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Natalie Gibb

What's in the Tank?

By July 18, 2010

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"Make sure you turn on your oxygen," a scuba diver reminded his son. I understood that the diver simply wanted to make sure that his son had opened his tank valve before gearing up, but hearing someone refer to a recreational scuba tank as containing pure oxygen makes me do a double take. Perhaps the father merely lacked precision of language, but it seemed to me he lacked something more fundamental: understanding. Diving with pure oxygen can kill a diver even at shallow depths.

If the father knew that pure oxygen can be deadly, it seems unlikely that he would accidentally refer to a tank as containing 100% oxygen. Recreational scuba tanks are filled compressed, purified air. This air contains about 20.9% oxygen. What worried me was not the diver's diction, but that he did understand the fundamental difference between pure oxygen and air. If this diver thinks that scuba tanks are normally filled with pure oxygen, he could conceivably grab a tank marked 100% oxygen and go diving with it. Several risks are associated with the use of pure oxygen in diving.

Oxygen Toxicity
The confusion as to what is in a scuba tank is easy to understand because most people know that we require oxygen to survive. However, our bodies can only handle certain quantities of oxygen. Diving with pure oxygen deeper than 20 feet can cause a person to absorb more oxygen than his system can safely handle, leading to central nervous system (CNS) oxygen toxicity. CNS oxygen toxicity causes a diver to go into convulsions (among other things). All that is needed to stop the convulsions is for the diver to ascend to a depth shallower than 20 feet. Unfortunately, a convulsing diver will be unable to retain a regulator is his mouth, let alone control his depth. Usually, divers experiencing CNS oxygen toxicity drown.

High Percentages of Oxygen Require Special Gear and Training
The use of pure oxygen (or mixes of oxygen greater than 40%) requires special equipment. Oxygen is a great catalyst, and can cause the ordinary lubricants and materials used in recreational scuba diving to explode or burst into flame. Before touching tanks filled with pure oxygen, divers should be familiar with special procedures such as opening tank valves of pure oxygen cylinders very, very slowly. Without going into exhausting detail, there is a significant amount of knowledge and training required to use oxygen safely.

Pure Oxygen Is Used in Technical Diving
Knowing that pure oxygen can be dangerous, it is easy to assume that you will be unlikely to encounter pure oxygen on a dive boat. Think again. Pure and high percentage mixes of oxygen (such as nitrox or trimix) are used by trained technical and recreational divers to extend bottom times and to speed decompression. On the surface, pure oxygen is recommended first aid for the majority of diving injuries. A recreational diver is likely to run across pure oxygen on a dive boat at some point in his diving career.

If a diver remembers the risks of pure oxygen: central nervous system oxygen toxicity, explosions and fires, it is easy to remember what is in a recreational scuba tank: air, pure and simple.

Have something to add? Scroll down and add your comments below.

Image copyright istockphoto.com, wwing


July 19, 2010 at 10:23 am
(1) One of the Mike's says:

Yes, there is a big misconcept mainly by non-divers that the SCUBA cylinder is a oxygen tank. I think the bigger problem is that the diver missed a concept during the OW class or it wasn’t covered fully by the instructor. It scares me that if they missed the concept of that air is only 20.9% oxygen what other concepted did they miss.

July 26, 2010 at 9:26 am
(2) johnny says:

Here is South Africa, you pay penalties for using the word tank. They like to use the word cylinder.
And i know of divers who still think we use o2….

November 7, 2011 at 3:38 pm
(3) a607077 says:

I’ve said that least 607077 times. The problem this like that is they are just too compilcated for the average bird, if you know what I mean

May 24, 2013 at 4:20 am
(4) Jeff says:

johnny, what is wrong with word tank?

October 4, 2013 at 5:45 am
(5) HonestJohn says:

The problem with the word tank is the least of the wacky things that have come from rapefrica.

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