Podcast: Thermal stress and decompression
All scuba divers know than when we dive we load our body with inert gas, and as we ascend we start offloading gas, (granted this is simplified and doesn’t take into consideration loading speed of tissue compartments, but anyway…) This offgassing continues for hours once we’ve reached the surface. That, after all is what the surface interval is for, right? Off-gassing enough, that our next dive can be done without incurring harsh decompression penalties.
No matter if you plan and execute your dive with dive tables or computers, you are basically looking at just two parameters to determine how long you can dive. Time and depth. The computer will of course give you additional bottom time, as it eliminates unnecessary rounding and gives you credit for making a gradual ascent, but essentially, it still only takes depth and time into consideration. (And always remember – dive computers aren’t magic bracelets!)
Neither tables or computers take into account the thermal stress you encounter during diving, and how that affect the loading of your tissues. Hardly news to tec divers, but it turns out that when you’re warm you off-gas much faster – this is why it’s good to be warm and cosy on your ascend. More surprising perhaps is that you too load gas much faster if you’re warm! Switching on your electric-heating west at the deepest part of the dive, when you’ve gone through a teeth-rattling thermocline, may significantly affect your deco obligation, as you’re loading your tissues much faster. …Or rather, it won’t because you’re trusting your computer, which doesn’t know about your thermal stress to get you safely out of the water. See the issue?
This and many more interesting findings on thermal physiology for divers are discussed on a new Podcast on Pod Diver Radio, where Dr Neal Pollock, the Research Director at Divers Alert Network and Senior Research Associate at the Center for Hyperbaric Medicine at Duke University Medical Center explores this in a very interesting interview. It’s a little technical in places, but if you’re interested in decompression theory or a technical diver you don’t want to miss it.
You may hear the whole podcast here. (about 22 minutes)
One lesson to learn, tongue in cheek, is that if you have to pee your wetsuit, the best time to do it is at the safety stop, where the warmth will help your skin off-gas.