Question: how effective are gas masks?
Answer: These masks are rated by the amount of particles they can filter: A mask rated 95 will stop 95 percent of airborne particles that are 0.3 microns in size and larger, while a mask rated 100 will filter out 99.97 percent of particles 0.3 microns and larger, making it comparable to a HEPA (high-efficiency particulate air) ...