Possibly stupid DCI question

[Alun]

Forgive me father for I have committed the sin of posting in the deco section without ownership of decoplanner...


At the back of this months (March issue) Diver magazine, there is an article on whales showing signs of DCI. This was caused by them ascending too quickly, and went on to blame navy sonar for scaring them out of the depths and causing them to bolt for the surface.

Daft question:
Given that whales take a lungful of air at the surface, how can ascending put them at any risk of DCI?

Daft question 2:
If it can and does and I'm missing something fundamental here, do freedivers get bent?

[aclivity]

a quick google search came up with this:
http://www.iwc.org/world_whale_news/whales-1-3.htm

I think the problem is that whilst freedivers spend comparatively little time at depth, whales spend an hour or more? So the breathed air is being absorbed into tissue / bloodstream for some time. Also the volumes of air in a whale lung is much higher than a freediver.

I don't know, I'm guessing. I think time has a lot to do with it - when submariners escape from a sub (and it's been done from 200m) immediately before they leave the sub they are able to plug in a reg to the air supply on the sub. They must in effect go from surface pressure (in the sub) to 200m (hatches opened) back to surface in a very short time. I had always assumed that if a freediver took a single breath off a DV at depth, they would immediately have to follow a deco schedule. Perhaps a very fast, breathing out ascent (to prevent barotrauma) would be feasible as long as they weren't hanging about at depth?

[edit]sorry for the garble, it's a stream of consciousness aided by too much caffeine and lemsip in my system[/edit]

[nigelH]

Originally Posted by aclivity

I think the problem is that whilst freedivers spend comparatively little time at depth, whales spend an hour or more? So the breathed air is being absorbed into tissue / bloodstream for some time. Also the volumes of air in a whale lung is much higher than a freediver.

I'd go with that. The shortest compartments on the deco models take several minutes to on and off gas and your lungs don't actually contain much volume once the pressure comes on. A whale however has lungs that will hold an hour's breathing and probably is more akin to a sat diver and does depths that would destroy all but the most specialist subs.

I don't know, I'm guessing. I think time has a lot to do with it - when submariners escape from a sub (and it's been done from 200m) immediately before they leave the sub they are able to plug in a reg to the air supply on the sub.

I guess it's all down to the how long you are under pressure. Once they crack the hatch and the water pours in you are probably very hyped up. If you are last man out and you hit the surface you have beaten the odds and are alive. The second question is what are they breathing in the sub as the pressure comes on? Air at 200m? What is in the hood at the surface? The Russians have a Trimix escape apparatus rated and apparantly tested to 300m. It is one of the IDA series and becomes an oxygen rebreather shallow using the 'Womble' FFM. On the way up, at less than 100m, it deploys a drogue to prevent the passenger being thrown too far out of the water. I know where they are available if anybody wants one....