68 THE NAVY OCEAN ENGINEERING PROGRAM 



In an effort to solve the problems involved with breathing compressed 

 air in deep-sea diving, in 1924 the Navy and the Bureau of Mines con- 

 ducted joint experiments with subjects breathing helium-oxygen mixtures 

 under pressure. Animals were used in the early experiments, and by 1927 

 the work had progressed to the point where human subjects could be used. 

 The Navy continued experiments with heHum-oxygen gas mixtures for deep- 

 sea diving. In 1937, using a helium-oxygen mix, two Navy divers reached 

 a simulated depth of 500 ft in one of the tanks at the Navy Experimental 

 Diving Unit. 



These dry land experiments were put to operational use in May of 1939 

 when the U. S. submarine SQUALUS sank in 243 ft of water off the New 

 England coast. Initial dives at the disaster scene were made with com- 

 pressed air, but most of the 640 dives employed helium-oxygen mixtures. 

 There was not a single death or serious injury suffered during this inten- 

 sive deep-sea diving operation. The new technique was proved far superior 

 to compressed air breathing. On the basis of data obtained during the 

 SQUALUS dives the U. S. Navy estabhshed 380 ft as the new limit for 

 operational diving with the time limit of 30 minutes on bottom. Without 

 complications, a dive of this depth and duration requires more than three 

 hours decompression, an unfavorable ratio of working time to decompres- 

 sion time of 1 to 6. 



This unfavorable ratio of bottom time to decompression time has been 

 overcome with a technique known as "saturation diving." In saturation 

 diving the diver is provided a fixed capsule on the sea floor or a personnel 

 transfer capsule which transports him to the deck decompression chamber 

 of a ship. The capsule is pressurized to the outside water pressure and pro- 

 vided with a suitable breathing gas mixture. After about 24 hours of expo- 

 sure under pressure, all tissues of the diver's body have a gas saturation 

 equivalent to the surrounding atmosphere, and the diver is considered to 

 be "saturated." Once he has been saturated, the diver's requirements for 

 decompression are based on depth rather than duration of the dive. A 

 diver saturated to 300 ft requires the same decompression time (approxi- 

 mately IVi days) whether his bottom time is one day or one month. 

 After hours of useful work at depth, he returns to the safety and comfort 

 of the underwater habitat or ship decompression chamber. Since there is 

 no appreciable difference between the pressure of the habitat and that of 

 the outside water, there is no requirement for decompression of a man 

 entering the undersea chamber. Rather, decompression of the saturated 

 diver for his total time spent at depth is accomplished in a single step when 



