I'm wondering if there is any ill effects from free diving straight after a scuba dive. Normally my residual nitrogen is under half the ndc rate and I just deflate my bcd until i'm neutrally buoyant and then proceed to free dive. Is this dangerous and if so why?
nitrogen nightmare?????
- Thread starter craysea
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Far_X
Contributor
Are you free diving with all your equipment on? I don't understand why you would be wearing a BCD and if you are deflating it, it seems that you have the rest of your equipment on. Are you taking your one breath at the surface or under the water?
goodknight411
Contributor
I have been told to never freedive after diving. My instructor explained that it could increase the chance of bends, because you are rapidly varying your depth and that reeks havoc on the nitrogen comming out of solution. Causes bubbles.
After you have completed your dive, for a period after (some say as short as hours and some as long as days), the nitrogen that has entered your tissues continues to exit your system. Even if you do not have classic DCS, the fact is that you will have some bubbles that form. You may feel fine, but you will still be bubbling. This is especially true right after the dive but lessens after peaking over time.
Here is what is happening inside of your body: When the gas leaves your tissues, it travels through your blood stream to the lungs. There, the lungs act like a filter, trapping the bubbles and allowing you to exchange gas from the lungs until the bubbles offgas. The more of these post dive bubbles you have in your system, the slower they leave your body when you exhale. What happens is that the bubbles get all backed up, like a traffic jam, blocking the access to the lungs, thereby not allowing them to leave your system as quickly and efficiently as they start to leave your system before lots of them develop into this traffic jam. This is one reason why many decompression algorithms consider that it takes longer to offgas than to ongas.
After conducting a dive, if you were to descend, the increasing pressure would take what has formed into bubbles, and would crunch them down until, depending on how deep you would go and for how long, you would eventually cause the bubbles to completely collapse (This is what they do to bent divers in a recompression chamber except that they add oxygen to speed this up and to prevent new inert gas from entering the system). The first 33 feet of descent will cause the bubble to do the most contraction/crushing. In that same regard, if you already have formed any bubbles, they will expand the most during the last 33 feet as you ascend (and some that have been in solution would start to form bubbles if they had not before this during the ascent).
If you start free diving after a dive, you take a bubble that is backed up in the traffic jam, crunch it down to a smaller size (but likely not enough to drive it back into solution completely), and allow it to go around the traffic jam, bypassing the lungs and going back into your arterial system. This will then travel to places like your brain. When you surface, lowering the surrounding pressure, the bubble again expands (in places like your brain), causing not just decompression illness but the most dangerous and severe form of DCI.
There are lots of technical facets to the whole thing, but this is a simple way to explain it. The bottom line is that you are subjecting yourself to increased risk by descending and ascending after conducting a dive, especially by making rapid ascents and descents.
Yes, eventually, it will all equal out but that is after you are bent.
Hope this helps.
Here is what is happening inside of your body: When the gas leaves your tissues, it travels through your blood stream to the lungs. There, the lungs act like a filter, trapping the bubbles and allowing you to exchange gas from the lungs until the bubbles offgas. The more of these post dive bubbles you have in your system, the slower they leave your body when you exhale. What happens is that the bubbles get all backed up, like a traffic jam, blocking the access to the lungs, thereby not allowing them to leave your system as quickly and efficiently as they start to leave your system before lots of them develop into this traffic jam. This is one reason why many decompression algorithms consider that it takes longer to offgas than to ongas.
After conducting a dive, if you were to descend, the increasing pressure would take what has formed into bubbles, and would crunch them down until, depending on how deep you would go and for how long, you would eventually cause the bubbles to completely collapse (This is what they do to bent divers in a recompression chamber except that they add oxygen to speed this up and to prevent new inert gas from entering the system). The first 33 feet of descent will cause the bubble to do the most contraction/crushing. In that same regard, if you already have formed any bubbles, they will expand the most during the last 33 feet as you ascend (and some that have been in solution would start to form bubbles if they had not before this during the ascent).
If you start free diving after a dive, you take a bubble that is backed up in the traffic jam, crunch it down to a smaller size (but likely not enough to drive it back into solution completely), and allow it to go around the traffic jam, bypassing the lungs and going back into your arterial system. This will then travel to places like your brain. When you surface, lowering the surrounding pressure, the bubble again expands (in places like your brain), causing not just decompression illness but the most dangerous and severe form of DCI.
There are lots of technical facets to the whole thing, but this is a simple way to explain it. The bottom line is that you are subjecting yourself to increased risk by descending and ascending after conducting a dive, especially by making rapid ascents and descents.
Yes, eventually, it will all equal out but that is after you are bent.
Hope this helps.
The Chairman
Chairman of the Board
Actually...
Off gassing would still occur somewhat... but it's just too much exercise after a dive. Vigorous exercise is to be avoided at all costs for 18 hours after your dive. This is the reason for MANY "undeserved" hits.
Off gassing would still occur somewhat... but it's just too much exercise after a dive. Vigorous exercise is to be avoided at all costs for 18 hours after your dive. This is the reason for MANY "undeserved" hits.
Taking all this into account. Then how is it that you can still do repedative dive's to deeper depths ( Other than Free diving ) Where the bubbles in your blood are compressed to a greater extent. This must also contradict an 18 hour non vigorous exercise period. So how long would it be practical to wait before I was to free dive after a scuba dive.
lamont
Contributor
craysea:
This can be done because the new dives take into account the amount of inert gas you already have in your system. When you descend for the next dive, you dive deeper than during the first dive (some agree with this and others disagree), so that you complete crush the previous bubble back into solution. Then, you take into consideration residual inert gas from the previous dive when making your dive plan.
In either case, when you ascend, you do so slowly, giving your system time to offgas but taking into consideration the previous dive history. Adding high partial pressures of oxygen and lowering those of inert gas during ascent also helps. This is why technical divers use high oxygen mixes during decompression even before surfacing. I also continue on oxygen for about five minutes after surfacing from these types of dives depending on how agressive my profile has been.
This is quite a bit different than a sudden plunge and ascent.
. The answer to that all depends on whom you ask. By the way, there are those who feel that exercising even before the dive increases risk but there are others that say it reduces the risk.craysea:
Ever notice how the flying after diving rules have changed over the years? The same reasoning applies: nobody knows for sure. There are many theories but nobody can say for sure which ones work other than to say: "Whatever works works."
There are a lot of good courses and books on this out there. Unfortunately, the better written books read more like math formulas. You may want to check out Weinke's "Basic Decompression Theory and Application."
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