80 DESIGN, CONSTRUCTION, AND OUTFITTING 



The deck is made of poured concrete two feet in depth and comprises a portion of the per- 

 manent ballast. The deck and overhead ballast tanks reduce the usuable internal volume and 

 consequently the amount of helium needed to fill the atmosphere, an important economic con- 

 sideration (Fig. 47). 



This usable internal volume, 7 ft in height, is divided into four separate areas (Fig. 48). 

 The aftermost area is the entry and contains two tub-showers to aid in regaining body heat 

 after a sortie in 50°F water, as well as stowage for wet-suits and breathing apparatus. 



The next area forward is the laboratory, separated from the entry by a 3-1/2-ft watertight 

 dutch door which gives an extra margin of safety if the water level should rise in the entry 

 trunk into Sealab itself. The laboratory contains counter and stowage space, a sink, a cable 

 trunk, instrumentation racks, the communications center, and the fan room, heart of the venti- 

 lation system. 



Next forward is the galley area, containing stowage and counter space, an electric range, 

 a refrigerator -freezer, wash basin and water closet, and the main power transformer enclosure 

 and distribution panels. 



Finally, forward most is the berthing area with ten bunks, a dropleaf table, locker and 

 stowage space. Access to the emergency exit hatch is through a removable cover in the deck. 



Mechanical/Electrical 



Ventilation System-The system consists of a central fan room with a 250 cfm capacity, 

 recirculating centrifugal fan, discharging through ducting to the berthing, galley, laboratory, 

 and entry areas. Return atmosphere is drawn into the fan room as follows: 



60 cfm directly through a LiOH CO2 scrubber, with the remaining 190 cfm by-passing the 

 scrubber through a duct in the water closet bulkhead. The combined 250 cfm is passed through 

 an activated charcoal filter, where noxious hydrocarbons are removed, and thence to the fan 

 inlet. Bracket fans are utilized to aid circulation. The pitch on the fan blades and the impeller 

 configuration are modified to allow for the increased density of the atmosphere as well as its 

 increased pressure. 



Atmosphere Control -The atmosphere in Sealab II is comprised of 80% He, 15% Nj and 5% O2 

 by volume at the proper pressure, i.e., hydrostatic pressure at the depth of the air -atmosphere 

 interface. Initial pressurization is at the surface and consists of two parts, initially with air 

 to give approximately the proper amount of O2 and then with helium to reach final pressure 

 and mixture composition. Care must be taken to avoid overpressurization of the internal bal- 

 last tanks. They must either be properly equalized or completely filled with water. 



There are two gas lines in the umbilical cord, a gas supply line to provide make-up helium 

 and a gas sampling line to provide continuous atmosphere monitoring for analysis and also to 

 provide an alternate means of oxygen make-up. 



Primary oxygen and helium make-up are from the gas bottles stowed externally. The 

 oxygen bottles are manifolded dually to a pressure regulator inside Sealab which automatically 

 replenishes oxygen to the atmosphere, responding to a specially designed sensor (Krasberg). 

 The helium bottles are piped into a manual regulator. All gas supply, make-up, and sampling 

 valves and fittings are centrally located inside Sealab n on a single gas control panel. 



Three external bottles are filled with a premixed supply of 95% He and 5% O2 piped into a 

 regulator on the gas control panel which supplies eight, four outlet manifolds to which standard 

 Scuba regulator -mouthpiece units can be plugged. This comprises the emergency breathing 

 system, (Bibb System), and is used in case of severe atmosphere contamination. 



In the overhead of the entry area four supply compressors and four vacuum pumps are 

 installed. Their function is to supply Sealab atmosphere through an external hose to the breath- 

 ing gear of a swimmer on sortie and return exhaled gases back to Sealab. This is called an 



