In scope: information about half-facepiece reusable respirators. Out of scope: whether you should wear a mask, etc.
Reasons to prefer a reusable respirator over a disposable one: they’re (i) more comfortable and (ii) prosocial, preserving disposable masks for medical personnel.
You need to buy two components: the mask and filters.
The mask. The wirecutter recommends 3M’s 6500 series. I have the next model up, from the 7500 series. The 7500 comes in three sizes, small (7501), medium (7502) and large (7503). I think the idea of the sizing is: medium fits most, but there are also small and large (evidence: some stores only stock mediums). If you are familiar with the size of my head, I’m a medium. If outside the US, say in Australia, 3M masks might be hard to find, so you might try other brands like Sundstrom.
The filters. These come in a vast number of options and it’s all quite confusing. A good source of information is this 3M guide. For viruses, we’re interested in particulate filtration. Summarizing page 3 of the 3M guide, a filter is described by a minimum efficiency (95%; 99%; or 99.97% \approx 100%) and a letter that describes whether the filter efficiency degrades in the presence of oil-based aerosols (N, R, P), which is not relevant for non-industrial use. You combine a letter with the minimum efficiency, e.g., N95 = minimum efficiency 95%, not suitable for use in the presence of oil-based aerosols, or P100 = minimum efficiency 99.97%, will not degrade in the presence of oil-based aerosols. Some brands will use European nomenclature: P2 = P95, P3 = P100.
A filter with higher minimum efficiency will be harder to breathe through. That said, I personally find it quite comfortable to breathe through a P100 filter (e.g., I find it easier to breathe through a respirator with a P100 filter than breathing through an N95 disposable mask), so I would recommend using a 99.97% efficiency filter. Maybe the trade-off between filter quality and how easy it is to breathe will be different for others.
Filters are sold in pairs. In terms of specific 3M P100 filter recommendations, the 2291 is the best (it’s more expensive but designed to be easier to breathe through), then the 2091 is next best, and the 2296, 2297, 2096, and 2097 are fine too—they have an extra layer of carbon filter for relief against nuisance levels of certain gases, which you don’t need for virus filtration (but if you’re walking around a busy city with lots of traffic, the 2297 or 2097 might be preferable). All these are fine though so get whatever is available. All of them are compatible with 3M 6500 or 7500 series masks.
I’m unsure how long a particulate filter lasts. I think the answer might be be months if you’re not working in dusty environments. They become more efficient over time but harder to breath through. This 3M guide doesn’t give a timeframe to expiry, it just says to replace them when they become dirty or difficult to breathe through.
Does the surface of a filter become contaminated? I don’t know. Presumably? Maybe don’t touch it. If you get a Sundstrom respirator, the filter is entirely encased in plastic, so you could regularly disenfect the parts of the mask that you can touch.
In the case of a shortage, there are a number of combination cartridges that filter against various gases as well as particles. For example, all those on page 18 of the first 3M guide. These will work for particulate filtration, you’re just also paying for the gas filtration (in money, heaviness, and possibly in that it is more difficult to breathe through them).
The University of Texas at Houston, McGovern Medical School, Department of Otorhinolaryngology also has some good summarized advice for P100 masks.
They recommend 15 mL of bleach per gallon for sanitizing the mask.
Also, I have the impression that as long as the filter is not visibly soiled and it is not hard noticeably harder to breath with the respirator on compared to when you are not wearing the respirator, then the filter can be used indefinitely.
Most filter replacement schedules assume that you are working with some sort of vapor that will attack the filter rather than using P100 filters for particular protection alone.
Reusable respirator guide
In scope: information about half-facepiece reusable respirators. Out of scope: whether you should wear a mask, etc.
Reasons to prefer a reusable respirator over a disposable one: they’re (i) more comfortable and (ii) prosocial, preserving disposable masks for medical personnel.
You need to buy two components: the mask and filters.
The mask. The wirecutter recommends 3M’s 6500 series. I have the next model up, from the 7500 series. The 7500 comes in three sizes, small (7501), medium (7502) and large (7503). I think the idea of the sizing is: medium fits most, but there are also small and large (evidence: some stores only stock mediums). If you are familiar with the size of my head, I’m a medium. If outside the US, say in Australia, 3M masks might be hard to find, so you might try other brands like Sundstrom.
To disenfect the mask periodically, you can soak it in disenfectant.
The filters. These come in a vast number of options and it’s all quite confusing. A good source of information is this 3M guide. For viruses, we’re interested in particulate filtration. Summarizing page 3 of the 3M guide, a filter is described by a minimum efficiency (95%; 99%; or 99.97% \approx 100%) and a letter that describes whether the filter efficiency degrades in the presence of oil-based aerosols (N, R, P), which is not relevant for non-industrial use. You combine a letter with the minimum efficiency, e.g., N95 = minimum efficiency 95%, not suitable for use in the presence of oil-based aerosols, or P100 = minimum efficiency 99.97%, will not degrade in the presence of oil-based aerosols. Some brands will use European nomenclature: P2 = P95, P3 = P100.
A filter with higher minimum efficiency will be harder to breathe through. That said, I personally find it quite comfortable to breathe through a P100 filter (e.g., I find it easier to breathe through a respirator with a P100 filter than breathing through an N95 disposable mask), so I would recommend using a 99.97% efficiency filter. Maybe the trade-off between filter quality and how easy it is to breathe will be different for others.
Filters are sold in pairs. In terms of specific 3M P100 filter recommendations, the 2291 is the best (it’s more expensive but designed to be easier to breathe through), then the 2091 is next best, and the 2296, 2297, 2096, and 2097 are fine too—they have an extra layer of carbon filter for relief against nuisance levels of certain gases, which you don’t need for virus filtration (but if you’re walking around a busy city with lots of traffic, the 2297 or 2097 might be preferable). All these are fine though so get whatever is available. All of them are compatible with 3M 6500 or 7500 series masks.
I’m unsure how long a particulate filter lasts. I think the answer might be be months if you’re not working in dusty environments. They become more efficient over time but harder to breath through. This 3M guide doesn’t give a timeframe to expiry, it just says to replace them when they become dirty or difficult to breathe through.
Does the surface of a filter become contaminated? I don’t know. Presumably? Maybe don’t touch it. If you get a Sundstrom respirator, the filter is entirely encased in plastic, so you could regularly disenfect the parts of the mask that you can touch.
In the case of a shortage, there are a number of combination cartridges that filter against various gases as well as particles. For example, all those on page 18 of the first 3M guide. These will work for particulate filtration, you’re just also paying for the gas filtration (in money, heaviness, and possibly in that it is more difficult to breathe through them).
Be wary of counterfeit filters. These are considerably cheaper.
The University of Texas at Houston, McGovern Medical School, Department of Otorhinolaryngology also has some good summarized advice for P100 masks.
They recommend 15 mL of bleach per gallon for sanitizing the mask.
Also, I have the impression that as long as the filter is not visibly soiled and it is not hard noticeably harder to breath with the respirator on compared to when you are not wearing the respirator, then the filter can be used indefinitely.
Most filter replacement schedules assume that you are working with some sort of vapor that will attack the filter rather than using P100 filters for particular protection alone.