Underwater Adventuring

[Steverooo]

i have a question.

That's two questions, and a ponder! ;p

do dolphins (and other air-breathing sea mammals) suffer from the bends and nitrogen narcosis?

Cetacea/delphines, and seals don't seem to suffer to the same extent as humans do, no. I believe it has something to do with blubber, but I dunno... Perhaps someone else does?

what about fish (and other "water"-breathing creatures)?

I'm sure you've heard of certain deep-sea species who decompress, explosively, when brought to the surface? This is the extreme end of bends (not to mention messy!), but, again, they seem to suffer less from it than humans. How and why, I don't know. The fact that MOST of a fish's body is empty space may have something to do with it (less volume for the bubles to get trapped in). The fact that they "breathe" through gills, and only oxygen suspended in seawater may also have something to do with it...

Any marine biologists on the boards?

i wonder what kind of biology merfolk, sahuagin, locathah, and other aquatic races have.

Merfolk have some magic to them, according to Greco-Roman mythology. The fish-man races probably operate much like fish... but since all these races are fictional, I leave it to their creators to determine...

Anyway, in MEG's book, the races have their pressure/depth limits listed. I don't know if they provide them for other non-player races. MEG Hal, Doug?

 

[Steverooo]

The oceans are thriving, in my undersea campaign...and I am recruiting

Heh! How would a normal Human (and not a Druid) survive, down there? Pearls of the Sirines just lying around, waiting to be picked up?

Speaking of which, the 3.x crew missed it, again... They could have allowed the pearl, or Necklace of Adaptation, ad nauseum, to protect from the bends, pressure differentials, nitrogen narcosis, etc., but they didn't...

 

[bret]

Nope! Even pearl divers and well divers, who use no equipment, must deal with nitrogen narcosis ("rapture of the deep") and the bends.

Nitrogen narcosis is caused by descending below 30' too quickly (IIRC, one minute's time). I don't recall the exact mechanics.

The bends are caused by coming up more quickly than 10'/minute. As you go down, the pressure increases, and the oxygen, and especially the nitrogen, becomes smaller bubbles in the bloodstream... When you come back up, they increase in size, again. The larger bubbles them stick in various capillaries, expanding further as you come back up, and rupture them...

All divers suffer some of these, and most are relatively harmless. Ones occurring inside the brain, of course, can be lethal. This is why you stop every 10' or so, and "decompress" for a minute, before coming up further.

The problems aren't caused by SCUBA gear. They're caused by the chemistry and physics of AIR!

There IS NO getting around them! (Of course, you can always invent a new spell to do that, but D&D NEVER HAS!)

Although they aren't unique to SCUBA gear, the gear does make it much worse.

When you are using SCUBA gear, you are breathing in compressed gas. The best way to think about this is probably with a plastic bottle.

If you fill a plastic bottle with air at the surface (not compressed, just atmospheric pressure) and take it down, it will compress in. When you take it back up, it pops back out. The thing it is doesn't burst.

If you take a plastic bottle down with you and fill it from your tanks while you're below water (depth of about 60' should be more than enough), then seal it with the cap and try to bring it up the bottle will burst. The air to fill the bottle was compressed (matched the pressure of the surrounding water) and as you brought it up the outside pressure is reduced causing the air inside to try and expand.

It is still simple physics, pv=nRT, but in the second case you've filled something with more than it can hold at surface pressure.

 

[Steverooo]

Dolphins 101:

I found this on the web:

As mammals, Bottlenose dolphins are required to breathe air and maintain a high body temperature. They surface to breathe about every two minutes from their blowhole,which is located at the top of their head. If needed, however, a dolphin can hold its breath for several minutes, with the ability to dive more than 1,000 feet (300 meters) underwater, and yet avoid getting the bends. A small muscular flap closes as it relaxes after every breath, keeping water from entering the dolphin's lungs. From this blowhole, they can emit a variety of squeaks and whistles, used in communication.

 

[Steverooo]

Another double-post!

 

[Aeolius]

In anticipation of "The Deep"

Today I will be catching up on my undersea D&D game, by posting Chapter 114 of "Beneath the Pinnacles of Azor'alq". I will be revising several of the campaign's web pages, over the weekend, and will continue working on the latest revision of the campaign background.

I have set up a series of forums, over at www.lobi.com/bpaa, tentatively entitled "Undersea D&D". I have set up three topics, thus far, "The Oceans of Oerth", "Seafaring/Undersea Supplements", and "Undersea D&D: General Q&A".

Major events are in store, for Chapter 115.

 

[Steverooo]

HERE's why WE can't (Yee-OWwch)!

This is from the PBS site: http://www.pbs.org/odyssey/odyssey/...transcript.html

Because they spend almost 80% of their lives at depth, the amount of time we see sperm whales at the surface is comparatively low. As a result, we spend the majority of our time tracking sperm whales by homing in on their sounds. While the dives of adult females tend to last around 45 minutes mathotoure males are capable of staying beneath the surface for more than 90 minutes. Male sperm whales can also dive to astonishing depths. They have been found entangled in submarine telephone cables at depths of 1,000 meters, while a study in the Caribbean Sea using acoustic transponders and sonar revealed whales diving to depths of 1,185 meters and another was possibly to 2,000 meters. (The Smithsonian Answer Book. James Mead & Joy Gold)

People often ask us how these air breathing mammals can dive to such great depths for extended periods of time without suffering from decompression sickness, also known as the 'bends.'

The 'bends' is a condition suffered by people when they breathe air under pressure and ascend to the surface too fast (for example, when scuba diving). As humans dive deeper, they continue to breathe air at increasing pressure where more nitrogen gets driven by that pressure into the blood stream. Upon a sudden return to the normal atmosphere - i.e., upon surfacing too fast, the nitrogen that has saturated the blood, comes rapidly out of solution and forms bubbles. These bubbles accumulate in joints, in the blood, the brain and other parts of the nervous system, resulting in a blockage which reduces the oxygenated blood supply-something that is usually severely painful and can cause death. To avoid the 'bends', a human diver must return to the surface slowly, stopping at specific depths to breathe for specific times in order to allow the body time to readjust, and for any nitrogen bubbles to dissipate.

Whales are not subject to the 'bends' because they don't breathe air under pressure the way a human SCUBA diver does when diving. Whales breathe at the surface only, then hold their breath and dive. It seems likely that they don't carry enough air down to have the 79% of it that is nitrogen cause them problems. And because they are able to avoid too much excess nitrogen in the blood, they don't get the 'bends'.

Because atmospheric pressure doubles every 10 meters, a whale at a depth of 500 meters experiences a pressure about fifty times greater than atmospheric pressure at the surface. Once it has dived to about 200 meters - the whale has far exceeded the depth at which humans can breathe air and still function properly. The air the whale dove with has been compressed to 25% of its original volume and the lungs and jointed rib cage have collapsed completely. The heart rate has dropped dramatically and non-essential processes have been much diminished because freshly oxygenated blood supply to peripheral regions has been cut off. Because of the compression and collapse of the cavities where gas-exchange takes place, air is excluded from most of the respiratory surface of the lungs, meaning that no gas exchange can occur between the blood and air in the lungs. This prevents absorption of the nitrogen that might otherwise pass into the blood and lead to the bends when the whale surfaces for its next breath.

 

[Steverooo]

The trick is, not to breathe!

This is from: http://www.mbayaq.org/efc/efc_fo/fo_mml_faq.asp

Q: How can a whale stay under water for so long?

A: These deep-diving mammals have numerous adaptations that enable them to extend their breath-holding time and to avoid the diving maladies (the bends and nitrogen narcosis) that plague human divers. The important factor in avoiding the effects of pressure is that the lungs of deep-diving mammals are able to collapse completely. All the air is then compressed into the large air ducts and nasal passages, where no additional gas exchange takes place with the blood. This explains how they avoid the bends and narcosis—no excess gas enters the blood during the dive.

 

[AnthonyJ]

Frankly, I pretty much LOATHE the typical underwater adventuring books... They don't deal with nitrogen narcosis, the bends, the fact that no core 3.xe spell deals with the pressure differential, etc., etc., ad nauseum... Is this book "just another of the same", or does it deal with the real obstacles, and provide ways around them (even if they're magical)?

Note that many of these obstacles _aren't_ obstacles with magic.

Nitrogen narcosis and the bends occur because at high partial pressures, nitrogen from the air you're breathing dissolves into your bloodstream (with some odd effects on the human nervous system); when the pressure drops the nitrogen dissolves out again. I am not at all convinced that divers who don't use tanks are capable of going deep enough long enough to suffer from either of these effects, though I'd have to check. Ceteceans don't suffer from these effects because they collapse their lungs before diving, and rely on oxygen stored in non-gaseous form.

If the water breating spell works by creating air, it will have the same problems as for nitrogen narcosis. If, however, water breathing works by actually making you able to breathe water, you won't be breathing pressurized air and dissolved nitrogen will not be an issue. Alternately, using Alter Self to transform into an aquatic lifeform will generally eliminate problems at the depths said lifeform normally lives at.

For items that allow underwater movement:
Plate Armor of the Deep: in 3e, specified immunity to pressure damage; 3.5e dropped that line.

Bottle of Air: same as a scuba rig, and thus dangerous.

Cloak of the Manta Ray: should be fine (it's a transformation, not creating air), though gaining/losing altitude too fast might be dangerous for reasons unrelated to the bends.

Helm of underwater action: creates air, and should realistically have the same problems as scuba gear.

Necklace of adaption: also creates air, but since it works in a vacuum, may sustain constant pressure as well. This ability to sustain constant pressure might be overloaded by going too deep, however.

Pearl of the Sirines: appears to grant the ability to breathe water, and should thus be safe.

 

[Steverooo]

Another one

This one has no explanations of how, but has some interesting info on dolphins and whales getting the bends:

http://www.abc.net.au/science/news/stories/s440411.htm