through a baralyme or sodalime canister which 
absorbs the carbon dioxide, recycling most of the 
exhaled gas for rebreathing. Semiclosed rigs are 
simpler than closed-circuit, mixed-gas rigs, but the 
improved gas economy (duration) of the closed- 
circuit rig compels its consideration in the future. 
Closed-circuit pure oxygen rigs are very simple; 
however, human physiological reaction to oxygen 
restricts their use generally to depths of 25 feet for 
one hour. Unless there is a basic breakthrough in 
diving medicine, closed-circuit pure oxygen rigs 
will find little application. 
The closed-circuit, mixed-gas rig offers the same 
gas economy as the closed-circuit, pure-oxygen rig 
(Figures 17 and 18). However, the consumption of 
oxygen in the mixture varies with work rate and 
depth, and addition of oxygen must reflect such 
changes. This requires precise sensors and control 
devices that increase cost and complexity while 
degrading reliability. 
Some of the most advanced rigs employ either 
polarographic or fuel cell oxygen sensors. Control 
of partial pressure of oxygen through cryogenic 
technology has been demonstrated. 
Because of the narcotic properties of nitrogen 
in compressed air and the very high air consump- 
tion rates, open-circuit sport scuba rigs and the 
WRIST METER 
P07855 | 
Figure 17. Closed-circuit, mixed-gas breathing 
rig (front view). (Westinghouse photo) 
AMPLIFIER 
INERT=GAS 
C05 BOTTLE 
< 
CANNISTER 
SENSOR 
OXYGEN 
REGULATO 
BOTTLE SULATOR 
SELECTOR 
VALVE 
EMERGENCY 
VALVE 
INERT-GAS 
BOTTLE 
Figure 18. Closed-circuit, mixed-gas breathing 
rig (back view). (Westinghouse photo) 
standard hard hat air rigs have little place in 
saturation diving. 
(2.) Protective Clothing Diving often involves 
exposure to cold water, making protective clothing 
essential. Even water that feels warm can result in 
important heat loss if an exposure suit is not worn. 
Notwithstanding the many advances in diving 
technology, much commercial diving still is done 
with the heavy rubber and canvas dress associated 
with hard hat diving invented by Augustus Beebe 
in 1837 (Figure 19). 
A recent notable departure has been the metal 
suits having rigid subsections with movable joints. 
These are one-atmosphere suits; whereas, the hard 
hat suits expose the diver to ambient pressure. The 
latest is a development from a space suit. Because 
of the complex geometry of the human anatomy, 
the joints are very difficult to make. To be useful, 
the joints must be flexed easily while an effective 
seal at pressures of several hundred pounds per 
square inch is maintained. 
In the last 25 years, close-fitting, pliable rubber 
and neoprene suits have been developed for free 
swimming divers. These fall into two main cate- 
