Deep-Six Underwater Systems, Inc.
"Add Depth to Your Life"

Table of Contents

1 Pressure and Gases
2 The Face Mask
3 The Snorkel
4 The Fins
5 Weight Systems
6 The Knife
7 The Wetsuit
8 Pressure and Water
9 The Ear and Pressure
10 The Sinus and Pressure
11 The Stomach/Intestine and Pressure
12 The Lung and Pressure
13 Barotrauma caused by External Air Spaces
14 The Buoyancy Compesation Device (BCD)
15 The Scuba Cylinder
16 The Scuba Cylinder Valve
17 The Regulator
18 Density and the Diver
19 The 4 Gas Laws
20 Hand Signals
21 Carbon Monoxide Poisoning
22 Hyperventilation
23 Nitrogen Narcosis
24 Diver's Flags
25 Sound Underwater
26 Color Underwater
27 Decompression Sickness
28 Breathing Oxygen
29 Deep Diving
30 Thermoclines
31 Thunderstorms
32 Underwater Life
33 Open Water Dives
34 The Final Examination
35 The Environment
36 Advanced Course

28 - Breathing Oxygen

     Ah! Oxygen - the gas of life! Without it for a few seconds and the world disappears from view. Too much of it can be a bad thing as well.

     Visiting a person receiving common oxygen therapy in a hospital refutes the notion that the oxygen is pure. A heart attack victim may be breathing oxygen through a nasal cannular. Air is also entering the nose at the same time the oxygen is. Even "oxygen tents" were not totally closed. Breathing pure oxygen over a period of time may lead to serious lung irritation. And, breathing pure oxygen at pressures greater than 1 atmosphere can lead to fatal consequences.

     Years ago there was a scuba introduced that allowed the diver to breathe pure oxygen. Because of the design, the small bottle of oxygen, about the size of today's pony bottles, allowed the diver to remain underwater for up to 4 hours! The unit had the appearance similar to an accordion. The air was extracted from it and then it was filled with oxygen from the bottle. As one breathed the bag would get smaller. As one breathed out the exhaled air would enter the bag and it would get bigger again. However, the amount of oxygen returning would be less due to the body's needs so more oxygen would have to be added as it was consumed. To remove the poisonous CO2 in the exhaled air there was a canister that contained caustic Barium Hydroxide (similar to Drano). As the exhaled air passed through the canister the chemical would combine with the CO2 removing it from the breathing oxygen. So, the oxygen molecules were breathed over and over again until they were converted to CO2. The unit was called a rebreather.

     Conventional scuba is wasteful. A breath is taken, 21% oxygen goes into the lungs, 18% comes out. Little CO2 goes in and about 4% comes out. Even though there is plenty of oxygen left in the exhaled air, it is discharged into the water. Just to get rid of the CO2 we waste the oxygen. Conventional scuba is know as an "open-circuit" breathing apparatus. Oxygen rebreathers are called, "closed-circuit." Rebreathers emit no bubbles unless the diver is ascending and the bag gets too full. So, U.S. Navy Seals use rebreathers to avoid detection!

     If a person breathes pure oxygen at a pressure above 1 atmosphere there is a possibility of it becoming toxic. Above 2 atmospheres almost insures it. The National Oceanographic and Atmospheric Administration (NOAA) prohibits their divers from exceeding 1.6 atmospheres of oxygen. The higher the pressure, the faster the poisoning. High-pressure oxygen toxicity starts with the twitching of smaller muscles that are in use such as the ones around the mouth holding the mouthpiece. Then the twitching can lead to full-blown convulsions. Needless to say, convulsions and diving do not really go together! Using a closed-circuit rebreather at 33' would allow the diver to breathe 2 atmospheres of oxygen.

     The U.S. Navy Seals are a hearty lot. They have a rather rigorous training program. They must be oxygen tolerant. One of the parts to that training consists of weeding out those that convulse easily when breathing pure oxygen. Potential Seals are required to sit in an oxygen atmosphere equivalent to 60' of seawater for 30 minutes. If convulsions do occur they are quickly returned to breathing air and booted out of the program.

     Don't think you are off the hook if you dive breathing air. Air at depth can cause oxygen poisoning. At the surface air supplies 21% oxygen. Since the pressure at the surface is one atmosphere, the pressure of the oxygen alone (partial pressure) is 0.21 atmospheres. Since the pressure at 33 feet of seawater (fsw) is 2 atmospheres, the oxygen partial pressure would be 21% of 2 or 0.42 atmospheres. If you project the partial pressure of oxygen at 132 fsw it would be 21% of 5 atmospheres or 1.05. That would be the samne as breathing pure oxygen at a depth of over 33'! The absolute pressure at 297' is 10 atmospheres, so the partial pressure of the oxygen would be 2.1 atmospheres and it could very well be toxic! Toxic air at 297' is a no-no!!

Copyright Information about this text, DIVING WITH DEEP-SIX is as follows: Copyright 1996 - 2007 by George D. Campbell, III; President. All Rights Reserved. This file may be posted on Electronic Bulletin Boards for download, but may not be modified, printed for distribution, or used for any commercial purpose without the author's written permission. is using this material with the permission of Deep Six. The full version is available at:
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