This packaging, ivhile convenient in 

 size, is not suited to the severe han- 

 dling and storage in the marine envi^ 

 ronment. Five-gallon (40 lbs) plastic 

 sealed containers are available and 

 can be expected to give better quality 

 assurance, 



A check of the l^ational Oceano- 

 graphic Data Center records on the 1- 

 degree square in which this incident 

 took place produced the curve pro- 

 vided on Figure 9.5. It will be noted 

 that the lowest temperature to be ex- 

 pected in this area is about 59°F. At 

 this temperature, using Navy Diving 

 Operations Manual performance fig- 

 ures, the load (24 lbs) carried in the 

 diving chamber should have lasted for 

 21 hours. The forward chamber (16 

 lbs) should have lasted 20 hours, as- 

 suming 70°F in that sphere and good 

 baralyme. The variation in actual per- 

 formance from that predicted here is 

 not readily explainable but could 

 have been the result of defective bara- 

 lyme packaging, improper packing of 

 the cannister, or spreading by the 

 crew when the cannisters were emp- 

 tied, — probably a combination of 

 these. 



I feel we (the expert panel) should 

 consider the following recommenda- 

 tions for inclusion in the final report 

 relating to CO2 removal systems: 



a. Submersibles should carry at least 

 a 48-hour supply of absorbent (this is 

 consistent with ref. 1). 



b. Lithium hydroxide is to be pre- 

 ferred wherever low temperatures are 

 encountered. 



c. Only absorbents which are her- 

 metically sealed should be carried. 



d. Such seals must be periodically 

 checked. 



e. Uniform chemical packing is vital 

 and steps should be taken to insure 

 this for both pre-packaged cannisters 

 and those re-loaded on scene. 



f. A program to develop accurate 

 performance parameters for absorb- 

 ents under the full range of antici- 

 pated pressures and temperatures 

 should be undertaken and the results 



made available to the entire diving 

 community.'''' 



Enclosure 2 to Nicholson's summation and 

 recommendations discussed the effects of 

 temperature, humidity and absorbent bed- 

 configuration on carbon dioxide removal. 

 The following is extracted from that enclo- 

 sure: 



"The rate at which carbon dioxide is 

 absorbed in absorbents is influenced 

 by temperature, and is considerably 

 lower at 40°F than at 70°F. In some 

 scrubbers sized for adequate perfor- 

 mance at 70°F, absorbing capacity at 

 40°F may be as little as '/s that at 

 70°F. This effect is strongly dependent 

 upon the cannister design and the rate 

 of carbon dioxide absorption, being 

 most evident in absorbers working at 

 peak flow rates, and least evident in 

 oversized scrubbers and those used in- 

 termittently. 



It appears highly desirable to pro- 

 vide external insulation and heating 

 of scrubbers for use in cold water as a 

 means of minimizing size and assuring 

 that the design absorbent capacity can 

 be obtained. This is also advisable as 

 a means of avoiding moisture conden- 

 sation. A possible alternative is to 

 design for about three times the ab- 

 sorbent capacity needed at 70°F. 



The efficiency of absorbents is influ- 

 enced by relative humidity. The ab- 

 sorbing capacity quoted for Baralyme 

 and Soda Lime absorbents is obtained 

 only when relative humidity is above 

 70 percent. Lower humidity levels re- 

 sult in less absorbent capacity. 

 Breathing-gas humidity would usually 

 be well above 70 percent unless the 

 scrubber is preceded by a dehumidi- 

 fier. 



Under conditions of high gas humid- 

 ity and low scrubber surface tempera- 

 ture it is possible to condense water on 

 the cannister walls or in the absorb- 

 ent. This is undesirable because wet 

 absorbent is inactive and impervious 

 to air flow, reducing absorptive capac- 

 ity and increasing pressure drop 

 through the cannister. Scrubbers for 



422 



