[Survival] Dealing with decompression and fatigue
conscioussoul
Canada Join Date: 2015-05-17 Member: 204607Members, Subnautica Playtester
Canada Join Date: 2015-05-17 Member: 204607Members, Subnautica Playtester
For those of us who love the survival and the realism aspect, here are some concrete suggestions 
DECOMPRESSION
Add one new meter called 'pressure'
Next to it is a number: N atm
It shows your pressure level in atmosphere
The meter is fully green as long as i remain at the same depth or dive deeper.
If i dive deeper, the meter remains green but the number next to it (the pressure) increases.
When i ascend back to the surface, the meter fills up with red for each level of difference in atm with previous pressure.
Say 1atm of pressure difference fills up 1/4th if your decompression meter.
So if you ascend strait 4atm of pressure nonstop you'd fill up your decompression meter fully.
However, the decompression meter decreases over time - say 10-20 seconds to go all the way back to green.
As long as your decompression meter is fully red you take damage until death.
Of course, you don't get +1 atm at each meter, rather a ratio has to be determined; ex: 30m = 1atm (don't know how realistic this is).
The idea is that from say, 300m depth, you'd go from 1atm to 10atm approx.
Impact on gaming mechanics:
You'd now have to take this into account when ascending, either by ascending diagonally slowly enough or by taking breaks in your ascend, to let your decompression meter go back to green.
1) its much more realistic.
2) it totally changes your survival strategy. Now intermediate-depth bases becomes mandatory before you can handle bigger depth. No more crazy ascend to get air! Management of your air supply becomes much more critical. Which means it's also a very interesting incentive to actually build several bases at different levels as you explore deeper areas.
3) the mechanics remains very simple game wise (no need for complicated decompression chambers with sceals, and the decompression time doesn't need to be calculated and is very quick, etc). For simplicity's sake, it could also be that this mechanics only works when the player is not in a sub like the cyclops or the seamoth, or it could also work when you are ascending your subs.
4) Going down can be done quickly, but going up takes planing and care
EDIT: This can easily be added as an option, so that it can be turned off for whose who want to explore without decompression issues.
FATIGUE
A meter for fatigue can be added. This one would drain very slowly, i.e., it can last a day and a night before it's exhausted.
When it is exhausted, you can no longer swim, so you fall to the sea floor (or base floor). When you don't swim, it's going back up, but also very slowly.
So you could "rest" a few minutes on the sea floor (provided you have enough air) to recover enough stamina, say, to reach your sub or your base. But mostly, if you are still in the water and you no longer have stamina, you are pretty much going to drawn.
Inside the base or sub a bunk-bed ca be added (constructed). When used, it:
DECOMPRESSION
Add one new meter called 'pressure'
Next to it is a number: N atm
It shows your pressure level in atmosphere
The meter is fully green as long as i remain at the same depth or dive deeper.
If i dive deeper, the meter remains green but the number next to it (the pressure) increases.
When i ascend back to the surface, the meter fills up with red for each level of difference in atm with previous pressure.
Say 1atm of pressure difference fills up 1/4th if your decompression meter.
So if you ascend strait 4atm of pressure nonstop you'd fill up your decompression meter fully.
However, the decompression meter decreases over time - say 10-20 seconds to go all the way back to green.
As long as your decompression meter is fully red you take damage until death.
Of course, you don't get +1 atm at each meter, rather a ratio has to be determined; ex: 30m = 1atm (don't know how realistic this is).
The idea is that from say, 300m depth, you'd go from 1atm to 10atm approx.
Impact on gaming mechanics:
You'd now have to take this into account when ascending, either by ascending diagonally slowly enough or by taking breaks in your ascend, to let your decompression meter go back to green.
1) its much more realistic.
2) it totally changes your survival strategy. Now intermediate-depth bases becomes mandatory before you can handle bigger depth. No more crazy ascend to get air! Management of your air supply becomes much more critical. Which means it's also a very interesting incentive to actually build several bases at different levels as you explore deeper areas.
3) the mechanics remains very simple game wise (no need for complicated decompression chambers with sceals, and the decompression time doesn't need to be calculated and is very quick, etc). For simplicity's sake, it could also be that this mechanics only works when the player is not in a sub like the cyclops or the seamoth, or it could also work when you are ascending your subs.
4) Going down can be done quickly, but going up takes planing and care
EDIT: This can easily be added as an option, so that it can be turned off for whose who want to explore without decompression issues.
FATIGUE
A meter for fatigue can be added. This one would drain very slowly, i.e., it can last a day and a night before it's exhausted.
When it is exhausted, you can no longer swim, so you fall to the sea floor (or base floor). When you don't swim, it's going back up, but also very slowly.
So you could "rest" a few minutes on the sea floor (provided you have enough air) to recover enough stamina, say, to reach your sub or your base. But mostly, if you are still in the water and you no longer have stamina, you are pretty much going to drawn.
Inside the base or sub a bunk-bed ca be added (constructed). When used, it:
- Sets your spawn point
- Refresh your stamina
- Recover life to a minimum (say to 50%, the rest can only be recovered using med kits)
Comments
Simple solution, it can be added as an option and you can just turn it off if you don't want to play with all the survival elements, just like the food/water element right now.
Well that is true, but is it really that fun to make a game extremly releastic in details? sure some details might be fun but, if it is lifelike 100% you can just go outside and dive and you have it 100% releastic
Some (perhaps like you?) might already dive and look for a game that makes it easier and more fun, and that's perfectly fair.
Some others like me don't / can't dive in real life (and never will) and enjoy the thrill and the challenge of something more realistic.
Since as an option, you get to keep it "simple" if you desire to do so, why the negativity?
The greatest games are the ones who manage to capture in simple game mechanics something close enough to reality to feel like a true challenge and immerse you into it.
I want to feel what a diver's challenges are.
I want the game to force me to think creatively and force me to plan my exploration as a true expedition in the deeper depth, as a truly alien place to explore.
Also, I was relieved/disappointed when I exited my Seamoth at ~300m depth and did not die instantly.
To enable it activate the console and type "Nitrogen" .
Does it uses the same mechanics as I propose here? I was under the impression that nitrogen nacosis was something different than decompression.
Basically
- Nitrogen narcosis = a state similar to being drunk, when you dive too deep. Solution: go little bit upwards. Caused by breathing compressed nitrogen.
- Decompression sickness = nitrogen bubbles form inside your body because of fast ascending. Can damage tissues and cause paralysis at worst. Solution: 're-compression therapy in a hyperbaric chamber' (from the site I linked).
Both are caused by nitrogen. I haven't tried the 'NITROGEN' command myself, but according to wiki it enables decompression sickness. We can assume that the technology in the game can decrease the effect of these two. Perhaps we need to upgrade swimming suits for really deep diving.@conscioussoul 10m = +1atm is a better approximation.
I don't hink there should be on/off -switch for this, but it would be disabled in Freedom mode.
They wouldn't affect you inside subs, because the pressure inside is kept at ~1atm. That's also why subs collapse when going too deep (crush depth in the game).
This kind of mechanics would be great, but it shouldn't be too harsh.
Although at 300m depth, that'd be 30 atm, wow! serious stuff.
If the sub remains at 1atm, then you don't suffer from decompression when you ascend with it.
But that means going out of your sub to take a swim at 300m you will go from 1atm to 30atm, and when you enter your sub back, from 30atm to 1atm.
So how does that works, then? Not sure I get that part.
Subs could have compression chambers. When you get in the cyclops, the first tiny room could be it.
The whole seamoth could be a pressure chamber. It would be impossible with todays technology, but this is in the future.
he forgot to add you must always count in the surface pressure aswell. so at 300m depth the pressure is 31 bar or atm as you can also call i.
as long as the sub holds the pressure at 31 bar and decends you slowly up to 2 bar/atm like deco chamber if not you will get dive sickness and mostly likely die.
As it is I only get brief explorations of areas before I need to get air or I am all full up on space. Further limiting the depths of my dives and the distance I can move would be too much.
Time to Ignore my personal opinion on the matter for a moment, and present an argument for the 'Gameplay > Realism' issue on this topic:
The areas in Subnautica are much smaller, and the variations in depth are massive. Decompression would limit exploration significantly. Heck, players wouldn't even to be able to explore some areas of the safe shallows properly. This would restrict gameplay far too much.
We need to consider complexity as well. while indeed, Hardcore mode should be Hardcore, it shouldn't be obtuse about it's diffculty. By that I mean, specific things should be difficult, but not everything can be difficult.
The more 'difficult' events a player has to manage, the more frustrating the gameplay becomes.
With a boss fight, the boss is hard to kill, or requires something specific, but player movement isn't made difficult, the weapons hard to aim, etc. Make some aspects hard, not everything.
Adding something like this would also require a massive amount of reworking things like oxygen, water and hunger. adding decompression chambers, increased resource usage with all the bases needed, so resources available need to be adjusted accordingly.
To look at it from another angle:
If this was implemented in the game, the above issues would crop up and need to be solved. How could we resolve this issue in a way that is reasonable in regards to time and effort to create, without 'nerfing it' to the point of redundancy?
This wouldn't require any additional coding to the but would come at a huge cost in development time. Rebuilding the game world to be much wider with the same current depth variations would massively improve the feeling of being on a large planet, but to rebuild the geometry and place all the models, creating the game world from scratch, would be an immense amount of work. Especially as it would be larger than before. Is this feasible?
Not only that, what impact would this have on performance?
Option 2: Dilute the effect from earth pressures, so that you can easily explore to a reasonable depth within a given area.
Some areas have quite large drop offs, and cave systems can take you really deep in the shallowest of areas. Making the variation in depth too much makes it redundant, but making it not enough can really limit exploration of areas. The balancing of the additional requirements allongside oxygen, food, water etc, would make this a nightmare to get right.
One last personal opinion:
If you read it all, you must have had some time to kill..
It appears that quite a few folks are having trouble with the physics of SCUBA diving.
I'd like to help out. Former qualified diver, open water certified. Freshwater cave diving experience. Former SCUBA equipment service and test technician.
I'm not exactly Captain Jacques-Yves Cousteau, but I've definitely been down there.
First, some basic information...
Basically accurate. In a similar real life situation, Jammer would have probably died almost immediately.
The presence of nitrogen in a diver's breathing mix poses two main hazards, not counting HPNS:
Nitrogen narcosis: Also known as 'The Narks' or 'Rapture Of The Deep'. Essentially, a case of The Narks is just like being drunk. Your judgement is subtly impaired at the initial onset of symptoms, and the effect becomes more pronounced with prolonged exposure and increased depth. There have been cases where 'narked' divers have removed their demand valves (mouthpieces) for no apparent reason, panicked or have just kept swimming down to oblivion. Any sport divers planning to exceed a depth of 120 feet for any appreciable time should consider using specifically-prepared gas mixes such as Heliox, Nitrox or Trimix. In these gas mixes, helium serves as a buffering agent to minimize the harmful effects of breathing nitrogen at extreme pressure.
Decompression Sickness: As one breathes underwater, gas molecules dissolve into the bloodstream. The deeper a diver goes, the greater the pressure exerted on that gas. If you have a balloon full of air at the surface and then submerge down to 33 feet (2 ATM), the balloon will reduce in volume by 50 per cent, 75 per cent at 66 feet, and so forth.
This demonstration illustrates Boyle's Law: "For a fixed mass of gas at constant temperature, the volume is inversely proportional to the pressure". Simply stated, "The greater the pressure, the smaller the volume".
Very important concept to remember, folks...
Guess what happens when a diver surfaces rapidly with all that dissolved nitrogen still trapped in their bloodstream? Vampires would call it "Vin Rosé". A fruity, sparkling red.
This is why deep divers have to make carefully planned stops at specific depths for a specific period of time. The procedure is called 'Decompression', and it allows dissolved nitrogen to safely diffuse out of the diver's bloodstream at gradually decreasing pressures. It can be an extremely lengthy process, which is why commercial and military divers are transferred to decompression chambers. Any extended periods of time spent at depth require a technique called 'saturation diving', and decompression takes considerably longer.
Here's the Wikipedia word on the subject: "Peter B. Bennett is credited with the invention of trimix breathing gas as a method to eliminate high pressure nervous syndrome (HPNS). In 1981, at Duke University Medical Center, Bennett conducted an experiment called Atlantis III, which involved taking divers to a depth of 2,250 feet (685.8 m), and slowly decompressing them to the surface over a period of 31-plus days, setting an early world record for depth in the process."
Oh, and nitrogen absorption is cumulative. You can forget about making any repetitive deep dives on the same day.
Sorry.
Also, 30 seconds worth of air from a single dive cylinder?
Absolute tosh. A standard 72 cubic-foot cylinder holds enough air for about 30 to 45 minutes at a depth of 33 feet (2 ATM absolute).
Actual consumption figures vary depending on diver fatigue, ambient water temperature and levels of exertion.
An advanced 'Subnautica' modular diving system capable of taking divers to 1,000 metres and returning them safely to the surface should provide no less than 24 hours of total life support capacity, use an onboard computer to control gas mixtures and be able to function as an actual rebreather that recycles the exhaled gas and vents off a metered percentage of the carbon dioxide it contains. Decompression could take place automatically whenever the diver re-enters a Seamoth or Cyclops. To be entirely accurate, the ship-board computer should provide a warning whenever repetitive dives are attempted.
Incidentally, the 'Rebreather' icon used in 'Subnautica' looks remarkably like a Kirby Morgan KMB-9 Band Mask. Commercial full-face diving helmet. Not a 'Rebreather' as such.
Profound and profuse apologies for the 'Wall Of Words', folks. Kind of passionate about the subject matter.
If the game is too restrictive, you have the freedom of using... the freedom mode.
As long as that option is there, adding decompression isn't removing any fun from people who wish to use the freedom mode.
This being said, I disagree that I am describing a simulator rather than a game.
For one, some of the greatest games are labelled "sim" (like the sims, but also sim earth, sim ant etc) and well, they are game TOO.
More so, a real simulator would require you to be decompressing for hours (or at least several minutes in game) in decompression chamber just to leave your sub.
This is not what I am proposed; it's a much, MUCH simplified mechanic. See below for (perhaps) a clearer explanation.
Seems you are saying yourself that the "problem" with limiting exploration, for you, is already there from the get go with the air limitations, regardless of a decompression effect? Remember decompression would not limit your depth, nor the distance you could move; what it would do is limit the speed at which you can ascend, and even not that much so compared to real life (again see below for a clearer explanation)
This is entirely a matter of balancing.
For instance, The developers could decide that the decompression meter increases one notch every 40m depth; and that it takes 4 notches for the meter to be full and health to start dropping. In that case, you could literally explore a depth of 160m without trouble. If you take a rest at least once, for say, 10-20 seconds, you could ascend as much as 320m already. Not that bad? Not to mention you can go the full 320m downward in one stretch.
The concept does not add a bother, it adds a challenge, forces you to think and plan your exploration, and the realism is just a nice extra, IMO.
Personally, I think the ideal fro what I have seen would be an increase of 1 notch of decompression for each 20 meters. That would allow you to ascend 80m before getting hurt, and 160m if you take a 10-20 seconds pause in between. But it can be twiked.
No offense, but as long as the various parameters are configurable in the options, everyone is free to make their game as difficult or easy as they wish. Look at Invisible inc, which was recently released on steam: all the options to make it easier or harder are fully configurable.
This being said, I insist this mechanics is WAY WAY WAY simplified compared to an actual simulator. There are not "dive table" to look at, you don't need to wait for long to ascend, you can leave your sub without decompressing etc. I think you are seeing it way more complicated that its intended to be.
I don't think so. There is already a mechanic in place in the console for nitrogen narcosis.
Implementing full fledged decompression might be difficult, but that's not what I am suggesting here.
The map will eventually get much bigger, from what I read from the developers. But it doesn't matter, because it's just a question of balancing.
I respectfully disagree. Game balancing is a difficult and delicate task and it's NEVER easy. The mechanics I propose for decompression frankly would not be very hard to balance, and I am telling you this from the point of view of a graduate in operational research in computer science: it's WAY WAY easier than MOST game mechanics you find out there on steam. Any competent dev will nail this in no time.
But - again - there is an even easier way: just make it configurable.
I really think you aren't getting how simple what I present here is.
You just have to wait a few seconds every XX meters before you continue going up. That's it.
XX is configurable. Your meter goes up as you ascend. It goes down as a few seconds passes.
If you go up too fast, it hurts you.
Voila. Is that so complicated, really?
I guess I have just as much time to kill as you, taking the time to write ALL these objections...
I think it's pretty clear from your explanations that what I am proposing is a very simple mechanic and is in no way an attempt to be "a simulator".
33m per atm is also quite interesting.
With my suggestion, say the decompression meter has 4 notches:
1/4th filled up when you ascend 33m
Half filled up when you ascend 66m in one shot
3/4th filled up when you ascend 99m in one shot
Full filled and harming you when you ascend 130+ meters in one shot
Each time you wait or swim at the same depth or within the same ATM of pressure (or deeper) for 15 seconds, you lose one notch on the decompression meter.
So going up from, say 200m, you could ascend to almost 70m before you are stuck there. After another 15 seconds, you could afford to go up at approx 35m and you'd have to wait another 15 sec to reach surface.
Or you could plan your ascend and just ascend slowly, from 200 to 165m then wait 5-10 seconds, and so on.
Or you could just rush from 200m above and take 40% damage or so.
Or you could ascend to an intermediate base you placed at 100m and just wait there for 30-45 seconds (which is the time it takes to renew your air tank anyway!!!!)
Nothing terribly complex. But way more realistic already... and way more challenging.
An Advanced Modular Diving System (AMDS) would solve this problem.
Basically a more high-tech version of the real-world "Computer-Lung" dive system of the late 70s, the AMDS is a computer-controlled, mixed gas, closed circuit rebreathing rig. Three cryogenic gas storage cylinders provide metered amounts of Oxygen, Nitrogen and Helium to a breathing bag or mixing chamber. Exhaled breath is passed through an absorption ('Scrubber') canister containing barium hydroxide (commercially known as 'Baralyme') to remove CO2 and effectively increase the proportion of oxygen available to the diver, rather than venting exhaled air directly into the surrounding water.
Computer game 'Science Magic' could be used to explain how a diver gets 24 hours of life support at 1000 meters, but I feel that Reality offers a much better solution.
Don't forget to implement the 1-ATM Armoured Dive Suit (Exo-Suit), either. Think of it as your very own wearable DSV. Bonus: No decompression required.
Lots of interesting comments there, thanks!
As already seen in experimental there are now some high capacity air tanks, 60sec each. With two, I get 120+45 = 165 sec air, which is not that bad, considering the night comes within 1 or 2 hour of game play (so I imagine this air time simulates more real life air time than just actually 2 minutes).
Everyone, please, at least add metric values if you are using other measuring systems. Just for clarity. There are people like me who don't know a thing about inches, pounds and stuff.
Also, the game is in the future, so we can assume that the equipment is a lot better. Maybe the character already has some tech on him that negates most of the harmfull effects. Or perhaps we could craft better equipment later in game. This is a game, so too many restrictions on free exploring would hurt the gameplay. Decompression etc would be nice additions, but only if they are properly balanced
I actually prefer to use Imperial measurement units, particularly where SCUBA diving is concerned. It's actually more precise than Metric in this application, at least.
Just my personal preference of course, although I do have sound reason for it.
Allow me to explain.
Water pressure comes on strong from the very moment your body is completely submerged. Put on a rubber washing-up glove, and stick your hand in a sink full of water. There is enough pressure in only 6 inches (150mm) of water to press that glove right up next to your skin. Now, suppose you were STUPID enough to take a deep breath from your SCUBA regulator in only 4 feet (1.3 metres) of water, and then surface without exhaling first.
By the way, you really, really shouldn't do this. Seriously. Never.
If you do this, you will most probably rupture both lungs. You have suddenly decreased the water pressure acting on your ribcage, simultaneously increasing the air pressure inside your lungs.
Boyle's Law strikes again. Pressure and volume are inversely proportional. You now need urgent medical attention, particularly if you enjoy breathing.
Remember, that this (spontaneous pneumothorax) happened in only 4 feet (1.3 metres) of water. Most analogue depth gauges would have trouble resolving that small a pressure differential in Feet, and a dial-type gauge calibrated in Metres would barely register at all. Safe diving requires absolutely precise measurements to be taken at all times. Tank contents pressure, depth, dive times at various depths, decompression levels and timings, etc.
I don't think that I'd be entirely happy making a Metric decompression stop at 10.06 metres (33 feet), mainly because of those fiddly little numbers after the decimal point. If I have to make another DC stop at 10 feet (3.04 metres), I'm going to be more than a mite concerned. Most analogue dial gauges wouldn't be able to register that low, turning the whole business into a guessing game. Remember, a lot of nasty things can happen within the space of a small variation of water pressure. In a situation such as this, a properly trained diver would add a generous 'fudge factor' to shallow DC times to account for any inaccuracies, as well as having a no-nonsense backup system such as a weighted shot line with decompression depth levels clearly marked with pennants or coloured bands.
I suppose I could always shell out roughly $1,500 or more for the latest combo digital dive timer, decompression meter, compass and Espresso maker...
Moot point. Need a new tank, regulator, wetsuit jacket, BCD and mask first. Oh, and a new body. This one doesn't work as well as it used to.
Incidentally, sixty seconds of air per tank still isn't much of an improvement.
I could get better bottom-time with a couple of Air Duster spray cans strapped to my back.
They are high-tech tanks, that fill themselves just by being on the surface, but the amount of air they can store is a lot lower.
It would be too easy to get around if tanks lasted for as long as current real ones, so there has to be some kind of nerf to them. It would of course be better if devs came up with a reasonable explanation for that.
In real-world terms, their capacity equates to that found in 'Pony Bottles', a small emergency air supply of around 1 to 2 litres. However, I do like the self-charging ability.
If Subnautica's tanks had a realistic capacity (15 litres or more), advanced game mechanics such as decompression, nitrogen narcosis and HPNS ('The Shakes') could be successfully implemented. This also means that the breathing gas mixture would have to be changed to something other than pure O2, if only to maintain the internal logic of the game.
Can't have adverse nitrogen effects when you're breathing pure oxygen. Also, diving any deeper than 10 to 15 metres becomes rather hazardous.
UWE have the basis for a truly memorable game in Subnautica. Unfortunately, their hit-and-miss approach to the actual mechanics of diving might drive a significant number of potential players to the nearest Wii Console and copies of 'Endless Ocean' I and II. From what I've seen of those games, there has been a lot more attention paid to little details such as air supply duration, equipment selection and diver instrumentation, balanced with a certain amount of fantasy elements to prevent the game bogging down in reality.
Don't get me wrong. I LOVE Subnautica. I merely feel that there are some glaring errors that desperately need correction to make the game feel 'right'. Other technical issues such as bugs, tech tree reworks and new gameplay features are obviously being addressed as they arise, although the Devs appear to be skipping lightly over equipment designs and the physics involved with diving. Admittedly, there has to be a balance between depicting a realistic diving simulation and what is possible within the game environment, as well as catering to the practical, technical and financial constraints involved with developing a finished product.
In some cases, having players offer suggestions during the development stage of a game may be extremely beneficial.
My greatest worry is that UWE is being pulled in so many directions about what players want in the finished product that they might lose sight of their original vision.
Some want multi-player or co-op gameplay. Some want a whole fleet of new submarines. Some want honking great harpoon guns to hunt Reapers. Some want realistic diving...
It's frustrating, but I can also see the Dev's side of things. Each little tweak to the game unleashes another rampaging Reaper Leviathan of unwanted knock-on effects.
A whole new crop of bugs and glitches to fix with each new update. A constant stream of annoyed players whinging and moaning about this and that.
Yes. Me too. Guilty.
You know, I feel sorry for those folks at UWE.
i think the easyest way to explain the bottom time would be to decrease the size of the in game model, make them look like a small back up tank (i belive they are called octopus tanks?) that would easliy explain the bottom time being so small.
hydrostatic pressure = density * gravity * depth
If you had half the gravity or liquid density that we have in our oceans on Earth, then you would have half the pressure at the same depth
But with a smaller liquid density you would not float, so maybe you would need a higher liquid viscosity to help you swim (not sure if that would help, just guessing)
Anyways, I think that it would be a bad idea to try to make this scientifically realistic in the same way it would be a bad idea to have 45 minutes of air in the tanks. In a game you need to fine a certain balance between realism (for immersion) and gameplay (for fun)
Err... can you explain this again for me - like, say, as you would for a 5 year old?
Maybe it's because I am not sure what a scuba regulator is, but I don't get how breathing air from 4 feet deep can rupture your lungs if you don't exhale first.
I mean, don't you always have *some* residual air in your lungs, even after you exhale (most) of its air? ** confused **
BTW @Bugzapper thanks for the detailed explaining here, it's absolutely fascinating
I'm not a diver, but I expect that it would be because when you reduce the pressure, then the air will expand. If you have only a little air in your lungs, then your lungs will just expand a bit, and you will be fine. But if you have just taken a deep breath, your lungs are already almost full. So when the air in them expands, they rupture, because there is not enough space.
Hard & Fast Rules of SCUBA Diving, Number One: Never hold your breath while ascending when using SCUBA. Always breathe normally.
The first stage of a regulator uses spring-loaded pistons to reduce the pressure in the dive cylinder(s) from 2,250 ~ 3,000 p.s.i (155.1 ~ 206.8 Bar) to around 120 p.s.i.
The air that's fed into the second stage ('mouthpiece' or 'demand valve') of a diver's regulator is delivered at roughly 120 pounds per square inch (0.8274 MPa), although
the actual delivery pressure to your lungs is balanced by external water pressure simultaneously acting on your lungs and a flexible diaphragm mounted inside the 'mouthpiece bit'.
This clever mechanism ensures that your lungs don't blow up like a clown's balloon animal with each and every breath. It would be a bit like trying to drink from a fire-hose.
Here's a Wikipedia link on diving regulators: http://en.wikipedia.org/wiki/Diving_regulator
The point is; you have taken a deep breath only four feet underwater and immediately surfaced with your lungs full of air that has been pressurized to your original depth of four feet.
The air currently inside your lungs will expand as soon as that external water pressure is lowered, most probably resulting in a pair of ruptured lungs.
Human lungs are not like bagpipe bladders. They are surprisingly fragile.
The 'average' lung capacity of a human male is approximately 6 litres. During the breathing cycle, about 0.5 litres of air is inhaled and exhaled per breath.
This is what's known as the 'Tidal Volume' of lungs.
Since your lungs are already full of air pressurized for a given depth, any significant increase in the pressure inside your lungs will damage them.
If an equipment malfunction forces a diver to 'ditch' their SCUBA tanks, the last breath taken should never be held all the way to the surface.
During a 'free ascent', the suggested practice is to whistle gently while heading towards the surface. This decreases the pressure inside your
lungs proportional to the decreasing pressure acting on the other (wetsuit) side of your ribcage as you ascend. There should be sufficient residual
pressurized air remaining in your lungs to get you to the surface safely. Keep cool, keep exhaling slowly and just keep swimming.
So, no lung-shattering KA-BOOM.
Little experiment: The next time you're in a swimming pool, try fully inflating a balloon roughly 4 feet underwater. Tie a knot in the neck and bring it back to the surface.
Yep. You're definitely going to need another balloon.