278 WET SUITS 



It was important to avoid using any substances in the insulating material which would cause 

 toxicological effects. Such effects could be quite hazardous, as the diver's body is nearly com- 

 pletely covered by the material. The compounds used were screened for toxicological effects 

 by a company toxicologist prior to being used in the garments. 



Natural rubber is particularly susceptible to surface cracking due to ozone in the atmos- 

 phere. Such cracking originates when the rubber surface is strained either statically or dy- 

 namically. Static ozone-cracking is more severe and will usually continue, allowing the initial 

 small cracks to grow deeper and longer. In a relatively thin (15 mils) skin, such severe crack- 

 ing would result in gas and water leakage and render the insulating structure virtually useless. 

 Chemical additives are often used to minimize ozone-cracking but these are usually aromatic 

 amines which possess toxic characteristics. All known anti-ozonants are toxic to some degree. 

 However, it is possible to prolong the life of rubber by providing a nontoxic wax coating on the 

 surface which prevents ozone from attacking the rubber. Initial protection was provided by 

 brush-coating the rubber parts with wax. In addition, wax was included in the liquid latex com- 

 pound. Long-term protection is provided when the wax in the compound blooms to the surface. 



Finally, with regard to ozone cracking, the problem is made severe by forming curved sur- 

 faces from flat laminate materials. The outer surface is always under static tension, while the 

 inner surface is under static compression. The high-curvature folds on the outer surface of a 

 garment so constructed are particularly susceptible to ozone attack. 



A layer of stretch nylon was added to the inner side of the insulating laminate to enhance 

 the ease of donning and doffing the suit. This procedure has become rather standard in wet- 

 suit construction, and it eliminates the need for talcing. The nylon lining must be fabricated 

 into the laminate so that it will not cause abrasion of the diver's skin. 



To summarize the insulating- mate rial structure, starting with the inner side, against the 

 diver's skin, we have a layer of stretch nylon, a thin rubber skin, a one-quarter-inch-thick 

 layer of latex foam, and an outer thin rubber skin„ 



The insulating material is subject to volume changes upon changing sea-water pressure, if 

 the garment is sealed to confine the gas in the foam. A decrease in ambient pressure would 

 cause expansion of the gas, with a resulting stress on the laminate material. Continued expan- 

 sion of the material can result in stresses of sufficient magnitude to cause delamination, a con- 

 dition which would seriously alter a diver's buoyancy. The mechanics of delamination depend 

 upon geometry and constraints as well as the tensile strength of the latex foam and the inter- 

 laminar strengths between layers. Finished suit parts were tested for delamination pressure, 

 which turned out to be nominally 3 psig differential. The limiting factor was the strength of the 

 latex foam, rather than the bond between layers of material. 



Increased ambient pressure causes a decrease in volume of the insulating material. Figure 

 107 shows the decrease of the open-cell latex insulating material with percent increase of ab- 

 solute external pressure. Buoyancy and thermal insulation experience changes with varying 

 volume. 



Relief of overpressure can be realized through use of appropriate valving in a diver's suit 

 constructed of such material. Such valving was anticipated early in the program but was aban- 

 doned at the suggestion of the government. The point of view was that it would not be necessary 

 so long as the Sealab n aquanauts remained within the change in pressure limits which were 

 physiologically safe for saturation-diving excursions. 



Insulating Gases— The thermal conductivity of an open-cell laminate depends upon the filling 

 gas within the cell pores as well as the volume fractions of material and cell spaces. Various 

 filling gases were considered for use during Sealab H, but the final choice, made in the field, 

 was to use the habitat atmosphere having a high helium content. The criteria for selecting a 

 gas to maintain the equilibrium volume of the insulating material and to enhance its thermal 

 characteristics are size and weight of the stored compressed gas, its thermal properties, and, 

 in the event the suit is worn in a submersible chamber, the physiological effects of the gas in 

 an elevated pressure environment. Table 32 lists the thermal-conductivity values of various 

 gases. 



