Understanding the Ratings of Particulate Filters

A man wearing a respirator and coverallsThere are various alternatives to select from when choosing an air purifying respirator. The first thing that will guide your choice is the contaminants you aim to protect yourself from. There exist two types of air-purifying respirators — disposable and reusable respirators.

A disposable respirator, at times referred to as a dust mask or particulate respirator, comes in a half-face assortment. It is typically useful for protection from airborne particles. These respirators fall into classifications — distinct groups symbolised by a letter and number. Here is a closer look at what the letters and numbers signify.


A dust mask of this type is not oil resistant and are suitable for use in environments with liquid and solid aerosol particulates which do not have oil. These include wood dust, pollen, flour, coal and iron ore. They fall into the classifications N100, N99, and N95. The numbers signify their efficiency level. The higher the number, the higher the dust mask’s efficiency and the more particulates it filters out. The N-series respirators do not have a specific service life.


Used to prevent inhalation of liquid and solid aerosol particulates (which contain oil), R-series respirators are oil resistant. They have a maximum service life of 8 hours. They are not common because of the service life limitations. Their classifications are R100, R99, and R95 respirators.


These dust masks are oil proof, just like the R-series masks. They, however, have longer service lives compared with the R-series. Disposal is recommendable after 30 days or 40 hours of usage; whichever of the two comes first. The long service life is dependent on the mask remaining undamaged. Experts categorise these masks into P100, P99 and P95 filters.

Experts consider particulate filters graded 100 high efficiency particulate air (HEPA) filters. N95 filters are suitable for protection against woodshop dust, airborne diseases, and allergens. R95 filters are typically used by painters to protect them from oil-based particulates.