water will become the most critical factor; 

 where the temperature is low, food will be- 

 come critical. As mentioned, storage of food is 

 easy and requires little space; water, on the 

 other hand, requires much more volume and 

 can become nonpotable. Whereas both food 

 and water are required, a compromise solu- 

 tion might be found in one of the diet supple- 

 ments (Metrecal, Nutriment, etc.) which pro- 

 vide both food and water. Such liquid supple- 

 ments require little space, they are nutritious 

 and have a long shelf life. Regardless of the 

 liquid and solid sustenance supplied, it ap- 

 pears rather paradoxical to supply a 3- or 

 5-day supply of oxygen and carbon dioxide 

 remover when the occupants might well 

 perish from lack of food and water before 

 these critical components run out. 



Removal 



Certain products of human and non-human 

 origin must be removed from or stored 

 within the cabin environment. These are: 

 Carbon dioxide, trace contaminants and solid 

 and liquid human waste products. The re- 

 moval of the first two products is necessary 

 for survival. Other metabolic wastes are held 

 in sealed or chemical storage. Although gas- 

 eous by-products may become noxious, if not 

 properly stored, they are not necessarily 

 toxic. 



Carbon Dioxide: 



The major source of carbon dioxide in a 

 submersible is human respiration. According 

 to reference (2), an average consumption of 

 1.0 SCFH of oxygen per person will generate 

 an average of 0.80 to 0.85 SCFH of carbon 

 dioxide (depending on dietary considera- 

 tions), an equivalent of 0.1 pound/man-hour. 

 To derive the rate of carbon dioxide buildup, 

 the Respiratory Quotient (RQ) is required, 

 and it is equal to the volume of carbon diox- 

 ide produced for each volume of oxygen con- 

 sumed, or: 



RQ = 



Volume of CO, Produced 0.85 



Volume of O5 Consumed 



1 



0.85 



In a closed submersible, carbon dioxide will 

 increase in accordance with: 



where: T = Time in hours 



V/N = Floodable Volume per per- 

 son 

 RQ = Respiratory Quotient 

 0.03 = % of CO2 in "Clean" Air 



Using this formula and the "standard 

 man" in the 3-man submersible DOWB (140 

 ft^ floodable volume) the following buildup 

 could be expected on an 8-hour dive where 

 there is no carbon dioxide removal system: 



%C0, = 0.03 + 



(RQ) X O2 (Consumption rate) x T 



V^N 



(0.85) (1.0) (8) 



140 

 %C02 = 0.03 + 



%C02 = 0.18 



The U.S. Navy recommends that 0.014 at- 

 mosphere of partial pressure (1.5%) be the 

 exposure limit of carbon dioxide, while 0.02 

 atmosphere (2%) indicates a dire emergency. 

 ABS recommends a maximum of one percent 

 for long term exposure and MTS agrees with 

 this maximum, but notes that a maximum 

 carbon dioxide level of 0.5 percent should be 

 the design goal for 60- to 90-day missions. 



The effects of various carbon dioxide levels 

 on humans as a function of time is shown in 

 Figure 9.4. The bar graph to the right of this 

 figure is for exposure of 40 days and shows 

 that concentrations of carbon dioxide in air 

 of less than 0.5 ATA (atmospheres) (Zone A) 

 cause no biochemical or other effects, con- 

 centrations between 0.5 and 3.0 percent 

 (Zone B) cause adaptive biochemical 

 changes, which may be considered a mild 

 physiological strain, and concentrations 

 above 3.0 percent (Zone C) cause pathological 

 changes in basic physiological functions. For 

 normal operations, the Navy recommends 

 that carbon dioxide removal rates should be 

 provided that result in carbon dioxide partial 

 pressures corresponding to Zones I and II for 

 short-term exposures, and to Zones A and B 

 for long-term exposures. 



It is obvious, therefore, that a means 

 should be available to reduce excess carbon 

 dioxide or control it at a level where it will 

 not affect the occupant's judgement or physi- 

 cal abilities on a routine dive — and especially 

 if the vehicle may be unable to surface or 

 open the hatch. 



In order of decreasing usage, four chemical 

 substances are used to remove carbon diox- 



419 



