We’ve been noodling on a variety of Personal Protective Equipment (PPE) we could help with. There’s been a big push internationally to try to replicate existing PPE like 3D printing N95 masks and attempting to clone forced air breathing systems – the challenge with these efforts is they’re starting with an item that was designed for mass manufacturing and trying to go back to DIY fabrication methods. Jim went back to the drawing board to try to come up with the least expensive off the shelf parts PAPR he could come up with:
The basic components are a political sign, a 2 liter bottle, 3D printer centrifugal blower fans, a power tool battery pack/adapter, and an off the shelf HEPA rated vacuum cleaner filter. While this isn’t the most beautiful creation, it fits the basic requirements of a PAPR in filtering air around your head and keeping contaminates away. One of the things missing is the hose – it’s hard to source breathing rated hose and nailing the flexibility and smooth interior walls is difficult. If you use off the shelf hose it off-gasses plastic additives forever, it’s what keeps the hose flexible.
We’re using:
- A Milwaukee Tools M12 heated jacket adapter as a convenient way to convert the bare pack into a 12V power source (bonus feature, you can charge your phone while you’re using it! /s) You can also run an M18 pack if you use 24V fans with this adapter.
- Coroplast, this is cheap polypropylene or polyethylene corrugated sign board, you can find one curbside (look at it this way, you’re still advertising for them) or pick up a sheet from Home Depot to make a ton of these from. Any fabric or compliant foam works for the gasket around the neck.
- You can purchase PETG as a sheet/or in a roll form as PVC, or you can use a clear 2 liter (or larger) bottle, you’ll need to adapt your coroplast cutout to match your “window” size.
- We chose fans we had handy, these are 50x50x15mm 3D printer hot end cooling fans, they’re commonly available in 5V/12V/24V. We used 24V fans as they’ll run on nearly any power tool battery you have available. You cannot use standard axial square fans, they will not drive enough flow with any restriction or backpressure from the filter or user. Don’t used brushed DC fans, they generate ultrafine carbon dust you don’t want to be breathing.
- Filters are widely available as long as you don’t search for the same thing everybody else is – don’t look for N95, look for HEPA vacuum filters, Miller welding PAPR filters, etc. You need to get something that’s rated at 99.97% filtration HEPA, not all HEPA filters are the same rating. Ideally purchase a PAPR filter, they’re NIOSH (breathing) rated, but a vacuum cleaner filter will still carry a recognized rating. Vacuum filters can’t be used for a mask because they’re too hard to breathe through, fortunately you have a fan doing the breathing for you.
Main improvement would be to use a hard hat as the frame so it transfers the load off your shoulders and centers on your head. We wanted to use off the shelf and widely available materials but there’s obviously room for improvement.
If they’re helpful you can see teardowns of:
Miller 235672 PAPR / OTOS AirWings I pictures and circuit boards