Dust masks, also known as filtering facepiece respirators, are used in environments where airborne particles such as dirt, dust generated from wood, drywall, insulation and other materials, and bioaerosols are present. They protect the wearer’s lungs and airways from damage caused by the inhalation of these fine particles. Dust masks have limitations and are appropriate only under specific use conditions.
Description - A dust mask is a negative pressure, particulate respirator containing a filtering medium as part or all of the facepiece. Negative pressure means that air flow through the filter occurs when the wearer inhales. Unlike other types of respirators, the paper or fabric filtering medium is the mask itself. It can be cup-shaped or folded, and is typically used when atmospheric contamination is less than 10 times the permissible exposure limit. It may contain an exhale valve that allows heat and humidity to escape the confines of the mask. A dust mask is designed to be disposable and should not be reused.
Types - Dust mask types are described using both a letter designation and a filtering efficiency. The letters N, R and P indicate the mask's resistance to oil degradation. The absence of oil particles in the work environment allows use of N-, R-, or P-series dust masks. The presence of oil particles, such as cutting fluids, glycerin and lubricants, requires use of an R- or P-series filter. Filtering efficiency is expressed as percentages of 95, 99, or 99.97. A mask with a 99.97 percent efficiency rating allows less particle leakage than one rated 95 percent. The amount of acceptable filter leakage determines face mask selection.
Limitations - Dust masks are inappropriate for use in environments containing gases, vapors, asbestos, arsenic, cadmium, 4,4'-ethylene dianiline and lead, nor do they provide adequate protection during sandblasting. N-series masks are not suitable for environments containing oil aerosols. Although R-series respirators resist oil degradation, their use is limited to 8 hours or one shift. P-series masks may be used in atmospheres containing oil for time periods specified by the manufacturer. Since dust masks do not supply oxygen or protect the eyes and skin, they should not be used in oxygen-deficient areas or as a sole sources of protection in environments containing eye or skin irritants.
Special Considerations - Dust masks used by health-care workers are commonly called surgical masks. It is important that medical professionals understand the difference between a surgical mask and a surgical respirator. A surgical mask traps respiratory secretions and protects the wearer from blood and bodily fluid splashes. It is not NIOSH-certified and, unlike an N-series 95 percent efficient surgical respirator, does not prevent inhalation of airborne contaminants such as bacteria and viruses.