Long snorkel breathing

[Hank49]

I'm stumped. A friend of mine is laying pipe in 4 feet of water and and his plan was to use a 20 foot section of ribbed, stiff hose as a snorkel so his worker could stay under and put it together. He attached a check valve and exhaust valve on the mouthpiece end because he knew he couldn't rebreath the CO2 that would build up in the long tube (he's not a diver). It apparently worked fine when sitting in the boat and breathing through it. But when his worker went down just 3-4 feet, they claimed it was like sucking a breath through a small straw. They couldn't breathe enough air. I asked him if the tube was collapsing and he said no. ?? Why would this happen?

I haven't seen the rig and there may be an obvious design flaw which upon seeing, I'll slap my forehead...but is there some physics law here that I'm missing?

 

[ACR]

is there some physics law here that I'm missing?

Yes, Boyles law as a matter of fact.

"For a fixed amount of gas kept at a fixed temperature, pressure and volume are inversely proportional (while one increases, the other decreases)

To breath the pressure in your lungs needs to be more or less equal to the ambient pressure. So, in order to take a breath at 33ft using a snorkel to the surface your lungs would need to be able to double the air pressure on the way down. Not humanly possible. It would be like trying to breath with a sumo wrester sitting on your chest.

At 4', that's about 1.12ata, so it would only be like a regular guy sitting on your chest

 

[fppf]

No its not Boyles law, that explanes the relation to volume and pressure for a gas.

It is the pressure of the fluid (water) at 4 feet that is causing the issue.
Your lungs are not strong enough to over come the roughly 2 PSI that is trying to collaps your lungs and push all the air back up to the surface.

When on scuba the pressure that your regulator supplies is refrenced to the surrounding pressure. This should all be explained in your basic OW class.

 

[the gooch]

Correct--your lungs are unable to overcome the added pressure of the water at depth to expand.

 

[Blazinator]

Good answer, Fppf.

I wanted to do the long snorkel thing too, at one time, before I got certified, but after some web searching, I discovered that 18" is pretty much the limit of what the body can suck against ambient water pressure.

This is why hookah and SNUBA systems were developed. They provide the pressurized air through either a topside scuba tank or a small compressor.

Cheaper to get certified and simply use SCUBA to do pipe laying at 4'

Or, (you didn't hear me tell you this) you can do what the kid on YouTube did, and simply breathe from a hand pumped garden sprayer compresser (new, clean). You would have to get used to pulling the trigger for every breath, then exhale through your nose or something. I would attach a second stage regulator to the hose.

Before I get flamed for advocating this "dangerous" method, remember that the OP is talking about only FOUR FEET DEEP. Yeah, I know that they say you can embolize from shallow pool depths, but I've tried it from pool depths, and you would really have to have a deep breath held to embolize from six feet or less. So, Hank, for safety reasons, your non-diver friend shouldn't try this unless trained to understand lung expansion embolisms (just exhale upon surfacing).

 

[phunk]

4 feet is enough to cause a barotrauma, if he takes a big lungful then stands up. Should be at least OW trained if he's going to breathe compressed air underwater at any depth.

 

[Blackwood]

Before I get flamed for advocating this "dangerous" method, remember that the OP is talking about only FOUR FEET DEEP.

Dr. Henry Kendall comes to mind. RIP.

 

[SPG3K]

That YouTube thing is nuts.

I watched it the other day. I did some dumb stuff as a kid, but a scuba unit made from a pump sprayer?

I bet that kids winds up at MIT if he isn't dead first. =/

 

[Hank49]

So as long as the tube doesn't collapse, the air pressure inside drops as you go deeper, which eventually would drop enough, to create more a less a vacuum relative to your lung pressure, and would suck the air back out of your lungs if you open your airway. I think I have the mental picture. I just never imagined this would occur at 3-4 feet depth. The guy called me and asked me if it would work a couple weeks ago and I told him about huka systems but that I had no idea how deep one could breath off a snorkel.

 

[Thalassamania]

You're lucky to be able to breath off a 2 foot tube. The reason is that with the tube in your mouth the pressure in your lungs is 1 ATM whilst the pressure pressing in on your ribcage exceeds 1 ATM plus 1 PSI. Just that 1 PSI is enough to keep you from being able to expand your chest and suck air in.

For laying the pipe ... learn to dive, hire a diver, or as a last resort think SNUBA (something I don't agree with, but there are those who feel it does not require training).