Is it OK to snorkel?

[John C. Ratliff]

Chad,

I agree that 66 feet (70 feet on the tables) isn't probably deep enough to cause the decompression problems that the articles discuss. I used that as an example of how a free diver can accumulate bottom time. But before you say that the surface interval is enough to out-gas, read this reference titled Taravana--Decompression Sickness fdrom Free Diving:

http://www.scubamed.com/divess.htm#anchor447923

These are actual cases of decompression sickness discussed by Fred Bove, M, PhD. Here is one quote:

The mechanism whereby free divers can develop decompression sickness was studied by Dr. P. Paulev in Denmark. Dr. Paulev studied free divers in a submarine escape training tower where free divers accompanied trainees as they performed the free ascents required to qualify for naval submarine duty. Dr. Paulev described the development of decompression sickness in a Danish Naval Medical officer. He states "The author has intimate knowledge of the event, because the medical officer happens to be himself." He performed about 60 dives to 100 feet with a two minute bottom time, and surface intervals of 1-2 minutes. After about 5 hours of free diving, he noticed pain, paralysis of the legs, nausea, visual changes and weakness of the right arm. He was treated with recompression, and following a full treatment table, all abnormalities disappeared.

Dr. Paulev calculated the nitrogen in his tissues after the repetitive breath-hold dives. He determined that the short surface intervals did not allow tissue nitrogen to be eliminated, and the tissue nitrogen was equivalent to that resulting from a continuous dive. Further studies by Dr. E. Lanphier indicated that the ratio of dive time to surface time, and the rate of ascent were important factors in the development of decompression sickness from free diving. He calculated that a ratio of surface interval to dive time of one gave a depth exposure equivalent to about 50% of the actual depth of the dive. Thus a dive to 100 feet with a 90 second dive and a 90 second surface interval would be equivalent to a continuous dive to about 50 feet. If ascent rate was rapid, the equivalent depth was about 65% of actual depth (65 feet). These relations explain why a free diver doing many repetitive free dives in the 100 -140 foot range will eventually develop decompression sickness...

...One other concern that has not been studied is the situation where you make a series of free dives after completing a series of scuba dives. There are several stories of divers getting decompression sickness doing free dives after scuba diving. This could occur if you are free diving during a surface interval between scuba dives. A surface interval with free diving is not really a surface interval, and the calculation of decompression will not be correct. The best advice is to avoid free diving during surface intervals between scuba dives. If you want to snorkel stay on the surface.

While it is unlikely that a free diver will be able to get decompression sickness from breathhold dive, it has happened. As Dr. Egstrom stated, you have to work real hard to do it. This is a free diving forum, and to have someone state categorically that you cannot get decompression sickness from free diving must be disputed. The reason is that this is read the world over, and it needs to be accurate. By the way, we did compare the Navy No-Decompression Limits with free diving bottom times for quite a while; it may not be a completely accurate way of doing it, but it is better than the assumptions that have been made here that decompression sickness cannot occur to free divers.

None of this discussion relats to the question raised at the beginning of this thread, which was about whether someone who had received a decompression "hit" should snorkel during the time he was told not to scuba dive. While this fellow's question resolved itself, and the guy did not go snorkeling, I really don't have an answer for it either. My opinion would be that if he was cleared for physical activity, then snorkeling with shallow dives (less than 20 feet depth) would probably be okay. But I also liked the answer that he should get an opinion from his diving doc, or a DAN doc.

SeaRat

 

[Chad Carney]

1. There can be a serious risk of decompression sickness in free divers who descend below 33 feet. This has been shown in historical information from even the 1950s and 1960s.

2. I agree that 66 feet (70 feet on the tables) isn't probably deep enough to cause the decompression problems that the articles discuss. I used that as an example of how a free diver can accumulate bottom time. But before you say that the surface interval is enough to out-gas, read this:

Dr. Paulev described the development of decompression sickness in a Danish Naval Medical officer. He states "The author has intimate knowledge of the event, because the medical officer happens to be himself." He performed about 60 dives to 100 feet with a two minute bottom time, and surface intervals of 1-2 minutes. After about 5 hours of free diving, he noticed pain, paralysis

3. While it is unlikely that a free diver will be able to get decompression sickness from breathhold dive, it has happened.

4. By the way, we did compare the Navy No-Decompression Limits with free diving bottom times for quite a while; it may not be a completely accurate way of doing it,

SeaRat

Searat,

Just debate here, no offense intended.

Only one guy said you can't get bent freediving, and he's obviously wrong.

Several freedivers posted it's very unlikely, with extreme cases excluded, and I agree.

I just questioned some of your conflicting statements of degree, (See 1., 2. and 3.) and your use of non-applicable data, underlined. The guy made sixty 100' dives for 2 minutes, with half or equal SI times at best. That's extreme.

And #4, is quite an understatement. Navy tables are way out-of-date for tracking repetitive recreational scuba dives.

Many serious freedivers have freediving computers today. Anyone good enough to even get close to extreme conditions should as well. All computers are reviewable, so divers can have accurate data and get proper SIs. Most divers are concerned for proper oxygenation, not DCS. Many computers are even downloadable, so this data could be collected the way scuba computers are often done today.

Chad

 

[John C. Ratliff]

Chad,

No offence taken, this is a good debate to have. I purposely did not use examples of computers, as I was reading my Suunto Cobra manual at the time, and it did not reference any warning statements, or give any examples, of free diving during surface intervals. My guess is that if a scuba diver were using a Cobra computer (or other computers), and went free diving to depths below 33 feet during the surface interval, the surface interval calculations that the computer made would not be accurate if it was not along with the diver. If it were along with the diver, it still may not be accurate, as they are not set up for the type of dives that free divers make.

I have the book for Suunto, and they have three computers that free divers use. One, the least expensive and therefore the most likely to be used, has this statement about the Suunto D3:

Suunto D3 is not a dive computer and provides no decompression calculations.

The Suunto Mosquito text reads:

For freedivers, Suunto Mosquito also provides a Freediving mode with an accurate, 2-second depth and time recroding interval. SCUBA and freedives are kept in separate profiles and history memories. All dive data can be easily downloaded to your own PC.

So yes, you would have the profile, but not the decompression information from the freedive memory, as it is a separate memory which does not interface with the SCUBA memory. There is nothing in their promotional materials that says they will try to integrate free diving during surface intervals either.

Their other model that free divers use is the D9, which is very expensive, but is used by free divers to track extremely deep breathhold dives (to 450 feet). It does provide profiles for these dives, and at least theoretically would be able to give some information on whether the diver was approaching a no-decompresion limit. But from what I've read, these are not really being used in that capacity, and rather are being used to track depth/time functions.

Concerning the apparent contradictions in the statements above, please realize that I was discussion the 60+ foot dives because that is something I can comfortably attain right now. Diving to 100 feet, while I probably can do it, is not something I'm ready to say I can do repeatedly for an hour or two. But even at 60 feet, there will be some residual nitrogen buildup from free diving to those depths.

The Ama, from my memory of articles that I read years ago, usually dove in the 35 to 75 foot depth range. This was enough for some of them to get into decompression problems with their free diving, according to the literature cited on the website above. This would also happen to pearl divers, who are going deep numerous times in a day.

Spearfisherman don't dive the same way. Usually, it is pretty shallow (35 to 50 feet, especially in my area of the Pacific Northwest where water is cold and visibility is limited). Even in warm, clear water, the spearfisherman (women too) dive to get the fish, then wrestle it to the surface and don't dive deep repeatedly like the pearl divers or the Ama, who both harvest from the bottom.

But referencing the computers, I really don't think they are made to track decompression problems for free divers.

SeaRat

 

[Chad Carney]

Searat,

I never claimed computers track nitrogen uptake for freedivers. I doubt any company would see the need to do such calculations.

However knowing how many dives you have done, how deep and how long your SIs have been, gives a freediver more valuable information than has ever been available in the past, when noted with how the diver felt while making them. As I said earlier, more freedivers are concerned with proper oxygenation, and breath hold dive proficiency.

I have used a Mosquito, just for freediving, for 3 years. Along with the Stinger and D3 they all download profiles. Studying them after diving provides even more information.

Safe diving!

Chad

 

[John C. Ratliff]

Chad,

I think we have agreement here! What do you think should be the main message that our dialog should give to free divers?

SeaRat

 

[Courtneyf82]

you guys are great.

 

[holdingmybreath]

John C. - main message should be.... get a D3 or mosquito...monitor surface interval time to double that of depth time... and if you're like me... it won't matter on the real deep stuff because I never feel ready to make a deep dive after even a shallow/short dive unless I've breathed up for at least 5 minutes.. and I know I'm not spending 2 1/2 minutes down on the previous dives... But.. it sure is nice to monitor the computer s.i. on the occassions I've got the inkling to do fairly quick repetitive dives.
and John C... if you're comfortable hitting the 60'.. I'm sure you're only a spotter away from easily getting to that 100' mark, there's just a few more stages to go through.. the difficulty of equalizing at 75' - 80', and then the difficulty of moving air to the mouth to equalize that one more time at 90' or so, which I'm sure you know, can be made a lot less difficult by filling your mouth full of air at the surface along with packing your lungs... shoot I wish I had 8ltr. capacity in my chest.

 

[John C. Ratliff]

I'm not sure where I got this document, as I found it in my historical files. But here it is--this is some of the first research on the problems of breathhold divers by E.R. Cross.

SeaRat

 

[pescador775]

Ratliff, you are a patient guy. Imagine, digging all that info and providing a reasoned discourse for the benefit of others. I wouldn't do it. It will roll off like water on a gadwall. I've been a freediver and bubble butt for many decades. I've had the bends severe enough to require walking with a cane for a six months stretch. I think I know the relationship between freediving/SCUBA and bends. Again, thanks for providing the documentation.