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Respirators come in a wide variety of types, shapes, and sizes. The specific type required for adequate protection depends on the type of hazardous substance in the work environment and the type of work being performed. To select the correct respirator, it is important to recognize your hazard and make sure the respirator is certified for the intended use.

This information and determination is performed by the employer in accordance with the American National Standards Institute, known as ANSI, Practices for Respiratory Protection Z88.2-2015. Some OSHA substance-specific standards include more detailed information and requirements for respirator selection. Otherwise, when an employee is wearing a respirator, the maximum use concentration of a hazardous substance they can expect to be protected from is determined by the assigned protection factor or class of respirators and the exposure limit of the hazardous substance. The assigned protection factor is the level of respiratory protection that a respirator or class of respirators is expected to provide to employees when the employer implements a continuing, effective respiratory protection program. It is important to select a respirator that maintains exposure to the hazardous substance, when measured outside the respirator, at or below the maximum use concentration.

There are two basic categories of respirators: air purifying and air supplied. The most common type of respirator is the air purifying type. As the name indicates, an air purifying respirator cleans or removes an airborne contaminant as it passes through a purifying element of the respirator, such as a mechanical filter or a chemical cartridge. Air purifying respirators do not supply fresh air, and therefore, must never be used in a potentially oxygen-deficient environment.

Air supplying respirators provide breathable air from a reliable source such as a special compressor or tank. They do not filter contaminated air; rather, they supply clean air to the user that is separated from the contaminated environment.