Produced in 1956 by the U.S. Navy, this training film for the Self Contained Underwater Breathing Apparatus (SCUBA) Closed Circuit Pure Oxygen (sometimes known as a CCUBA) This type of unit has no bubbles, but is limited to 25 feet of depth and the duration of the dive is limited. This type of unit was used by the U.S. Navy SEALs. The film shows the assembly of the unit, its use and care. At 8:48, a carbon dioxide absorbent is seen being placed into the unit; this absorbent is the key to the function of the closed circuit system and allows it to not produce bubbles.
Military, photographic, and recreational divers use closed circuit rebreathers because they allow long dives and produce no bubbles. Closed circuit rebreathers supply two breathing gases to the loop: one is pure oxygen and the other is a diluent or diluting gas such as air, nitrox, heliox or trimix.
A major function of the closed circuit rebreather is to control the oxygen partial pressure in the loop and to warn the diver if it becomes dangerously low or high. Too low a concentration of oxygen results in hypoxia leading to unconsciousness and ultimately death. Too high a concentration of oxygen results in hyperoxia, leading to oxygen toxicity, a condition causing convulsions which can make the diver lose the mouthpiece when they occur underwater, and can lead to drowning. The monitoring system uses oxygen sensitive electro-galvanic fuel cells to measure the partial pressure of oxygen in the loop. The partial pressure of oxygen in the loop can generally be controlled within reasonable tolerance of a fixed value. This set point is chosen to provide an acceptable risk of both long-term and acute oxygen toxicity, while minimizing the decompression requirements for the planned dive profile.
The gas mixture is controlled by the diver in manually controlled closed circuit rebreathers. The diver can manually control the mixture by adding diluent gas or oxygen. Adding diluent can prevent the loop gas mixture becoming too oxygen rich, and adding oxygen is done to increase oxygen concentration.
In fully automatic closed-circuit systems, an electronically controlled solenoid valve injects oxygen into the loop when the control system detects that the partial pressure of oxygen in the loop has fallen below the required level. Electronically controlled CCRs can be switched to manual control in the event of some control system failures.
Addition of gas to compensate for compression during descent is usually done by an automatic diluent valve.
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This film is part of the Periscope Film LLC archive, one of the largest historic military, transportation, and aviation stock footage collections in the USA. Entirely film backed, this material is available for licensing in 24p HD and 2k. For more information visit http://www.PeriscopeFilm.com
