I'm late seeing this post - but, wow! Sean, thanks for giving us all a wake up call about how serious air quality is. It's one of those insidious risks that can sneak up on any of us in a shop. I wish you a speedy recovery.
With a beard I've found the 3M half masks only kinda work for me. I'm now a big fan of a Resp-o-rator. There have been a number of earlier posts discussing the pros & cons. While a full face PPE with input air offers better protection, I find that I'm lazy and will cut corners and fail to put the mask. But, the Resp-o-rator usually hangs around my neck all the time and I just simply insert the mouth piece and nose clip when grinding - it's fast and efficient. All my incoming air enter from behind me through 3M filters that I modified to fit. It's puzzling, but it appears these filters are not in stock in the usual places.
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A couple of years ago I did a posting on an air filter I built for my shop.
https://knifedogs.com/threads/dust-collecter-air-filter-a-design-for-my-shop.52148/#post-417939
It has stood the test of time and is now a permanent fixture, used on anything dust related - grinding or welding. It has 2 modes - one for point source pickup with the nozzle down, and second, with the nozzle flipped up, and cardboard filter blocks removed, it is a whole shop ambient air filter. In the whole shop cleaning mode, it turns over the entire shop air volume about every 10 minutes. At the end of the day I'll set the timer for several hours and let it pick up ambient particles. This filter box is a rather simple easy to build design using mostly angle iron.
Configured for point source pickup. In this photo a friend is using a 3M filter while grinding.
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Configured for general ambient air cleanup
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It uses a stack of 2 filters on each face and a metal filter on the incoming nozzle side. The metal filter acts as a spark arrestor. Magnets on the incoming nozzle baffle gather most of the ferrous grinding material. The paper filters are a MERV 8 and the inner filters are a MERV 13 (if I recall correctly). This large filter surface (6 faces total) greatly improves the air particle pickup.
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