Free Diving and DCS
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It's been done but unless you're extremely good at free diving, such as 100' plus dives, it's unlikely to be an issue. In tournaments we used to do 60-80' dives more or less non-stop for up to 4 hours, never had a problem. Likely a person with more knowledge of the actual physiology will answer you soon and I would recommend you take their advice over mine.
Tom
Tom
pescador775
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EYY, I remember a case which occurred in the Fla Keys over 30 years ago. During a spearfishing tournament a freediver who was making dives to 100 ft was reported to have bends.
If you make a scuba dive on the same day following freediving you will have to estimate your repetitive dive group (B, C, etc) and figure this in to your scuba plan. Possibly, you could wear a wrist meter if you were making really deep breath hold dives and planned a tank dive that day. Otherwise, you might be at risk for bends.
I speak from personal experience.
If you make a scuba dive on the same day following freediving you will have to estimate your repetitive dive group (B, C, etc) and figure this in to your scuba plan. Possibly, you could wear a wrist meter if you were making really deep breath hold dives and planned a tank dive that day. Otherwise, you might be at risk for bends.
I speak from personal experience.
Piscean
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...but that won't stop me spouting!
I would think that there is very little risk of DCS even on very deep breathhold dives simply because you can't stay down very long.
On the other hand, I would be very worried about doing breath hold dives, not so much before scuba, but after. Once you have loaded your body with N2 during your scuba, you would effectively be doing a saw tooth profile if you then did breathhold dives afterwards. I think everyone agrees that saw tooth profiles are bad and on top of that you would be doing exercise and the wise Dr. Deco has mentioned on several occasions that that is bad.
May I ask, since we are on the topic, if anyone knows any good free diving sites? In particular, an online free diving course? I would like to learn how to free dive. I am going to do a course this summer, but I would like to read up about it before I do. Any help would be much appreciated.
Piscean.
I would think that there is very little risk of DCS even on very deep breathhold dives simply because you can't stay down very long.
On the other hand, I would be very worried about doing breath hold dives, not so much before scuba, but after. Once you have loaded your body with N2 during your scuba, you would effectively be doing a saw tooth profile if you then did breathhold dives afterwards. I think everyone agrees that saw tooth profiles are bad and on top of that you would be doing exercise and the wise Dr. Deco has mentioned on several occasions that that is bad.
May I ask, since we are on the topic, if anyone knows any good free diving sites? In particular, an online free diving course? I would like to learn how to free dive. I am going to do a course this summer, but I would like to read up about it before I do. Any help would be much appreciated.
Piscean.
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Follow the link in my signature for a couple links (and a good book...)
Tom
Tom
First let me restrict my commentary to the recreational/enthusiast realm of free diving. Extreme free diving a la Pipin Ferraras causes physiological effects that are more complicated and beyond what regular free divers would experience. With that said, free diving, by itself, does not result in anywhere near the same amount of nitrogen bubble formation that results from SCUBA. The reason for this is that a person free diving takes a breath at the surface. He /she does not take subsequent breaths at depth. As a result, the gas in the lungs will get compressed as a person dives, but no additional air (and consequently, nitrogen) is breathed at depth. As a result, the only nitrogen that enters the blood stream is that contained in the original breath of air.
A SCUBA diver, in contrast, breaths air at depth. This air is compressed and contains a high partial pressure of Nitrogen. As a result, more nitrogen enters the blood stream with each breath at pressure until some level of saturation is reached (depth and theoretical compartment dependent). A free diver experiences very little nitrogen build up in the blood due to the limited supply of nitrogen (that from one breath) and extremely short bottom time (compared to SCUBA). Due to this, the risk of getting DCS due to free diving is very, very low.
With this said, DCS has been reported (or at least suspected) in free divers who dive repeatedly and go very deep (100 feet +), such as pearl divers. In addition, a free diver who has just completed one or more deep dives will still have significant residual nitrogen in their body. Free diving immediately after this will add small amount of nitrogen to this total and may increase the risk over free diving alone. Free diving is also not allowed for those individuals recovering from DCS episodes for the same reason. Anecdotally, I frequently free dive on the same day as diving. I do, however, wait a few hours before free diving after SCUBA dives.
I would be interested in knowing if research has been conducted in this area. All in all if one wishes to mitigate risk, one can avoid free diving until a sufficient surface interval time has elapsed. This also would allow a person to recover from any physical/mental stress incurred from a dive.
A SCUBA diver, in contrast, breaths air at depth. This air is compressed and contains a high partial pressure of Nitrogen. As a result, more nitrogen enters the blood stream with each breath at pressure until some level of saturation is reached (depth and theoretical compartment dependent). A free diver experiences very little nitrogen build up in the blood due to the limited supply of nitrogen (that from one breath) and extremely short bottom time (compared to SCUBA). Due to this, the risk of getting DCS due to free diving is very, very low.
With this said, DCS has been reported (or at least suspected) in free divers who dive repeatedly and go very deep (100 feet +), such as pearl divers. In addition, a free diver who has just completed one or more deep dives will still have significant residual nitrogen in their body. Free diving immediately after this will add small amount of nitrogen to this total and may increase the risk over free diving alone. Free diving is also not allowed for those individuals recovering from DCS episodes for the same reason. Anecdotally, I frequently free dive on the same day as diving. I do, however, wait a few hours before free diving after SCUBA dives.
I would be interested in knowing if research has been conducted in this area. All in all if one wishes to mitigate risk, one can avoid free diving until a sufficient surface interval time has elapsed. This also would allow a person to recover from any physical/mental stress incurred from a dive.
Piscean,
I do know some great sites for free diving in the Galapagos or BVI's if you ever go to either. I try not to free dive off the east coast myself...it's a bit to cold, murkey, and soupy for my freediving tastes.
Dmc
I do know some great sites for free diving in the Galapagos or BVI's if you ever go to either. I try not to free dive off the east coast myself...it's a bit to cold, murkey, and soupy for my freediving tastes.
Dmc
pescador775
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Cabrerad says that: ". With that said, free diving, by itself, does not result in anywhere near the same amount of nitrogen bubble formation that results from SCUBA. The reason for this is that a person free diving takes a breath at the surface. He /she does not take subsequent breaths at depth. As a result, the gas in the lungs will get compressed as a person dives, but no additional air (and consequently, nitrogen) is breathed at depth. As a result, the only nitrogen that enters the blood stream is that contained in the original breath of air."
Actually, for humans the only limitation on nitrogen uptake is the average depth and duration and doesn't depend on the method of diving. Clearly, free divers do not generate exposures as large as most scuba divers simply because they don't go as deep or stay as long. The theory about differing nitrogen content of the lungs needs to be examined. Free divers have as high a percentage in their lungs as does a scuba diver, 78%. The partial pressures in the free divers lungs are also the same as the scuba diver when the depth increases. The air is simply sqeezed into a smaller space. Yes, this means the total quantity of nitrogen is less compared to a scuba diver but that is irrelevant. In the short time that a freediver is submerged his total uptake is subject to absolute partial pressure of the gas, not the total quantity of the gas. If this were not true a scuba diver could avoid bends by taking smaller breaths or by skip breathing. Furthermore, neither the total amount nor the partial pressure of nitrogen in the freediver's lungs will decrease significantly given the short duration of a single dive, and it is noted that there is significant outgassing as the air is replenished each time the diver "breaths up" on the surface.
Your statement may be valid for whales or turtles whose dives last for an hour or more, but not for humans where the average duration is more like 2 minutes, and the average depth is only half the maximum.
Actually, for humans the only limitation on nitrogen uptake is the average depth and duration and doesn't depend on the method of diving. Clearly, free divers do not generate exposures as large as most scuba divers simply because they don't go as deep or stay as long. The theory about differing nitrogen content of the lungs needs to be examined. Free divers have as high a percentage in their lungs as does a scuba diver, 78%. The partial pressures in the free divers lungs are also the same as the scuba diver when the depth increases. The air is simply sqeezed into a smaller space. Yes, this means the total quantity of nitrogen is less compared to a scuba diver but that is irrelevant. In the short time that a freediver is submerged his total uptake is subject to absolute partial pressure of the gas, not the total quantity of the gas. If this were not true a scuba diver could avoid bends by taking smaller breaths or by skip breathing. Furthermore, neither the total amount nor the partial pressure of nitrogen in the freediver's lungs will decrease significantly given the short duration of a single dive, and it is noted that there is significant outgassing as the air is replenished each time the diver "breaths up" on the surface.
Your statement may be valid for whales or turtles whose dives last for an hour or more, but not for humans where the average duration is more like 2 minutes, and the average depth is only half the maximum.
Pescador,
Point taken. I only meant to illustrate how a SCUBA diver can develop significant tissue loading at depth with a constant supply of nitrogen. For a short free dive, there would not be sufficient absorption and off gassing to significantly decrease the partial pressure of nitrogen in the lungs. I imagine if a person did not need oxygen and stayed at depth, there is probably sufficient nitrogen in a single breath of air to result in the same tissue loading seen in a diver using free circuit SCUBA. (Given the same depth and duration). I should have been more clear on that.
As you mentioned, duration of a dive and partial pressure of nitrogen at depth drive dissolution into the blood and tissues. Only a not so alive free diver at the bottom has to worry about tables, but then he/she has bigger problems. So another question is why animals such as turtles, cetaceans, and pinnipeds don't get the bends.
Point taken. I only meant to illustrate how a SCUBA diver can develop significant tissue loading at depth with a constant supply of nitrogen. For a short free dive, there would not be sufficient absorption and off gassing to significantly decrease the partial pressure of nitrogen in the lungs. I imagine if a person did not need oxygen and stayed at depth, there is probably sufficient nitrogen in a single breath of air to result in the same tissue loading seen in a diver using free circuit SCUBA. (Given the same depth and duration). I should have been more clear on that.
As you mentioned, duration of a dive and partial pressure of nitrogen at depth drive dissolution into the blood and tissues. Only a not so alive free diver at the bottom has to worry about tables, but then he/she has bigger problems. So another question is why animals such as turtles, cetaceans, and pinnipeds don't get the bends.
pescador775
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Whales were not known to get bent until recent research suggested there may be exceptions. Examinations of beached whales indicate that this may occur when whales are exposed to low frequency underwater sounds such as produced by certain types of sonar or explosions. This according to the Navy Marine Mammal Program in San Diego.
The theory appears supportable in view of experimental results published by other parties, but far from conclusive.
Unfortunately, the various theories which attempt to explain why whales DO NOT get the bends are even less convincing. Personally, I suspect that the blood of whales has a very high surface tension which inhibits nitrogen bubble formation. Tests of beaked whales indicate 4 times normal levels of dissolved nitrogen following a dive.
Suggest you look into it further if convenient but this is not my strong suit.
The theory appears supportable in view of experimental results published by other parties, but far from conclusive.
Unfortunately, the various theories which attempt to explain why whales DO NOT get the bends are even less convincing. Personally, I suspect that the blood of whales has a very high surface tension which inhibits nitrogen bubble formation. Tests of beaked whales indicate 4 times normal levels of dissolved nitrogen following a dive.
Suggest you look into it further if convenient but this is not my strong suit.
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