Something I want to get together today is a DIY air filtration unit. The thing I wonder about is how air circulation in my garage/shop will effect this. I'm wondering if fans will just blow the small dust particles around instead allowing the filter system to work. I can't afford a portable ac unit yet though I would love one but I have to have some air moving. I have even considered a small through the wall fan to pull dust out but would rather avoid that.
Air circulation vs air filtration
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If you are sucking the air out you are sucking the dust out as well. I would suggest you consider what kind of air currents you are generating with your ventilation, where you are generating the fine dust, and locate your air filtration where it is out of the general air currents and picking up the areas needed.
Steve: I'm not sure I understand exactly what you're trying to accomplish. Are you trying to create some air movement for cooling, and at the same time filter out some of the fine dust in the air? If so, I've built several units for my shop using old squirrel cage fans and motors I picked up cheap at flea markets and auctions. The biggest mistake I've made on all but one was having the air pass through only one furnace filter before being exhausted. I'd recommend pulling it through at least two, and preferably three.
Bill
This one (below), used as a base for my band saw, pulls air through three filters, then exhaust it out the back. It works better than the others for cleaning air.
View image in gallery
View image in gallery
Bill
Thats correct Bill. Let me try to explain the situation a bit more clearly as I should have done the first time. I'm in a two car garage but only using half. I just can't talk the wife out of her half, yet. There is a ceiling fan in the center and a 20" box fan on a table near the back wall. I'm the kind of guy that really doesn't like to work outside much when the temps start climbing above 80. I have one of those dual fans that you can put in a window also that I was thinking of using to filter air. I was planning on putting it in a box and mounting it on the ceiling. I'm not sure how much it would really pick up with other fans going and just blowing dust everywhere. I'm not against taking the ceiling fan out and hard wiring something there. I'm starting to wonder if I should just use multiple fans and just make each one a filter kind of like yours looks like. I would like to use lower power fans since I don't have much power ran to the garage, though an upgrade will coming there at some point.
Just to comment on an earlier post about using multiple filters. Multiple filters will make relatively little additive effect unless they are progressively finer filters.
Commercially made ambient air cleaners ("air filter" or "air cleaner" for this conversation) typically use something along the lines of a 'coarser' 5-micron prefilter (often times a washable electostatic filter, but may also be a disposable paper filter), followed by a second very 'fine', very large pleated bag filter rated at 1-micron.
The second 1-micron bag filter is the most critical element in the equation, as the inital filter exists solely to filter out the majority of the larger dust components, thus prolonging the life of the much more costly 1-micron bag filter. Without the 1-micron filter, all your air filter will give you is an *apparently* cleaner shop because it will remove all the larger nuisance dust (much of it 'safer dust' due to its much larger size), leaving behind ALL the most harmful dust (which you won't much see due to its much smaller size). Below 1-micron is generally safe to breath because it tends not to settle in the lungs and remains suspended in your exhaled breath.
The reason the second filter is a deeply pleated 'bag filter' is due to the physical restriction created by 1-micron filter material, therefore the use of a filter with much greater surface area helps to maintain adequate air flow, as well as greatly extending the life of the filter between replacements.
An air filter without a 1-micron (with a 85% to 99% capture rating) is useless, and pointless, from a health-benefits perspective since such an air filter will not capture the most critical dust -- which will remain suspended for many hours -- potentially even days -- in your shop without proper filtration.
As an example of the consequence of a three filter air cleaner without that 1-micron filter, let us consider a unit with seemingly good specs using three high-quality 5-micron 85% efficiency electrostatic filters.
1) After the first filter, 85% of all particles larger than 5-microns have been captured. Essentially 0% of particles between 1-5 microns have been captured. The ratio of 1-5 micron particles captured will slowly increase (modestly) but only once this filter becomes increasingly clogged by larger dust particles, but not enough to help much since the filter would likely be washed/replaced by this point.
2) After the second filter, we have now captured 87.25% of all particles larger than 5-microns. Essentially 0% of 1-5 micron dust particles will be captured by this stage, unless it has become clogged with larger particles and is in desperate need of cleaning -- unlikely to happen any time soon since the outer filter will have captured the majority of the dust large enough for this filter to trap.
3) After the third (and final) filter, we have now captured 89.1% of all particles larger than 5-microns. Essentially 0% of 1-5 micron dust particles will be captured by this stage -- and likely never will be since this stage is unlikely to ever become clogged with larger particles before it is cleaned as a matter of routine mainenance while cleaning the first and second stages.
So, after all three filters have done their job, we have captured 89.1% (versus 85% for a single filter) of all dust 5-microns and larger. At best, once the first filter begins to become signficantly clogged, we might eventually reach 5-20% capture of dust below 5-micron, with the ratio captured dropping off rapidly as the particle size decreases toward 1-micron.
If you opt for cheaper, lower-quality furnace filters, then the above specs will be considerably less favorable than in the example above.
For comparison, my JDS 750-ER air cleaner, with two-stage filtration will have done the following: After stage one (with a perfectly clean filter, with filtration improving as it dirties) will have removed around 80-90% of 5+ micron dust, with little capture of dust finer than 5-microns. The second stage (a pleated bag filter) will remove approximately 99+% of dust larger than 5-microns and between 85-95% (depending on the specific filter installed) of all dust in the 0.3 to 1-micron size range (again, with improvement as the filter dirties).
So as demonstrated above, it is not the number of stages that matters, but rather the specs of the filter selected. My JDS air cleaner could achieve the same filtration with a single stage (the pleated bag filter only). The second filter (the initial filter in actual use) exists ONLY to capture the majority of the larger dust particles, thus greatly extending the service life of the considerably more expensive pleated bag filter. Your choice of filter material is the one area of air-cleaner design that you do not want to skimp on.
Not looking to start any arguments, but did want to clear up some myths regarding air filtration. I'm all for home-made gear (we can't always justify shelling out $$$ for commercially made gear), but we should always try to ensure our homemade equipment delivers the performance -- especially in 'invisible' respects like our health -- of the commercially made gear we are trying to copy.
Commercially made ambient air cleaners ("air filter" or "air cleaner" for this conversation) typically use something along the lines of a 'coarser' 5-micron prefilter (often times a washable electostatic filter, but may also be a disposable paper filter), followed by a second very 'fine', very large pleated bag filter rated at 1-micron.
The second 1-micron bag filter is the most critical element in the equation, as the inital filter exists solely to filter out the majority of the larger dust components, thus prolonging the life of the much more costly 1-micron bag filter. Without the 1-micron filter, all your air filter will give you is an *apparently* cleaner shop because it will remove all the larger nuisance dust (much of it 'safer dust' due to its much larger size), leaving behind ALL the most harmful dust (which you won't much see due to its much smaller size). Below 1-micron is generally safe to breath because it tends not to settle in the lungs and remains suspended in your exhaled breath.
The reason the second filter is a deeply pleated 'bag filter' is due to the physical restriction created by 1-micron filter material, therefore the use of a filter with much greater surface area helps to maintain adequate air flow, as well as greatly extending the life of the filter between replacements.
An air filter without a 1-micron (with a 85% to 99% capture rating) is useless, and pointless, from a health-benefits perspective since such an air filter will not capture the most critical dust -- which will remain suspended for many hours -- potentially even days -- in your shop without proper filtration.
As an example of the consequence of a three filter air cleaner without that 1-micron filter, let us consider a unit with seemingly good specs using three high-quality 5-micron 85% efficiency electrostatic filters.
1) After the first filter, 85% of all particles larger than 5-microns have been captured. Essentially 0% of particles between 1-5 microns have been captured. The ratio of 1-5 micron particles captured will slowly increase (modestly) but only once this filter becomes increasingly clogged by larger dust particles, but not enough to help much since the filter would likely be washed/replaced by this point.
2) After the second filter, we have now captured 87.25% of all particles larger than 5-microns. Essentially 0% of 1-5 micron dust particles will be captured by this stage, unless it has become clogged with larger particles and is in desperate need of cleaning -- unlikely to happen any time soon since the outer filter will have captured the majority of the dust large enough for this filter to trap.
3) After the third (and final) filter, we have now captured 89.1% of all particles larger than 5-microns. Essentially 0% of 1-5 micron dust particles will be captured by this stage -- and likely never will be since this stage is unlikely to ever become clogged with larger particles before it is cleaned as a matter of routine mainenance while cleaning the first and second stages.
So, after all three filters have done their job, we have captured 89.1% (versus 85% for a single filter) of all dust 5-microns and larger. At best, once the first filter begins to become signficantly clogged, we might eventually reach 5-20% capture of dust below 5-micron, with the ratio captured dropping off rapidly as the particle size decreases toward 1-micron.
If you opt for cheaper, lower-quality furnace filters, then the above specs will be considerably less favorable than in the example above.
For comparison, my JDS 750-ER air cleaner, with two-stage filtration will have done the following: After stage one (with a perfectly clean filter, with filtration improving as it dirties) will have removed around 80-90% of 5+ micron dust, with little capture of dust finer than 5-microns. The second stage (a pleated bag filter) will remove approximately 99+% of dust larger than 5-microns and between 85-95% (depending on the specific filter installed) of all dust in the 0.3 to 1-micron size range (again, with improvement as the filter dirties).
So as demonstrated above, it is not the number of stages that matters, but rather the specs of the filter selected. My JDS air cleaner could achieve the same filtration with a single stage (the pleated bag filter only). The second filter (the initial filter in actual use) exists ONLY to capture the majority of the larger dust particles, thus greatly extending the service life of the considerably more expensive pleated bag filter. Your choice of filter material is the one area of air-cleaner design that you do not want to skimp on.
Not looking to start any arguments, but did want to clear up some myths regarding air filtration. I'm all for home-made gear (we can't always justify shelling out $$$ for commercially made gear), but we should always try to ensure our homemade equipment delivers the performance -- especially in 'invisible' respects like our health -- of the commercially made gear we are trying to copy.
Ethan has done a pretty good job of explaining air filtration methods and goals. The August edition of Fine Woodworking has an article about testing done by a college engineering professor of commercial air cleaners. I was quite happy to see that the Jet AFS-100B I purchased a while back on sale was at the top of his list. :eusa_danc Prior to buying this unit I was using a shop built ceiling mounted air cleaner using a 1/2 HP furnace blower similar to the ones Bill shows. I found that by using a thick pleated filter designed for Honeywell whole house air cleaners with a furnace type pre filter dust collection was greater than furnace filters alone. The FWW article gives a quantative chart including a control test with no air filtration which I found very informative. The testing was done using real woodworking tasks in a simulated shop space which IMHO is a lot more relevant than some commercial testing.:wsmile:
I've gone the Ventilation route. I've got a decent DC with 1 micron bags (supposedly) which does a pretty good job. To handle the rest I installed a ventilation fan in the corner of my shop opposite the windows. Anytime I'm making dust or using "smelly stuff" I open the far window and flip on the fan. It's a very good solution for me.
This is a basement shop, uninsulated, that has outside access along one wall. It is not heated or cooled. In the winter the shop rarely falls below 55 degrees and in Summer it generally maxes out in the upper 70's. It's been my experience that having the window open and the fan on make a minimal difference in ambient temperature even when outside temps are at hot/cold extremes....
Travis
This is a basement shop, uninsulated, that has outside access along one wall. It is not heated or cooled. In the winter the shop rarely falls below 55 degrees and in Summer it generally maxes out in the upper 70's. It's been my experience that having the window open and the fan on make a minimal difference in ambient temperature even when outside temps are at hot/cold extremes....
Travis
Ethan, you're absolutely right about the efficiency of the shop made filtration devices I'm using. You also raised some good points about the quality of filters making a difference. So far I've been using the el-cheapo furnace filters, but after reading your explanation, I think I'll at least switch to the better quality ones. Two of mine (the blue roll-around and the double fan mounted high on the wall) were originally made to provide some cooling air on hot days. I kinda added the filtration as a bonus. The others were made to provide some filtration, with the understanding that I wasn't getting the best solution, but better than nothing. :wsmile: The other thing I didn't mention in the earlier post is that I have a 5hp cyclone DC plumbed throughout the shop. When I'm doing anything that creates fine dust (e.g. sanding) I'll often open one of the blast gates and that sucks a lot of dust out of the air. Still not perfect, but. . . what can I say, I'm too cheap to buy one of the really good ones. :tinysmile_cry_t:
Salem, you asked about the bandsaw fence. It attaches to the support w/ the T-track you see in the pic. The support on the other end is just to hold it up when I have it all the way back against the column. It doesn't attach on the back end. I designed the fence specifically to accomodate the drift of different blades. I'll try to put the fence in place this week and take a pic. Maybe that'll show it a little better.
Bill
Salem, you asked about the bandsaw fence. It attaches to the support w/ the T-track you see in the pic. The support on the other end is just to hold it up when I have it all the way back against the column. It doesn't attach on the back end. I designed the fence specifically to accomodate the drift of different blades. I'll try to put the fence in place this week and take a pic. Maybe that'll show it a little better.
Bill
M
McRabbet
Gentlemen,
Remember that any dust particles that are airborne in your shop -- 10 micron, 5 micron, or sub-micron in size -- are entering your lungs with every breath you take. While a high volume shop air filter system with multi-stage filters is efficient over a few hours for removing fine airborne particulates, your primary particulate removal strategy should be to eliminate them before they become airborne and into your breathing space. This really can only be accomplished by high volume, high velocity dust collection at each source as dust is generated. If you turn off your shop lights and shine a flashlight with a focused beam through the air, you'll see just what is going into your lungs with each breath. A minimum of 400 cfm at the source at 4,000 feet per minute is minimal for most fine dust removal -- 800 cfm at that velocity is preferred and can usually only be achieved with a cyclone. If you realize you cannot keep those fine particulates out of the air, then wear a sub-micron dust mask while working in that airspace and run the air filter for a few hours after you leave the shop.
Remember that any dust particles that are airborne in your shop -- 10 micron, 5 micron, or sub-micron in size -- are entering your lungs with every breath you take. While a high volume shop air filter system with multi-stage filters is efficient over a few hours for removing fine airborne particulates, your primary particulate removal strategy should be to eliminate them before they become airborne and into your breathing space. This really can only be accomplished by high volume, high velocity dust collection at each source as dust is generated. If you turn off your shop lights and shine a flashlight with a focused beam through the air, you'll see just what is going into your lungs with each breath. A minimum of 400 cfm at the source at 4,000 feet per minute is minimal for most fine dust removal -- 800 cfm at that velocity is preferred and can usually only be achieved with a cyclone. If you realize you cannot keep those fine particulates out of the air, then wear a sub-micron dust mask while working in that airspace and run the air filter for a few hours after you leave the shop.
Rob:
I agree that ideally whenever possible we should capture dust at the source where it is produced. Having said that, there are those who challenge the effectiveness of air filtration machines including one dust collection system manufacturer who does not sell such machines. You mention an air filter system "being efficient over a few hours". The real world testing done by the engineering professor in the article I mentioned showed that the air is cleaned in less than 20 minutes using each of 5 commercial machines. I would suggest that anyone looking for facts rather than negative hype regarding commercial air cleaners read the article in the Aug. 2010 edition of Fine Woodworking. :wsmile:
M
McRabbet
I had read Eric Constans article in the July/August FWW and agree that your information is correct -- sadly, he did not outline his test conditions other that to indicate that they set up "a typical shop space" and that they "conducted three typical woodworking tasks". From the pictures in the article, it is not possible to see the size of the shop nor to surmise the tasks, other than ripping a plank. It also appears that the testing was done after the tasks and no other dust-producing activities were done (I would expect none in a test like this).
He does start the article with two key statements:
While I agree that these commercial filters do a great job after dust is in the air, we must all strive to capture as much as possible before it becomes airborne. My estimate of longer times for getting the air clean is based more on shop-built units and the fact that most of these commercial units have timers that allow run times for several hours. The air filter systems are a third line of protection and that is my real point.
In my own shop (800 SF), I always connect my sanders and mitersaw to a mini ClearVue cyclone on a shopVac and wear an OSHA-approved dust mask. All of my other machines are connected to a DC.
I had read Eric Constans article in the July/August FWW and agree that your information is correct -- sadly, he did not outline his test conditions other that to indicate that they set up "a typical shop space" and that they "conducted three typical woodworking tasks". From the pictures in the article, it is not possible to see the size of the shop nor to surmise the tasks, other than ripping a plank. It also appears that the testing was done after the tasks and no other dust-producing activities were done (I would expect none in a test like this).
The article did state that in addition to sawing, sanding and routing were also done to produce airborne dust to establish a baseline dust concentration. I agree that the size of the shop space would have been helpful but that does not detract from the findings that the machines are helpful in a short time frame removing dust which was not collected at the source. My most recent project has been routing grooves, dados, and rabbets in MDF to make 18 drawers. My air filter did a great job of grabbing dust which was not captured by the dust collection on my router table. IMHO MDF is the absolute worst material we work with being composed of glue and sawdust with the consistency of talcum powder. As a secondary means of dust collection the air filtration machines definitely have intrinsic value. I have found an absolute means to eliminate dust hazards but unfortunately not turning on any of my woodworking machines severely impacts my productivity. :rotflm:
The article did state that in addition to sawing, sanding and routing were also done to produce airborne dust to establish a baseline dust concentration. I agree that the size of the shop space would have been helpful but that does not detract from the findings that the machines are helpful in a short time frame removing dust which was not collected at the source. My most recent project has been routing grooves, dados, and rabbets in MDF to make 18 drawers. My air filter did a great job of grabbing dust which was not captured by the dust collection on my router table. IMHO MDF is the absolute worst material we work with being composed of glue and sawdust with the consistency of talcum powder. As a secondary means of dust collection the air filtration machines definitely have intrinsic value. I have found an absolute means to eliminate dust hazards but unfortunately not turning on any of my woodworking machines severely impacts my productivity. :rotflm:
Re: Useful Information
Here is some info that may be helpful.
Here are some general rules based on Nagyszalanczy's "Workshop Dust Control" and some of my own experiences and thoughts.
The two most important criteria for an air cleaner are the CFM and the filters. You want a CFM factor that will clean the size of your shop and a filter that removes the particle size that you are concerned about.
To determine the size or required air flow, use this formula: Volume of your shop (Length x width x Height) times Number of air changes per hour (typically 6 - 8) divided by 60. This will give you an answer in Cubic Feet per Minute which is how air cleaners are measured. MOST AIR CLEANER MANUFACTURERS RATE THE CFM OF THE FAN ONLY, but there are losses due to the filters. If you are building your own or if the air cleaner you are purchasing rates only the fan, figure you will lose about 25 - 40% for filtering losses.
As important as the air cleaner size is how and where you mount it. Try to mount at about 8-10 feet above the floor (no lower than 6'or 2/3 of the floor to ceiling distance if less than 8' ceiling). Mount along the longest wall so the intake is approximately 1/3 the distance from the shorter wall. Mount no further than 4-6 inches from the wall.
The exhaust is the largest determiner of the circulation pattern. You are trying to encourage circulation parallel to the floor/ceiling so ceiling mounting is not recommended. Use a smoke stick (or a cigar) to observe and maximize circulation. Use a secondary fan to direct air to the intake if necessary. Also, consider that a standard 24" floor fan moves a lot of air and, in some shops, just positioning it in a doorway with a window or other door open can accomplish as much or more than an air cleaner. It's all in the circulation patterns.
The exhaust is the clean air so that is where you want to position yourself. Do not place the air cleaner over the a dust producer. That will guarantee that the operator will be in direct line between the dust producer and the air cleaner. The operator wants to be in the clean air stream. If the dust has to pass your nose to get to the air cleaner, you get no benefits. If you have an odd shaped shop, two smaller units may be better than one large one.
DO NOT RELY ON A AIR CLEANER TO ACT AS A DUST COLLECTOR. The purpose of and air cleaner is to keep airborne dust in suspension and reduce airborne dust as quickly as possible AFTER THE DUST PRODUCER HAS BEEN TURNED OFF.
Finally, if you are looking for health benefits, you will not find any air cleaner manufacturer that makes health claims because there are few health benefits. CATCHING DUST AT IT'S SOURCE IS THE BEST LONG TERM GOAL. Rick Peters', author of "Controlling Dust in the Workshop", makes the point that spending your money getting the dust at its source is a better investment than trying to capture it after it is already airborne. If the dust is in the air, it's going to be in your nose and lungs too. Robert Witter of Oneida Air Systems has noted that "overhead cleaners can only lower ambient dust levels AFTER THE SOURCE OF EMISSIONS IS SHUT DOWN, and they take several hours to do this. This is why they are not used in industry." The absolute best answer, if health is the primary concern, is to use a NIOSH approved respirator. The dust cleaner will help keep your shop cleaner but have minimal or no health benefits. OSHA takes this position too. They measure the number of particles per a volume and most air cleaners will not satisfy their specs.
Here is some info that may be helpful.
Here are some general rules based on Nagyszalanczy's "Workshop Dust Control" and some of my own experiences and thoughts.
The two most important criteria for an air cleaner are the CFM and the filters. You want a CFM factor that will clean the size of your shop and a filter that removes the particle size that you are concerned about.
To determine the size or required air flow, use this formula: Volume of your shop (Length x width x Height) times Number of air changes per hour (typically 6 - 8) divided by 60. This will give you an answer in Cubic Feet per Minute which is how air cleaners are measured. MOST AIR CLEANER MANUFACTURERS RATE THE CFM OF THE FAN ONLY, but there are losses due to the filters. If you are building your own or if the air cleaner you are purchasing rates only the fan, figure you will lose about 25 - 40% for filtering losses.
As important as the air cleaner size is how and where you mount it. Try to mount at about 8-10 feet above the floor (no lower than 6'or 2/3 of the floor to ceiling distance if less than 8' ceiling). Mount along the longest wall so the intake is approximately 1/3 the distance from the shorter wall. Mount no further than 4-6 inches from the wall.
The exhaust is the largest determiner of the circulation pattern. You are trying to encourage circulation parallel to the floor/ceiling so ceiling mounting is not recommended. Use a smoke stick (or a cigar) to observe and maximize circulation. Use a secondary fan to direct air to the intake if necessary. Also, consider that a standard 24" floor fan moves a lot of air and, in some shops, just positioning it in a doorway with a window or other door open can accomplish as much or more than an air cleaner. It's all in the circulation patterns.
The exhaust is the clean air so that is where you want to position yourself. Do not place the air cleaner over the a dust producer. That will guarantee that the operator will be in direct line between the dust producer and the air cleaner. The operator wants to be in the clean air stream. If the dust has to pass your nose to get to the air cleaner, you get no benefits. If you have an odd shaped shop, two smaller units may be better than one large one.
DO NOT RELY ON A AIR CLEANER TO ACT AS A DUST COLLECTOR. The purpose of and air cleaner is to keep airborne dust in suspension and reduce airborne dust as quickly as possible AFTER THE DUST PRODUCER HAS BEEN TURNED OFF.
Finally, if you are looking for health benefits, you will not find any air cleaner manufacturer that makes health claims because there are few health benefits. CATCHING DUST AT IT'S SOURCE IS THE BEST LONG TERM GOAL. Rick Peters', author of "Controlling Dust in the Workshop", makes the point that spending your money getting the dust at its source is a better investment than trying to capture it after it is already airborne. If the dust is in the air, it's going to be in your nose and lungs too. Robert Witter of Oneida Air Systems has noted that "overhead cleaners can only lower ambient dust levels AFTER THE SOURCE OF EMISSIONS IS SHUT DOWN, and they take several hours to do this. This is why they are not used in industry." The absolute best answer, if health is the primary concern, is to use a NIOSH approved respirator. The dust cleaner will help keep your shop cleaner but have minimal or no health benefits. OSHA takes this position too. They measure the number of particles per a volume and most air cleaners will not satisfy their specs.
Thanks Bill! I am still pondering a fence for my 1950's Delta. I had a shop made one on my last bandsaw and it was no good for fine adjustments. I have plans for another one drawn up but it is quite complex. I would appreciate pictures of a simpler design.
Salem
Salem, as promised I took some pics today of the fence I made for my Delta 14" band saw and uploaded them to the Members Gallery. I think the link below will take you directly to them. If not, go to my name in the Members Gallery and it will be a separate album titled, "Shop made band saw fence". It's not pretty! In fact, it's pretty crude, but it works. There are two adjustment knobs: one to adjust the width of cut, and the other to adjust for drift. Both are pretty simple.
http://www.ncwoodworker.net/pp/showgallery.php?cat=1988&ppuser=5348
After you take a look, please feel free to come back if something doesn't make sense. I tried to put a simple description w/ most of the pics, but they may still be a little fuzzy. :wsmile: Incidentally, I bought a Rikon 14" (10-325) in February to get additional resaw capacity. I love the saw, but the fence is another matter. When I get a few spare minutes, I'm probably going to build another fence for it. I'll try to make it prettier this time. :gar-La;
Bill
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