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CHAPTER 1 — History of Diving 1-17 The first experiments showed no detrimental effects on test animals or humans from breathing a helium-oxygen mixture, and decompression time was shortened. The principal physiological effects noted by divers using helium-oxygen were: n Increased sensation of cold caused by the high thermal conductivity of helium n The high-pitched distortion or “Donald Duck” effect on human speech that resulted from the acoustic properties and reduced density of the gas These experiments clearly showed that helium-oxygen mixtures offered great advantages over air for deep dives. They laid the foundation for developing the reliable decompression tables and specialized apparatus, which are the corner - stones of modern deep diving technology. In 1937, at the Experimental Diving Unit research facility, a diver wearing a deep- sea diving dress with a helium-oxygen breathing supply was compressed in a chamber to a simulated depth of 500 feet. The diver was not told the depth and when asked to make an estimate of the depth, the diver reported that it felt as if he were at 100 feet. During decompression at the 300-foot mark, the breathing mixture was switched to air and the diver was troubled immediately by nitrogen narcosis. The first practical test of helium-oxygen came in 1939, when the submarine USS Squalus was salvaged from a depth of 243 fsw. In that year, the Navy issued decompression tables for surface-supplied helium-oxygen diving. Figure 1-14. Helium-Oxygen Diving Manifold.

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