Theoretically the most versatile gas?

As a diver, I've always been fascinated by "voodoo gas" and the benefits and dangers. Shortly after getting my Open Water certification, I got my Nitrox C-Card and haven't looked back. Now that I'm working through the Divemaster program with my LDS, I'm picking up some additional freedom around the shop, including mixing my own gasses, after I become a certified Gas Blender.

I just completed all the pre-work for my DSAT Gas Blender course that I'll be taking in two weeks. It cemented everything I knew about Nitrox, taught me the inner workings and potential dangers of certain kinds of blending environments and how to oxygen clean. Then, the trimix chapter really spawned my interest.

The trimix chapter got me thinking... what is the most versatile gas for recreational diving? Open circuit technical diving?

Considering PADI TecRec will certify up to 65m without a CCR, I calculated the ppO2 of all percentages of oxygen in a gas, at all depths from 0-214ft (65m). I marked off mix/depth combinations where the ppO2 fell below .18 and rose above 1.4 (for the sake of conservatism)

And there is only one gas that never fell below a pp02 of .18 nor rose above 1.4, and that's 18% oxygen. Cost aside, wouldn't heliox-18 be the most versatile gas for open circuit diving down to 65m? Are there any drawbacks to this gas other than price and availability?

Of course, staying within recreational limits, which I'm currently certified for, air is more than adequate. Just doing some theoretical calculations to brush up for the class.

I'd say 18/45 trimix would be more practical. HPNS shouldn't be an issue that shallow, but I've seen speculation that N2 is somewhat protective against oxygen toxicity.

If you define versatile as the ability to dive the broadest range without being hyperoxic or hypoxic, then yes. But depending on your dive profile it may not be the most efficient in terms of decompression. Also, without stating the He% the END may not be ideal either. The typical mix is 18/45.

---------- Post added June 5th, 2013 at 09:23 PM ----------

Sorry. Just saw that you said Heliox. Forget the comment on END. Keep in mind that He has its own deco obligations (some facets better, some worse than N).

18/45 is a really good, versatile gas.

Using heliox(18/82) to dive to 65m? Why?
I would use 18/30 for ow dive and a bit more He(35-40) in wreck penetration.

Since you are soon to be a cerrtified blender, you are going to find out that ideal gasses have alot to do with how they are produced. If you continue on the dsat path, with experiance you will be less focused on perfect mixes and just decide if you are going to accept or decline the gas choice for a given depth based on the amount of time you are willing to hang in any given enviroment.

In answer to your question, the most versatile gas is 21%, but you may not be impressed with some of the side effects.
Where are you getting your blender card?
Eric

20/20 trimix is the most economical for tropical wreckdiving in the calm clear waters of Truk Lagoon; it can cover all the depths of the popular wrecks, including nearly all of the deeper ones of the 4th Fleet Anchorage (San Francisco Maru, Aikoku Maru etc) to MOD 60m.

waterpirate:

Since you are soon to be a cerrtified blender, you are going to find out that ideal gasses have alot to do with how they are produced. If you continue on the dsat path, with experiance you will be less focused on perfect mixes and just decide if you are going to accept or decline the gas choice for a given depth based on the amount of time you are willing to hang in any given enviroment.

In answer to your question, the most versatile gas is 21%, but you may not be impressed with some of the side effects.
Where are you getting your blender card?
Eric

Click to expand...

Just doing some ideal quick calculations and was surprised to see that only one percentage of oxygen (18%) is neither hypoxic or toxic at any depth up to 65m. Regardless, I agree with what many here say that 18/45 trimix might be more ideal, and I've only considered the pp02.

Also keep in mind that I'm not certified to dive trimix, and won't be certified to blend it for some time. Just will be doing Nitrox off the bat, which is okay because the shop doesn't have trimix capabilities at the moment.

And yes, air is still pretty versatile, but I probably wouldn't dive it much past recreational limits with it.

I'll be getting my blender card at Underwater Adventures in Short Hills, NJ but it will be taught by Keith from Blue Water Divers.

tplyons:

Cost aside, wouldn't heliox-18 be the most versatile gas for open circuit diving down to 65m? Are there any drawbacks to this gas other than price and availability?

Click to expand...

Here's the thing, if you're going to plan the dive and mix the gas yourself you might as well dive an optimal mix for the dive. Try this: Plan a :30 minute dive at 165 feet on Tx18/45 and then plan the same dive using Tx23/20. Do not use accelerated decompression (i.e. deco gases) for this experiment and see what happens.

HIGHwing:

Here's the thing, if you're going to plan the dive and mix the gas yourself you might as well dive an optimal mix for the dive. Try this: Plan a :30 minute dive at 165 feet on Tx18/45 and then plan the same dive using Tx23/20. Do not use accelerated decompression (i.e. deco gases) for this experiment and see what happens.

Click to expand...

If your implication is that the 23/20 is optimal, I'd disagree, with the 23/20 having an END of 125' vs 75' for the 18/45(O2 considered as narcotic). Why would you consider doing either without accelerated deco?