Nitrox Saturation Logistics

[Akimbo]

I thought of asking via a PM to Thalassamania, but though others may also have insights or be interested. Except for one, the only air saturation dives I have ever been involved with were treatment dives that devolved into saturation schedules. The PPO2 was well above today's recommended maximums, but the chambers were not equipped with scrubbers, metabolic oxygen make-up, analyzers, or diluent gasses. Fortunately, there were no Pulmonary Oxygen toxicity symptoms. So here are the questions:

1. During operational air sats, do you pressurize the chambers or the habitat with air and let the divers breath the PPO2 down to target levels?

2. If not, do you have compressed or liquid Nitrogen available for diluent gas?

3. What is provided for open circuit breathing gas, air or Nitrox?

4. If Nitrox, how are the logistics handled?

5. What are normal operating depths and what is considered deep air sats?

6. How are excursion (dives deeper than the saturation/living ) depths and time determined?

7. What absorbents for CO2 and human generated trace gasses used in habitats?

8. How aggressive are electrical systems isolated for fire safety in habitats? I imagine it is a real inconvenience for scientists. We only worry about it while shallow (pressing down and decompression) on mixed gas saturation dives since the Oxygen percentage is too low to support combustion on deep mix. We just turn off all internal power during that period, hou$e them at one atmosphere, or purge electrical systems with pure Helium.

9. Has there ever been a habitat fire, electrical or otherwise?

10. Do you tether the divers on excursions? If not, how do they find their way home?

11. How much of the NOAA Nitrox work was in support of their early habitat work versus intended for surface based divers?

 

[Thalassamania]

I thought of asking via a PM to Thalassamania, but though others may also have insights or be interested. Except for one, the only air saturation dives I have ever been involved with were treatment dives that devolved into saturation schedules. The PPO2 was well above today's recommended maximums, but the chambers were not equipped with scrubbers, metabolic oxygen make-up, analyzers, or diluent gasses. Fortunately, there were no Pulmonary Oxygen toxicity symptoms. So here are the questions:

Let me open by saying that it's been about 15 years since I've been involved in habitats.

1. During operational air sats, do you pressurize the chambers or the habitat with air and let the divers breath the PPO2 down to target levels?

Air sats are typical of very shallow (24 ft) habitats, like Jules Undersea Lodge and MarineLab. That depth is dictated by the push-pull problem of not going so deep so as to not be able to surface without a stop on one hand and minimizing the possibility of oxtox on the other hand.

Aquarius, while a little deeper can not permit an "any-time" ascent to the surface, about 17 hours of deco is required. However the hatch depth of
47 feet is determined by Oxtox considerations.

Aquarius is an open circuit system during missions, a constant “bleed” of air is pumped from the surface energy buoy. With a full complement of six there is too much CO2 produced to be flushed and so scrubbing with sodasorb is done by three habitat conditioning units (HCU) that also act as heat exchanger/dehumidification systems. Each HCU holds just shy of 50 lbs of sodasorb. There are 3 backup, battery powered scrubbers to cover a loss of power from the energy buoy that would compromise the HSCs.

Other similar habitats like Hydrolab and Tektite were deployed at similar 40 to 50 foot depths.

Deeper sats (like LA CHALUPA, AEGIR and HELGOLAND) were deeper and required other approaches. if not so deep as to require trimix or heliox they used to use NARTOX, that is Nitrogen enriched air. LA CHALUPA deployed using 8% NARTOX at 50 feet and 5% at 100 feet. HELGOLAND was used down to 328 feet on 0.35 ATA Oxygen with the rest being helium and AEGIR (my favorite habitat) which supported dives down to 516 feet on Heliox (where thermal problems cut the mission short).

2. If not, do you have compressed or liquid Nitrogen available for diluent gas?

The best book on the subject that I know is "Living and Working in the Sea" by Miller and Koblick. It says, "A common method is to have the aquanauts breathe down the habitat gas (air) until the oxygen partial pressure reaches the desired level. A flow meter is the activated to allow for sufficient air to be admitted to the habitat to makeup for the oxygen utilized by the aquanauts."

3. What is provided for open circuit breathing gas, air or Nitrox?

Typically divers exit the habitat using the same gas that they breathe in the habitat. But extensive work has been done on NOAA OPS and REPEX, the use of NITROX for habitat depth excursions. This is covered in the Mixed Gas chapter of Bove and Davis, which also covers mixed gas excursion for NARTOX storage.

4. If Nitrox, how are the logistics handled?

I do not know. As best I can remember analyzed and marked tanks were delivered to the rack outside the moon pool.

5. What are normal operating depths and what is considered deep air sats?

As noted earlier, air becomes problematic at about 50 feet and it is normal then to switch the breathing media to normoxic mixtures.

6. How are excursion (dives deeper than the saturation/living ) depths and time determined?

Special tables are available that reference storage depth and breathing mix. This is the big advantage of a habitat. For example, storage at 50 feet permits unlimited diving down to about 110 feet.

7. What absorbents for CO2 and human generated trace gasses used in habitats?

Same as in subs and rebreathers.

8. How aggressive are electrical systems isolated for fire safety in habitats? I imagine it is a real inconvenience for scientists. We only worry about it while shallow (pressing down and decompression) on mixed gas saturation dives since the Oxygen percentage is too low to support combustion on deep mix. We just turn off all internal power during that period, house them at one atmosphere, or purge electrical systems with pure Helium.

What we know we have learned from the commercial world. Electrical system are handled just like a submersible, ground fault checks, meg-ohming the system routinely, etc. Face it, electrolysis is a big worry along with fire and electrocution.

9. Has there ever been a habitat fire, electrical or otherwise?

I know of none, but my knowledge is far from encyclopedic. I suggest you look at Shilling, Werts and Schandelmeier: Undersea Handbook or Schmidt, Door and Hamilton: Chamber Fire Safety.

10. Do you tether the divers on excursions? If not, how do they find their way home?

There is a preference for hooka or surface supplied for excursions. Most site have guidelines laid out on the bottom and/or emergency waystations.

11. How much of the NOAA Nitrox work was in support of their early habitat work versus intended for surface based divers?

I can't cut the pie up that way, I'd have to research all the budgets. The best hipshot answer would come from Jim Miller or Morgan Wells.

 

[Akimbo]

It seems like most habitats, except maybe Helogland and SeaLab II & III, were operated exclusively in tropical water. What did they do for humidity control? Are there anything cleaning agents you can kill fungus inside under pressure? We required coil temperatures below 50° F to keep humidity under 60%, which kept the crawling crude in check inside deck chambers. Hot salt-water wash-downs in the bells seemed to manage it there. It is hard to imagine what you could do with such warm water outside the hull.

 

[Thalassamania]

Aquarius has three habitat conditioning units (HCU) that also act as heat exchangers dehumidification units and scrubbers built into one. In La Chalupa a lot of Clorox kept the mold at bay. Cold keeps the mold down but sure is a downer for the divers, effective rewarming keeps coming up as an issue. When Aquarius was the George Bond and headed for Catalina there was a plan to put a hot tub out on the wet porch.

 

[Ethyl_MerMan]

"When Aquarius was the George Bond and headed for Catalina there was a plan to put a hot tub out on the wet porch."

Found this thread via Googling "SEALAB" (a favorite subject) and joined the forum. Do you gentlemen know more about this proposed set-up? (I shall avoid the obvious Californian jokes about hot tubs )

Environmental management seems to be the great challenge in habitat design: gas mix, contaminants, temp, humidity. My brother-in-law Nate works at Biosphere II near Tucson and has shared stories of their environmental-control challenges. (4 acres under glass @ 1 bar, completely sealed off from the planet.)

 

[Thalassamania]

What's to know? Standard residential hot tub installed on the wet porch so that cold divers could soak. Idea was nixed due to concerns over paradoxical cooling and unknown effects on dissolved nitrogen.