How an SCBA operates: The major components of an SCBA include a cylinder, pressure reducer, backframe, and facemask. Cylinders come in a variety of durations and pressure ratings from 2216 psi or 4500 psi. The cylinder is mounted on the backframe and a high-pressure hose attaches from the cylinder to the pressure reducer. The cylinder air enters the pressure reducer and reduces cylinder pressure to approximate 100 psi. That air goes through a hose to the pressure reducer in the facemask. The facemask has a secondary pressure reducer that reduces the air pressure to a breathable pressure. The air pressure inside the facemask stays positive, meaning if there is a leak inside the facemask, the air will flow outward, not allowing any outside contaminants into the facemask. As the user inhales, a valve opens to deliver air at the exact amount the user demands. This is done by monitoring pressure inside the facemask constantly and detects minor pressure changes and delivers air to keep these changes constant. When a user starts to exhale, pressure starts to build inside the facemask and stops the flow of incoming air. When the pressure is decreased as the user starts to inhale, the valve opens delivering air again to the facemask. This allows the user to breath normally with no undo stress.