Respirators

NIOSH air filtration rating refers to the publications of (NIOSH) of the US government pertaining to respirators and masks worn to filter contaminated air, regardless of cause.

NIOSH Ratings
The first part of the filter's classification uses the letters N, R, or P to indicate the filter's ability to function when exposed to petroleum.


 * "N" = not resistant to petroleum
 * "R" = somewhat resistant to petroleum
 * "P" = strongly resistant to petroleum

The second part lists the percentage of particles that the mask is certified to block (such as 95, 97 or 99 percent).

The most common is N95, which is recommended by the (CDC) for most cases of air contamination. These filters are designed to seal tightly around mouth and nose and are made of material certified to block 95% of particles 0.3 or larger in diameter, roughly the size of a single  and include.

They are however "... relatively difficult to breath through ...", and their full effectiveness also depends on a good fit – NIOSH recommends that each respirator wearer receive "... an initial fit test and annual fit tests thereafter".

Contrast with plain surgical mask
Plain are standard for staff in hospital operating rooms, and often recommended to the public as part of avoiding seasonal flu. They do not carry a NIOSH rating. They are designed to filter out relatively large particles, such as sputum droplets and hair – but the, , the , the , and the  all recommend these except in cases of "high risk".