So on the AMA's website today for COVID-19 they are asking for ideas from medical professionals to help protect the doctors and nurses that are really at the forefront, the ones that are working the ICU's etc. Are any of you doctors that you can submit something? They have the filters already, on their masks, and these filters work. Apparently however its possible to breath air that gets by the filter as the mask slips on the face. I know you guys are gonna think I'm silly here.... but if it were me... I would take a small battery operated air pump, and draw the air through the filter... and then send it to the mask under positive pressure. It wouldn't take much at all... just slightly above atmospheric pressure would do the trick. The trick being "positive pressure" on the facial enclosure. It would work. If I was on the front line... I'd be breathing filtered air that was under pressure in my mask.... not ambient pressure. Its simple.
It's been done w/some repurposed CPAP machine components. The device you're asking about is a Powered air-purifying respirator https://en.wikipedia.org/wiki/Powered_air-purifying_respirator https://github.com/jcl5m1/ventilator/wiki/Build-a-Low-Cost-PAPR
Then why aren't they using them? Why are they asking for ideas? Of course you can do a google search the minute I post something... and find something... everything has been made at some point dude... but whatever. If these folks need ideas... here's a simple one that costs nil. This is obviously a basic flow-chart... Either way... if they want to solve that problem.... positive pressure with the filtered air is the solution.
don't kill the messenger, I'm fairly positive I floated the idea of repurposing a cpap a few weeks ago so thought you forgot, as you say "everything's been though up of at some point" so found the above info on PAPRs at the time. I'd use a lithium ion battery power tool inflator as a pump. As to why it's not being used? I reckon same reason we don't have enough n95's to begin with. I don't know if your mask idea is to use a face shield or a rig an n95 to the air source, but basically you'll have a hard time finding face shields in significant numbers. It likely also comes down to liability...no hospital will want to use their healthcare workers as guinea pigs on a jerry rigged device that hasn't been at least experimentally ruled as safe...., what is the duty cycle of an inflator pump for instance?