Dust Collection Basics - Blog

This blog shares the dangers of fine dust and how to provide good fine dust protection. It targets woodworkers but applies to all who work in dusty situations such as those who work with stone, sand blasting, finishing, etc.

Introduction

I did my research carefully then installed the top magazine rated small shop cyclone. This system badly blindsided me and landed me in the hospital where I was left with only 42% respiratory capacity and stuck on supplemental oxygen for life. This inspired me to figure out what happened and come up with solutions to protect my family and me. My respiratory doctor talked me into sharing which led to my Cyclone and Dust Collection Research web pages. Now thousands daily read my web pages and over 10,000 people worldwide use cyclones of my design to help with their dust collection problems. I was asked to build this blog as a quick way to get out the basic information.

Background

After a lifetime of teaching university engineering and woodworking I had a healthy respect for fine dust and it still badly blindsided me. I always wore my dual cartridge respirator mask plus ran a strong fan in a side door with the main door in my shop cracked when making dust. Tired of being stuck in my respirator, freezing during the cold months, and burning up during the hot months plus wanting a better system for when I retired and could do more woodworking, I did my homework and bought the top magazine rated cyclone dust collection system. I soon hated this system. It provided far worse collection than my dust collector. Its cyclone cone, filter and ducting clogged constantly. Clearing these clogs wasted lots of time and left me and my shop covered in the dust I bought this unit to avoid. I kept using it thinking it protected my health. After using this system for three months I was so disgusted I decided to junk it, but instead got rushed to the hospital with an apparent heart attack.

I refused to believe my doctors when they diagnosed an allergic reaction to wood dust. A recent allergy test showed no problems. I used the best small shop dust collection system that money could buy with vendor designed and supplied ducting and vendor recommended upgraded fine filter. Moreover, even with that system I still 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. In three months this dust pump moved me from no allergy problems to such bad allergies that my lungs would not supply enough oxygen for my heart.

Wanting to know just how bad things were I brought in a certified air quality inspector. He said because I mounted my cyclone inside my garage based shop my system would fail both building and fire marshal inspections. My cyclone lacked the fire and explosion proof certifications so must go outside behind an explosion and fire proof barrier. He was very troubled by its cardboard collection bin and said that is a fire just waiting to happen. I later learned the National Fire Protection Association that writes the standards most building inspectors and fire marshals use strongly opposes use of aluminum impellers in dust collection systems. All dust collectors and cyclones with full bins put all right through impeller. When an aluminum impeller gets hit with a piece of metal tiny slivers of aluminum can burst into dangerously white hot flames. Burning aluminum is known as a thermite reaction and is exactly how 4^th of July sparklers work. My vendor who boasted of their custom designed aluminum impeller forgot to mention this real risk.

He said the major vendors who guarantee customer air quality long ago worked out and published exactly what we need for good fine dust collection. They found woodworking makes so much fine airborne dust and it spreads so rapidly that there is no chance that air cleaners and exhaust fans will get rid of enough dust fast enough to avoid failing an air quality test. To have safe air to breathe we must collect the fine dust at each source. My system lacked the upgraded hoods we need to control and capture the fine dust. My tool ports and ducting needed enlarged to carry the air volumes needed for good fine dust collection. I also needed a bigger much higher horsepower blower to move enough air for good fine dust collection.

His predictions all proved true. My long unused shop looked and tested clean at first but just moving around a little stirred up enough invisible dust that it failed its air quality test. As soon as we turned on my cyclone my shop failed the five times easier maximum allowed airborne limit. His meter showed my fine dust filter was a dust store that filled my shop. A few minutes of woodworking pushed the airborne dust level as high as normal room air currents can carry and bust every different air quality standard. His meters showed my home badly contaminated as well. His air gauges showed my cyclone at most provided one third the vendor advertised airflow and my ducting design was deplorable because it cut that airflow as much as five fold. This dismal airflow is why my ducts kept plugging and building up huge piles. He said these piles are very dangerous as they can create a nasty duct fire, and when they break loose they create one of the few times in small shop woodworking where we have a potentially explosive dust to air mixture. Clearly this expensive system I installed to protect my health was a dangerous dust pump. In short my system created a bad false sense of security leaving a clean looking shop that tested with dangerously high invisible dust levels.

First let's understand the medical risks from fine dust

Medical research shows the unhealthiest inhalable dust particles cause the most damage to our health. Fine dust particles get right by our natural protections and their barbed shapes makes them very difficult for our bodies to get rid of them. Their sharp particles jab and poke holes in our cells leading to scaring. The medical research clearly shows every exposure to these particles causes a measurable loss in respiratory capacity and because of the scaring some of this loss becomes permanent. Worse, when lodged in our tissues the toxic chemicals carried in and on these particles, plus the toxins created as these particles break down causes everything from allergic reactions to poisoning and in some cases even cancer. Almost all woods can eventually trigger allergic reactions but some woods can generate allergic reactions in just a few hours. Always check a good wood toxicity table before working any wood to make sure you amply protect yourself. Clearly, you want minimum exposure to these particles which is why the EPA, medical recommendations and European Union all set maximum exposure standards around 0.1 milligrams per cubic meter.

Fine Dust Definition

Fine dust consists of particles sized under 10-microns. These particles are also known by medical people as inhalable particles, meaning particles sized small enough that they get right by our natural protections. Researchers have so extensively studied fine particles that they now use shorthand to designate the size of dust particles. They call fine inhalable dust PM10 meaning particle material smaller than 10-microns. For reference there are one million microns in a meter which is about thirty nine inches long. A fine human hair is about 60 microns thick and a coarse human hair is about 100-microns thick.

Fine Dust Behavior

Fine invisible dust particles are so small and light that normal room air currents are enough to keep them airborne. Fine dust behaves like a bad odor. These fine light particles quickly spread to evenly fill all available air. Think about working with a skunk in your shop. If your shop is in your garage like mine, just opening the door can contaminate your home. In fact, just about any air movement will launch previously made fine dust particles which are known as residual dust. Just about any activity stirs 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. Residual wood dust lasts a very long time so an area stays contaminated until you clear it out. 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 is this glass shell embedded in very tough lignin fibers. So under an electron microscope we see that wood is essentially a big bunch of glass composite tubes. Even the sharpest plane blade that appears to make no visible dust shavings launches lots of fine invisible particles when the blade smashes through these tiny tubes.

Dust Pumps

In woodworking shops I find most shop vacuums, dust collectors, cyclones, and air cleaners are terrible dust pumps. There are no standards or oversight on small shop equipment except what we as buyers exercise ourselves. Most of our vendors sell equipment not based on how well it works, but instead on what they advertise. Our truth in advertising permits them 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 but will have little to no airflow. This is why ASHRAE who sets the filter standards requires that all indoor filters be tested when clean and new. My professor friends carefully tested every major brand of so called fine filter used in small shop air cleaners, dust collectors, shop vacuums and cyclones. No dust collector, cyclone or air cleaner and only two brands of shop vacuum in spite of all claiming 2-micron or better filters filtered of the 10-micron and smaller particles. Most shop vacuums can be upgraded with HEPA quality filters but they move too little air to pull in the fine dust except when using newer tools that totally enclose the working areas.  The bad news is adding fine enough filters to almost all dust collectors, cyclones, and air cleaners works poorly. They simply plug so quickly that they become useless.

Risk Analysis

A risk analysis compares how bad things can be against the chances of that happening then tries to make a measured response. Woodworking makes about one and two thirds pounds of fine dust for every one hundred pounds of sawdust. It takes less than two tiny thimblefuls, which is less than one hundredth of a pound to again cause a typical two car garage shop to fail an EPA air quality test. Just slapping a dusty shop apron or hand sawing 7” of ¾” stock generates enough fine dust that a typical two-car garage will fail an air quality test. Even hand planning nice curls generates considerable fine dust. In other words the exposures are huge and the risk is large, so all should do our best to protect ourselves from too much fine dust exposure. 

 

Recommended Minimum Protections

1. Always wear a mask whenever you make fine dust and continue to wear that mask until your shop is cleaned 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 in 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 show it takes no less than twenty 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 a 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, plus wash up before leaving your shop.
5. 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 like we use in our small shops.

1. They found long ago that we make 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 avoid failing an air quality test. This means the only way to get good air quality is to collect the fine dust as it gets made before it has a chance to spread. 
2. To get good source dust collection we must start by upgrading tool hoods to block and trap all the fast moving dust laden air streams. My ducting page shares many good hood solutions.
3. Although many make dust collection seem complicated it really is well understood. Since the 1920's firms have been required to provide good chip collection. Good chip collection keeps floors, tools and work surfaces clear of sawdust to minimize accidents and fire risk. 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.
4. They also share that 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.
5. 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 since. 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 three times Pi times the distance squared. We need at least 50 FPM out to about 15" 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, far more than what we need to just pull in the heavier sawdust and chips. 
6. At typical dust collector blower pressures we also need at least 7” diameter flex hose and ducting to carry this required 1000 CFM from our 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 makes a bit more noise.
7. They also found 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. 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 needs its cabinet port plus a 4" port on the blade guard the covers the blade and keeps that blade from spraying dust all over.
8. Picking the right kind of blower is easy. Our blowers must overcome roughly 7" of resistance between our hoods, ducting, and filters. A typical squirrel cage blower does not work because they only generate about ½” of pressure which is too little pressure to overcome our resistance so we get almost no airflow. Shop vacuums generate over 60" of pressure but rarely move over 100 CFM which is too little air to pull in the fine dust before it escapes. Airfoil and caged blowers move enough air at enough pressure, 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.
9. Our material handling blower must move at least 1000 CFM with at least 7” of pressure to overcome the resistance of our hoods, flex hoses, ducting, and filters. Blower technology is mature meaning blowers of the same types and speeds from different makers 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 push 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.
10. They also found the best way to deal with the collected fine dust is to separate off the larger particles then simply blow what is left outside. Use of infrared heat dishes deals with the heat loss in even the coldest climates, but in hot areas and in areas where you cannot vent outside, you then need to filter. Likewise, many like me live in areas where it is illegal to vent outside, so we must filter.
11. If you must filter then you should use a good cyclone separator that keeps the fine filters we need to protect our health from clogging too quickly.
12. With no other viable options I chose to invent my own cyclone. 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. I personally am not allowed to vent outside, so vent my 1200 CFM cyclone into a pair of “300” 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.

This is probably far more than you ever needed or wanted to know. So the bottom line for most is always wear a good mask while making dust and use a good commercial duty fan for at least thirty minutes after your woodworking then enjoy.