Double Masked 3M 8210s vs. 3M Aura - Are 2 Better Than 1?

Can you make 2 good N95s into a great mask by doubling them? I doubled 2 3M 8210 N95 Respirators and tested them against a single 3M Aura 9205+ N95 Respirator to find out.
The score to beat is 48. That is the Fit Factor I got earlier testing a single 3M 8210.
Just wearing a good N95 is a great start, and will put you above most people's level of respiratory protection. But to get the best results, consider mask fit testing to find out which masks work best for you in particular.
You can google mask fit testing in your area to see if a local vendor tests individuals. The best kind of testing is the kind I'm doing, with a mask fit testing machine. It gives you a numerical score for how well your mask fits you, the "fit factor". This kind of fit testing is called "quantitative" or PortaCount fit testing. The other kind, where you see if you can taste if an aerosol has leaked in to your mask, also works. It is called "qualitative" fit testing.
Fit Factor
Fit factor is the the concentration of particles outside the mask divided by the number inside the mask. So if there were 100 particles outside and 10 inside, 100 divided by 10 is 10, so the air inside the mask is 10 times cleaner and the fit factor is 10. If there are 100 particles outside and only 1 inside, the mask would be a 100x cleaner inside, for a fit factor of 100.
PortaCount Fit Testing
Particle counter fit testing is objective and more accurate than other kinds of fit testing, but the machines are expensive so it's not used as often as it should be.
Here is a video from the maker of PortaCount fit testing machines on how a full OSHA test is performed using a current model PortaCount. Note that they do various exercises for official fit testing that I skip during my quick experiments.
• Fit Testing N95s with ...
PortaCount fit testing involves putting a hole in your N95 masks to test the air inside them, so you'll need new, spare N95s to test. It will not be usable as respiratory protection once a hole has been inserted. And bring more than one kind in case the first one doesn't work out.
Home Fit Testing
You can do mask fit testing at home by checking your mask with an aerosol that you can taste if your mask leaks. Your mask is worn normally and no hole is required, which is one advantage of this method.
You can do a professional fit test by purchasing a complete Alegro, MSA, Moldex or 3M fit test kit with a hood, two nebulizers and either saccharine or Bitrex solutions. I got one of these aerosol fit test set ups for $50 on eBay, but it took some looking before finding one at a discount. A discounted pro fit test set up cost me less than some people pay just to get a nebulizer to make a home kit.
This is a long instructional video by someone who has helped write the standards for doing fit testing with these kits, Dr. Roy McKay:
• Respirator Fit Testing...
The professional version of fit testing shown in the Dr. McKay video is approved by OSHA. Dr. McKay's video can help you learn how to do the pro version correctly for reliable, repeatable results.
For a less accurate version that nonetheless can still help you identify some masks that leak there are home brew versions of mask fit testing.
You can do a version at home using a single nebulizer and a commercial saccharine or Bitrex fit test solution under a large plastic bag - using commercial fit testing solution. Be aware of the possible suffocation hazard of using a bag over your head - the commercial hoods are stiff have a lower suffocation hazard. *You should not cover your head with a plastic bag without another person to supervise and help you keep safe.*
You can dilute some of the commercial saccharine Fit Testing solution 1 part fit testing solution to 100 parts water to create Threshold check solution to make sure you can taste it without a mask. Then you use the full strength solution for when you wear the mask. (This dilution ratio only applies to saccharin Fit Test solution. Bitrex is different.)
www.zoro.com/3...
u/philipn Has done improvised fit testing with sweet n low and a nebulizer which I have not tried.
• How to do a DIY mask f...
Sweet n Low is mostly filler, so you can't make the solution as strong as commercial fit test solution. The stronger concentrations help you find smaller leaks. But any fit testing is better than none, especially if you don't assume the fit tested mask is perfect nor that it makes you invulnerable.
Keep in mind that only the professional method of using 2 solutions as approved by OSHA and shown in the Dr. McKay video will confirm fit. The simpler home versions will help you identify masks that leak, but can't guarantee that masks that pass that simple testing are completely safe.

[@asmrfoodieuk7965]

What's a good score?

[@gerardhughes]

The basic score required for occupational use of half mask respirators (including filtering face piece respirators like in N95s) in the US is a fit factor of 100, which means the air inside the mask is 100 times cleaner than outside or better and the mask leaks less than 1%.
This means that higher scores are better. And I should remember to take time explaining what they mean in each video.
For elastomeric respirators, the rubber kind of take cartridges, sometimes a fit factor of 500 or even more is required. The rubber seal on an elastomeric respirator fits so much better, they can set standards higher.