snorkel after diving - No fly time risk?

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

Johnmpcny -- you didn't ask about freediving after diving, but here's some free advice that is worth what you've paid for it .....

It's not a good idea to do any freediving for the first several hours after diving. The problem is that it is common for you to have some small bubbles in the venous side of the circulatory system for a couple hours after diving. They don't normally cause any problems because they are filtered out by the lungs. People with a heart defect called PFO can sometimes have problem, because the PFO can open up a direct path between the two sides of the heart and let the small bubbles through into the arterial side ... often the opening opens up when coughing or when you hold your breath when lifting something heavy.

Bubbles in the blood on the arterial side can block capillaries, preventing blood from getting to critical bits of your body, like the brain.

When you freedive, the increased pressure will reduce the size of the bubbles in the venous system, thereby letting some of them get past the lungs. Then as you come back to the surface, the bubble will expand back to the larger sizes that can cause problems.

The above cautions don't apply to freediving the day after diving, since you won't have any bubbles in your venous system at that point.
 
In the OP's case, the increased chance of DCS is minimal...near nonexistant.

1 breath-held descent will not cause an increase in DCS because of the limited amount of air you have in your lungs.

The documented cases of bends in pearl collectors is because they do this A LOT during a very short period. In many cases, pearl divers (especially freediving pearl hunters, such as Japanese "Ama" Divers) needed to collect nearly one ton of oysters in order to obtain three to four high quality pearls.

PS: I've always been fascinated by pearl divers...one tough breed of divers :D


BA
 
If you want to be safe, look at the tables, and calculate it as 5-10 minutes at 20-30 ft.

The physiology is still there, no matter what you breathe from. Your body still circulates the compressed gas from your lungs while you are looking, and it will expand when you come back up. Yes it is minimal, but it is still happening and each dip will add to the amount that needs to come out of your tissues.
 
Snorkeling will not add nitrogen to your body since you are not breathing compressed air. It shouldn't even affect the residual nitrogen already in your body since there won't be a significant volume change within.
 
If you want to be safe, look at the tables, and calculate it as 5-10 minutes at 20-30 ft.

The physiology is still there, no matter what you breathe from. Your body still circulates the compressed gas from your lungs while you are looking, and it will expand when you come back up. Yes it is minimal, but it is still happening and each dip will add to the amount that needs to come out of your tissues.

As far as I'm aware, this is incorrect.

Unless your body volume changes under depth (ie, your body is squeezed so hard that it changes volume), then the pressure inside your body cannot and will not change.

Our body puts up with pressure quite well. In fact it's under a lot of pressure at the surface. Adding 1 or 2 more atms shouldn't change our internal volume.

Edit: Perhaps the area around the lungs does compress some. I doubt it would be a significant amount, but I could see it being enough to cause the problems that Charlie99 alluded to above.
 
Increasing pressure on a liquid or solid doesn't result in proportional volume changes. The pressure is transferred through the human body without substantial volume change because it's mostly either a solid or A liquid. However, the air spaces, including bubbles in tissue or blood will contract due to the pressure around them.


Sent from my iPhone using Tapatalk
 
Increasing pressure on a liquid or solid doesn't result in proportional volume changes. The pressure is transferred through the human body without substantial volume change because it's mostly either a solid or A liquid. However, the air spaces, including bubbles in tissue or blood will contract due to the pressure around them.


Sent from my iPhone using Tapatalk

I'm not quite sure what you're meaning to say, so here's a breakdown of 3 simple well known "solids" under pressure:

1. Scuba air tank. Very rigid. Thus, the air inside does not compress more at a greater depth.
2. Plastic bottle with cap on. Not very rigid. Thus, the container shrinks with depth, decreasing the volume and increasing the pressure within.
3. Human body. Not super rigid, but way more rigid that a plastic bottle. There will be some compression in the lungs, especially at deeper depths, but that difference is small.
 
...3. Human body. Not super rigid, but way more rigid than a plastic bottle. There will be some compression in the lungs, especially at deeper depths, but that difference is small.
We disagree. Your lungs expand and contract significantly every time you breathe. When you breath-hold submerge, your lungs contract (are compressed) as if you were exhaling.

When a snorkeler (on the surface) submerges and becomes a free-diver, physics dictates that his/her lung will compress. Recall from open water class what happens to balloons.

The air in a free-diver's lungs is compressed while he is underwater. That is why aggressive, repetitive, free-divers can suffer DCS. See, for example: Taravana - Wikipedia, the free encyclopedia

However, in the example cited by the OP, the DCS effect is vanishingly small, even though the lung compression is dramatic.
 
knotical already corrected some issues in another post, but since there seem to be several potential hazardous errors in this one as well, it seemed worth explicitly highlighting them.

fresh_fish:
The physiology is still there, no matter what you breathe from. Your body still circulates the compressed gas from your lungs while you are looking, and it will expand when you come back up. Yes it is minimal, but it is still happening and each dip will add to the amount that needs to come out of your tissues.
As far as I'm aware, this is incorrect.

Actually, fresh_fish (and all the others who have stated this in this thread) are correct.

Unless your body volume changes under depth (ie, your body is squeezed so hard that it changes volume), then the pressure inside your body cannot and will not change.

When diving, the pressure inside your body is the same pressure as outside. Your body is mostly liquid, and it only takes a minuscule volume change for quite a significant pressure change. Gas pockets are subject to Boyle's Law, which is why you clear your ears while diving: to allow passages to stay their normal size by venting gas at ambient pressure into them. Lungs stay the same size because they're constantly being vented by breathing ambient pressure gas.

Our body puts up with pressure quite well. In fact it's under a lot of pressure at the surface. Adding 1 or 2 more atms shouldn't change our internal volume.

Edit: Perhaps the area around the lungs does compress some. I doubt it would be a significant amount, but I could see it being enough to cause the problems that Charlie99 alluded to above.

Lung tissue has the strength of wet tissue paper, and it's ability to retain any size under pressure is negligible. They're completely subject to Boyle's Law, i.e. descending to a depth of 33 fsw without breathing in will cause their size to drop in half inside your rib cage. Going even deeper without gas to replace the volume will cause them to shrink proportionately. Freedivers going deep routinely acknowledge and face this issue.
 
Ok, so I guess the lungs compress much more that I thought!
I'll be the first one to admit I was wrong. Sorry about that. :(

I guess my biggest confusion was that you say the body changes pressure inside to equalize outside, when I assumed that the skin and muscles (and bones too) acted as a rigid platform to resist pressure changes.

I'll have to do some more research now!

Should I delete my previous posts?

Also, why doesn't your blood pressure change and kill you?
In addition, how does the inside of your body "magically" gain the pressure it experiences outside of your body? To change pressure, you either need a change in temperature, a change in volume, or a change in the amount of material itself. There isn't a temperature change, or you would either freeze to death or overheat, and there can't be a volume change in your entire body or you would die (the blood pressure question listed above), and your body obviously isn't adding or deleting itself. I'm just having a hard time reasoning how your internal pressure can change like that, at least scientifically.
 
Last edited:

Back
Top Bottom