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Comment by dahdum | Hacker News Reader

> When I ran short of air at the wreck, Tom would swim over and hold out his backup breathing line, known to divers as a "reserve regulator." I'd catch a breath to stay down longer.

Taking breaths off a scuba tank at depth is something only someone trained as both a diver and freediver should do. I don’t get the impression the reporter is either. Tom seems a bit cavalier.

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The article specifies that the wreckage in question was 10 feet below the surface. Is that deep enough to matter?

If you took a deep breath and held it on the way up, maybe. Otherwise, probably not.

Yes, the fractional pressure change is greatest near the surface, so shallow water is the most dangerous region for lung damage if you hold your breath on ascent.

You know what you’re talking about.

Wow, TIL! Thank you for sharing!

there are community center pools deeper than that, so no.

The difference is this: in a community centre pool, a diver doesn't give you compressed air to breath at the bottom of the pool.

The thing the commentor above is concerned about is pulmonary barotrauma, a.k.a. "burst lung". Between 10 feet depth and the surface the gas in your lungs will expand by 30%. If you took a deep breath at 10 feet deep, and held it, then that expansion can cause rupture of the alveoli.

For this reason one of the first things you are told (or should be told!) in a scuba diving course is to breath continuously, i.e. never hold your breath.

https://en.wikipedia.org/wiki/Shallow-water_blackout

As an experienced scuba diver and freediver, I would never mix the two and take air from a scuba diver while freediving…. The habit of holding my breath on ascent while freediving is really ingrained, and I think it is very likely to forget to exhale when doing this.

I know very little about either of these worlds -- can you explain why that is such a dangerous thing to do? Is it just that you might run out when you don't expect to?

Breathing pressurized air from a tank while you're under pressure in the water can dissolve extra nitrogen into your system, as you ascend the nitrogen can bubble out in your blood stream causing nitrogen narcosis aka the bends https://wikipedia.org/wiki/Decompression_sickness

Nitrogen narcosis is a different thing than the bends.

That's not the problem with this. When you inhale from a scuba regulator, you're breathing in air at ambient pressure, which means an extra one atmosphere of pressure at 30 feet depth. As surrounding pressure drops, that air will expand proportionally. If you take a deep breath and then ascend, the air can overinflate your lungs and cause serious damage. SCUBA divers are trained to exhale while ascending to avoid this, but freedivers tend to hold their breath.

I don't know how you could hold your breath with double the volume in lungs. That at only one atmosphere.

Not to mention your ears. Part of releasing air as you ascend is to help your ears adjust. Its only natural. Same with descending.

I have seen alot of minor injury as a summer dive boat mate. Mostly blood vessels burst in the eyes from people holding their breath ascending..

I saw a guy pop out of the water like a cork because the ran out of air. Of course he said he was Navy UDT. Didn't need a buddy. Steel doubles and a speargun. Thankfully nobody got hurt.

NAUI Diver with over 45 dives in Hatteras.

Lung over expansion injury if he holds his breath on ascent like many free divers naturally do. He was taking compressed air breaths at depth and then ascending. If you fill your lungs at 33ft and ascend, the gas will double in volume at the surface, causing tons of damage and bleeding.

What? No, not at all. That’s a technique that’s taught at the most basic levels of even open water diving. It might be not as ideal if you’re near maximum depths for a general air mix where you might start to run into nitrogen saturation (say longer than 10 mins) at 100+ ft depth, but in the article they were down what seems like no deeper than 15 ft. You could pretty much stay down all day that shallow.

It’s standard training, at least with my NAUI knowledge to practice rescue breathing with another divers spider. My instructor added a few curveballs in that he’d mess up my tank, make me take it off and fix it while without a mask with my eyes closed and breathing off a fellow student’s tank. Nothing to it.

Edit: ok I see you mean as the reporter ostensibly not having any dive training, yeah, probably a bit inadvisable, but they dove with someone with experience and only at shallow depths, the danger is probably a bit overblown after a short amount of instruction. You’re not gonna get bent at 15 ft.

It’s not getting bent, it’s lung over expansion injury from taking a compressed air breath at depth and ascending afterward as a free diver. Yes, you could explain the danger to him, but people panic and forget.

Except in that trained scuba situation, both divers ascend together while still breathing. If you are freediving it is possible to forget to do this, after getting air from a scuba diver.

> Tom seems a bit cavalier.

We should all aspire to be more like Tom.

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