Protects against gases, vapours, and acid gas. When the wearer inhales, the contaminated air enters and flows through the cartridges, it removes the contaminants from the air stream and allowing the wearer to breathe in clean, fresh air. MSA Comfo Classic, Ultra-Twin, Ultra Elite Twin, and Duo-Twin reusable respirators are compatible with these filters and cartridges. To filter out airborne contaminants, NIOSH-rated particulate filters and vapour cartridges are installed in reusable half-mask or full-face respirators. They are chosen based on the environment and the type of respiratory hazards to be filtered. They can be replaced if they become dirty or if the type of contaminant changes.