depending on exposure levels, this should terrify us. Cal-OSHA testing found small shop workers including hobbyists who vent inside build up so much fine invisible dust that our exposures are hundreds if not thousands of times higher than full time large facility workers where most fine dust gets vented outside. The medical research clearly shows the more dust we take in the greater the damage. Most have poor collection systems that either miss collecting the fine dust or blow it right through too open filters. My shop was better than most shops tested. Before my shop was tested it had been three months since any woodworking and during that time my cars constantly went in and out. Still, the dust levels in my shop were so high that a couple of hours in my shop generated more exposure than commercial woodworkers get in months of full time work. At these exposure levels all should do our best to protect ourselves from too much fine dust exposure. The most certain and least expensive protection is wear a good NIOSH dual cartridge filtered respirator mask and use a strong fan blowing out a back door or window with a main door open a bit. We can minimize our exposure by also having good fine dust collection but this is much more work.

Recommended Minimum Protections

  1. Always wear a good NIOSH approved dual cartridge filtered mask whenever you make fine dust and continue to wear that mask until your shop is well blown out. I recommend the 3M 7500 series masks fit properly to not leak. I personally also use the 3M organic vapor cartridges with their special pre-filters. You should keep your organic filters (or whole mask) in a zip lock freezer back that you suck all the air out of before sealing. This slows the activated charcoal in the filters from getting worn out.
  2. The best way to keep your shop cleaned out of the fine dust is to always work with a good industrial 30” or bigger fan blowing out a side door or window with an opposite door or window open when you are making fine dust. Always run that fan for another 30 minutes after you finish making fine dust. My test meters showed most need thirty minutes for the shop air to get cleared back to outside levels. This keeps the fine invisible dust from building and creating a bad residual dust problem.
  3. Because we cannot avoid making some fine dust with our tools, I recommend those that work in shops or garages that attach to our homes also install a simple bathroom vent that comes on when we turn on the light. This creates low pressure that keeps the dusty air from rushing into our homes whenever we open a connecting door to our homes.
  4. Avoid tracking dust into your home, office and vehicle. Always wear a good long apron that you leave in the shop. When doing really dusty things, also wear a smock, scarf and hat, then blow yourself off well and wash up before leaving your shop.
  5. Also provide good chip collection. Good chip collection requires about 350 cubic feet of air per minute (CFM) air volume at most small shop stationary tools. We need to move this air at a speed of not less than 3800 feet per minute (FPM) to pull in the sawdust and chip plus keep our vertical ducts from plugging. We also need to maintain at least 2800 FPM airspeed in our horizontal ducts to keep them from building up piles. Dust piles in ducts pose a serious fire hazard. When these piles break loose is just about the only time in small shop woodworking where we can get a potentially explosive dust to air mixture.
  6. A broom and dust pan will clean up the sawdust, but I prefer using my Jet 1.5 dust collector with its upgraded fine filter to control the sawdust when firing up the cyclone would be a chore. 

Next Steps

The next step which involves collecting the fine dust is much harder. We already know that a good shop vacuum does an excellent job of collecting the fine dust for some of the new tools that totally enclose the working area. Unfortunately, such tools are expensive and most traditional tools cannot be made to totally trap the dust. Fortunately, those firms who guarantee customer air quality have shared exactly what we must do to get good fine dust collection at most traditional stationary tools which are the same as we use in our small shops.

  1. Experts found long ago that woodworking makes so much fine dust and it spreads so quickly that air cleaners and exhaust fans have zero chance of clearing the air fast enough to provide good protection or avoid failing an air quality test. This means the only way to maintain good air quality is to collect the fine dust as it gets made before it has a chance to spread.
  2. Good fine dust collection must start by upgrading tool hoods to block and trap all the fast moving dust laden air streams. The reason is simple. Most dust collection systems move air at around 40 miles an hour but our blades, bits, cutters, and even sandpaper launch dust filled air streams at over 100 miles an hour. Our dust collection systems cannot keep up, so we need good hoods to contain, control, and deliver these fast moving dust filled air streams for collection. My ducting page shares many good hood solutions.
  3. The top experts who guarantee customer air quality found most small shop stationary tools need about 1000 CFM to get good fine dust collection. At first this might not make sense. Why would we need three times more air volume to collect fine dust that we can move with the slightest breath? The reason is simple. Blown air hangs together a long time before becoming dispersed. Sucking pulls air from all directions at once so airspeed falls off at four times Pi times the distance squared. We need at least 50 FPM out to over 15.26" around the working area of our tools to pull in the fine dust before normal room air currents can disperse it. Building this big bubble requires moving lots air, just about three times more than what we need to just collect the heavier sawdust and chips.
  4. Unlike compressed air or air pulled by a vacuum cleaner, the low pressure air used for dust collection will barely compress at all. Any small hose, small tool port, or sharp bend in our ducting or hoses will kill our airflow just like partially closing a water valve. At typical dust collection blower pressures a 4" duct will only support about 350 CFM, a 5" only 545 CFM, a 6" only 785 CFM, and a 7" only 1069 CFM. This means at typical dust collector blower pressures we need at least 7” diameter flex hose and ducting to move the required 1000 CFM for good fine dust collection from most stationary tools. What I do for my cyclone designs is use an over sized blower which generates about 12” of pressure. This permits me to get a real 1000 CFM through a 6” duct but doing so makes more noise and wastes power.
  5. The experts show most tools need either a larger port or an extra port. Almost all current tools are setup to move about 350 CFM which only requires a 4" port to pass enough air to collect the heavier sawdust and chips. To fix my band saw it required adding a 5” port under the blade and a 4” pickup port over the blade. Likewise, my table saw needed adding a much better blade guard with a 4" port plus upgrading the 4" port on the saw cabinet to 5".
  6. Picking the right kind of blower is easy. Depending on shop size our blowers must overcome 5" to 12" of resistance between our hoods, ducting, filters and filter loading. A typical squirrel cage blower does not work because they only generate about ½” of pressure which is too little pressure so we get almost no airflow. Shop vacuums generate over 60" of pressure but even the largest rarely move over 250 CFM which is too little air to pull in the fine dust before it escapes. Airfoil and caged blowers move enough air, but their impellers (fan blades) clog and cannot tolerate material hits from knots, chunks, hardware, etc., so we must use a material handling blower just like we see on almost every dust collector and cyclone separator.
  7. Our material handling blower must move at least 1000 CFM with at least 5" to 12" of pressure to overcome the resistance of our hoods, flex hoses, ducting, filters and the dust that builds on and blocks our filters. Blower technology is mature meaning blowers of the same types and speeds from the professional blower firms all perform near identically. Sadly, most of the less expensive import blowers found on small shop dust collectors and cyclones are not nearly as well made so tend to move much less air. The bottom line is no dust collector blower less than 3 hp or cyclone less than 5 hp will move enough air. The cyclone blower needs to be bigger to force the air to spin in a tight separation spiral inside the cyclone. Using smaller blowers may pickup the visible sawdust but will not do a good job on collecting the fine dust.
  8. They also found the best way to deal with the collected fine dust is to separate off the larger particles then simply blow the remaining fine dust outside. Fine dust will last forever if kept dry, but almost any moisture causes it to quickly breakdown. Use of infrared heat dishes deals with the heat loss from venting outside in even the coldest climates, but in hot areas and in areas where you cannot vent outside, you then need to air condition and filter. Likewise, many like me live in areas where it is illegal to vent outside, so we must filter.
  9. If you must filter then you should use a good cyclone separator that keeps the chips out of our filters because chips jam the filter pleats so when cleaning they poke holes and ruin our fine filters. Almost any cyclone will do this well, but expect to need to replace your fine filters roughly every three months of full time work. The problem is airborne dust ruins fine filters because it gets into the filter pores where the razor sharp edges and sharp often barbed points coupled with cleaning cause this dust to tear up the filter strands. This opens the filters and although they may still filter off the visible dust, they soon freely pass the unhealthiest fine invisible dust.
  10. Frustrated by the high cost of fine filters, need for constant cleaning, and short filter life I designed a much more efficient cyclone that separates the airborne dust six times better than any other option. This cyclone worked so well Clear Vue Cyclones licensed this design from me and now makes these units in a clear tough plastic, the same stuff used to make police shields. My area makes venting outside illegal, so vent my 1200 CFM cyclone is vented into a pair of “200” square foot cartridge “nano” filters I bought from Wynn Environmental. I also made my own air cleaner using an 8” in line duct fan that produces nearly 800 CFM. That fan sits on weather stripping on a third “nano” filter. My gauges show it takes about 3 hours of that air cleaner running to pull the dust level down in my home to what is considered medically safe even on the smoggiest days.


Clear Vue Cyclone Ad


If you want lots more detail and free plans to built the units I use to protect my family, please visit my Cyclone and Dust Collection Research pages. Still, the bottom line for most is even if it is work to get good fine dust collection, good fine dust protection is easy, always wear a good properly fit NIOSH approved dual cartridge mask while making dust and a good commercial duty fan blowing air through your shop to avoid building fine dust. Our particle counters show most need to leave their mask and fans on for at least a half hour after making dust. Enjoy.