My friend who is a regular here at the ShopSmith forums sent me an email saying that one of the members is dumping their ShopSmith for a Saw Stop because he worried about safety, yet this same fellow works out of a basement shop with almost no dust collection. This fellow has clearly been led down the garden path in terms of safety priorities.
Particle counters consistently show dangerously high fine dust contamination in our shops and homes if we do woodworking in our homes, basements or home attached garages and don’t vent outside. This dust can really mess up our health, the health of our families, and even our pets.
I spent some time today reading over dust collection posts on this site and almost all focused on providing good chip collection instead of good fine dust collection. Below is some draft information from the rewrite of my web pages that I am currently working on. Hopefully this information will help. Sadly, I am so buried with my dust collection work I cannot give this individual forum that much time.
Wood Dust Risks
Wood dust poses many risks. Sawdust and chips allowed to build on our floors, work surfaces, and tools cause slipping, injury, accidents and fires Enough airborne dust may explode. Sawdust and chips cause irritation, splinters, eye injury, stuffy noses, and skin injury. Fine airborne wood dust is a double threat.
OSHA testing shows we make about one pound of airborne dust out of every twenty pounds of sawdust. One pound of airborne dust can plug even a large fine filter. It takes far less to harm our lungs.
Electron microscopic images show fine wood dust particles have sharp edges, points and even barbs. This is why the peer reviewed medical research shows every fine dust exposure causes a measurable loss in forced expiratory volume, meaning lung capacity, and some of this loss becomes permanent.
Fine dust is so heavily studied by medical researchers they call it PM short for particle material. A Google search on “PM health risks” gives over forty million references if you want to read more.
After decades of testing, research and debate the medical community, European Union and EPA all set fine airborne dust limits of about 0.1 milligrams per cubic meter. Buildings that exceed this limit get closed until they are cleaned up.
By definition airborne dust consists of particles sized under 30-microns and we call the under 10-micron sized particles fine dust. Fine dust makes up about one third of airborne dust by weight. For reference there are a million microns in a meter and a typical human hair is about 70 microns thick. Our eyes cannot see particles sized under 10-microns so fine dust is invisible without magnification.
In addition to cell damage, wood dusts contains and carries toxic chemicals including toxins from molds that are among some of the most poisonous chemicals known to man. Wood borne chemicals cause irritation, allergic reactions, poisoning, diseases, and increase our cancer risks. A Google search on “wood dust health risks” provides 1,770,000 more references.
We each have different susceptibilities to these chemicals that are normally in very tiny amounts, so one person may work for a lifetime with walnut, cocobolo, rosewood or other sensitizing woods that we know often causes worsening allergic reactions while you might end up in the hospital after just one use. Yew, oleander, mimosa, and some other woods are so toxic just breathing their dust can cause severe neural damage and even death. You should always check a good wood toxicity table before working any wood and no matter what dust collection system you get, always wear a good NIOSH certified dual cartridge respirator mask when working really toxic or unknown woods.
Woodworkers and many vendors wrongly believe woodworking makes almost no fine dust. Unlike visible dust the invisible fine dust particles rarely make our shops look dusty or dirty and are so light they don’t settle quickly in normal room air currents so we rarely see a buildup of fine dust. Fine dust particles are not heavy enough to break through surface tension so they don’t mess up our finishes like heavier airborne dust.
In spite of what we see, OSHA testing shows we make about to 5 1/3 ounces of fine dust out of every twenty pounds of sawdust. This may seem like little dust until we do some math. An average two-car garage sized shop contains about 100 cubic meters of air. Multiply this by the 0.1 milligrams per cubic meter maximum fine airborne dust level and just 10 milligrams of fine dust launched airborne will cause our shops to fail an EPA air quality test. For those unfamiliar with milligrams, 10 milligrams is just over 0.00035 ounces. Two tiny thimblefuls, slapping a dusty shop apron, or hand sawing just over seven inches of ¾” stock launches more than this much dust. Divide that 0.00035 ounces into our 5 1/3 ounces and we see that every twenty pounds of sawdust that we make creates over 15,000 times more fine dust than it takes for our shops to fail and EPA air quality test.
Newer particle counters show even worse news. Woodworking makes unbelievably huge numbers of fine dust particles. This really did not make much sense to me until I was contacted by Graham Cliff, one of the world’s top electron microscope scientists. He is very interested in fine particle health problems and has been studying their adverse health effects for decades. In fact, Graham is the expert who exposed the dangers of asbestos particles to the world. He and many other experts now believe wood dust may be even more dangerous.
Wood gets much of its strength from silica, better known as glass. Silicosis is a bad respiratory disease common in those who work with fiberglass and other glass products. Electron microscope pictures show wood looks and behaves like a big bundle of glued up glass tubes. Our blades, bits, cutters, and especially sandpaper explode these tiny tubes into tiny nasty shards with every contact no matter how clean looking our cut. Our particle counters show a razor shop hand plane that makes a perfect long shaving with no visible dust launches huge amounts of fine invisible dust.
OSHA testing shows wood dust is fairly evenly distributed by weight, meaning one third of our under 30-micron airborne dust consists of fine under 10-micron sized particles. It takes a lot of fine particles to equal the weight of one heavier particle. It takes 27,000 1-micron sized particles and 216,000 0.5-micron sized particles to weigh the same as a single 30 micron sized particle.
Most had to trust the experts when it came to fine particles, because particle counters were too expensive. I spent nearly $8,000 to buy my first particle counter. Fortunately, we now have much more affordable units that count 0.5 to 5-microns particles available from Dylos Products and you can even get a little discount if you use my name. Many individuals, clubs and organizations are buying these meters and using them.
Our meters show that even very clean looking shops that vent their dust collectors and cyclones inside build up so much fine invisible dust that just walking around stirs up dangerously unhealthy amounts airborne. Our meters show normal room air currents quickly spread fine dust like an odor to contaminate all shared air. Worse, these meters are showing heavy contamination of our homes if we work inside our homes, in basement shops, or in home attached garages and do not vent the dust outside.
Minimum Protections
Over half of my email comes from small shop woodworkers who all ask variations on the same question, “How can I get good fine dust collection in my small shop without lots of expense and preferably only using 120V power?” Most already have shop vacuums and 120V dust collectors, plus have done some upgrades such as finer filters, larger diameter duct and air cleaners.
The answer is simple, but not what most want to hear. You can’t easily get good fine dust collection, but you can get good fine dust protection without much work or expense. A good mask, good cross ventilation and proper clothing provide excellent protection.
To protect your respiratory health you need to forget paper masks and instead wear a properly fit dual cartridge NIOSH respirator approved mask like the 3M 7500 series with appropriate HEPA quality filter meaning 99.97% effective down to 0.3-microns. You need to run a strong fan in an open side door or window with your main door open three to five inches so you have good cross flow ventilation while you work. You should also always wear a jumper and hat when working toxic woods and leave these in my shop.
The mask, fan and clothing must go on before you start making dust even if you are only using hand tools. Our particle counters show you must leave the mask and fan on for thirty minutes after you stop making fine dust to get your shop air back to outside air quality. Then you can take your mask off. Also make sure you clean yourself, clothes and hair off before you leave your shop so you do not contaminate your vehicles, offices and homes.
Without the fan on while you work your shop will rapidly build up fine dust. The fan will not clear previously made dust unless you help with a strong blower such as a leaf blower.
Collecting the fine dust takes much more work. You can read more than you ever wanted to know about good fine dust collection on my web pages.
Hope this helps.
bill
Dust Collection - Bill Pentz
Moderator: admin
Hi Bill,
Great post- welcome to the forum. I've seen your name pop up a few times. I hope you can share your expertise i dust control with us all. It's one of this invisible things we can't see, but regardless, we really need to know information like you have shared. Thank you.
Tony
Great post- welcome to the forum. I've seen your name pop up a few times. I hope you can share your expertise i dust control with us all. It's one of this invisible things we can't see, but regardless, we really need to know information like you have shared. Thank you.
Tony
One Greenie, Two Mark 7s,Three 510s and much more…
I've looked at Bill's site several times and believe he has some good information. Unfortunately, my pocket book isn't going to allow me to buy a 5 HP cyclone unit.
However, I appreciate that he offers cheaper ideas that will help such as using a full face dust mask with HEPA filtration, running a fan and keeping the windows/garage door open. I would think moving that SS DC3300 outside so that if it spews dust, it vents outside your workspace. I'm sure I'm missing many more.
I definitely had a chance to see the dust idea with spray painting in an enclosed area this weekend with a 500W halogen work lamp. Between seeing the fine particles that become visible in the light, the collection of overspray far outside of my working area and the fact that the noxious fumes hung around for hours if I didn't open the garage door to "air out" things. I know it isn't dust, but I imagine that dust moves in a similar way and this was a visible example.
Being in my mid-thirties and knowing I hopefully have a long time to woodwork, I want to be careful to protect my lungs (and ears) so that I can continue to enjoy this hobby for many years. I lost an relative at 58 to lung related issues who spent most of his life as a contractor. I sure besides wood dust he was exposed to asbestos, paint fumes and many other hazards, but it scares me when I see others with reduced lung function. I've had a case of anaphylaxis for other reasons and having difficulty breathing is scary.
Bill I hope you can post here once and a while and guide us with limited means in the direction of making out shops safer for our lungs.
However, I appreciate that he offers cheaper ideas that will help such as using a full face dust mask with HEPA filtration, running a fan and keeping the windows/garage door open. I would think moving that SS DC3300 outside so that if it spews dust, it vents outside your workspace. I'm sure I'm missing many more.
I definitely had a chance to see the dust idea with spray painting in an enclosed area this weekend with a 500W halogen work lamp. Between seeing the fine particles that become visible in the light, the collection of overspray far outside of my working area and the fact that the noxious fumes hung around for hours if I didn't open the garage door to "air out" things. I know it isn't dust, but I imagine that dust moves in a similar way and this was a visible example.
Being in my mid-thirties and knowing I hopefully have a long time to woodwork, I want to be careful to protect my lungs (and ears) so that I can continue to enjoy this hobby for many years. I lost an relative at 58 to lung related issues who spent most of his life as a contractor. I sure besides wood dust he was exposed to asbestos, paint fumes and many other hazards, but it scares me when I see others with reduced lung function. I've had a case of anaphylaxis for other reasons and having difficulty breathing is scary.
Bill I hope you can post here once and a while and guide us with limited means in the direction of making out shops safer for our lungs.
Thanks Bill great info.
Confirms my practice of opening both garage doors as wide as weather permits when making dust.
Also lets me know about some of my bad habits.
Confirms my practice of opening both garage doors as wide as weather permits when making dust.
Also lets me know about some of my bad habits.
Bruce
I didn't know what a Shopsmith was...
Three days later I owned one...
One week later I was rebuilding one...
Four months later I owned two....
Ok Ok, I'm up to four now...
I didn't know what a Shopsmith was...
Three days later I owned one...
One week later I was rebuilding one...
Four months later I owned two....
Ok Ok, I'm up to four now...
Yankee Magazine, which has been in publication since 1629 NOT, has always published good tips on woodworking. I picked up a very old publication last week and one thing that was suggested was inserting the child-proof two-pronged plastic caps into the receptacles where you have wood working equipment. The reason. Wood dust is drawn into them and there have been numerous house fires attributed to ignition because of that. Not a bad idea since they are so cheap. Whatever doesn't have something plugged in gets one of these.
Fine Dust Collection
Thanks to the many who welcomed me to this forum and the many of you who sent emails asking how to get good fine dust collection.
I’ve been a ShopSmith user since the 1950s and like to understand and improve things. After teaching university engineering for thirty one years with contributions in many areas, I was blindsided by the top rated small shop cyclone system. That inspired me to figure out what went wrong and design a better cyclone. It is so hard to get good fine dust collection I always recommend you wear a properly fit dual cartridge respirator and run a big fan blowing outside to get good ventilation. Put the mask and fan on before making dust and keep them on for a half hour after you stop making dust.
Requirements
The major firms who guarantee and monitor customer air quality have long shared what we need for good fine dust collection. Their math, testing and refinement are shared with their solutions for almost every type and size of stationary tool. Most small shop tools are the same as small commercial tools so we get to use the same solutions.
As shared before each twenty pounds of sawdust we makes contains over 15,000 times the fine dust it takes for a two-car garage sized shop to fail an EPA air quality test. Fine dust is so fine and light that it behaves like an odor to rapidly spread to contaminate all attached areas, including our homes, offices and vehicles. The way fine dust behaves and it taking so long to break down showed the experts that air cleaners and exhaust fans work far too slow, so the only way we can avoid failing an air quality test is to capture the fine dust as it gets made. They found we must ensure our traditional tool hoods control and capture the fast moving air streams, build a low pressure area around our tools big enough to pull in the fine dust before normal room air currents spread it, and then get rid of the dust.
Hoods
A typical 10” table saw blade launches fine dust at just over 100 miles an hour as do many of our blades, bits and cutters, but our shop vacuums and dust collectors only move air at 45 to 60 miles an hour. Our dust collection equipment loses unless our hoods control and capture the fast moving air streams.
Air Volume
We know the lightest breath will blow dust away, so it is confusing why our powerful shop vacuums and dust collectors poorly collect fine dust. We already know why if we think about using our shop vacuums. On blow our vacuums move dust all over the shop, yet on suck our vacuums only pickup dust if the nozzle gets put right next to what we want to collect. Unlike blown air that holds together for a considerable distance, sucked air comes from all directions at once. Sucked airspeed falls off at about the same rate the surface area of a sphere expands, roughly 4*Pi*r*r. We can use the air formula CFM=FPM*Area and sphere surface area formulas to calculate how much air good fine dust collection requires. Decades of expert fine dust experience found we need at least 50 feet per minute (FPM) airspeed all around the working areas of our tools out to about 15.15” to overcome normal room air currents and amply pull in fine dust. We multiply 4*Pi *15.15*15.15 = 2884.625 square inches then divide by 144 to get an Area of 20 square feet. Putting that 50 FPM and 20 square feet back into the air formula, CFM=20*50 = 1000 CFM. Decades of experience verify small shop stationary tools need about 1000 CFM airflow for good fine dust collection.
Duct Size
The ducting size we need to move this 1000 CFM is easy to calculate but not obvious. Most think about air from working with compressors or shop vacuums which operate with so much pressure they easily squeeze air through small openings and tight corners. Dust collection is done with much lower pressures. At lower pressures air is just like water and will barely compress at all. Just about any restriction anywhere will limit our flow just like a partially closed water valve limits garden hose flow. With 4000 FPM needed to move the dust through our duct and 1000 CFM need for good fine dust collection our air formula Area=CFM/FPM shows 1000/4000 or 0.25 square feet which shows a 7” diameter duct is ideal to carry 1000 CFM. Clearly our 2.5” ShopSmith ports are way too small so we must compensate with auxiliary hoods. Rather than force all to use expensive and hard to find 7” diameter duct, I use an oversized blower impeller. It creates enough pressure to boost the duct airspeed to over 5200 FPM to permit us to use more available and less costly 6” diameter duct.
Blower Type
Even with cyclones all goes right through the blower if we get a full bin or plug in our cone, so we need material handling blowers to handle material hits with a self cleaning impeller to avoid an unbalanced condition that can quickly destroy motor bearings. We make this a backward curved impeller to reduce noise.
Blower Impeller Size
We size our blower impeller big enough to move the needed air at the highest resistance level. Our tool hoods, ducting, flex hoses, separators, and filters all add resistance. The resistance overhead for almost every part of dust collection systems has been carefully measured and shared in tables and spread sheet calculators called static pressure calculators. There is a good static pressure calculator on my web pages to help calculate our highest resistance. Most two-car garage sized small shops wiht a dust collector have a maximum resistance of 10 water column inches (4” W.C.) or 12” W.C. of resistance with a cyclone. Cyclones take more work to force the air in a tight separation spiral. Blower technology is mature, so the same size and type blower from any of the big makers gives near identical performance. The blower tables show at 10” W.C. we need at least a 14” diameter impeller for a dust collector or 15” diameter impeller for a cyclone to get a real 1000 CFM.
Blower Motor Size
Our blowers use the most horsepower when moving the most air against the least resistance. We calculate the lowest resistance in our shop which is with a new clean filter and biggest shortest duct run. Most small shops have about 4” minimum resistance. To size our motor we see how much horsepower the impeller size we picked pulls at 4”. Our 14” dust collector impellers draw 3 hp and our cyclone 15” impellers draw about 4 hp. Since our motors come in 3 hp or 5 hp sizes, a cyclone needs a 5 hp motor. Our blower tables show a 5 hp motor can turn a 16” impeller to give us even more airflow.
Dust Elimination
Dust collectors and cyclones must be placed outside in their own enclosure behind a fire and explosion proof barrier and we must provide makeup air to avoid sucking deadly carbon monoxide backward through vents to comply with NFPA codes and pass a fire marshal inspection. This is why most large commercial facilities vent outside and operate with main doors open. If your system does not have to pass inspections, good safety practices say you should still follow these rules and provide makeup air. Putting your properly sized dust collector or cyclone outside keeps the dangerous fine dust missed during collection from quickly building to dangerously high levels. Thousands of shops prove infrared heat easily compensates for any heat loss even in the coldest weather. If you live in a really hot area then air conditioners cannot keep up.
Filters
Most small shop fine filters supplied on dust collectors, cyclones, shop vacuums and air cleaners are too open so they turn these units we buy to protect our health into dangerous dust pumps. Almost all of these use filters designed for outdoor use that are not ASHRAE rated. They are instead tested after they are fully seasoned meaning they have built up as much fine dust in the filter pores as the filter can carry through normal cleanings. It takes up to a year for small shop filters to fully season. During that time if we vent inside we breathe the fine dust that these filters miss. Worse, even though a fully seasoned filter filters ten to twenty times more efficient than a new clean filter, it also constantly leaches the finest unhealthiest dust right through. Those with particle counters regularly find just turning on these units including their air cleaners launches enough fine dust to create dangerously unhealthy air. In short most small shop filters act as reservoirs that save up and dump the unhealthiest dust every time they are used.
If you really want to filter your shop air instead of vent it outside, the medical experts say we need filters that provide at least 99.9% separation of all particles sized 0.5-microns and larger and should use HEPA quality filters that provide 99.97% separation of all particles sized over 0.3-microns. This fine filter material is expensive and we need lots of it. Air engineers say we need at least one square foot of filter area for every four CFM of airflow, but the filter makers and experience shows one square foot for every two CFM provides much longer filter life and reduces cleaning. Woodworking makes so much sharp fine filter destroying dust that fine filters fail quickly. Even with large filters commercial firms that do fine filtering replace fine filters roughly every three months. To minimize filter cleaning and maximize filter life you need a far better separating cyclone than any of the normal units. My cyclone design is in use worldwide in over 10,000 small shops and has been medical school tested to provide six times better fine dust separation, but I still tell people to vent outside whenever possible. Most go many years between filter replacements. You can build a cyclone of my design from the free plans on my web pages or buy one.
Summary
We either wear our masks and vent outside, or do the work and pay for good fine dust collection.
I’ve been a ShopSmith user since the 1950s and like to understand and improve things. After teaching university engineering for thirty one years with contributions in many areas, I was blindsided by the top rated small shop cyclone system. That inspired me to figure out what went wrong and design a better cyclone. It is so hard to get good fine dust collection I always recommend you wear a properly fit dual cartridge respirator and run a big fan blowing outside to get good ventilation. Put the mask and fan on before making dust and keep them on for a half hour after you stop making dust.
Requirements
The major firms who guarantee and monitor customer air quality have long shared what we need for good fine dust collection. Their math, testing and refinement are shared with their solutions for almost every type and size of stationary tool. Most small shop tools are the same as small commercial tools so we get to use the same solutions.
As shared before each twenty pounds of sawdust we makes contains over 15,000 times the fine dust it takes for a two-car garage sized shop to fail an EPA air quality test. Fine dust is so fine and light that it behaves like an odor to rapidly spread to contaminate all attached areas, including our homes, offices and vehicles. The way fine dust behaves and it taking so long to break down showed the experts that air cleaners and exhaust fans work far too slow, so the only way we can avoid failing an air quality test is to capture the fine dust as it gets made. They found we must ensure our traditional tool hoods control and capture the fast moving air streams, build a low pressure area around our tools big enough to pull in the fine dust before normal room air currents spread it, and then get rid of the dust.
Hoods
A typical 10” table saw blade launches fine dust at just over 100 miles an hour as do many of our blades, bits and cutters, but our shop vacuums and dust collectors only move air at 45 to 60 miles an hour. Our dust collection equipment loses unless our hoods control and capture the fast moving air streams.
Air Volume
We know the lightest breath will blow dust away, so it is confusing why our powerful shop vacuums and dust collectors poorly collect fine dust. We already know why if we think about using our shop vacuums. On blow our vacuums move dust all over the shop, yet on suck our vacuums only pickup dust if the nozzle gets put right next to what we want to collect. Unlike blown air that holds together for a considerable distance, sucked air comes from all directions at once. Sucked airspeed falls off at about the same rate the surface area of a sphere expands, roughly 4*Pi*r*r. We can use the air formula CFM=FPM*Area and sphere surface area formulas to calculate how much air good fine dust collection requires. Decades of expert fine dust experience found we need at least 50 feet per minute (FPM) airspeed all around the working areas of our tools out to about 15.15” to overcome normal room air currents and amply pull in fine dust. We multiply 4*Pi *15.15*15.15 = 2884.625 square inches then divide by 144 to get an Area of 20 square feet. Putting that 50 FPM and 20 square feet back into the air formula, CFM=20*50 = 1000 CFM. Decades of experience verify small shop stationary tools need about 1000 CFM airflow for good fine dust collection.
Duct Size
The ducting size we need to move this 1000 CFM is easy to calculate but not obvious. Most think about air from working with compressors or shop vacuums which operate with so much pressure they easily squeeze air through small openings and tight corners. Dust collection is done with much lower pressures. At lower pressures air is just like water and will barely compress at all. Just about any restriction anywhere will limit our flow just like a partially closed water valve limits garden hose flow. With 4000 FPM needed to move the dust through our duct and 1000 CFM need for good fine dust collection our air formula Area=CFM/FPM shows 1000/4000 or 0.25 square feet which shows a 7” diameter duct is ideal to carry 1000 CFM. Clearly our 2.5” ShopSmith ports are way too small so we must compensate with auxiliary hoods. Rather than force all to use expensive and hard to find 7” diameter duct, I use an oversized blower impeller. It creates enough pressure to boost the duct airspeed to over 5200 FPM to permit us to use more available and less costly 6” diameter duct.
Blower Type
Even with cyclones all goes right through the blower if we get a full bin or plug in our cone, so we need material handling blowers to handle material hits with a self cleaning impeller to avoid an unbalanced condition that can quickly destroy motor bearings. We make this a backward curved impeller to reduce noise.
Blower Impeller Size
We size our blower impeller big enough to move the needed air at the highest resistance level. Our tool hoods, ducting, flex hoses, separators, and filters all add resistance. The resistance overhead for almost every part of dust collection systems has been carefully measured and shared in tables and spread sheet calculators called static pressure calculators. There is a good static pressure calculator on my web pages to help calculate our highest resistance. Most two-car garage sized small shops wiht a dust collector have a maximum resistance of 10 water column inches (4” W.C.) or 12” W.C. of resistance with a cyclone. Cyclones take more work to force the air in a tight separation spiral. Blower technology is mature, so the same size and type blower from any of the big makers gives near identical performance. The blower tables show at 10” W.C. we need at least a 14” diameter impeller for a dust collector or 15” diameter impeller for a cyclone to get a real 1000 CFM.
Blower Motor Size
Our blowers use the most horsepower when moving the most air against the least resistance. We calculate the lowest resistance in our shop which is with a new clean filter and biggest shortest duct run. Most small shops have about 4” minimum resistance. To size our motor we see how much horsepower the impeller size we picked pulls at 4”. Our 14” dust collector impellers draw 3 hp and our cyclone 15” impellers draw about 4 hp. Since our motors come in 3 hp or 5 hp sizes, a cyclone needs a 5 hp motor. Our blower tables show a 5 hp motor can turn a 16” impeller to give us even more airflow.
Dust Elimination
Dust collectors and cyclones must be placed outside in their own enclosure behind a fire and explosion proof barrier and we must provide makeup air to avoid sucking deadly carbon monoxide backward through vents to comply with NFPA codes and pass a fire marshal inspection. This is why most large commercial facilities vent outside and operate with main doors open. If your system does not have to pass inspections, good safety practices say you should still follow these rules and provide makeup air. Putting your properly sized dust collector or cyclone outside keeps the dangerous fine dust missed during collection from quickly building to dangerously high levels. Thousands of shops prove infrared heat easily compensates for any heat loss even in the coldest weather. If you live in a really hot area then air conditioners cannot keep up.
Filters
Most small shop fine filters supplied on dust collectors, cyclones, shop vacuums and air cleaners are too open so they turn these units we buy to protect our health into dangerous dust pumps. Almost all of these use filters designed for outdoor use that are not ASHRAE rated. They are instead tested after they are fully seasoned meaning they have built up as much fine dust in the filter pores as the filter can carry through normal cleanings. It takes up to a year for small shop filters to fully season. During that time if we vent inside we breathe the fine dust that these filters miss. Worse, even though a fully seasoned filter filters ten to twenty times more efficient than a new clean filter, it also constantly leaches the finest unhealthiest dust right through. Those with particle counters regularly find just turning on these units including their air cleaners launches enough fine dust to create dangerously unhealthy air. In short most small shop filters act as reservoirs that save up and dump the unhealthiest dust every time they are used.
If you really want to filter your shop air instead of vent it outside, the medical experts say we need filters that provide at least 99.9% separation of all particles sized 0.5-microns and larger and should use HEPA quality filters that provide 99.97% separation of all particles sized over 0.3-microns. This fine filter material is expensive and we need lots of it. Air engineers say we need at least one square foot of filter area for every four CFM of airflow, but the filter makers and experience shows one square foot for every two CFM provides much longer filter life and reduces cleaning. Woodworking makes so much sharp fine filter destroying dust that fine filters fail quickly. Even with large filters commercial firms that do fine filtering replace fine filters roughly every three months. To minimize filter cleaning and maximize filter life you need a far better separating cyclone than any of the normal units. My cyclone design is in use worldwide in over 10,000 small shops and has been medical school tested to provide six times better fine dust separation, but I still tell people to vent outside whenever possible. Most go many years between filter replacements. You can build a cyclone of my design from the free plans on my web pages or buy one.
Summary
We either wear our masks and vent outside, or do the work and pay for good fine dust collection.