Scuba diving & freediving on the same day FAQ
Freediving after scuba diving is more of a concern; it requires consideration of the existing inert gas load, the intensity of the exercise during the freediving and the depth of the freediving. The goal is to reduce bubble formation and the potential for migration of bubbles into the systemic circulation.
Even shallow freediving after scuba diving is a problem because of the diver's inert gas load. The primary concern is not the additional gas loads the freediving can produce but the pulmonary shunting that will occur with exercise. Any bubbles present following a scuba dive can be driven across the lung at a much higher rate because of physical activity. (Physical activity may also increase the bubble load.)
It is reasonable to recommend that divers not mix meaningful freediving and compressed-gas diving on the same day. I realize that the word "meaningful" is vague, but it's probably necessary given the wide range of ability and activity possible. I would not worry about casual freediving after a 30-minute scuba dive to a maximum depth of 40 feet because the risk of substantial bubble formation would be low. But maintaining a low level of physical effort during the freediving would still be advisable.
The deeper the freediving and the more intense the exercise, the greater the recommended delay after scuba diving. The primary issue is that bubble formation is more likely after significant decompression stress. As a rough rule of thumb, when a scuba dive approaches half of the U.S. Navy no-decompression limit, the stress of postdive freediving becomes an increasing concern.
If the breath-hold activity is in the "snorkel" zone (that is, with vertical excursions of not much more than two body lengths) and relaxed, I would not be concerned at all. The "relaxed" part is subjective though, so thoughtfulness is needed. The risk for depths beyond 50 feet increases before or after scuba diving — before, because of potential exertion and middle-ear stress issues, and after, because of exertion, shunting and, increasing as a function of depth, direct gas loading from the freediving. Increasingly deeper depths warrant increasingly longer predive surface intervals.
Ultimately there is theoretical risk that should be controlled by conservative surface intervals and the lowest exertion levels possible. There is very little outcome data, but that should not discourage smart practice. Shallow, truly relaxed freediving before scuba diving probably has negligible consequences, given a modest surface interval and provided that equalizing during the subsequent dive is not compromised. But even shallow, relaxed freediving after scuba diving should be delayed if only for an abundance of caution. More aggressive freediving is best left for the next day. The potential negative outcome is simply not worth the risk.
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Great article, thanks for this content.
Question: when you say "concern" in the below sentence are you concerned with effects from the bends... or in the worst-case scenario a build-up of gas in the blood that will cause a stroke in the brain or something along those lines. I am specifically referring to freediving around 70 feet after a fully saturated scuba dive with limited surface interval.
"As a rough rule of thumb, when a scuba dive approaches half of the U.S. Navy no-decompression limit, the stress of postdive freediving becomes an increasing concern."
From the DAN Medical Team.
Thank you for the great question!
The concern relates to the development of decompression illness – in particular, we expect to see a “fast-tissue bend” (typically neurological in nature). We have treated a number of cases of cerebral (brain) decompression sicknesses in people who performed deep freedives without having done any scuba at all. It is therefore important to consider the risk of build-up of inert gas during a free dive: as the pressure of the gases in the lung increases, more inert gas will dissolve in the body (Henry’s Law). Therefore, whether you have increased gas pressures in your lung at depth that you have breathed at the surface yourself, or whether you first compress that gas and then breathe it at depth – the question is still whether you spent enough time at depth to increase your risk of developing decompression sickness.