Free Diving same day as Scuba?!

[divebunnie]

Free diving cerainly doesn't have the issue of nitrogen… so long as you haven't been scuba diving before hand.

If you have taken on sufficient nitrogen during a previous dive, then it is logically possible for that nitrogen to recompress during a freedive. If you then ascend from that dive quickly, then the release of pressure could potentially be great enough to cause the nitrogen to bubble. I can see from previous posts, that it has obviously happened to people, so this can't be entirely theoretical.
I don't know enough about it at present to be specific about depths, however we all know that the sharpest increase in pressure happens within that first 10 metres. So personally, whilst I would be happy to pootle around snorkelling at the surface, I would be wary of duck diving after a SCUBA dive.

 

[IndigoBlue]

Read this;
http://www.wkpp.org/articles/Decompression/why_we_do_not_bounce_dive_after_diving.htm

All of the people I have known who had a bad DCI hit had done a bounce dive or free dive after a deep dive.

Unfortunately in the citation, G.I. only says "dont do it" rather than giving an explanation specifically related to freediving after scuba.

After a scuba dive, during the surface interval before the next dive, the venous blood supply is being "scrubbed" of its dissolved N2 by the lungs, during normal breathing. Holding one's breath, either out of the water or underwater, will potentially interrupt that scrubbing process. This has the potential for returning unscrubbed venous blood back to the heart and onto the rest of the body via the arterial blood supply. Hence, the potential for DCS.

The NAUI basic open water manual for students warns against freediving after scuba, and I mention it during the classroom instruction.

 

[pipedope]

Remember that it is hard to give any absolutes in diving.

The basic idea is that after a dive you are offgassing absorbed N2. How much and how fast depends on the dive profile.

Most of us can have a fairly large amount of bubbles in the venous blood without problems as they get filtered out by the lungs. We generally don't notice and they are not a problem.
The problem comes in because we don't know which dives are producing lots of bubbles and which are not producing significant bubbles.

If we have lots of bubbles in the venous side and do a free dive (yes even 15'-20') we can compress a bunch of those bubbles, let them through the lungs and into the arteries and then they cause trouble.

What to do?

I like to do my free diving first thing in the morning, that way I have all night to offgass first.

These days I am so far from the NDLs that it is unlikely to be a problem for me in any case. :sad:

BTW Most new OW divers are unlikely to build enough N2 load to be bubbling that much so the risk is small. As you start diving deeper and/or longer the risk increases but the diver will have had more time to learn more about how this stuff works.

Do what you want, but know what you do.

 

[IndigoBlue]

Remember that it is hard to give any absolutes in diving.

The basic idea is that after a dive you are offgassing absorbed N2. How much and how fast depends on the dive profile.

Most of us can have a fairly large amount of bubbles in the venous blood without problems as they get filtered out by the lungs. We generally don't notice and they are not a problem.
The problem comes in because we don't know which dives are producing lots of bubbles and which are not producing significant bubbles.

If we have lots of bubbles in the venous side and do a free dive (yes even 15'-20') we can compress a bunch of those bubbles, let them through the lungs and into the arteries and then they cause trouble.
.

Michael, I would call that a secondary consideration. I am not even sure it pertains to most freediving-after-diving situtaions.

It definitely does pertain to spike diving on scuba, of course.

But the main culprit I see from freediving after scuba is merely the breathholding effect on the normal N2 scrubbing process.

 

[DandyDon]

I just posted and referenced this thread to Doc Deco in his forum to see what he says.

I vaugely remember reading something that nitrogen loading is not an issue for free divers as they are diving on one breath and are not breathing while they're under water and under pressure - the same reason air breathing water mammals do not get the bends.

However this doesn't address nitrogen that may already be present from earlier scuba dives.

Marc

Actually, it's been discussed in that forum a lot, but how many Newbies read that one? I opened it in New To Scuba in hopes to getting the word out to the Newbies who are not being taught, and - it's not whether this is a bad idea, or even how bad, but why aren't Newbies being warned...? :jump013:

Anyway, DrD will be back in 4 days, and I'm sure he'll get to this when he can. I always appreciate his comments; I've certainly learned a lot from him and his forum. But then :martian: I read accident and fatality reports from DAN, too - in hopes of avoiding the same mistakes. Seems like a great idea to me, but not a popular one it seems.

 

[jacket_fan]

I am one who just got certified. I do not remember any mention of freediving (snorkeling) limitations after a scuba dive. So here is one vote cast for not being told.

The comments made here make sense, and I sure do not want to do anything stupid.

I plan to be in Belize in June and plan on the first day to be scuba and the rest of the trip to snorkel. Plan on getting some lobsters.

How much nitrogen loading is acceptable to be able to snorkel the next day? I learned to dive using a computer so any reference to that would be appreciated. Is overnight enough of a surface interval, or should I go by what the computer tells me? Or is this a question for DrD?

Thanks

 

[BigJetDriver]

I plan to be in Belize in June and plan on the first day to be scuba and the rest of the trip to snorkel. Plan on getting some lobsters.

How much nitrogen loading is acceptable to be able to snorkel the next day? I learned to dive using a computer so any reference to that would be appreciated. Is overnight enough of a surface interval, or should I go by what the computer tells me? Thanks

Jacket Fan,

When in Belize, if you are out on Ambergris Key, stop in at ProTech Belize on the dock at the Belize Yacht Club. They are great people there, and are fully rec to tech!

Putzing around in the shallows after your dive, at Shark/Ray Alley, for instance, is certainly O.K. and a lot of fun!

Overnight is fine for SI, and your computer should be clear as well, if you are within the rec NDL's. If you are clear to dive the next day, you are certainly cleared to snorkel.

Have fun!

BJD
IANTD IT
DMT :doctor:

 

[jonnythan]

Unfortunately in the citation, G.I. only says "dont do it" rather than giving an explanation specifically related to freediving after scuba.

Uhh? :06:

George specifically stated the reason. Everyone has nitrogen bubbles in their venous system after any significant dive. These bubbles get bigger as they absorb gas from the surrounding blood.

The lungs present a good filter for these bubbles in the venous system. Diving, whether free diving or scuba diving, will temporarily compress these bubbles. They can get compressed so small they can move by the lungs, then when you resurface they're suddenly in your arteries and you're going to have problems when the bubbles move into and block smaller vessles. From the rest of your post, it looks like you more or less know this. [edit: score one against me for not reading your post.. you don't seem to get this]

All of this was explicitly stated in his article. The article is quite appropriately titled "WHY We Do Not Bounce Dive After Diving in the WKPP" You may want to go back and read it. There are a few other articles on that web site, most of which contain some actually useful information. Whatever you think of GI, making stuff up about him doesn't help your cause.

 

[BigJetDriver]

The main culprit I see from freediving after scuba is merely the breathholding effect on the normal N2 scrubbing process.

Indigo, et al,

If I may correct a bit of a misconception here, the problem with breath-hold diving after scuba diving is as our favourite neighborhood commercial diver, Pipedope, has expressed.

The lungs are a very efficient filter-bed. They can actually handle a lot of bubbles (up to a certain critical size) by holding them at the blood/gas interface in the alveoli and exchanging the trapped gas out of them.

The problem is that, if you have a lot of them trapped, AND you suddenly squeeze them down to a much smaller size, there is the possibility, through various mechanisms, for some of them to pass to the arterial circulation side. Then, as they are pushed to various REALLY sensitive areas and re-expand, they can be very troublesome!

While this condition requires a combination of circumstances, it is something to think about. Now, if you are diving within the NDL's, and your tables and/or computer indicate that you are cleared to dive again, you are almost certainly O.K to snorkel in the shallows. Deep breath-hold diving is another matter, due to the expand-crush-expand problem.

You can find a good discussion of this in Bove's "Diving Medicine" or Edmunds, Lowry, Pennefather, et al, "Diving and Subaquatic Medicine".

While I am a pale substitute for Doc Deco, I am a trained and certified DMT.

BJD :doctor:

P.S.---(And I did stay at a Holiday Inn Express last night!)

 

[H2Andy]

dumb question:

what is DMT?