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I am going to make a filter for the enclosure of a 3D printer and want to remove both VOC's (with activated carbon) and Ultra Fine Particles (with a HEPA filter). But in what order should the filters be?

I am thinking that if I put the HEPA first, one will get carbon dust into the air (and that is probably not harmful), and if I put the carbon filter first the carbon will be clogged up with UFP faster and the HEPA will be clogged up with carbon dust.

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The easiest way is to look at a profesional dry filter stack first to learn how a filter stack is usually made. So, let me grab my Dyson vacuum cleaner. On the intake side I get the following stack:

  • large particle trap
  • foam filter for medium particles
  • HEPA filter

Incidentally, that's the same setup as my Shop-Vaccum has (though the foam filter gets replaced by a paper bag)

When I googled other dry filters, I found these filter stacks as common:

  • large particle wavy paper filter then combined Carbon-HEPA filter (carbon first)
  • 2 x Nylon-Mesh, Carbon, HEPA

The idea is to reduce the particulate grain the deeper you go into the filter. The rough filter is cleanable, the carbon filter traps chemicals and odor that might damage the HEPA filter, the HEPA filter catches any remaining particles.

If you want to know more about various filter types and applications, you might want to read an article on engineering 360.

Safety pointer

Carbon dust is not not harmful - it is both flammable to explosive, as well as resulting in Black Lung (Coalworker's pneumoconiosis) if it is thrown into the air like in a mine.

However, commercially produced carbon filters don't usually release any coal dust: after making the activated coal, the product is shaped (as you can see in this manufacturer video) and sorted into various grains, like in the photo below. These granulate are then put into the carbon filter and trapped in a mesh that is small enough to keep them even after having been broken apart some. Very fine grains like the Bead Barbon are usually used in wet applications.

enter image description here

In a kitchen, you have sticks of 3-4 mm diameter, often trapped in a metal mesh. ABC-Mask filters usually use very porous carbon-grains in the half to millimeter grain size, trapped between paper sheets.

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  • $\begingroup$ I find it a little hard to belive that the carbon granulate don't contain coal dust as well. Is it not made just like charcoal by heating it with little oxygen? And charcoal certainly have coal dust in it. $\endgroup$
    – Stormer
    Feb 1 at 15:36
  • $\begingroup$ @Stormer Activated carbon is made by heat treating coal in a way. it is bound and after production washed and sorted based on grain size. The powder would create black lung but the pellets used in filters are no longer dusty. $\endgroup$
    – Trish
    Feb 1 at 15:51

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