Physics of diving with a "straw"

[spectrum]

Take a regular snorkel, hang onto the side of the pool and, whilst breathing through the snorkel, hold your head underwater so it is completely submerged but the tip of the snorkel is still above the water.

If you can draw air down at all you're doing well, if you can draw air down in a normal breathing pattern for any length of time time then you are doing extremely well.

Yes, just bobbing vertical in the water breathing from your snorkel your lungs may be a foot or so below the surface and the effect on breathing resistance is very noticeable if you pay attention. You can feel this when vertical head up underwater with a scuba regulator as well. Pressure is balanced to mouth depth and you have to pull that next foot. If you go head down breathing will be very easy. When swimming prone in good trim the regulator and your lungs are at nearly the same depth and life is good.

Your ability to breathe is based on the movement of your diaphragm that causes a very minor change in differential pressure that drives inhalation.

So it won't work at 1m, let alone 30.

 

[ScoobaChef]

This thread kinda got me thinking a bit, so let's take the idea further and add a "magical" vest that allows you to breathe at depth, but doesn't change the ambient pressure on your body.

How would this affect nitrogen absorbtion and ppo2?

 

[Storker]

This thread kinda got me thinking a bit, so let's take the idea further and add a "magical" vest that allows you to breathe at depth, but doesn't change the ambient pressure on your body.

How would this affect nitrogen absorbtion and ppo2?

If it were possible, I'd guess that it'd affect your lungs in a rather unfortunate way (ambient pressure on the inside, 1ATA on the outside - equivalent to a CESA with your mouth and/or glottis closed, e.g. lung overexpansion).

I don't think any effect on N2 saturation or pPO2 would be my primary concern...

 

[ScoobaChef]

If it were possible, I'd guess that it'd affect your lungs in a rather unfortunate way (ambient pressure on the inside, 1ATA on the outside - equivalent to a CESA with your mouth and/or glottis closed, e.g. lung overexpansion).

I don't think any effect on N2 saturation or pPO2 would be my primary concern...

Nah mate, you missed the point. You're breathing surface air at 1ATA through a tube, the "vest" merely allows your diaphragm to overcome the ambient water pressure in order to inhale. So it would be the opposite, 1ATA in your lungs, 4ATA pressing on your body.

 

[Bob DBF]

aint going to happen. try it with a snorkel that is as short as 3'..as you exhale you will definitely feel the air rush out of you , try to inhale and you will find it next to impossible at as shallow a depth of 3ft.
over 30 years ago in a NASDS course we had a short length of hose attached to a jet snorkel to demonstrate how pressure at a depth as shallow as 3ft would make this next to impossible..was good for a few laughs in the pool.

Just one more reason all that "wasted" time in the old OW classes wasn't as wasted as the Agency's would like you to believe. Training a competent SCUBA diver takes time, regardless of what the promotions might tell you.



Bob
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That's my point, people, by and large, are not taught that diving can be deadly, they are taught how safe it is, and they are not equipped with the skills, taught and trained to the level required to be useful in an emergency.

"the future is uncertain and the end is always near"
Jim Morrison

 

[scagrotto]

Nah mate, you missed the point. You're breathing surface air at 1ATA through a tube, the "vest" merely allows your diaphragm to overcome the ambient water pressure in order to inhale. So it would be the opposite, 1ATA in your lungs, 4ATA pressing on your body.

In that case I suppose it would be a bit like what a free diver experiences. IIRC, a lot of blood is squeezed into the chest, which is what prevents it from being fairly thoroughly crushed by the extreme depths that some freedivers get to. I suspect that has implications for circulation that would be much more significant for a diver that breathes regularly and stays at depth far longer than it does for free divers.

N2 uptake would depend on the pressure gradient, and we're imagining a very speculative scenario where it may not be clear what the gradient is. Even if you can expand your pleural cavity, what guarantees that it's the 1 ATA air that flows in and not something from your 4ATA body, like a spleen or liver? Still, as long as the N2 gets into your blood and is transported to areas subject to 4ATA absorption would be the same as under normal diving circumstances, except that you'd only have inhaled 1/4 as much N2.

 

[BRT]

Simple fact is that if you put a tube in your mouth and head for the bottom while keeping the tube above water at some point your insides are going to be pushed up through that tube. Probably will not be all that comfortable. Picture drysuit squeeze on steroids.

 

[redacted]

Simple fact is that if you put a tube in your mouth and head for the bottom while keeping the tube above water at some point your insides are going to be pushed up through that tube. Probably will not be all that comfortable. Picture drysuit squeeze on steroids.

I don't suppose you could explain how that would happen.

 

[T.C.]

Nah mate, you missed the point. You're breathing surface air at 1ATA through a tube, the "vest" merely allows your diaphragm to overcome the ambient water pressure in order to inhale. So it would be the opposite, 1ATA in your lungs, 4ATA pressing on your body.

So...Part of your body is at low pressure, part at high pressure.

See the Mythbusters video. As BRT said, you'd end up inside your snorkel. It would not be comfortable.

There's a reason we compress the air in scuba tanks; and it isn't just so we can breath off them longer.

 

[Dr. Lecter]

I don't suppose you could explain how that would happen.

The tube, assuming it is sufficiently rigid to resist collapsing along its length, has created an area of 1ATA through a water column that is higher pressure. The water pressure will attempt to push into that space through the open end, but since you are attached to that end it will be compressing *you* into it first...though you'd have to hit a pretty decent depth for that to happen, I would think.