Do you mean that n95 masks can't work fine? If so, I'm genuinely curious as to how they failed for you. I've used them while working on-site at a coal mine, as

Do you mean that n95 masks can't work fine? If so, I'm genuinely curious as to how they failed for you. I've used them while working on-site at a coal mine, as long as you're using a genuine high quality n95 mask and have it properly fitted you can absolutely wear one for 4+ hours without the inside getting contaminated. It's certainly not fun but I've done it many times without issues.