WET SUITS 277 



2. Utilizing the body's own thermal protective mechanisnas to maximum advantage 



3. Use of adequate external body insulation to limit heat loss 



4. Use of supplementary body heating to replace the heat loss. 



Control of the exposure duration imposes a serious limitation on the useful work time of 

 both military and commercial divers. This approach is impractical and, in some cases, im- 

 possible. The second factor, utilizing the body's own thermal protective mechanisms to max- 

 imum advantage, can contribute relatively little to the thermal-balance problem. Cold-water 

 tolerance by training and/or conditioning has only limited value. 



External insulation and supplemental heating are the only two body-heat-loss factors con- 

 sidered [l]. Insulation alone cannot satisfy the thermal requirements, because of the adverse 

 geometries of the hands and feet. It is necessary to replace body heat to provide thermal sta- 

 bility for immersed subjects. On the other hand, supplemental heating alone is not the answer, 

 because of the severe power requirements it would impose on a portable power pack. A com- 

 bination of effective insulation and supplemental heating of critical areas is a logical engineer- 

 ing approach to cold-water thermal protection. 



For the interest of the reader, the reports by Beckman, et al. [l, 2, 3] include detailed in- 

 formation about the physiological processes and problems, references to thermal protection 

 for Arctic troops and for aviators, a summary of power-source and heat release methods and 

 hardware, and a list of 21 references. 



Delimitation of Technological Research 



The accelerated-program schedule dictated that applied research be limited to short-term 

 work. Studies carried out inhouse prior to the contract award made it possible to select re- 

 search tasks on the basis of maximum probability of near-future results. Of the numerous ap- 

 proaches to thermal protection, the electrically heated pressure-compensated wet suit was 

 selected as the best candidate for rapid development. This approach was specified in the con- 

 tract. Power efficiency of the self-contained power source was a major criterion in determin- 

 ing the heating system. Another major criterion was the need to perform only minor develop- 

 ment to off-the-shelf hardware for the integration of components. Power efficiency and hardware 

 availability indicated the use of silver-zinc batteries, resistance wires for heating, commer- 

 cially available gas and underwater electrical fittings, and an insulating sandwich material 

 which had already been developed to an advanced degree by U.S. Rubber Company. 



INSULATING MATERIAL 



The need to provide constant buoyancy and thermal insulation regardless of the depth in- 

 dicated the use of an insulating material which would either be incompressible or capable of 

 being pressure-compensated. Both approaches were investigated. Foremost among the re- 

 quirements for the insulating material was low stretch modulus, to provide adequate diver mo- 

 bility in a form-fitting wet suit. 



Pressure-Compensated Insulation— Open-cell foamed elastomers were reviewed as candi- 

 dates for a pressure-compensated insulating material. Natural rubber latex foam was chosen 

 above all others for its low modulus of elongation, high rebound, low compression set, small 

 and uniform pore size, behavior at near-freezing sea-water temperatures, and relative ease of 

 fabrication into a laminate. Relatively thin elastometric skins on both sides of the foam layer 

 were required to serve as water-impermeable membranes. 



The skin material research included natural rubber, neoprene, and butyl latices. Despite 

 the severity of ozone -cracking, natural rubber latex was chosen for the same reasons (except 

 pore size, of course) as given above for the selection of natural rubber latex foam. The skin 

 material was formed by latex-dipping methods and was applied to the latex foam. 



