How deep can an average person dive with and without basic scuba gear?

Factual Questions
1

If you’re just an average 20-40 year old, without any diving experience and it’s effects on your breath holding, then:

  1. How deep can you dive without any equipment and for how long?

  2. How deep if you have a basic air tank and the minimal equipment you can get?

I remember when I was a kid I used to dive, if I remember correctly, some 2, 3 human lengths down to grab large rocks and whatever I found there, but once I reached them my breath would go away and it was hard to even get there due to pressure, so I got up right away. That got me wondering to what are the actual limits to how deep an average inexperienced person can go…and how much those limits are enlarged once you introduce a simple air tank and suit.

2

How long can you hold your breath?

World record for free diving is > 200 m. Recreational SCUBA limit is, let’s call it 40m, 20m for beginners.

3

But is it just about the breath or about the pressure as well? I don’t understand exactly how it works, but I know that some chemicals can cause you to feel like you are intoxicated.

That’s why I asked the air tank question, assuming you have “infinite” air, where would be this pressure limit that causes you to feel intoxicated?

4

They cannot predict exactly when it might hit you, but let’s say 30-40m, which is why nobody will certify you to dive that deeply if you are totally untrained.

Depth Symptoms
0–10m Unnoticeable minor symptoms, or no symptoms at all
10–30m Mild impairment of performance of unpracticed tasks; Mildly impaired reasoning; Mild euphoria possible
30–50m Delayed response to visual and auditory stimuli; Reasoning and immediate memory affected more than motor coordination; Calculation errors and wrong choices; Idea fixation; Over-confidence and sense of well-being; Laughter and loquacity which may be overcome by self-control; Anxiety (common in cold murky water)
50–70m Sleepiness, impaired judgment, confusion; Hallucinations; Severe delay in response to signals, instructions and other stimuli; Occasional dizziness; Uncontrolled laughter, hysteria; Terror in some
5

I can dive about 10 meters snorkeling, with fins. But I’m a former competitive swimmer and lifeguard. I don’t think most average swimmer can make it that deep.

6

For amateur breath-hold diving, there are 3 limiting factors:
-how long can you hold your breath?
-how fast can you swim while holding your breath?
-how good are you at equalizing the pressure on you ears?

For a typical 20-40-year old who can swim but has no freediving experience, I’d be impressed if they made it deeper than 15 feet.

For scuba diving, breath-holding is not in play, and you have more time to descend and clear your ears slowly. But there are other limiting factors:

-amount of air (or other breathing gas) in your tank-- they come in different sizes, the most common being an AL-80 (which actually holds only about 77 cubic feet of air, not 80.) The biggest standard size holds 130 cubic feet, but you can bring more than one tank. How much air you need depends on many factors, depth being a very significant one. Every 33 feet increases the pressure by the same amount as the entire earth’s atmosphere, so at 33 feet you’ll breathe through your tank twice as fast as you would on the surface, and at the recreational depth limit of 132 feet, it’ll be 5 times as fast. Body size and exertion/stress level count too. Most people breathe between .3 and .7 cubic feet of air per minute on the surface when sitting on the couch. But new divers often blow through an AL-80 in as little as 20-30 minutes on relatively shallow (above 60 feet) dives.

-avoiding decompression sickness, aka the bends. Most divers do this by observing the “no decompression limit,” a sliding scale of depth and time that, if you stay under it, you can come up to the surface without making decompression stops and without getting bent. Dive computers and tables can help you fine-tune this, but a good rule of thumb is the depth in feet plus the time in minutes should not exceed 120. So, you can stay at 60 feet for an hour, but as you go deeper you get less time. If you go deeper or stay longer, you need to bring extra tanks, because mere minutes beyond the no decompression limit at greater depths can translate into hours of decompression stops.

-gas narcosis, which, as pointed out above, can kick in at relatively shallow depths well above 100 feet, but pretty much everyone starts to get drunk-ish below that depth.

But there are human rules that kick in before the laws of physics will stop you. If you’re not a trained and certified scuba diver, you’ll be hard-pressed to find a shop that will rent you equipment or fill your tank. You can hire a divemaster to take you on a Discover Dive, sort of a tandem experience with minimal training, but they’re not supposed to take you below 40 feet. If you had an idiot diver pal who agreed to help you try to cheat death, you might pull off a bounce dive to somewhere around 150 feet and come back alive. But there’s a lot that could go wrong in the attempt.

7

Here’s a very basic explanation. The air we breathe is roughly 21% oxygen, the rest nitrogen. (All the other trace gases combined make up less than 1% and aren’t germane to the discussion.) Both of those gases cause a feeling of intoxication at depth, because of how dense they become. Exactly how this happens at a molecular level is not fully understood, but think of it as a dose-makes-the-poison situation. When you fill your lungs at 100 feet, you’re taking in 4 times as many molecules as you could inhale at the surface, and it makes you loopy.

All gases can be narcotic, but not equally so. Helium’s narcotic effect is very minimal. Commercial divers building oil rigs and whatnot on the bottom of the ocean breathe a gas mix that contains no nitrogen at all, only oxygen and helium. For many reasons, this isn’t practical for most recreational divers going deep, but many of those recreational divers use a gas mix in which at least some of the nitrogen is replaced with helium, to avoid making stupid mistakes at depth. Using these breathing gases requires extra training and involves extra risks.

There are some other risks that come into play at greater depths than most divers will ever visit, but that you would need to know about if you were trying to set a record. Too much oxygen can cause seizures; regular air becomes toxic in this way around 187 feet. Pure oxygen, which some deep divers use to speed up their decompression stops, can only be breathed safely above 20 feet. Helium, helpful as it is with narcosis, can cause tremors at around 500 feet. I have a morbid fascination with this stuff and can recommend some books if you’d like to learn more about the surprising ways extreme deep divers have managed to kill or injure themselves.

8

Do you mean how much they could (medical max,) or how much they could (willpower?)

The former - I don’t know, I am no doctor. The latter - I highly doubt more than 25 feet. At that point their urge for air would be desperate.

9

I don’t know if they can be considered “the average person” since they’re trained, but I’ve always been fascinated by the “pearl divers from Ceylon” in C.S. Forester’s Hornblower and the Hotspur. Yes, it’s fictional, but Forester supposedly based his novels on ship’s journals as well as research. The divers can dive “sixteen and a half fathoms” / a hundred feet, but just “Five dives a day . . . Then they bleed at the nose and ears.”

Here’s the description of the preparations taken by one of the divers: “sitting systematically inflating and deflating his chest, inhaling as deeply as he could, forcing air into his lungs. Hornblower could see how widely the ribs moved at each breath. One of the other two Ceylonese put a [nine-pounder] cannon-ball into [his] hands, and he clasped it to his naked chest. Then he let himself slip from the gunwale and disappeared below the surface”.

10

About a 100 feet for recreational SCUBA.

Interesting tidbit - As you descend you need to put more air in your buoyancy compensator because the increased pressure compresses the air in it and it becomes less buoyant. As you surface, you need to let air out or your pop up like a cork. It’s a balancing act.

Once at the Blue Hole My Wife was not putting air in as she descended and started dropping like a rock. Caught her. I think she may have had a bit of nitrogen narcosis.

11

It’s a hard comparison to make, because an inexperienced person wouldn’t take the same risks that an experienced person might.

Inexperienced people can hold their breath for 1-3 minutes, without swimming or exerting themselves. The world record for breath-holding is 24:37. So that’s your range for simple breath-holding at rest.

If you’re actually diving and swimming, it’s more challenging because exertion consumes oxygen and produces CO2. If an inexperienced person jumps in the water holding a heavy rock, it depends how far they can descend and ascend in that 1-3 minutes before they black out. Wild-ass guess, based on what I’ve done, most people could manage 15 feet, and if very determined maybe 30 feet.
The deeper you go, the more fear can play a role. Experienced pearl divers have done 100-125 feet.

The world record for freediving (no scuba, just weights and fins) is 702 feet. Incredibly risky, and frankly terrifying to think about.

12

I used to snorkel a lot in my 20s. There were a whole bunch of crawfish in a particular spring fed lake about 15 feet down- I’d scoop a couple dozen up with a net for a crawfish boil. But the painful pressure on my ears when I’d get below 15 or so feet would start to get intolerable. If I tried to equalize pressure by the ‘trying to exhale while still holding my breath’ method, it would make me feel like my air was depleted and I’d have to come up to the surface sooner. Never quite got the hang of equalizing my ear pressure successfully.

13

I also have difficulty equalizing while descending more than about 10 feet on a breath-hold, although I have dived to 130 feet without issue on scuba. There are more effective techniques than the hold-your-nose-and-blow Valsalva maneuver, and if I ever get into freediving I’ll have to spend some time practicing them. But yeah, the pressure change in diving down a mere 15 feet is significantly greater than what you experience in an airplane, and it happens much faster, too.

Also, fun fact about breath-hold diving. The urge to breathe comes not from lack of oxygen, but from buildup of carbon dioxide. You can’t feel the lack of oxygen itself. It used to be common for freedivers to deliberately hyperventilate before a dive; some thought this could pack extra oxygen into the body. It doesn’t. What it does is purge carbon dioxide below normal levels, making it easier to hold your breath until you suddenly pass out from lack of oxygen and maybe drown if you don’t have a buddy watching you from the surface. (The decreasing pressure on ascent contributes to the loss of consciousness as well.) So that technique is not recommended anymore.

14

Yeah, the ear equalization can be a real problem. It’s easier for some than others. I live and 11,200 feet and regularly drive back and forth to Denver which is a mile below my altitude.

Luckily, I can clear my ears without holding my nose. I just do it. I can open my estuation tubes and equalize at will. Don’t need to hold my nose.

Huh, my Wife also doesn’t seem to have any difficulty with this either. It’s just never come up.

I think It’s kinda like some people can roll their tongues.

15

Lot’s of weird things about diving with SCUBA comes into play. For instance, if you don’t blow into your mask with your nose (a little bit) as you descend, the mask will be a suction cup on your face from the pressure differential. When you ascend, the extra pressure in the mask will leek out around the edges.

The other weird thing about SCUBA diving is that while, yes, you are basically floating with nothing around you other than your buddy and reefs or what ever, it can be very claustrophobic because of your mask and listening to your own breathing. You’re in your own mini world, depending on technology to keep you alive. I guess sort of like sky diving.

16

15 ft is about the limit for comfortable free diving, 100-140 ft is the fuzzy limit to recreational diving. There is not much stopping someone from getting to 100 ft except light and temperature. It’s just breathing. After 100 nitrogen narcosis sets in, and if feels really good (at least to me), but that sort of sets up a fuzzy limit of how ‘drunk like’ you want to feel. With different gas mixes you can go deeper before that happens and perhaps eliminate it with helium (IDK). As such the limit is not so much getting down, but coming back up safe and for a novice one could end up down at depth as a ‘dead man swimming’, not able to make it back up and checking in to Davy Jone’s locker.

17

Also having enough air to do decompression stops when ascending. At the Blue Hole, the dive boat had tanks suspended at about 25 feet in case you needed to switch over during your stop.

18

You can spend around 20 minutes at 100 feet without having to do decompression stops. More if you’re breathing Nitrox (air with extra oxygen added, which lowers the amount of nitrogen and therefore makes you less susceptible to the bends). Casual divers going deep at places like the Blue Hole do occasionally forget to check their remaining no-deco time as well as their remaining air, which makes the practice you describe prudent. (Some might say a better practice is to stop taking numptys to 100 feet.) But I frequently dive to 100+ feet without incurring mandatory decompression stops. You just have to pay attention.

19

Yeah, we don’t dive anymore, but if down to 100’ we would stop on the accent at ~ 20’ if we had enough air. We usually stayed above 80’ maximum though.

Deep places can also be dangerous since your BC will start to compress as you descend and you can start dropping like a rock if you’re not careful.