N stands for "non-oil". Generally, non-oily particles refer to coal dust, cement dust, acid mist, microorganisms and so on. At present, in the raging smog pollution, suspended particles are mostly non-oily. And oily particles refer to oil fume, oil mist, asphalt smoke, etc.
R stands for "oil resistance" (limiting oil-resistant particles).
And P means "oil-proof", which means that both oily and non-oily particles can be filtered.
Extended data:
Usage time of 3M brand masks of different grades:
When used to protect oily particles, the cumulative use time of grade R shall not exceed 8 hours;
The cumulative use time of grade P shall not exceed 40 hours, or reach 30 days from the beginning of use, whichever comes first.
Precautions:
1 and 3M protective masks cannot be washed, because washing will destroy the filter material and mask structure; If it is not damaged by pollution and meets the hygiene requirements, it can be considered for reuse.
2.N95 mask is not a product trademark or brand. N95 is the minimum requirement of NIOSH (National Institute of Occupational Safety and Health) for the filtration efficiency level of American occupational particulate respirators, that is, the filtration efficiency of non-oily particles (such as dust, paint mist, acid mist, microorganisms, etc.). ) at least 95% under the test conditions specified in the standard.
References:
People's Network-How to choose a "smog" protective mask