LEEAMITe's Systems

    On the trip down to the ocean floor from the surface, the passengers in the submersible require adequate oxygen, removal of carbon dioxide and trace contaminants, and a comfortable temperature and humidity (factors also vital to the proper operation of submersible systems). As the round trip duration in the submarine is expected to be only a few hours, large amounts of water and provisions are not required for routine operations and human waste management need not exceed containers for temporary storage and disposal, like those currently used in submarines such as ALVIN and in other applications. Passengers and the pilot will bring "bag lunches" when a meal on board is necessary. However, should the submersible for any reason become separated from its surface support ship for an extended period, (a circumstance not likely to arise,) it will carry sufficient emergency provisions for 8 occupants for 3 days, and sufficient water for 5 days.

Atmosphere

    The passenger compartments of the submersible will be maintained at 1 atmosphere for the duration of the trip, in an atmosphere equivalent to that on the surface (.7 atm nitrogen, .2 atm oxygen, .1 atm other). Commercially available instruments will monitor the composition, temperature, pressure, and humidity of the cabin.

Oxygen

    pressurized oxygen storage tanks will provide the necessary oxygen for human respiration. The ship will store enough oxygen, in two or more tanks, in reserve for 10 hours, which, for 8 passengers, is approximately 3*10^3 liters at 1 bar. Oxygen will be slowly bled off the tanks at a rate dependent upon the number of passengers. The pilot will be in primary control of the oxygen flow rate, but there will be a failsafe system which will increase oxygen flow should the partial pressure fall below .2 atm and will decrease flow if partial pressure of oxygen should rise above .3 atm.

Carbon Dioxide

    Lithium Hydroxide containing canisters, with enough canisters to operate for 10 hours, will remove the toxic gas carbon dioxide from the cabin atmosphere. Lithium hydroxide has the advantages of high absorptive density and ability to continue to function even at low temperatures, unlike other substances such as Barylime, which may fail if cabin temperature drops too far. Although the passenger compartments will be regulated for temperature, it would be unacceptable for the carbon dioxide scrubbers to cease functioning if the temperature regulation fails. Lithium hydroxide works much in the same way as most chemical scrubbers, by taking advantage of carbon dioxide's acidic nature and neutralizing it with a strong base as air flows through. Additional air circulation mechanisms and canisters would automatically be brought online if the partial pressure of carbon dioxide rose above 0.005 atm.

Trace Contaminants

    Lithium hydroxide also serves to remove trace contaminants from the atmosphere, but activated charcoal air filters would also be used for this purpose. Trace contaminants can be created by the body, by electric equipment, or may be present in surface air.

Temperature

    Heat in the submersible will be released by passengers, by electric equipment and by the exothermic reactions involved in carbon dioxide removal. Heat is also lost to the water and to the expansion of oxygen gas. Without heaters of some sort, the submersible would quickly become too cold to be comfortable in the subsurface waters. For that reason, electric heaters will be included on the vehicle. Passengers will also be advised to dress in layers, including very light clothing for launch in the tropical surface atmosphere, and heavier clothing for the cooler trip to the bottom, as the submersible will be unable to maintain a normal room temperature for the entire trip due to power constraints.

Humidity

    Excessive humidity can cause condensation, interfere with equipment, slow carbon dioxide scrubbing reactions, and cause an uncomfortable environment for the passengers. Relative humidity on the surface in the area of the vent system is likely to be high, and will rise as the air cools, and water vapor is also produced by passengers during respiration. Humidity in the sub will be controlled by silica gel, a commercial desiccant. Additional air circulation over the desiccant will be activated should the relative humidity rise above 95 percent.

References

1. Anthony, T.G. "Improved Methods of Absorbing Carbon Dioxide". International conference Divetech '81, vol. 2, pg 24-26 nov, 1981.
2. Busby, Frank. Manned Submersibles. Office of the Oceanographer: Annapolis, 1976.