Having studied the necessary physiology and chemistry in his spare time, Fleuss concluded that if the diver carried with him a supply of compressed oxygen and a means of chemically absorbing carbon dioxide, then he could remain completely independent of the surface. In 1878 he left the P&O and set about building his first self-contained diving apparatus. He proved to be both resourceful and innovative, building much of the apparatus himself, including a means of generating and compressing oxygen.
Fleuss had no previous experience of diving yet fearlessly tested his invention himself, attracting widespread interest through public demonstrations. A second, much improved model proved its worth in the flooded Severn Tunnel. Although there was considerable publicity for Fleuss and his apparatus, its significant potential as a means of rescuing trapped miners diverted attention away from its diving applications.
Fleuss collaborated with Robert Davis at the Siebe Gorman Company and developed the self-contained diving apparatus further. The Davis Submarine Escape Apparatus was a neat and compact derivative of the Fleuss apparatus and it also found use as a shallow diving apparatus, paving the way for the Frogmen and Human Torpedo riders of World War II.
Henry Fleuss was an habitual inventor, turning his mind to solving many diverse problems. He went on to produce the first practical tubeless tyres, the highly efficient Gerryck vacuum pumps, a steam car and more besides. However, it is for his pioneering work in developing the first practical closed-circuit breathing apparatus for mine rescue and diving that he will always be remembered. He died in 1932.