Respirator filters are rated according to how much particulate matter they can reliably block. A P100 rating is the highest for personal respiratory protection. As long as your mask fits properly a P100 filter will block 99.9% of particles .3 microns or larger. (If you're interested in the nitty-gritty the CDC has a comprehensive and fairly unreadable guide to particulate respirators.) In defense of the CDC, there are a huge range of hazards, and not everyone can wax poetic about lung protection like the folks at PK Safety. We recently had a question about using a P100 filter for blocking asbestos, which as most folks know, is particularly hazardous. Their question was about the . If you type in P100 filter, it's one of those items that comes up in a Google search. Yes, this type of combo filter/cartridge does meet P100 requirements. But it's not the kind of thing that's right for everyone. If you're looking for an all-in-one solution that blocks the widest range of hazards, the 3M 60926 Multi-Gas P100 Cartridge generally covers more bases. But most people have at least a pretty good idea of what they're going up against, and only in specific circumstances to they need protection from Acid Gas. Looking for a reliable respirator? The 8233 n100 mask is a great choice for those who want the high-rated by NIOSH filter efficiency in their respirator. This mask is approved for lead abatement, metal fumes from welding, radioactive particulate materials, and non-oil containing mists. If you've got flying particles of dangerous substances - fiberglass dust, sanded or chipped lead paint, asbestos, that kind of nasty stuff, a simple 3M 2091 filter is rated P100 and provides all the protection you could want. If you have strong smells or vapors from paint or certain solvents that are hazardous, then something like the 60926 Multi-Gas Combo might fit the bill. It has two parts: One is the P100 filter that’s under the pink cover. The second is a cartridge of activated charcoal that absorbs vapors. A final note on the combo cartridge – people use these because they are convenient. They protect you from a range of hazards. However, if the filters get clogged before the cartridge is spent, you have to toss them out. There is no way to change out the filter and keep the cartridge. And vice-versa. If you start smelling the things you’re trying to block, the cartridge is done for even though the filter might still be fine. How do you know when the filter is spent? Great question. The answer is you will no longer be able to breath through it. P100 filters are amazing. They block all these particles and only allow air and the tiniest particles through that your lungs can easily handle. When the filters get full of all the material they have been blocking, they don't start to let it in. It simply becomes more and more difficult to draw a breath through. For asbestos you can’t do better than anything rated P100. The only question is whether or not you need the additional protection from the cartridges. If your main mission is to block asbestos but there are also some smells that aren’t as specific and hazardous as, say, bleach or ammonia, you might want to consider the . This is the full-sized filter and has a layer of activated charcoal to remove some organic vapor and bad smells from the air you’re breathing. If you are looking for a reliable respirator, the 8233 n100 mask is a perfect choice for those who want the high-rated by NIOSH filter efficiency in a respirator. It is approved for lead abatement, metal fumes produced from welding, certain radioactive particulate material, and non-oil containing mists. My advice for asbestos – 3M 2097 with a good . It fits the best and is comfortable for long work days. And I don’t know of many quick asbestos clean-up jobs.