CHST Worksite Audit Practice Test 2026 - Free CHST Practice Questions and Study Guide

Breathing air is either purified from the environment or supplied from a separate source. Air-purifying respirators clean the ambient air the wearer inhales, using filters or cartridges to remove contaminants. A self-contained breathing apparatus, by contrast, carries its own air supply in a cylinder and does not filter or purify the surrounding air at all. Because it provides breathing air from within the device rather than purifying ambient air, it is not an air-purifying respirator. Gas masks purify ambient air with filters, airline respirators deliver clean air from a remote source, and abrasive blasting helmets are used with supplied air to ensure clean breathing air—each relies on a separate source of air rather than filtering the environment itself.