Scuba at morning, Freediving afternoon ?

[Tal-Shahar Marzuk]

Freediving after Scuva diving?

Hi guys! thanks for showing interest on solving my issue.
I am currently working as a scuba underwater photographer for people coming for introduction scuba dive for PADI.
I usuelly don't pass 8m with them during this intro dive.
The thing is, I work everyday, starting early in the morning and I want to finish my working day and practice my free diving.

Am I going to get DCS??
Can I go through a freediving session that ends in a certain depth?
Can my diving computer give me any knowledge about how to minimize risks when combining these 2 sports?

I KNOW - that every guide, manual, course says to avoid freediving after scuba.. but the situation is complicated and depths are shallow.

any opinions ?

THANK YOU !
♥

 

[hteas]

I doubt it would be a problem as long as you keep it shallow.

How deep are your training dives?

 

[Frenzyfinder]

Rule of thumb says no. That rule applies very vaguely obviously.

I think you're asking a question you know the answer to.

I'll agree it being Shallow would lessen risks and complications. However you doing this daily is something to keep in mind.




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[cdavis]

Ascent speed while freediving is the complicating factor. You should never worry about dcs with scuba in 8 meters, but the body is still picking up substantial N2 load. Switch to freediving, with its much much faster ascent speed and it is very hard to say what will happen. For sure, you are much more likely to form N2 bubbles in your system than if you were only freediving. My guess, keep your freedives to less than 10 m and you are "probably" safe, not for sure. Start spending significant time at 16 or 18 meters and I think you are running way too much risk. But then, what do I know.

 

[J Campbell]

This not something you want to "guestimate" on.

 

[Kiekerjan]

Ascent speed while freediving is the complicating factor. You should never worry about dcs with scuba in 8 meters, but the body is still picking up substantial N2 load. Switch to freediving, with its much much faster ascent speed and it is very hard to say what will happen. For sure, you are much more likely to form N2 bubbles in your system than if you were only freediving. My guess, keep your freedives to less than 10 m and you are "probably" safe, not for sure. Start spending significant time at 16 or 18 meters and I think you are running way too much risk. But then, what do I know.

That sums it up pretty good, I'd just like to add that "probably" would not be good enough for me. I've seen people with the bends and it's not pretty!

I understand the frustration though, I used to work in scuba diving before and had the same problem. I never risked it though, I would just get up at first light sometimes and do it before my scuba dives.

 

[cdavis]

Just to add a strategic sense: all decompression tables, scuba computers, etc and designed based on compressed gas reactions. All assume very slow ascent speeds. They tell you nothing about bubble formation or the bodies reaction given higher ascent speeds or other ways in which freediving differs.

 

[Jaap]

Some liquivision dive computers have an experimental freediving deco algorithm. I have never tried to use the computer for both scuba and freediving but you may want to look into those. If dissolved nitrogen is kept live when you switch from scuba to freediving and back it may work for you.


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[GLS]

Tal-Shahar,

I'm new to this forum, but I don't agree with most of the advice you've received. Here's Why.

The problem is more with Boyle's law than Henry's law.

Everyone is offgassing after a dive. When you do a short duration dive after already diving, the potential exists for normal offgassing bubbles that would normally be caught in the "filter" of the lungs, to compress enough at depth, to slip past the lungs , then re-expand on surfacing, on the arterial side of the heart.

I don't have a lot of confidence in the clarity of my explanation, so here's a link to better explain.

http://www.wkpp.org/?page_id=2595

While the context of the article is technical diving, the last four paragraphs clearly explain what is going on, with the last sentence of the article summing up that freediving AFTER diving is a bad idea. I've been on dive boats on several seas over the last couple years; while snorkeling/swimming with whalesharks, dolphins, etc. is fine during surface intervals, freediving is expressly prohibited for this reason.

If you're going to mix the sports, get up early, and freedive first.

ps. I had a similar job doing the photo/video thing with new divers about a decade ago. Enjoy! I miss seeing the excitement of people underwater for the first time. (and all the good looking gals in bikinis )

 

[Jaap]

The problem is that as freedivers, we have no way of measuring or knowing dissolved nitrogen, so we cannot use that info for subsequent dives. Whether diving before or after a scuba dive, if you accumulate significant amounts of nitrogen you are setting yourself up for DCS. It is hard to know whether you are accumulating nitrogen or not. If you do five 30 meter dives with 2 minute bottom times on breath hold prior to scuba diving, you will have a lot of nitrogen in your body, and you won't be able to scuba dive as deep or long as you'd want to. Do them after and the same problem holds, but added to that is the micro-bubble problem.

If you care to look it up, I believe the research for the lungs as a bubble filter GLS refers to started with Butler and Hills, 1979.

Butler and Hills, 1979; The lungs as a filter for microbubbles. Journal of applied physiology: respiratory, environmental and exercise physiology 47(3):537-43 · October 1979