Deco Gas

[DevonDiver]

If you are interested in learning more, Deco for Divers by Mark Powell is an excellent source ...

... Bob (Grateful Diver)

I did my first technical dive training with Mark some years ago...he's a great instructor. I really need to get his book!

 

[b1gcountry]

I've heard a little about "deco gas" being more oxygen-rich than whatever the diver is normally/otherwise using. Is that because they are normally diving deeper than is safe for nitrox toxicity levels so they dive air then use a high O2 gas for their stops? Or is there some other reason?

The deeper you go, the lower percentage of Oxygen you need to have in your breathing gas. So even though a deep diver is taking with a few bottles with a high percentage O2, they aren't breathing them until the last 70 or so feet.

As you start to get into deeper diving, you start needing low O2 mixtures for the bottom portion of your dive. A typical mixture for 150-200' is 18% oxygen 45% helium. If you were to decompress on this mixture after a dive for 20 minutes to 200', then the decompression would take almost 2 hours. Doing the same dive, but breathing 50% nitrox from 70' to the surface, our deco only takes 40min.

The increased Oxygen content helps the body eliminate the nitrogen that gets absorbed on the bottom.

This is even true for shallower dives. On a decompression dive with 32% nitrox, you deco will still be sped up with the use of deco gasses. Even though the mix you are breathing on the bottom is higher than normal air, a decompression mixture will be higher still, and therefore more efficient at offgassing.

Tom

 

[openhelix]

If you are interested in learning more, Deco for Divers by Mark Powell is an excellent source ...

... Bob (Grateful Diver)

Thanks! I ordered a copy to read.

 

[Gene_Hobbs]

There is some good history of this procedure discussed in this article:

Berghage, TE; McCracken, TM. Use of oxygen for optimizing decompression. Undersea Biomed Res. 1979 Sep;6(3):231-9. RRR ID: 2836

I think you will be VERY happy with Mark's book.