SCBA Breathing Apparatus

Overview

A self-contained breathing apparatus supplies a firefighter with clean breathing air independent of the surrounding atmosphere, protecting against smoke, toxic gases and oxygen-deficient environments. This is an open-circuit, positive-pressure SCBA: a high-pressure cylinder of compressed air is reduced in stages and delivered on demand to a sealed full-face mask, held always slightly above ambient pressure so any leak pushes outward rather than letting contaminated air in. Built to NFPA 1981, it integrates a distress alarm and an in-mask display so the wearer and rescuers can monitor air supply and motion.

Air is stored in the Air Cylinder, a carbon-fiber-wrapped composite bottle charged to 4500 psi with a burst disc for overpressure relief. The whole unit rides on the Backframe & Harness. The First-Stage Pressure Reducer drops cylinder pressure to a stable medium-pressure supply, and the Second-Stage Demand Valve releases air only on inhalation into the Facepiece Mask, which seals to the face and carries the voice amplifier and HUD. The PASS Distress Alarm is a motion-and-pressure alarm that sounds if the wearer stops moving, and the RIC/UAC Rescue Connection lets a rescue crew refill the cylinder from another unit.

How it works

Opening the cylinder valve admits air at 4500 psi to the first-stage reducer, where a balanced piston referenced against a spring holds the downstream supply at roughly 100 psi regardless of falling bottle pressure. That medium-pressure air travels through a hose to the second-stage demand valve mounted on the mask. When the firefighter inhales, the pressure drop deflects a sensing diaphragm that opens the valve and admits air; a spring biases the diaphragm so the mask stays slightly positive even between breaths. Exhaled air leaves through a one-way exhalation valve. The PASS device watches a MEMS motion sensor and triggers a 95 dB distress alarm after about thirty seconds of inactivity, and a mechanical whistle plus the HUD warn the wearer when the cylinder falls to roughly one-third remaining.