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Comment by ArtWomb | Hacker News Reader

Am certain if you ask 100 beginner divers, 99 will have their own brush with death adventures!

Mine came in the form of a six foot barracuda getting a bit too close for comfort. I am sure if I hadn't played it cool. Had somehow attacked or acted aggressively to shush it away (when I was a guest in it's deep sea domain). It would have enjoyed a nice lunch of fresh human flesh.

The second was going below the hard deck at 300 feet whilst diving the continental shelf in the Caribbean. It's stunning. Floating weightlessly over the void that drops suddenly over a mile in depth. Feeling the rush of frigid current rise from the abyss. And seeing mysterious shapes as light filters down into darkness. But I too ran low on air. And had to come up fast.

I haven't been diving in decades. And would require re-certification. But I've always heard legendary tales of the Red Sea and Australia's Coral Reef. Definite bucket list items ;)

https://oceana.org/

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I've done a few hundred dives (so, intermediate? with some additional certifications for deep/nitrox/rescue/divemaster) and the biggest problems I've had were 1) dropping a steel cylinder on my toe on a boat 2) getting sunburned on my scalp before I started wearing a hood even in warm water, due to an extended surface interval 3) dodgy food on a liveaboard.

I don't think most recreational divers push things close to the line at all.

Most definitely misremembering the depths! 300' begins to collapse lung & heart cavities ;)

Scuba diving is done at ambient pressure. Lung and heart cavities don't collapse.

(Lungs do compress during breath hold freediving.)

The issue with depth is 1) you can't do a direct ascent to the surface past...18m or so?...with a high level of safety, for a large number of users, and from 30m or so (the recreational limit for most programs) it's even harder, plus that's the upper bound where nitrogen narcosis starts to set in. I've done down to 40m on air which is the next limit and the point where a lot of people have more serious nitrogen narcosis. Beyond that you really should be doing decompression diving and start to be looking at different gas mixes which makes it all a lot more complex. At depths beyond >50m oxygen toxicity on air would be bad too. The current normal limit is ~56m on air, previously people have done 60-65m pretty consistently on air, and the record is probably 155m (but that is insane and almost certainly caused harm, plus had high risk).

Ascent from depth without having cavities open to equalize pressure will be a really bad deal even from 18m (and really from comparatively shallow depths like 3-6m), but that really just means breathing out at slow rate during ascent. For that it'd be explode vs. implode though :)

I'm no marine biologist but you can be certain that humans are not a regular diet of barracudas.

Once, a 5-meter tiger shark came to me out of the blue and got too close, but as humans aren't a regular diet of tiger sharks either, it swam away.

I've met literally dozens of people who talk about their close brush with a barracuda while diving.

They are a minimal threat but they look kind of scary so people always always think that they had a close call with one when the barracuda is just doing what they do which is checking out a human who might hand them a fish.

It always makes me chuckle because I hear people tell their barracudas stories and they always sound the exact same. At no point were they in any danger but they really think they were.

Just like masses being overscared with sharks because of Jaws, its probably because another but much less popular movie “The Depth [1977]” with Nick Noltie where in a final scene Noltie wins underwater battle because he knows where huge Murena lives and put a villain head in there. Then we see that Murena litterally sicking him into her hole with a force that break his mask and break him in half. Definitely one of the most memorable scenes of the movie and definitely what made me start my doving adventure (now cerified with CMAS and PAID up to deep dive / rescue diver). Definitiely movie worth rewatching.

Barracudas can freak you out because they seem to be curious. They just hang out and watch you. The only time I've heard of someone getting bitten was on a YouTube sailing channel where the group was making fun of one of the crew for being the only known human to actually be bit by a barracuda. IIRC he was messing with it.

Jelly fish, OTOH, suck.

Barracudas really aren't dangerous to divers. There are a few recorded cases of bites but I don't think anyone has been killed.

I've read they sometimes bite because of flashing jewelry which they mistake for shiny small fish.

When on a snorkel trip in the Florida Keys I was told not to point at the barracuda, because tourist often fed them hotdogs to get a close up look, and so they were trained to eat anything hotdog shaped... no idea if it was true.

If the Great Barrier Reef is on your bucket list then you really want to get on that asap. It's getting more and more bleached.

Yep. Sadly, I'd say that even now you might want to spend your travel dollars elsewhere.

I'm very curious what gas blend were you using at 300 ft - I'm fairly sure that would be fatal on air or even nitrox.

I'm also shocked that you could come up from that depth with any sort of urgency and not be seriously injured / killed by some form of DCS.

Maybe I misunderstood and you were not a beginner, because otherwise that tour operator has no business running a dive op.

Nitrox is 100% fatal at depths beyond prescribed limit. The whole point of Nitrox is to increases the oxygen content in the gas to minimize nitrogen absorption. A side effect of this is that you will get to hyperoxic poisoning thresholds earlier on a deeper dive profile. This is why Nitrox requires additional certifications, to help understand these limitations and learn how to calculate your max operating depth. (when using nitrox wihtin these thresholds I find I have more energy at the end of my dive).

To go deeper you need to blend in inert gasses and decrease o2 and n2 to keep partial pressures below fatal doses. This means most commonly mixing in Helium to cut down on over o2 and n2 in your gas mix. Human tissue I guess doesn't absorb helium the same way it does n2.

Source: Open Water Scuba Instructor with multiple agencies... I havent taught in about 5 years though so some of this information may have changed, especially in light that global helium shortages (or US stock piles?) may have driven the price of He up to high to be used for mixed gas diving.

We still use helium for mixed gas diving but it is more expensive now. Human tissue does absorb helium in much the same way as nitrogen (or any other inert gas). The rate of diffusion is a little different which can impact the decompression profile.

You can see the coral reef in Eilat (Israel) without really diving since it is in shallow water, not sure if it is as good as in Egypt but at least there is a decent hospital near by if something goes wrong.

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