I’ve had to handle a lot of questions over the past 4 months concerning the NIOSH filter rating system so I made a little chart to help explain it. Here’s the chart:
As you can see there are (9) potential ratings for filter media when used as respiratory protection against particulates. Particulates in practical terms mean stuff like dust, ie tiny particles that fly around your nose and mouth when you cut drywall or concrete or sand wood, etc. It also refers to silica sand and radionucleotides and asbestos and any really fine ‘thing’ that can get into our lungs by way of our breathing passages (mouth and nose) and cause a problem. These are not gases but actually particles that we breath in.
The lowest rated filter media as you can see from the chart above is an N95 rating. The highest rating filter media can receive is a P100. A P100 filter, like a filter in some vacuum cleaners today, would be similar to a HEPA filter (High Efficiency Particulate Air). We use these in the home to maybe trap dust mites and pollen, pet dander and smoke. It’s a similar concept with respiratory protection except that we put the filters over our face using what are commonly called respirators.
So what the heck is a N95? Basically, it’s a special mask…many people call them ‘dust masks, NIOSH calls them ‘disposable respirators’…made of filter material and formed to go around your nose and mouth that has a NIOSH rating of N95.
There are also ‘reusable respirators’, usually made out of rubber, that take replaceable cartridges. When a disposable respirator is ‘used up’ you throw the whole thing away. With a reusable respirator you only throw away the cartridges, replacing them with fresh ones.
It gets kind of confusing for some folks because both the respirator cartridges that go on a reusable respirator AND the disposable, throw away respirators, use the same rating system.
Okay so, what do these ratings mean? Basically the 95, 99 and 100 refer to efficiency. A 95 rated filter will filter out 95% of all particulates larger than 3 microns in diameter. A 100 rated filter will filter out (almost) 100%. That’s why it’s similar to a HEPA filter: it’s highly efficient.
What about the letters in front of the numbers: N, R and P. What are they about? Well it gets a little weird here but the operant word is OIL. Yeah, oil, believe it or not. Here’s the exact excerpt from the NIOSH site explaining the situation:
The selection of N-, R-, and P-series filters depends on the presence or absence of oil particles, as follows:
- If no oil particles are present in the work environment, use a filter of any series (i.e., N-, R-, or P-series).
- If oil particles (e.g., lubricants, cutting fluids, glycerine, etc.) are present, use an R- or P-series filter. Note: N-series filters cannot be used if oil particles are present.
- If oil particles are present and the filter is to be used for more than one work shift, use only a P-series filter.
Then they go on to give us a handy little way to remember it:
- N for Not resistant to oil,
- R for Resistant to oil
- P for oil Proof
So, there you have it. Basically, you can use a P series filter in any environment and since 100 is the top efficiency and 95 is the lowest efficiency, an N95 is an entry level rating to be used in a DRY environment. And a P100 is the top dog on the ratings chart which can be used in these pesky oily envirnoments.
Now you know the rest of the story.