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Johnmpcny
April 19th, 2011, 01:03 PM
If I snorkel the off diving day before or even morning of my return flight after a week of diving does that add to my no fly time or risk? I do get down 20 to 30 + ft when I do this and was asked by one person since I equalize do I increase any risks when flying the next day or same day? It had never occurred to me.

DBailey
April 19th, 2011, 01:57 PM
If I snorkel the off diving day before or even morning of my return flight after a week of diving does that add to my no fly time or risk? I do get down 20 to 30 + ft when I do this and was asked by one person since I equalize do I increase any risks when flying the next day or same day? It had never occurred to me.

Are you breathing compressed air at depth?

knowone
April 19th, 2011, 02:04 PM
I think I heard from an uncle of a friend's cousin's wive's son, or just read
that it depends on the size of your snorkel

Bedros A
April 19th, 2011, 02:39 PM
In my limited experience...I dont think it would be a problem if you're snorkeling.
If you're not breathing compressed air, then your no fly time should not be affected.

However, if during the previous day's dive, you surpassed the NDL times and were forced into making a DECO stop, then intensive snorkeling (or any tiring physical work) is not recommended directly after the dive.

Enjoy

BA

awap
April 19th, 2011, 02:53 PM
Submersion will increase the PP of nitrogen in you body and effect the off-gassing process. It can even result in increasing the body's nitrogen loading. In an extreme example, Japanese pearl divers (free divers) have been known to get the bends.

That said, I don't think I would worry much about a total bottom time of 5 to 10 minutes at 20 to 30 feet. But, you always have the option of just remaining on the surface and not taking any added risks.

Karibelle
April 19th, 2011, 02:57 PM
That said, I don't think I would worry much about a total bottom time of 5 to 10 minutes at 20 to 30 feet.

I had to read this a couple of times to realize you said "total" and didn't mean all at once. I thought wow... that guy can really hold his breath.

duh. :shocked2:

Kenny13
April 19th, 2011, 03:38 PM
I had to read this a couple of times to realize you said "total" and didn't mean all at once. I thought wow... that guy can really hold his breath.

duh. :shocked2:

I think you and I read that the same way lol. I was thinking the same thing.

nomro
April 19th, 2011, 03:40 PM
What I know , if the air is not compressed then dont worry about it . plus how many minutes did you spend below the surface ?
What is important from my point of view (I'm not a doctor) is the no fly time on your dive computer that is based on actual diving .

Downing
April 19th, 2011, 04:24 PM
On an episode of Planet Earth I watched an Indonesian (I think) free diver who can hold his breath for up to five minutes at 60 feet. Incredible.

knotical
April 19th, 2011, 05:02 PM
Submersion will increase the PP of nitrogen in you body and effect the off-gassing process. It can even result in increasing the body's nitrogen loading. In an extreme example, Japanese pearl divers (free divers) have been known to get the bends.

That said, I don't think I would worry much about a total bottom time of 5 to 10 minutes at 20 to 30 feet. But, you always have the option of just remaining on the surface and not taking any added risks.
+ 1 what awap said.

The air in your lungs while free-diving is compressed, to the ambient pressure, so there is some increased risk of DCS. However, in the scenario described by the OP, the increase is likely extremely negligible.

Charlie99
April 19th, 2011, 05:15 PM
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.

Bedros A
April 19th, 2011, 06:06 PM
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

fresh_fish
April 20th, 2011, 08:07 AM
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.

temet vince
April 20th, 2011, 09:58 PM
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.

temet vince
April 20th, 2011, 10:01 PM
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.

fisheater
April 20th, 2011, 10:06 PM
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.


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temet vince
April 20th, 2011, 10:15 PM
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.


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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.

knotical
April 21st, 2011, 08:58 AM
...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 (http://en.wikipedia.org/wiki/Taravana)

However, in the example cited by the OP, the DCS effect is vanishingly small, even though the lung compression is dramatic.

bleeb
April 21st, 2011, 12:03 PM
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.




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.

temet vince
April 21st, 2011, 05:48 PM
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.

Charlie99
April 21st, 2011, 07:55 PM
Water is nearly incompressible, so the volume of water changes very little as the pressure changes. This is also true of most of the body. What does compress is any gas filled areas of the body .... lungs, ears, etc.

Regarding blood pressure, I think you are confusing the absolute pressure of the blood with the differential pressure between different parts of the circulatory system.

Blood pressure readings are normally expressed in millimeters of mercury. 760mm of mercury is 1 atm, so a normal blood pressure of 120mmHg is about 0.16atm. On the surface, your arterial blood pressure is about 0.16atm (120mm Hg) above the ambient 1ata pressure. When you are down at 100' or 4ata, your arterial blood pressure will still be about 0.16ata relative to the ambient. The fact that your absolute blood pressure when at 100' is about 4.16ata doesn't matter.

awap
April 21st, 2011, 07:56 PM
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.

Gas Laws don't hold for liquids. Your heart works like a 1st stage - it automatically adjusts for ambient pressure. What is the volume of 1 pound of water at 1 ATM? What is the volume of that same pound of water a 4 ATM? You could pour it in a balloon and see for yourself.

temet vince
April 21st, 2011, 09:37 PM
Gas Laws don't hold for liquids. Your heart works like a 1st stage - it automatically adjusts for ambient pressure. What is the volume of 1 pound of water at 1 ATM? What is the volume of that same pound of water a 4 ATM? You could pour it in a balloon and see for yourself.

Ah, so that's my problem. That's right, you can't apply gas laws to liquids because of the intra molecular forces. Duh. You'll have to forgive me, it's been a long time since chemistry.

So, let me get this straight: every time you snorkel down to say, 30 feet, are you facing the same effects as diving to 30 feet? Or is there a difference? I always thought there was a difference because in diving you are breathing compressed air, which is where the nitrogen problem comes about.

knotical
April 21st, 2011, 09:50 PM
So, let me get this straight: every time you snorkel down to say, 30 feet, are you facing the same effects as diving to 30 feet? Or is there a difference? I always thought there was a difference because in diving you are breathing compressed air, which is where the nitrogen problem comes about.
You are facing some of the same effects. When free-diving, you are experiencing a similar increase in the pressure of the gas within your lungs, so there will be on-gassing of nitrogen. The amount of nitrogen absorption will be significantly limited because you will only be a depth briefly.
However, when free-diving you are not replenishing the air in your lungs with air from your regulator so your lungs decrease in size. The exterior of your body experiences the same increase in ambient pressure. Your middle ear and mask air spaces both want to compress, so must be equalized from the limited air in your lungs if you don't want to experience pain in your ears and mask squeeze.

awap
April 21st, 2011, 10:08 PM
Ah, so that's my problem. That's right, you can't apply gas laws to liquids because of the intra molecular forces. Duh. You'll have to forgive me, it's been a long time since chemistry.

So, let me get this straight: every time you snorkel down to say, 30 feet, are you facing the same effects as diving to 30 feet? Or is there a difference? I always thought there was a difference because in diving you are breathing compressed air, which is where the nitrogen problem comes about.

The pressure of the gas in your lungs is ambient pressure just like the gas inside your 2nd stage. Only your tank, ist stage, and hoses (up to the LP seals) see elevated pressures. If the pressure in yourt lungs ever rises above ambient (like when ascending with the airway closed), the overpressure will do severe damage to your lungs.

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