Free diving after SCUBA

[WhaleTail]

I'm not sure where I should post this question but here it goes:

Should I be taking my residual nitrogen into consideration when free diving after a SCUBA dive? While working on the dive boat I have been SCUBA diving my first dive in around 30 feet of water. After this dive, I start practicing my free diving (during my surface interval) going no deeper than 23 feet (so far) and breath holding no longer than a minute. After that, I do my second SCUBA dive to 40 feet. I know that my repeitive free dives that shallow and breath holding that little is not making too much difference but is the nitrogen from my SCUBA dive important to think about when free diving? My dive computer is counting my free dives as SCUBA dives and therefore taking the nitrogen into comsideration. Thanks for the help!

[naiad]

Originally Posted by WhaleTail

Should I be taking my residual nitrogen into consideration when free diving after a SCUBA dive?

Yes. I'm not sure what the safe interval between them should be, maybe someone who knows more can explain.

[Bill]

The latest thinking is that mixing scuba and free is a no no. One of the problems with a computer is that it cannot handle the descent and ascent rates while free diving.

[Lobo Marino]

The recommendations for freediving after scuba diving are the same as for flying after diving.
12h minimum for a single dive ,18h for multiple dives.
Or check the desaturation time on your dive computer.

I find it amazing that the PADI Open Water manual does not mention that freediving after diving is dangerous (even shallow),as it can make silent bubbles bond and make a bigger one or block some small capillaries.
Did they just "forget" to speak about it ?

[Samourai]

Don't know about PADI, but when I did CMAS Scuba my instructor warned me about freediving after scuba, and it's in the CMAS manual as well.

[TheDude]

Freediving after SCUBA can make the same mess as a rapid ascent from your scuba dive... And the basic rule for both is - just don't do it!

[WhaleTail]

I had a feeling it was not safe. Thanks everyone. The only reason I questioned this at all is because my PADI instructor, who is also a competitive free diver, and the other divemaster told me it was nothing to worry about at all! (I am doing my divemaster course with these people)
I will continue to use my surface interval...ON THE SURFACE!

[Fitz-Clarke]

This is a fascinating question. I agree that, as a general rule, free diving and scuba should not be mixed. However, from a theoretical perspective, free diving AFTER scuba would act as a form of recompression, provided depth is no more than 20 feet. This would accelerate resolution of any silent bubbles by pushing free gas back into dissolved gas, yet not allow enough additional gas uptake in the tissues to cause problems, as the safe saturation depth on air is somewhere around 25 feet. On the other hand, free diving BEFORE scuba is potentially dangerous because it adds to the dissolved gas load in tissues before making deeper dives, increasing risk of DCS after the scuba dive. Either way, this argument is theoretical, and there could be other factors involved, like carbon dioxide effects on cerebral vasodilation enhancing brain gas uptake. It is interesting to think about, but I would not recommend testing it on yourself.

[Ondro]

Originally Posted by Fitz-Clarke

This is a fascinating question. I agree that, as a general rule, free diving and scuba should not be mixed. However, from a theoretical perspective, free diving AFTER scuba would act as a form of recompression, provided depth is no more than 20 feet. This would accelerate resolution of any silent bubbles by pushing free gas back into dissolved gas, yet not allow enough additional gas uptake in the tissues to cause problems, as the safe saturation depth on air is somewhere around 25 feet. On the other hand, free diving BEFORE scuba is potentially dangerous because it adds to the dissolved gas load in tissues before making deeper dives, increasing risk of DCS after the scuba dive. Either way, this argument is theoretical, and there could be other factors involved, like carbon dioxide effects on cerebral vasodilation enhancing brain gas uptake. It is interesting to think about, but I would not recommend testing it on yourself.

Well, theoretically if you stay down there long enough and if your ascent speed is under the safe rate (so lets say lower than 12 metres/minute if the SCUBA dive was really short and shallow) it could work...but the process would be very slow because you dont breath... I think that nobody, who has at least some brain will not try it and believe it is safe. As my scuba instructor would say "it is a straight way to the pathology department"

More truth is in the statement, that freediving before scuba is not safe - especially when going too deep (50+) or diving a lot (lets say 10-15 times to 30-40). But again, then you can have DCS from freediving itself.

[WhaleTail]

This information is wonderful. I am a bit frustrated at my Instructor, who is also a compeitive free diver, and the other divemaster! Of anyone, these two SHOULD be aware of the potential dangers (even theoretical) of mixing SCUBA and freediving. Also, as mentioned in previous replies, I wonder why the certification organizations do not mention any of this? I will present this information to my intsructor and see what happens. I also agree with not being the test dummy! The nearest hyperbaric chamber is in Bonaire...I am in Venezuela.....

[drunkinbda]

I actually was going to ask about the opposite. As i know freediving after scuba is a no no, i was wondering about freediving before scuba. Ondro was getting into it, but i assume the numbers he's giving is in meters?

Would it be safe if the freediving was around 50 feet? The situation being, a two dive outing, i freediving the first reef/wreck, and scuba the second.

Could this be a case of "well withing safe limits" or a case of "dont even test it"?

[trux]

At moderate freediving there will be little or no nitrogen saturation, so scuba diving afterward is not a problem. Though the fatigue, and possibly higher CO2 saturation and CO2 buffering may make you more susceptible to narcosis and DCS than you would be when perfectly fresh. On the other hand, decompression tables or algorithms for recreational diving are made with sufficient reserve that should well cover even such cases.