The purpose of air-purifying respirators (APRs) is to filter out particulates or absorb small toxic vapors, which is what makes option C the correct choice. APRs are designed to clean the air inhaled by the user by using filters that capture harmful airborne contaminants. This capability is essential in various settings where individuals may be exposed to smoke, dust, chemicals, or other hazardous materials.
In contrast, the other options do not accurately represent the function of APRs. For instance, APRs do not supply fresh oxygen; they rely on the ambient air available in the environment. They also do not create an oxygen-rich environment, as they cannot increase or enhance oxygen levels. Additionally, while APRs filter air, they do not handle large volumes as a primary function; rather, they focus on filtering specific pollutants and particulates efficiently. Hence, the defining characteristic of APRs is their ability to protect the user by filtering contaminants from the air they breathe.