Question

what is the main purpose of a respirator?
to keep air contaminants out of a persons respiratory system
to enable a person to breath in a vacuous atmosphere
to enable a person to respire efficiently
to provide oxygen in hazardous gas environments

Explanation:

A respirator is primarily designed to filter out air - borne contaminants like dust, chemicals, and pathogens to protect the respiratory system. It is not mainly for breathing in a vacuum (which requires a different type of equipment), enhancing normal respiration efficiency under normal conditions, or providing oxygen in all hazardous gas environments (some respirators are not oxygen - supplying).

Answer:

To keep air contaminants out of a person's respiratory system