Post by LSDeep on Nov 30, 2005 9:30:43 GMT -5
By Alex Brylske
Q: A question from Nancy Balboa revisits an issue that always makes for an interesting discussion. "I was in Bonaire recently and a group of us staying at the resort had an ongoing but friendly argument over an issue that we could never settle satisfactorily. It involved snorkeling when scuba diving. What I mean is, is it safe to snorkel during a surface interval between scuba dives? There were many theories, and some of our group thought that it should never be done, while others saw no reason not to because of the minimal time of any freedive. Still another opinion was that it depends; relaxed snorkeling and no surfacing diving would be OK, but nothing rigorous, and certainly no deep freedives. Others thought that snorkeling and scuba diving had nothing to do with each other. They maintained that you can only get the bends from scuba diving, not from snorkeling. We decided before we left that I'd write to you for your insight. What do you think?"
A: I've probably addressed this topic at least a half-dozen times in the 15-year history of this column, which indicates just how common a discussion this is among vacationing divers. Still, it's an important issue, and there are some factors that divers often don't consider. Let's first dispel a myth held by some in your group. Although it's extremely uncommon, freedivers can, in fact, get decompression sickness (DCS). It has, for example, been documented in Japanese pearl divers, and others who engage in deep freediving over periods of days or years. Another example is the DCS-like symptoms seen among freedivers in Polynesia. There, in the course of studying more than 200 divers, one researcher documented almost 50 cases of what the islanders call taravana, which translates as "fall crazy." Some have even died from the disorder. Even Cuban freediving champion Francisco "Pipin" Ferreras maintains that he's gotten DCS at least twice.
But let me balance what I've said with the fact that it's highly unlikely for any freediver, aside from perhaps world-class competitors, to ever succumb to DCS. Given the modest depths and times of the average freediver, as some in your group concluded, the amount of nitrogen absorbed is just too little to make any difference.
However, the issue just isn't that simple. When you combine freediving with scuba diving, there are some important concerns related to DCS. Generally, it's good practice to avoid freediving between or even soon after scuba dives. Particularly, aggressive freediving, where you're making multiple trips to considerable depths, is a definite no-no. In fact, one should always avoid vigorous exercise of any sort between or directly after diving. Most authorities caution against it because of how it changes circulatory dynamics and the rate at which the body eliminates nitrogen. But it is worthy to note that such warnings are based on speculation rather than empirical evidence. Still, as no one can answer the question with any certainty, the best advice is to avoid freediving until the nitrogen levels in a scuba diver's tissues have returned to almost normal. This takes at least six hours. The bottom line is this: No freediving while you're still in a repetitive dive status.
Recently, I've heard that some divers think that they can avoid the concern of freediving during surface intervals by wearing their computer at all times, including when they're freediving. The logic is that this would allow the device to continually track one's decompression status, even during their freediving activities. While this might make sense intuitively, it may not be advisable. First, the fast ascents associated with freediving will likely activate the rapid ascent warning on most computers. But an even more important issue than computer mechanics is the physiological effect of rapid ascents. No decompression model has been validated to take this sort of behavior into account. However, medical evidence seems to support a relationship between rapid ascents and DCS. This is still a poorly understood issue, so prudence should dictate a very conservative approach. In other words, once again, nix the freediving between and immediately after scuba diving.
However, so there's no confusion over this, let me close with an important clarification. What I'm talking about is freediving, not snorkeling. Lying on the surface between dives with mask, fins and snorkel watching the action below is not a problem. Just don't exert yourself too much.
Q: A question from Nancy Balboa revisits an issue that always makes for an interesting discussion. "I was in Bonaire recently and a group of us staying at the resort had an ongoing but friendly argument over an issue that we could never settle satisfactorily. It involved snorkeling when scuba diving. What I mean is, is it safe to snorkel during a surface interval between scuba dives? There were many theories, and some of our group thought that it should never be done, while others saw no reason not to because of the minimal time of any freedive. Still another opinion was that it depends; relaxed snorkeling and no surfacing diving would be OK, but nothing rigorous, and certainly no deep freedives. Others thought that snorkeling and scuba diving had nothing to do with each other. They maintained that you can only get the bends from scuba diving, not from snorkeling. We decided before we left that I'd write to you for your insight. What do you think?"
A: I've probably addressed this topic at least a half-dozen times in the 15-year history of this column, which indicates just how common a discussion this is among vacationing divers. Still, it's an important issue, and there are some factors that divers often don't consider. Let's first dispel a myth held by some in your group. Although it's extremely uncommon, freedivers can, in fact, get decompression sickness (DCS). It has, for example, been documented in Japanese pearl divers, and others who engage in deep freediving over periods of days or years. Another example is the DCS-like symptoms seen among freedivers in Polynesia. There, in the course of studying more than 200 divers, one researcher documented almost 50 cases of what the islanders call taravana, which translates as "fall crazy." Some have even died from the disorder. Even Cuban freediving champion Francisco "Pipin" Ferreras maintains that he's gotten DCS at least twice.
But let me balance what I've said with the fact that it's highly unlikely for any freediver, aside from perhaps world-class competitors, to ever succumb to DCS. Given the modest depths and times of the average freediver, as some in your group concluded, the amount of nitrogen absorbed is just too little to make any difference.
However, the issue just isn't that simple. When you combine freediving with scuba diving, there are some important concerns related to DCS. Generally, it's good practice to avoid freediving between or even soon after scuba dives. Particularly, aggressive freediving, where you're making multiple trips to considerable depths, is a definite no-no. In fact, one should always avoid vigorous exercise of any sort between or directly after diving. Most authorities caution against it because of how it changes circulatory dynamics and the rate at which the body eliminates nitrogen. But it is worthy to note that such warnings are based on speculation rather than empirical evidence. Still, as no one can answer the question with any certainty, the best advice is to avoid freediving until the nitrogen levels in a scuba diver's tissues have returned to almost normal. This takes at least six hours. The bottom line is this: No freediving while you're still in a repetitive dive status.
Recently, I've heard that some divers think that they can avoid the concern of freediving during surface intervals by wearing their computer at all times, including when they're freediving. The logic is that this would allow the device to continually track one's decompression status, even during their freediving activities. While this might make sense intuitively, it may not be advisable. First, the fast ascents associated with freediving will likely activate the rapid ascent warning on most computers. But an even more important issue than computer mechanics is the physiological effect of rapid ascents. No decompression model has been validated to take this sort of behavior into account. However, medical evidence seems to support a relationship between rapid ascents and DCS. This is still a poorly understood issue, so prudence should dictate a very conservative approach. In other words, once again, nix the freediving between and immediately after scuba diving.
However, so there's no confusion over this, let me close with an important clarification. What I'm talking about is freediving, not snorkeling. Lying on the surface between dives with mask, fins and snorkel watching the action below is not a problem. Just don't exert yourself too much.