EANx32 vs. 36 for older divers

[bluebanded goby]

I know that a lot of older divers use nitrox for relatively brief and shallow diving as a hedge against decompression illness, and also because they generally feel less fatigued after diving on it.

For a diver like this who is generally well above the maximum operating depth for either one (say, routinely making dives around 50 fsw for 30 minutes), is EANx32 or 36 a better choice for general diving? While older divers stand to benefit from the DCS protection, I'd think they would also be more sensitive to subtle oxygen toxicity from higher concentrations, so there'd be a tradeoff in weighing the right oxygen concentration to use. Thanks for any input.

 

[DocVikingo]

Hi bluebanded goby,

No one seems to be jumping on this post, so I'll gingerly venture forth.

For a diver of any age whose dive plan puts him "well above the maximum operating depth for either one," EANx36 will provide more of the well known benefits of nitrox than will EANx32.

As for "older divers" (not otherwise specified), I can't readily see any reason why EANx36 v EANx32 would put them at significantly greater risk for oxygen toxicity than "younger divers."

Happy holidays.

DocVikingo

 

[The Iceni]

Why not calculate your mix to aim for a bottom PPO2 of 1.4 bar to optimise deco safety and no-stop limits?


A maximum depth of 50 feet (15 M) gives an ambient pressure of 2.5 bar and there is no reason whatsoever why you should not use Nitrox 55 at that depth. Oxygen only become problematic when its partial pressure exceeds 1.6 bar.

 

[bluebanded goby]

Interesting idea to use mixes with a higher percentage of O2, Paul. But if one is getting fills at a local shop rather than mixing them in the garage, mightn't it be more challenging to find a shop that will pump a 55% mix? Also, I'm not (yet) nitrox-certified, but above 40% don't different requirements apply in terms of oxygen-cleaning equipment, etc?

 

[The Iceni]

Quite right.

Any equipment using more than 40% Oxygen must be in oxygen service.

1) The equipment must be made of materials that are not likely to to ignite and are fit for oxygen service.

2) The equipment must be oxygen clean and certified as fit for Oxygen service.

3) When blending the tanks must be topped up with clean air.

All an additional expense but this is negligible in comparison with the costs of diving.

I have a good arrangement with my local dive shop and do all my own blending, for which I am qualified, by the way!

As I usually dive deeper than 50 feet I seldom use mixes richer than Nitrox 36, except for accelerated deco.

 

[FloridaDiver]

Diving EAN36 within it's depth limits is, to me, the simplest answer. It's readily available, and only the cylinder and valve need O2 cleaning. Diving a richer mix presents more problems than it's worth for most recreational situations.

 

[The Chairman]

My PADI NitrOx manual clearly states that EANx is great for older divers for all of those reasons. As an old fart myself, I love the way it makes me feel post dive.

 

[sharpenu]

Goby, perhaps what you are referring to is not OXTOX, but is COPD(chronic obstructive pulmonary disease). COPD is the only thing I can think of where age would play a part in oxygen sensitivity. This is due to changes in the breathing drive that are caused by COPD. Since COPD is also a contraindication to diving at all, I don't think it would be an issue. What do you think DOC?

 

[The Iceni]

I think Goby meant what he said.

As you know, there are no clear predictors for CNS Oxygen toxicity but it is known that fatigue, dehydartion, stress and CO2 retention play their parts.

Intuitively one could suppose that an older diver is less physically fit and therefore more prone to Oxtox compared with a "fit" young diver (who may be less prone to the above) but I know of no evidence to justify this presumption and very much doubt any reliable evidence will ever be forthcoming because there is such a low incidence of this condition.

I also know of no evidence to support the following statement but, empirically, one could suppose that an older diver is more prone to DCI due to a general reduction in "fitness" with age (which is not directly related to lung function, in any case.)

Therefore, as the latter is more common than the former and since Nitrox diving protects against DCI and is far more pleasant than air diving, I put my money on it's benefits, as you are also aware!

 

[vicp]

One also needs to be aware of other effects of breathing higher ppO2 gases. While tissue loading of inert (N2) gases is lowered - less chance of DCI - and also while CNS is the big culprit, there are other long term effects of breathing higher than the ~21% O2 including lung/airway irritation and "free radical" cell damage. Google "free radical" and diving to see/read some interesting studies and opinions.

As far as Nitrox 32 vs. 36 for 50' 30 minute dives, I doubt that there is much, if any, tangible benefit to using EAN36 (vs. EAN32) unless it is just as cheap (or cheaper) and/or you plan on staying down a very long time (at 51' the NDL for EAN32 is 130 min and at 50' the NDL for EAN36 is 160 min). If diving 50' for 30 min infrequently the EAN36 would probably be fine. If diving the same frequently (as in daily or more - as on a liveaboard) I would stick with a lower EANx. In North Florida "cave country" we typically use 30 to 32% and we have plenty of older divers.

I guess what I am trying to say that while higher ppO2s are a benefit in some cases, they are not in others. As in anything else, one needs to balance out the pros and cons for each situation.