at 100 ft., but also the effects of high N2 partial pressures in the production 

 of nitrogen narcosis at that depth were unknown. Both standard and emergency 

 decompression schedules for these missions, as well as ascent-descent 

 excursion limits, were accordingly devised after a limited amount of 

 experimentation at the J&J Marine Diving Co. under the supervision of 

 Mr. Peter Edel, (Pasadena, Tex.). It remained, however, for the actual open- 

 sea Minitat dives to prove the validity of the tables, and the 100-ft missions 

 were consequently of crucial interest in the medical program. 



Any undersea experiment involving prolonged hyberbaric exposure requires the 

 careful planning of decompression tables, both standard and emergency, that 

 are safe with respect to life and health, yet efficient with respect to time. 



Helium-oxygen mixtures had been used in earlier experimentation in saturation 

 diving (notably SeaLab I and II) at the same depth, or greater, as that of the 

 proposed 100-FSW Minitat habitat. Helium's assets lie in its lightness and its 

 minimal adverse effect on the human body. But He presents some unique problems 

 that render its use impractical for protracted pressure exposures. It is very 

 expensive; it is scarce in some areas, and is difficult to handle; body heat 

 is difficult to maintain in a helium-saturated atmosphere; and He distorts 

 speech, making vocal communications awkward--an important consideration in the 

 circumstance of men living in cramped, isolated quarters. 



The choice of nitrogen, then, as the inert-gas diluent in saturation diving 

 becomes an attractive and logical one, because it is a simple, inexpensive gas, 

 readily available, and physiologically normal. The experience of TEKTITE I 

 demonstrated that at reasonably shallow depths--i.e. , less than 50 FSW--N2 can 

 be safely used in prolonged hyperbaric exposures, and that it will not interfere 

 with work capability. It therefore became a primary goal of the Minitat missions 

 to prove that marine scientists can effectively and efficiently carry out 

 prolonged undersea research while living and working at 100 FSW in a habitat 

 with a 94.87o N2-5.27o O2 breathing mixture. 



Saturation Diving and Decompression Sickness 



When a diver remains for a given length of time at depth, of necessity he 

 breathes gas compressed to the pressure of the seawater around him in order 

 to inflate his lungs against the seawater pressure. Eventually--within 72 to 

 120 hours--the partial pressure of the inert gas (PI) in his tissues becomes 

 equilibrated or saturated to the higher molecular pressure of the same gas in 

 his breathing mixture; hence the term saturation diving. 



When the PI in the diver's tissues has reached certain maximum levels, he 

 cannot then ascend directly to surface pressure without incurring the risk of 

 decompression sickness or dysbarism. The symptoms relate primarily to the 

 respiratory, integumental, musculoskeletal, and central nervous systems. 

 Severity of such attacks quite naturally vary, depending on such circumstances 

 as the depth from which decompression has occurred and its rapidity, the gas 

 mixture used at depth and during decompression, and the individual's particular 

 or situational susceptibility. And the variance is wide--from vague, transitory 

 "niggles" in the joints to coma and death. 



IX-15 



