Rebreather

The rebreather emerged in 1878 when Henry Fleuss developed a self-contained breathing apparatus that recycled exhaled air by scrubbing carbon dioxide with caustic potash and replenishing oxygen from a compressed reservoir. This solved the fundamental problem of underwater breathing: humans consume oxygen and produce CO2, but carrying enough compressed air for extended dives is impractical. Rebreathers extend dive time by reusing the 75% of oxygen in each breath that the body doesn't absorb.

What had to exist first? Understanding that CO2 removal, not oxygen depletion, limits breath-holding—too much CO2 triggers the breathing reflex before oxygen runs out. Chemical scrubbers (calcium hydroxide, later soda lime) capable of absorbing CO2. Compressed oxygen storage in portable containers. Watertight construction preventing seawater contamination. And critically, applications where extended underwater time justified the complexity.

Fleuss's rebreather was designed for underwater rescue and salvage, not recreation. Coal mines flooded regularly; divers needed to navigate submerged tunnels to rescue trapped miners. Conventional surface-supplied air required hoses that snagged on obstacles. Self-contained rebreathers gave divers mobility. Fleuss personally tested his apparatus in a flooded tunnel, staying underwater for an hour—proving the concept.

Military applications drove development. Submarines needed escape systems for crew if the vessel sank. Combat divers needed stealth—rebreathers produce no bubbles, unlike open-circuit scuba that vents exhaled air. By World War II, rebreathers enabled covert underwater infiltration. The British used them for harbor sabotage; the Italians for attacking Allied ships. Silence was tactical advantage.

The rebreather exhibited path dependence that delayed recreational adoption. Open-circuit scuba, invented by Jacques Cousteau in 1943, was simpler, safer, and cheaper. It vented exhaled air after one use, wasting oxygen but eliminating CO2 scrubber complexity. For recreational diving, open-circuit was adequate—most dives last under an hour at depths where compressed air suffices. Rebreathers' efficiency advantage didn't justify their risk.

Modern rebreathers use electronic sensors to monitor oxygen partial pressure and inject gas precisely. This eliminates the manual oxygen addition that made early rebreathers prone to hyperoxia (too much O2) or hypoxia (too little). Electronic closed-circuit rebreathers extend dive times to 3-6 hours on a fraction of the gas open-circuit requires.

Today, rebreathers dominate technical diving—caves, deep wrecks, extended bottom time. Military uses persist for covert operations. Scientific diving employs them to avoid disturbing marine life with bubbles. But recreational diving remains overwhelmingly open-circuit because path dependence through training infrastructure, equipment familiarity, and risk tolerance makes rebreathers a niche tool.

The rebreather reveals how efficiency alone doesn't determine adoption. Open-circuit scuba wastes 75% of oxygen but succeeds because simplicity matters more than efficiency for most users. Rebreathers optimize the wrong variable for recreational markets but the right variable for technical and military applications. The conditions created the technology; the applications selected which version survived where.