Self-contained breathing apparatus (SCBA) provides autonomous breathable air from high-pressure cylinders (2,200-5,500 psi) in oxygen-deficient, toxic, or smoke-filled environments like fires, industrial accidents, and chemical plants. Open-circuit SCBAs standard for firefighting feature a face mask, pressure regulator, harness, and air cylinder, delivering 30-60 minutes of air. Closed-circuit models recycle exhaled air for 1-4 hour durations using oxygen-generating chemicals. Key safety includes low-air alarms, HUD displays, and PASS devices. Used by firefighters, hazmat teams, and rescuers, ergonomic designs ensure mobility in IDLH atmospheres. Compliant with NIOSH/OSHA standards, SCBAs enable safe operations in confined spaces and emergencies worldwide.