284 



WET SUITS 



limit. The sealed battery also presents an explosion hazard should a hot short occur within the 

 cell. However, hot shorts can be predicted through proper maintenance procedures. The 

 pressure-housing approach was ruled out mainly because the apparent weight concentrated on 

 the swimmer's back could render him hydro statically unstable. Also ruled out was the approach 

 of filling the upper part of the individual cells with insulating oil, because the oil would find its 

 way between the plates whenever the diver inverted himself. 



The design of the silver-zinc cells will be discussed in the section of this chapter titled 

 "Battery Pack and Power Control." 



Heat-Release Material 



Heat- release material research was oriented toward those materials which derive power 

 electrically. The principal candidates were metallic resistance wires, carbon yarn and cloth, 

 and electrically conducting rubber. Despite some disadvantages, resistance wires were se- 

 lected as the near-future solution. All heat-release materials investigated will be discussed. 



The main factors to consider in selection of heat- release materials for a diver's suit are 

 as follows: flexibility of the material configuration to maintain mobility of the diver, preven- 

 tion of hot-spotting and shock hazards, compatibility with the insulating materials, appropriate 

 power distribution at relatively low voltage, adequate fatigue resistance, minimal fabrication 

 effort, availability of materials, constancy of heat release with static pressure, and ease of 

 attaching feed wires and underwater electrical connectors. 



Heat Power Requirements— The maximum power level required of the heating system is 

 about 350 watts. This level is based on experimental data obtained on NMRI subjects sitting 

 motionless in a wet pot while wearing 1/4-in. -thick unicellular neoprene wet suits in 40° F 

 water. The distribution of the total power is given in Table 39 [13]. 



Table 39 

 HEAT POWER DISTRIBUTION 



The data in Table 39 are based on subjects breathing compressed air; there were no data 

 available on subjects breathing helium-oxygen mixtures. 



An average man with a skin surface area of 1.8 square meters was considered for the cal- 

 culations of heat release per unit area. The body-region areas [14] were corrected to allow 

 for the hood opening of the suit and for heating the hands and feet from the dorsal sides only. 

 Beckman found that dorsal heating to the hands and feet is adequate and that subjects could not 

 tell whether their extremities were heated from one side only or from all sides. The results 

 are given in Table 40. The resistance required for each body area is also given based on a 

 12-volt supply, with the various body-region heaters connected in parallel. 



Electrically Conducting Rubber— Electrically conducting rubber was studied as a possible 

 heat-release material. Resistivity of electrically conducting rubbers is a fvmction of carbon 



