"Assess the Street Value of their Equipment"
by Elbert Greer, Master SCUBA Diver Trainer #37494
This piece of advice was given to me by a very famous SCUBA instructor in confidence. He wanted me to understand something about a certain rescue scenario titled 'Unconscious Diver at Depth'. His point was clear, if I discovered a diver unconscious below 130 feet I should not risk my life for someone who is dead.
Lately in San Pedro a group of instructors and divemasters have been 'Dare Devil' diving to depths below 300 feet on compressed air and I feel compelled to express my opinion about it. 130 feet is the limit set for recreational divers for many reasons. The air that we all breathe is approximately 21% oxygen and 79% nitrogen. Certified SCUBA divers learn a lot about what nitrogen does to them when they breathe it under the pressure of water, but little is taught about the 21% oxygen because they are not expected to go below 130 feet.
Every 33 feet a diver descends, he is under an extra atmosphere of pressure (atm) and the normal air he has brought with him becomes denser by 1 atm. This means at 33 feet the diver is getting twice as much oxygen than at the surface; three times at 66 feet, four times at 99 feet and so on. Bellow 300 feet they are getting 10 times the oxygen their central nervous systems are accustomed to. A research organization called NOAA (National Oceanic and Atmospheric Administration) says safe oxygen exposure limits are PO2 1.4 with a contingency plan for 1.6 atm, beyond this there is an unacceptable risk of the diver convulsing from oxygen toxicity and drowning. The PO2 for normal air at 300 feet is 2.10.
Oxygen toxicity is not like nitrogen narcosis when the diver can feel its symptoms and decide to ascend to relieve them. An oxygen toxicity convulsion comes on with little warning and is unresistable.
I probably shouldn't go on about how I feel about daredevils, but let me say this, they usually have nice equipment.
Before you go on your next dive below 130 feet take this little test.
1. The primary hazard of exceeding the oxygen exposure limits by going below 300 feet on 21% oxygen is:
a. The guys will call you chicken.Answer: The correct answer is "c".
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