lated to time of exposure. For this reason 

 there are widely varying approaches con- 

 cerning what should be replenished, removed 

 or measured during a dive. On one end of the 

 spectrum is the K-250 series in which the 

 builder relies upon hourly surfacing to re- 

 fresh cabin air. On the other end is BEN 

 FRANKLIN which supplies virtually every 

 means to monitor and control cabin air and 

 store waste products. Both of these ap- 

 proaches are discussed more fully in a later 

 section; however, the majority of vehicles 

 fall somewhere between these two extremes. 



Replenishment 



Within this category are consumables 

 which the occupants require during submer- 

 gence to survive and perform their tasks. 

 The first of these, oxygen, is required during 

 any submergence longer than an hour or two 

 (depending on pressure hull volume); the sec- 

 ond, food and water, may or may not be 

 required on a routine dive of one or more 

 hours duration, but they are generally car- 

 ried. 



Oxygen: 



At atmospheric pressure, the recom- 

 mended oxygen concentration within a pres- 

 sure hull varies according to the following 

 sources: 



Marine Technology Society (1): 18-24% 



U.S. Navy Material Command (2): 17-23% 



American Bureau of 



Shipping (3): 



18.4-23.6% 



While there seems to be no clear dividing line 

 between a normal oxygen content and one 

 which represents an excessive fire hazard, 

 MTS and ABS both point out that 25 percent 

 concentration produces noticeable differ- 

 ences in combustible materials. The Navy, on 

 the other hand, clearly states that the sub- 

 mersible should immediately surface and 

 ventilate the hull whenever oxygen exceeds 

 25 percent. Conversely, as oxygen concentra- 

 tion (partial pressure) decreases, the effects 

 on occupants of the pressure hull are shown 

 in Table 9.3. 



According to the Standard Man's require- 

 ments, 0.9 cubic foot of oxygen per hour is 

 consumed. The MTS and ABS suggest speci- 

 fying oxygen storage duration on the basis of 

 1.0 cubic foot/hour of submergence. Because 

 of the small internal volume of present sub- 

 mersibles, a supply of oxygen is virtually a 

 universal requirement. All but two vehicles 

 carry compressed, gaseous oxygen in flasks 

 either inside or outside the pressure hull; K- 

 250 and BEN FRANKLIN are the two excep- 

 tions. The former carries no additional oxy- 

 gen other than what is in the cabin air, and 

 the latter carries liquid oxygen. 



The location of the oxygen storage flask 

 inside or outside the pressure hull is a trade- 

 off decision on shallow-diving vehicles. Ex- 

 ternal storage saves internal pressure hull 

 volume, reduces total vehicle submerged 

 weight and is somewhat easier to replenish. 

 Additionally, ABS requires that if the filled 

 oxygen storage system contains a volume of 



TABLE 9.3 EFFECTS OF VARIOUS OXYGEN CONCENTRATiONS [FROM REF. (2)] 



Oj Concentration 

 Partial Pressure Atmospheres 



Effect 



.21-0.18 

 0.16-.12 

 0.14-.10 



Normal sea-level conditions 



Increased breathing rate, lack of coordination 



Easily tired; easily upset emotionally; passible loss of pain or injury; abnormal fatigue from 

 exertion 



0.10-.06 



Lethargic; apathetic; confused thinking; physical collapse; possible unconsciousness, nausea and 

 vomiting 



0,06 or less 



Convulsive movements, gasping, cessation of breathing 



412 



