What factors determine the maximum length of a snorkel?

[yasar1967]

What limits the length of a snorkel?
Our chest muscles strenth?
If they are strong enough will we be able to swim under 3m of water with a loong snorkel?

 

[Borek]

You have to take a dead volume into account - the longer the snorkel, the more air it contains and you breath this air only, there is no exchange.

 

[yasar1967]

How about the water pressure we have to deal? Wouldn'T be much more diffucult to expand your chest at deeper sea levels? Then how scuba divers breath? Do their tubes give much more pressurised air to chest to overcome water pressure?

 

[mgb_phys]

For practical lengths of snorkel they are limited by the dead volume but deeper than this you would have a problem with pressure.
The 'clever' part of a scuba rig is the regulator (the plastic thing in your mouth) this delivers air at exactly the surrounding water pressure.

 

[tonyh]

What limits the length of a snorkel?
Our chest muscles strenth?
If they are strong enough will we be able to swim under 3m of water with a loong snorkel?

Yes. I think the muscles are the most important factor. It's just a question of pressure difference between the air in a diver's lungs (at atmospheric level until he breathes out) and that on the body (due to the water).
An example from one of my physics textbooks uses a simple model of a diver in still, fresh water (density 1000kg/m^3). A snorkel length of 6m would lead to a pressure difference of about 60,000 Pa - more than enough to collapse the lungs and force pressurised blood into them, i.e., extremely dangerous. In this model, the pressure difference is directly proportional to the depth, and so, under the same conditions, a 3m snorkel would give a pressure difference of half of this. I'm not sure how dangerous this would be. Obviously it will vary somewhat depending on the strength of the person.