Neutral Buoyancy Lab and nitrox - -

[Dr Deco]

Dear readers:

One of the readers of the Scuba Board asked about diving with nitrox in NASA’s Neutral Buoyancy Laboratory (NBL). I thought that I might put this on the Dr Deco FORUM since it might be of interest to others. The NBL was constructed a few years ago to replace the Wet Environment Test Facility (WETF). The latter was too small for training involving the much larger components of the new International Space Station (ISS).

The new facility is about 50 feet deep and would pose a decompression hazard for the astronauts training there for periods of up to six hours. The original plan called for the use of air and an elaborate decompression facility. This was actually envisioned to be entered underwater. The problem with this lay in the cost, which was deemed to be prohibitive. An answer was found in nitrox, and a mix with 45% oxygen was chosen based on the time/depth requirements. While new hardware was required to plumb the facility, this was feasible and easy since the NBL was under construction.

This mix has eliminated all decompression problems although some have wondered if there might not be some pulmonary problems in the support divers who dive several times a week. These individuals assist the astronauts during their ISS training in the water. To date, no one has reported any pulmonary difficulties of which I am aware.

Dr Deco
:doctor:

 

[daylight]

Dr. Powell,

Thanks for the info.

I hope you are able to offer your highly regarded decompression seminar in the Houston area in the near future.

Larry

 

[The Iceni]

Hi Dr Deco,

It has taken quite a while for the British establishment to recognise that when used properly that "devil gas" oxygen has much to recommend it. The example you give highlights it's advantages.

I am of the firm opinion that Enriched Air Nitrox is safer than air and honestly fail to understand why basic scuba training is centered on air as the breathing medium and divers only "graduate" to using richer oxygen mixes after they qualify.

The Nitrox ticket is treated as a postagraduate qualification, which to me is a shame becase it dissuades sports divers from using Nitrox. "its far too complicated for the likes of us".

OK oxygen does have its hazzards and one must be aware of the concept of Maximum Operating Dept but it is not a gas for deep diving and extends bottom times no end. I also find it far less tiring and so worth the marginally extra cost.

I feel that the majority, if not all, diver trainees could be taught how to calculate pp O2 and the concept of MOD so fail to see why Nitrox should not be included in the basic syllabus.

Is this blasphemy, or does this seem a reasonable position to adopt?

I would be interested in your views.

 

[Piscean]

Dr. Paul,

I must disagree. Lately as part of my divemaster training, I have been helping out with some PADI Open Water Courses and one of our students, a woman who is learning to dive with her son, continually asks questions like, "Should I have the regulator in my mouth when I am doing my fin pivot?", or "If I add air to my vest, do I go up or down?" I would not like to try to teach her about MOD or ppO2. Also beginners in my brief experience are limited by how much air they breathe and not by bottom time except on very deep dives, which at least in the PADI system and I believe in the BSAC system too, they are not allowed to do initially. I personally am limited by bottom time deeper than 20m, based on 14l/min (0.5cu. ft/min) surface equivalent air consumption. PADI OW divers are not allowed to do dives deeper than 60ft (20m) so they will pretty much always be limited by air supply. Finally, being down for a long time is not an important skill, being able to get back to where you came from is, so if I have to choose between teaching someone navigation or nitrox, I choose navigation every time. Being down for a while is fun, being able to navigate is safe and to have fun, you have to be safe first. In the PADI system decent navigation is not taught until the advanced open water course.

Piscean.

 

[Liquid]

I don't think nitrox is such a vital tool. aspecialy for new divers. Most divers will limit themselves to shalow dives, led by a dive-master, once or twice a year, in their vocation. Teaching this kind of divers further skills, which are actulay not sessacery may, instead of contribute to them, delute what they already know. Take also into consideration the fact that a lot of divers today are not trained by good instructors in good conditions (look at the weekend-course for example. I think it's rubbush, no matter what other people can say for it).

People that want to further their knowledge, by all means, should take the nitrox. Maibe it should be made a part of the AOW course, but OW divers it is practically useless (as stated in above message). Maibe a LSU course is more practical for beginers (Limited Enriched Air User- uses only 2 kinds of blends).

 

[The Iceni]

Hi Guys,

Everything you say is true but I was not advocating novices being taught to use or to blend Nitrox, but that it might - that is might- be more sensible for it to be used during training simply because of its advantages.

I agree that's not what I said but ;-

Now, I would be the first to admit that a lady who does not understand the basic principles of bouyancy could be expected immediately to understand MOD, but

Even at the depth and exposure limits advocated by PADI it is possible to get a DCI using air.

The instructor is in a position to advise on the mixes required. (Eg 40 % at 20 M?)

NASA have realised the benefits of EAN.

With Nitrox, not only is the diving more pleasant, the risks of DCI are reduced.

I do not think for a minute that Nitrox will ever be adopted during training because of the litiginous times in which we live. The other considerable downside is Nitrox costs more.

But like many an idea, I thought it was a good idea at the time!


;-(

 

[Rick Murchison]

Originally posted by Dr Deco
To date, no one has reported any pulmonary difficulties of which I am aware.

Dr Deco
:doctor:

Hi Doc,
This is sort of new ground isn't it? Without more specifics it's hard to tell if there's significant long term risk, but reading it I thought "emphysema."
I think it was NAMI that found a correlation between emphysema and jet jocks who breathed 100% oxygen for hours routinely several times a week - but they were unsure of the data because
(1) the damage could be attributable more to constant positive pressure breathing than to oxygen
(2) in those days most of the guys smoked
Have you ever read anything on it?
Rick

 

[Dr Deco]

Hello Rick:

No, I am not familiar with this situation. Sorry....

Rather than emphysema (connections between alveoli), I believe that the problem feared is the growth of fibrous tissue.

:doctor:

 

[devilfish]

Nitrox, The Good, The Bad and The Ugly.
Is it more difficult to teach Nitrox to basic divers?
There is no differance between learning Nitrox 32, Nitrox 36 or Nitrox 21, same physics apply.
Is Nitrox safer?
Only if it is dived on air schedules. There is too much contradiction with the two words together in one sentence, "longer bottom time" and "safer".
Do divers feel less tired after diving with Nitrox?
Yes, if dived on air schedule, the diver is less bend.
Is Nitrox safer for new divers?
Not really. New divers often can't control planned depth regardless if they are diving air or Nitrox. With air they use up and run out of air, go home to mama at warp seven, embolize and die. With Nitrox same situations apply with addition of possibility of O2 tox, in which case instead of going up they go down.
Does Nitrox reduces DCS possibility on extended bottom times?
No, only reduces deco time.
Does Nitrox increase bottom time?
Only if there is more gas available.
Should Nitrox be a standard diving gas?
Absolutely. But only if a diver can demonstrate the ability to maintain maximum planned depth and discipline to execute the planned dive. But that should apply to Nitrox 21 as well.
OK, I'm from Mars, but that's my 2 cents.

 

[Rick Murchison]

Originally posted by Dr Deco
Hello Rick:

No, I am not familiar with this situation. Sorry....

Rather than emphysema (connections between alveoli), I believe that the problem feared is the growth of fibrous tissue.

:doctor:

I'm sure the growth of fibrous tissue is correct - I seem to remember those exact words when we were being cautioned on the effect. The NAMI docs probably used "emphysema" because that was something us dumb aviators could readily understand - translation "hard to breathe, very bad ju-ju"...
Rick