of high pressure air into the pressure hull. 

 This procedure would seem inadvisable un- 

 less the submersible can make a very rapid 

 ascent to the surface to relieve internal pres- 

 sure and avoid decompression sickness. Con- 

 versely, too-rapid an ascent might produce 

 an air embolism in the occupants. 



Fire 



The principal type of fire anticipated in a 

 submersible is an electrical fire. For this 

 reason, one or several dry chemical type 

 extinguishers are carried; these do not pro- 

 duce large quantities of toxic gasses or va- 

 pors and their effect is minimal on adjacent 

 equipment. When such extinguishers are em- 

 ployed the occupants, for additional safety, 

 are advised to don their emergency breath- 

 ing systems. 



Loss of Normal Life Support/Toxic 

 and Noxious Gasses 



In the event that a submersible's life sup- 

 port system fails, or expires, or gasses and 

 fumes evolve vi^hich are harmful to the occu- 

 pants, the response is the same in both 

 cases: Employ the emergency breathing de- 

 vices and surface as quickly as necessary. 

 There is, as can be expected, a gray area 

 between the time life support fails or noxious 

 gasses are detected and the decision is made 

 to don the emergency equipment. For exam- 

 ple, if the blower unit which forces cabin air 

 through a carbon dioxide removal system 

 fails, the submersible may be at a depth 

 where routine surfacing and retrieval can be 

 accomplished before the need of emergency 

 breathing arises. In an actual case, a buildup 

 of carbon monoxide was detected in BEN 

 FRANKLIN in the first stages of its 30-day 

 drift mission. Though carbon monoxide is a 

 potentially fatal gas in sufficient concentra- 

 tions and over a given time period, it was 

 decided that the trip could safely continue 

 until 50-ppm concentration was reached. The 

 decision was correct and allowed completion 

 of the mission with no immediate or long- 

 term effects on the submersible's occupants. 

 On the other hand, the decision may be in- 

 stantaneously made in the advent of fire, 

 which is the most likely, but not the only 

 source for the evolution of noxious or toxic 

 gasses. 



Owing to the availability of instruments to 

 monitor a life support system's performance, 

 its failure or inadequacy is relatively easy to 

 determine. Release of noxious or toxic gasses 

 is not easily measured because they may 

 come from a variety of different sources. For 

 example, when exposed to the atmosphere, 

 many of the following may lose solvents, 

 plasticizers and unpolymerized materials by 

 volatilization: 



Surface coatings 



Cords of synthetic or natural fibers 



Plastic films 



Molded and cast plastics 



Wire insulation 



Thermal insulation 



Adhesives 



Electronic encapsulation compounds 



Silicones and organic lubricants and 

 fluids 



Metallic dust and oxides 



Casting compounds 



Ozone-emitting electronic and electrical 

 equipment 



Tapes 

 A direct and visible source of contamina- 

 tion is from strip chart recorders (e.g., echo 

 sounders) that burn an imprint on a chemi- 

 cally treated paper to record data. The chem- 

 ical composition of the by-product's fumes 

 may be unattainable because the paper man- 

 ufacturer considers the recording paper's 

 composition proprietary. 



A variety of emergency breathing systems 

 are used in submersibles, but they basically 

 fall into two categories: Open circuit and 

 closed circuit. 



Open-Circuit Breathing: 



These systems are termed open-circuit be- 

 cause the occupants inhale directly from the 

 gas supply and each breath is exhaled into 

 the surrounding atmosphere. The majority 

 of submersibles employ some variety of open- 

 circuit emergency breathing modified from 

 scuba. The system may consist of: 1) A 

 mouthpiece and pressure regulator con- 

 nected by high pressure tubing to the vehi- 

 cle's low or high pressure ballast-blowing air 

 supply, or 2) the same components connected 

 to either portable or non-portable tanks of 

 compressed air. Exception is found where 

 the mouthpiece, regulator and hose are con- 



667 



