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So as a engineer with a background in aerosol science I can help explain a few things. Probably the easiest thing to tackle is that only particles about >10um are really settling out. For say a 1um particle, it settles at a rate of about about 0.21cm/min or 0.4 ft/hr! So they just float around for a really long time. So where are these particles going? First you have natural ventilation in a room, in other words drafts from windows or other outside air entering the room. The other mechanism that reduces count is agglomeration of a particles, so say two 100nm particles bump into eachother, they will stick together and form a new particle, but it's not a 200nm particle it's about a 150nm. So it takes roughly three to four 100nm particles to agglomerate together to get 1 "200nm" particle. So while the mass is conserved, number count is not conserved. So we begin to see particles drift from 100nm --> 1-2um they significantly reduce in count. Then as they get bigger we start to see some settling, but not until they grow big enough. Using the fan helps mix it up, if you had the counter on the floor, it would see a steady concentration until all of the particles were gone. Think about if had a mixture of water and mud, the mud settles out from the top to bottom, so the top of the glass gets the cleanest, the bottom will be the dirties longer, mixing it gives a more average measurement. Not surprised that the other particle generation methods didn't generate a ton of 5um bins. Let me know if you all have more questions.

Given the wide range of topics that you cover, I'm curious how your kids would describe what you do for a living. I remember bringing my kids to work and listening to them explain what I did. I can only imagine what their thoughts would be if I recorded mice in a maze on day and on another day spreading dust around the house.

These two videos so clearly demonstrate the need for proper extraction when soldering

Thank you for your integrity in saying your sponsor is not the ideal solution for specific uses.

Noticed an interesting, similar effect in fish tanks - simply adding a pump to circulate water (unfiltered) encourages detritus to settle out of the water column *much* more quickly, and toward particular nooks and crannies in the tank. Without this additional water movement, fine and coarse particles take a lot longer to settle out.

The UK Health and safely executive are currently checking air quality in commercial work working shops. Dust extraction is a thing here. MDF dust and wood types which contain silica are damaging to health, so bringing this to light hopefully will help. 👍

The random or unexpected results could be the electric charge of air molecules and/or dust particles. If the air and dust have the same charge, dust hangs in the air longer. If the air and dust have the opposite charge, dust clumps and settles. In low humidity conditions, a fan blade can impart a mild electrical charge to the air, or perhaps even to the dust that rubs against the blades. Great video and I really like my Dreo!

This brings up another thought. We have an Ecoquest air purifier. It has an "ionizer" that is supposed to force dust particles to stick together until they become too heavy to float. I've always wondered if it works at all.

We need you wisdom finding the best miter saw dust collection ideas. Thumbs up if anyone agrees. Thank you

Thanks for these air cleaning videos. There is tons of misinformation and marketing noninformation with people talking about how wood dust is terrible for you and how you are wasting your time without crazy airflows over hepa filters and thousands in equipment. This info really sheds a lot of light on what kind of stuff wood dust really is and what a huge difference even the most basic filter over a fan makes when compared to the other options.

🤧 Aaachoo!! Great one Matthias, glad to hear woodworking dust isnt as harmful as others. And interesting how well a fan by itself worked to displace the dust 👍

Doing a google search on "aerosol size vs suspension time" brings up some interesting studies. Naturally studies concerned about airborne pathogens like SARS first, but there has been tons of work over the years on other concerns. I recall an aerosol measure instrument in storage in our physics department, never knew who used it though.

Yay! I love when creators listen to their fan!

I appreciate the depth with which you went through for this question. Hopefully it was worth the hassle of people like me bugging you about it on your previous video, I find this kind of control data super interesting. While Dyson isn't as good as the others, it's still WAY better than nothing, and really seemingly significantly better than nothing.

Pretty interesting indeed, Matthias! Fantastic testing! Let me nerd a bit here... Yes, small particles are dangerous and so on, but it's not that simple. Everything depends on the material and on the person! For example, any kind of pine dust gives me a LOT of allergies, for example, while some other woods (like Garapeira, that I use a lot)... It's the same as nothing. That's the reason why those kind of studies never have "100% results", it's always a fraction. Because it's going to be bad for some people and not for others... And we still don't even know why! Anyway, stay safe there with your family! 🖖😊

Always love your content you give such amazing information in a concise manner. I love that.

I got one of the Dreo filters for my tiny workshop in the second bedroom of my San Francisco apartment. I have had it on for about two weeks and have been surprised at how infrequently it turns on (in auto mode), only once so far because of using a mini table saw.

I wonder if the the basic non filtered fan is generating static electricity and collecting the dust. It would be cool to test a non moving static generator for dust collection. Though, I'm not sure the oil smoke is electrostatically charged.

Hi Matthias, thanks for responding to the dust-settling questions so quickly!

Interesting! Maybe the fan adds electrostatic charge to the dust and makes it cling to surfaces, instead of just hanging in the air.

It would be interesting to see how effective air ionizers (and electrostatic filters) are in comparison.

A rabbit hole indeed. I was thinking it could also be the particles impacting the fan blades and sticking there or clumping together. I'd love to see a particle analysis for what comes off FDM 3D printers based on filament material but it looks like you're dedicated to woodworking.

Great follow up video-thank you for making it.

I bought the Dreo after your last video, so far it has been excellent

One thing worth testing is to see if what the fans were doing was simply homogenizing the particles in the room. Without the active circulation, it could be that the particles are forming a density gradient along the vertical space in the room, altering the perception of the half-life as the formation of the gradient could maintain a higher concentration at the height of the sensor. To test for this, you could mount your different PM2.5 sensors at different heights to see if they track differently

A couple years ago I made the mistake of sanding in my closed garage for an hour or so w/o a respirator. Within a few hours had horrible flu symptoms. Don't remember how long it took to get better(was only a few days I'm sure) but I'm pretty sure I was hacking up stuff for weeks. Normally I do all my wood work outdoors in the breeze and just don't think about the wood dust but it was winter Now I wear one even outside. Not making that mistake again

These are some terrific videos. Highly interesting experiments.

Maybe the movement of the particles inside the cyclone creates a static charge and they end up sticking to the walls?

Running a fan probably increases the likelihood that a particle hits something, which increases the likelihood of it sticking to whatever it hit: other particles, furniture/tools, or people. So it's out of the air but not out of the environment.

You might look up laminar flow hoods and clean rooms. This isn't my area of expertise, but I think the idea is that small particles can be suspended in eddies of turbulent air, but settle out of laminar flows. This seems contrary to turning on a fan, which should cause turbulence, but maybe the fan sets up laminar flow throughout the room? The question then is, what would be the source of eddies when the fan is not on? Convection? And does the fan somehow overcome that? In any case, if this is the explanation, then the decrease in particulates in the air is arising from the particles falling out onto surfaces all around the shop. Regarding fan on / fan off in the presence of filters, that is a tough game to study because the fans that I saw are all extremely low pressure fans. Adding a filter in front of them could have a large effect on how much air that fan can move. So filter vs. no filter may be more of a matter of no fan (effectively) vs. fan. I built a filter for my shop from a furnace blower that is rated somewhere in the ballpark of 700 cfm. More importantly, it can delivery that volume even with a reasonable amount of resistance from the filter (and from ducting in the original application). I set this up with 20"x20" filters...there is a 4" MERV 12 filter with a 1" cheapie ahead of it as a pre-filter. I have a Dylos counter, too, but never took the time to read it out and just eyeball how it responds.I ought to do more. I'll tell you a good way to make dust. Sweep the floor. I have a concrete floor, so maybe that is related, but sweeping sends the counts through the roof. I don't sweep anymore, actually, and use a HEPA shop-vac. I rake up shavings, then use the shop-vac. You'd think the outlet stream from the vac would cause problems, and I suppose it does, but I've not seen that as a problem in practice, based on the Dylos meter. Finally regarding conclusions about making fine dust. You need to consider the diffusion time of very small particles. Honestly, I'm not sure how to do that quantitatively because I don't have the underlying data, but I can say that even though putting on my filter clears out the shop in 15' to half an hour, the time between doing woodworking and seeing increased counts has been unpredictable to me. There are times when I think that air infiltration from outside is affecting the reading. End of random dump. Hope some of it is helpful.

Hi Matthias, I was watching Tim Hunkin's video The Secret Life of Chains today. He uses your sofware to make his cogs. Best wishes, John

The dust collector on your belt sander reminds me of something I put a lot of thought into once upon a time and never got around to building. My sandblast cabinet has a ring around the cylindrical air filter that you can access via a rod into the housing that allows you to shake the filter to remove the bulk material from the pleats. I know some high end vacuums (Festool perhaps) use a similar concept, except automatic and with alternating filters. Seems you got half-way there by orienting your air filter at the top, and a mechanism to rake or shake the pleats - perhaps automatically each time the vaccum stops, would be a fun project.

This is fascinating! Thank you for sharing your research.

Excellent. I'd love to see the counts in a kitchen when cooking. I'm sometimes concerned about workshop particles but dread to think what my frying pan does.

Great stuff!! I love how you analyze problems. Thanks for putting it all together. I'm guessing, but burn anything would be more harmful that cut "anything" because the process of burning releases oils and breaks down the carbon making it more sticky - I'm guessing.

Test air ionizers next! They make particles clump together so they fall out of the air. Could also test them in concert with filters. You can buy cheap kits that are basically just a little high voltage transformer connected to a needle point.

Wow you go over board with the details, thanks for going in so deep. …. Maybe it’s the weight of the particles.

cool analysis, great job!

Seeing my car covered in pollen, I was thinking if there was a way to generate a charge in the body to repel dust and keep it cleaner. Could this charge also be used as a more effective dust mask effectively creating a force field that repels dust from around your breathing space.

Particles are removed from your room by two mechanisms: (1) Settling (2) Ventilation (I doubt that your "test chamber" is perfectly sealed) Running a fan might improve removal by ventilation, since the particle distribution at the edges of the room will be kept higher. I'm guessing that your particle sensor is near the center of the room.

I like your testing of various things . Yesterday I was wondering what grit of sandpaper was equivalent to a plane and a scraper. In other words if I planed a board what sandpaper grit would I need to achieve the same surface. Or what surface finish have I achieved with simply using a hand scraper instead of sand paper. Would you care to find out for me?👀

Could the reason for the fan speeding up the decay of the dust particles simply be do to static electricity? The blowing around of the dust particles bumping into each other and the walls, causing them to stick to each other and other things in the room.

Awesome video, as usual! Some high end cameras use a motor to vibrate dust off of the mirror/sensor. I'm wondering if your dust collector that you vacuumed out at the end could benefit from a vibrating agitator - maybe one that just ran a few minutes after the motor had shut off? Also - 5:05 "fit to decay" is my new death metal band name.

Is there a UV light reactive material you could make into a fine dust? It would be interesting to do these experiments and then turn on a UV light to map where it settles

Nice video, and an interesting result about particle type. Certainly makes you wonder about particle "stickiness" and static charges too. I would imagine the wood smoke particles contain a lot of tiny liquid droplets (composed of furans, furfurals, levoglucosan, etc). Have you tried modeling particle settling using Stokes' law? I would be curious to see how the results/theory compare.

I'm just random theory crafting here since I don't really fully know how the particulate sensors work. It could be that the air movement from the fan prevents particles from being detected (some are too fast or something.) It could also be that the movement causes an electrostatic charge (like some sizes are repelled from the electronics or attracted to something else in the room.)

Matthias, you should try making an DIY version of the 3M versaflo. That thing costs €1500 and it’s basically an air filter and battery attached to a helmet

I love these videos. Thank you.

I think the fan agitates the dust which causes them to collide more often and clump which would drop them onto the ground. I think it really depends on where the fan is aimed. If you had it blow at the floor it would probably make things worse.

If you want to generate a lot of particles, slowly cut MDF using a chop saw.

@Matthias random stuff, Smoke from a forest fire is negativley ionized, I was told in fire school. If those particle are ionized they will tend to repell each other. The smoke collecting on the walls and floor are going to repell the smoke in the air and keep it aloft.

Higher pressure and higher humidity cause the particles to fall out faster. The fan is blowing the particles into surfaces causing them to collect.

No one expects the wood worker to go full data scientist.

Well it makes sense when you think how fans get dirty and also the surfaces upon which they blow the air. I used to have a fan that was set close to a wall and the area where the fan was blowing against got some dirt accumulation from the wind. That type of aggregation of particles look like crystal growth in the sense that it does not form an even layer but particles seem to get stuck over "nucleation sites" that are usually other particles or imperfections on the surface. When the particles are very fine and very small I assume it can take a while before the accumulation over the fan and over the surfaces in contact with the wind show visible sign of dust. To me it could be something to do with electrostatic, or just mechanic impact of the particles or maybe both.

I am one of the folks commenting on the lack of a baseline. And as in typical Matthias' form, You want a baseline? I got your baseline! Mic drop....

About the wood smoke settling out faster. I'm an avid smoker. I smoke everything. Even liquids. Cheese! I've always had to clean my smokers several times a year. What I really hate about cleaning time is digging the old flatbar out. The sugary residue glues the doors shut. The best way to get the sticky substance out of the smokers is with a pressure washer ( and a hazmat suit which I don't have ). If only I had a nonstick smoker! All I'm saying is that wood smoke is extremely sticky. So all that smoke is probably on the walls floor and ceiling, and everything else. Ever have to clean a small office habitually occupied by up to four smokers. I mean small enough where three of the four have to stand. The windows, the mirror over the basin, anything white, clear, chrome, or silver had a really nice gold tone to it. Manager said "Wow! That's just a regular mirror. Kinda wish you didn't clean it." I don't believe smoke settles on to the floor so much as it just sticks to everything.

Finally some important science is being done!

Another great video! Can you, or do you have a video somewhere describing your dust measuring setup and how to build one?

Dammit Matthias, you need to explain this to me like I’m 5! 🤣

would be interesting what happens if you add a ionizer or an electrostatic surface the particles can stick on.

I'm guessing that the particulates blow around until they settle on something where they are held by gravity, charge or physical bond. The fan agitates the air and causes the particulates to move more, increasing the chance of finding some bond. I think it is unlikely that the running the fan is causing a significant amount of particulates to leave the room.

Matthias can you run an experiment with your apparatus to check the particles emitted by a plug-in air freshener I once read an article that those particles are as deadly as cigarette and diesel smoke and that the particle size contributes to hardening of the arteries etcetera

This is awesome. I love this kind of stuff! Thank you!

I'm wondering if the final result - showing that cyclone can separate fine dust - runs hand-in-hand with the observation that just running a fan knocks woodworking dust out of the air.

Have you thought about using some sort of offset weight to help keep the dust collector for your sander from getting too clogged up? Either that or giving it a few kicks now and then would probably help.

As one of those who asked, thanks!

I heard a theory that when the air in an enclosed volume is moving the chances are greater that a dust particle will move through a surfaces boundary layer and becomes trapped in the stationary air at the surface. Basically the dust collects on any nearby surfaces and if its moving it encounters more surfaces.

show us how you built your particle counter and hooked it up to your PC

I wonder if having something metallic in the room with a positive and/or negative charge and the fan running would speed up dust collection. I know quite a few units will put a charge onto the dust to the air cleans more quickly, at the cost of some items in the room getting more than their fair share of dust.

I don't know how the hell I got here, but I just spend 12 minutes totally nerding out to learn that I should run a fan to reduce dust. damn.

I wonder if you added some kind of vibration to the sander filter if it would knock the larger dust loose. Might have to run it when the blower is off.

Any chance the high speed blowers are centrifugally flinging the fine particles out and coating the inside of the blower housing with them?

Curious stuff. Is it possible that these decays are dilution effects; i.e. particles just equilibrating in the total air volume?

From experience, sanding discs on angle grinders make a lot of fine dust really quickly and circular saws on mdf, maybe those would work better?

Another one analyzes the dust 🎶

Thank you for your rigor! Question: do you have any video/doc on how you read out your ZPH02? Looking online the info seems to be meager

Curious if particles settle faster in laminar or turbulent flow. Intuition says laminar, but this experiment suggests that it might not be as straight forward.

Angle grinder with a sanding disk on it throws dust. Not much "wood working" related but it happens 😅

i could certainly see there being much more polarization of particles in high speed and more static forces which I would think could make particle sizes bigger. The amount of static electricity that a dust collector can generate is just insane to me... many thousands of volts to develop arcing. So that has to have some effect on tiny particles floating in those charged environments.

Now i wonder how an open window will compare, or open window with the fan on

I'd be curious of the particulate counts produced by FDM 3D printers in confined spaces.

Thank you for the follow up with the controls. (Do you ever wear a mask when you are working with dust?)

Maybe interesting to test different types of sandpaper? The higher the gridnumber the more dust flying?

You are so wasted for you tube , your knowledge and expertise, just blows my mind.

Test an ioniser / electrical dust precipitation?

I wonder if the dust settle even faster if an ionizer is used...

wow, feedback, amazing

How about static plates and such?

Kind of off topic, but I have always wondered something. If there was a candle burning in a room with airborne particulates, would the flame of the candle burn the particles and eventually clear the air? I know the burning candle will be emitting it’s own gasses as the fuel in the candle burns. But I wonder if two identical rooms with two identical particle sensors would register any difference with the addition of an open flame in one room. Also, I know about the dangers of a flame in a particle filled room. The reason I wonder about it is because I wonder about possible benefits of an open flame as a type of air purifier.

Can you do experiments with air washers that use water instead of hepa filter’s

I have an idea, don’t know if it’s been tried but a blower, blowing the air through a bucket of water with a lid and vent holes. Would introduce water but would be fascinating to see how effective and only consumable is water.

I wonder how opening a window performs. But I guess that depends on various factors aswell...

I did not expect moving air to HELP dust settle. I guess it increases the chance of dust hitting surfaces?

Why cant adders use log tables?

since gravity pulls the dust to the floor, can you get a sample on clear tape/count or move the sensor closer to the floor?

Mattias, would it be possible to use the burned mineral oil and one of the sensors that measures those particles to measure the natural air changes per hour in a house? Sort of a poor man's tracer gas? Also, is you knew a decay rate what math would one use to calculate air changes per hour in a space? Thanks!!!

Awesome

We love you Matthias, but please build something. I'm trying to hang in there, but spreadsheets about 2.5 micron particles gets boring rather quickly. It's like listening to someone talk about the different ways of generating fractals.

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