Quick up and quick down?

[kayakdiveman]

I was wondering if anyone could settle a disagreement that I have with a dive buddy. A few buddies and I regularly sea scooter around Laguna Beach, CA. One of the guys in our group often points his scooter straight up and shoots up very quickly about 25 feet to go over one of the local reefs. We tell him he is ascending way too fast and won't follow him. He says that it does no harm because he exhales as he goes and then shoots right back down again as soon as he is past the reef.

In a nutshell, he says going up very fast is OK as long as you go down again just a few seconds later. I say he's wrong. Does anyone out there have any insight on this?

Thanks,
Mike

 

[O2BBubbleFree]

Seems to me he's considered the air embolizm side, but not the nitrogen. Your tissue is absorbing compressed nitrogen. Ascending rapidly allows the compressed gas to expand in your tissue, and returning to depth isn't sufficient to recompress the gas so that it will leave the tissue. Unless, of course, you return to depth for an extended time, but it would have to be much longer than standard SCUBA tanks would allow. If a person gets bent, it requires many hours in the chamber to recompress the nitrogen and get it out of his tissue.

On a similar note, my OW instructor told the class to use the safety stop "to your advantage." He suggested going to the surface, taking a bearing on the boat, returning to 15', and spend your 'safety stop' swimming to the boat at 15'. If you surface, you've blown it, and returning to 15' for 5 minutes is no 'safety stop.' I got him fired.

 

[DandyDon]

In a nutshell, he says going up very fast and then going down again very quickly is OK, I say he's wrong. Does anyone out there have any insight on this?

Thanks,
Mike

You're right - the idiot is wrong. But it's hard to tell if he'll get bent first, or hit the rocks first...

 

[BlueDevil]

I know a diver who was doing a rapid drift dive in poor visibility when suddenly there was a rock ledge in front of him. He had to ascend fairly quickly over it to avoid hitting it. He ended up in a chamber after the dive - no other part of his profile was in question, and the hyperbaric specialist felt the most likely factor was the brief rapid ascent.

 

[BlueDevil]

On a similar note, my OW instructor told the class to use the safety stop "to your advantage." He suggested going to the surface, taking a bearing on the boat, returning to 15', and spend your 'safety stop' swimming to the boat at 15'. If you surface, you've blown it, and returning to 15' for 5 minutes is no 'safety stop.' I got him fired.

Don't you think "re-education" would be more appropriate than having the bloke fired. I have known instructors and dive masters who have given a lot worse advice than this.

While I am not endorsing his practice it is not too far removed from what happens with many commercial diving operations. I believe it is fairly common practice for commercial divers to surface with minimal decompression, quickly shed their gear, and then get straight into a recompression chamber onboard the boat/dive platform. They are then recompressed, then gradually 'surfaced' with appropriate deco stops. It is also not that different to an omitted decompression procedure - ie asymptomatic divers who have missed a decompression stop return to the water to complete their stops (plus a bit extra for safety)

In one regard he is certainly right - swimming back to the boat underwater is certainly an advantage. It is just the surfacing to check bearings that reduces it's benefit. I have done a lot of 'hookah' diving (ie surface supplied hoses) and it is always our practice to swim back to the boat underwater at around 3-5m. The advantage we have is that we can simply follow our hoses back to the boat and so don't have to surface. If this instructor had one of those new-fangled underwater navigation beacons then he would be spot on with his advice.

 

[O2BBubbleFree]

Don't you think "re-education" would be more appropriate than having the bloke fired. I have known instructors and dive masters who have given a lot worse advice than this.

Saying I got him fired was taking more credit than I'm due. I politely questioned the advice with his boss, a retired Navy diver, and then never saw him around the shop after that.

I've had no experience with a chamber (thank God) or decompression diving, but I was under the impression that once the bubbles expand, it takes hours in the chamber to recompress them, and that simply returning to depth for a few minutes did next to nothing? I know I read this somewhere, but don't remember if it was in my OW text or elsewhere.

 

[Charlie99]

I've had no experience with a chamber (thank God) or decompression diving, but I was under the impression that once the bubbles expand, it takes hours in the chamber to recompress them, and that simply returning to depth for a few minutes did next to nothing? I know I read this somewhere, but don't remember if it was in my OW text or elsewhere.

But the bubbles don't form instantaneously. It's a relatively fast event, but my guess is that bubble formation has a time constant in the 10's of seconds to a few minutes. For example, both surface deco and omitted deco treat 5 minutes as the time limit on the surface before recompression.

Obviously, if ones tissues are highly oversaturated problems occur faster. Popping to the surface from a long dive at 200' is clearly a much more severe insult to the body than swimming around the Florida Keys at max depth of 30', then surfacing for a few seconds before swimming back to the boat at 15'.

See Dr. Deco's comments in the How Long Before We Fizz Upl thread.

 

[FreeFloat]

While I am not endorsing his practice it is not too far removed from what happens with many commercial diving operations. I believe it is fairly common practice for commercial divers to surface with minimal decompression, quickly shed their gear, and then get straight into a recompression chamber onboard the boat/dive platform. They are then recompressed, then gradually 'surfaced' with appropriate deco stops. It is also not that different to an omitted decompression procedure - ie asymptomatic divers who have missed a decompression stop return to the water to complete their stops (plus a bit extra for safety)

I work at DCIEM in a job loosely connected with diving in general, although not within the Experiemental Dive Unit. However on an infomal tour of the hyerbaric chamber facilities, my 'tour guide' was explaining Surface Decompression Diving to me (which you've described above)and I asked much the same question - about whether or not the surfacing itself is a bad idea. He told me that they've been doing this for some time with no bad outcomes. I guess their divers regularly go to depths beyond rec limits in quite cold water and this is the best way to safely decompress them - get them out of the cold water so that temperature and immersion are no longer factors. I think he said (when I asked) the the time limit they use was somewhere around 7 inutes from getting out of the water, to getting into a chamber and recompressing.

 

[Dr Deco]

Hello Readers:

My thanks to the other responders. They got to this posting before I could.

Quick Ascents

I have studied this in the laboratory with animals, and I doubt that such a quick, minimal ascent for a relatively short period would be all that detrimental. This probably sounds surprising to many readers.

While nuclei will expand during the pressure decrease, there is only a small amount of dissolved nitrogen that can diffuse into the bubbles because of the diffusion resistance of the tissue. The reapplication of pressure would shrink the nucleus back to its initial size [almost completely].

Surface Decompression

As mention above, and in other Dr Deco forums, “surface decompression” is common with divers having a decompression chamber and a long decompression time. It affords the diver the change to remain warm and dry, a chance to eat and drink, and all around safety from the elements. :dazzler1:

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[Northeastwrecks]

I was wondering if anyone could settle a disagreement that I have with a dive buddy. A few buddies and I regularly sea scooter around Laguna Beach, CA. One of the guys in our group often points his scooter straight up and shoots up very quickly about 25 feet to go over one of the local reefs. We tell him he is ascending way too fast and won't follow him. He says that it does no harm because he exhales as he goes and then shoots right back down again as soon as he is past the reef.

In a nutshell, he says going up very fast is OK as long as you go down again just a few seconds later. I say he's wrong. Does anyone out there have any insight on this?

Thanks,
Mike

In addition to the DCS issues, I suppose that Mr. Darwin has also figured out how to equalize rapidly when he's ascending. Or doesn't he need eardrums?

Scooters are for lateral travel, not for imitating a Polaris missile.

Geniuses like this shouldn't even be admitted to a chamber when they finally get hurt.