Clearing the air on respirator ratings

I recently started to order some disposable dust masks to use in my shop and was a bit overwhelmed by all the choices. What do the different ratings mean and which one is best for woodworking?
—Guy Rule, Boise, Idaho

Before answering your question, Guy, let's make a distinction between the different types of dust masks and respirators. So-called "nuisance" dust masks are the inexpensive, loose-fitting masks often sold in bulk packs. While these may help prevent large dust particles from causing a sneezing or coughing fit, they aren't very effective at filtering out fine dust. Respirators, on the other hand, form a tight seal around your mouth and nose, filtering the air as you inhale and preventing that fine dust from entering your lungs where it can cause damage. Respirators are available as disposable, paper/cloth masks or as half- or full-face elastomeric masks with replaceable cartridges.

In order to help users select the proper respirator for the task at hand, the National Institute for Occupational Safety and Health (NIOSH) sets standards for respirators sold in the United States. Manufacturers label all NIOSH-approved respirators and cartridges with a letter/number designation based on the type of particles they filter and their efficiency. The three classes of respirators are N for non-resistant to oil, R for oil-resistant, and P for oil-proof. But the effectiveness rating matters most to woodworkers. A respirator with a rating of 95 filters out 95% of particles down to three microns in size. (For comparison, the average human hair measures approximately 70 microns in diameter.)

Disposable N95 respirators adequately protect your lungs from airborne sawdust and are a little more comfortable to wear than a full-face respirator. If you have lung issues or a health condition requiring added protection, choose an N99 or N100 respirator. When spraying oil-based paints or finishes, choose a half- or full-face respirator equipped with cartridges capable of filtering out organic vapors.

Keep in mind that any respirator works only if you wear it properly. Check for a good seal around your nose and mouth to prevent air from entering around the filter. And most important, remember to put it on before you fire up that tablesaw, sander, or spray gun.