Mixing SCUBA and freediving?

[Pezman]

On a recent SCUBA outing, we were doing some freediving between dives. We though this was perfectly OK, since we weren't inhaling compressed air. However, when we asked around about this later and got a lot of diverse opinions on whether this was advisable or not. Some subsequent research turned up articles that said that you could actually get a form of decompression sickness from doing too many deep dives w/ too little time between them (pearl divers for example).

I have a bunch of questions on this topic:

* It is best to just freedive or just SCUBA and try to avoid mixing the activities at all?

* Does freediving effectively reduce your surface interval time (i.e. an hour might count only for 45 minutes)? I'm kind of cheering for this one ...

* If you use a computer during the free-dives, I should think that it would correctly compute your nitrogen levels, but can dive computers handle the extreme profiles and short bottom times involved in freediving?

 

[jvoets]

There's only one way to mix scuba & freediving:

Do your freediving first, then scuba.
After scubadives you should wait for at least 12 hours to go freediving again.
It's like the rule for not flying after a scuba dive.

The problem is in the rapid descent and ascent rates when freediving. The extra nitrogen in your tissues gets recompressed when descending, bubbles will get smaller and have a chance of entering tinier spaces in your tissues. On the ascent (going 60 - 90 meters / min), there is not enough time to let the nitrogen escape in a controlled manner. Which could lead to decompression sickness (or worse ....)

 

[immerlustig]

hi pezman

you´ll find some threads here somewhere that covered this topic already.

basically it´s unwise to do that and the safe option is to not freedive after scuba.
you´ll find some related articles on www.diversalertnetwork.com or dan-europe´s website. there´s another one www.scubamed.com (if i remember correctly).

would be cool if one could quicken offgassing after scuba by going freediving. unfortunately it doesn´t work. you actually increase the risk of dcs.

dive computers are not really a good thing to take out for freediving. firstly they beep on ascent cause you are mostly faster than 7-10 m/min and also any dive within 5 minutes (depends on model) will be added to the first dive giving you no clear indication about your divetimes and depths of your freedives (unless you like to calculate while doing breathups or read the display all the time).

computing nitrogen levels on yo-yo dives is something computers have problems with since on/offgassing processes are getting very complicated to simulate. that´s why every computermanual (and dive training) stresses the point to do perfect profiles.
modern computers tend to add conservatism to compensate for yo-yo diving therefore giving you shorter dive times for repetitive dives and longer desaturation times.

for more information i could recommend john lippman ´deeper sportsdiving` or some publications that are not from 1986 (like padi books, if i´m informed properly).
dive research happens all the time and one has to keep updated.


hope that helped.

enjoy diving

roland