Sunday, September 7, 2008

Free diving during your SIT?

[This was posted a long long time ago]

It was a beautiful night, Sher and I were sitting around enjoying a couple of beers...  when all of a sudden our conversation turned totally romantic and went down the road of SCUBA and the bends. 

The question is, can one get bent while free diving, during their surface interval time?  I'm thinking that yes it's quite possible.

For you recreational SCUBA divers out there, you know that you should do a three minute "safety stop" at around 15 feet prior to surfacing at the end of your dive. *

For you non-divers, this practice adds an additional margin of safety (hence it's name), by allowing more inert gas to escape while they are compressed before breaking the surfaces which is at 1 atm. 

Either way, that safety is a self-imposed "decompression" stop done during a no-stop dive.   However, regardless of whether a diver chooses to do a safety stop or not, one must look at the surface interval time as the final decompression stop of the dive.  Once at the surface, the diver is no longer breathing compressed air and by normal breathing will eventually off gas saturated nitrogen. 


As an FYI, The YSCUBA and PADI programs both agree that 12 hours is the acceptable time for the body to return to it's normal, atmospheric, levels of gas saturation after a dive.

So, now, throw in free diving between SCUBA dives. 

Free diving is breath-holding diving.  So at depth, you're not loading any more nitrogen; however you're no longer allowing nitrogen to escape.  Additionally, if your surface time between free dives is low, there's definitely little off gassing being done. These simple facts alone mess up decompression calculations, if a diver is using dive tables. 

One last thought, when one free dives down to depths greater than 33 feet, there is further recompressing of inert gas bubbles at depth and ascending again at a rate more that suggested when SCUBA diving.  One would think this is bad.

So, in conclusion I would have to say it would be best to avoid free diving during your SCUBA dives and if one would want to snorkel, they should stay at the surface.