How long a scuba diver can stay under water

There is a Scuba Diving Time Limit

There is a Scuba Diving Time Limit

Except for Michael Phelps, human beings are not created to spend most of their time in the water. We are a community of creatures who walk on dirt, and if you’re reading this right now, it is likely that you desire to extend your human limitations and experience to that which cannot be possible without the aid of scuba diving technology.

Sadly, even the distance and depth that technology has given to us cannot last for eternity. You buy a battery, it runs out. An Apple product gets released, YouTube asks, “Will it Blend?” Time destroys everything. This is evidenced by my Mum’s 8-pound cell phone rotting in some corner that rats call home. In scuba diving, time limits are also present. And our lack of functional gills tells us that managing our time underwater is the surviving equivalent as breathing on dry land.

The Technical Aspects

This part of the article deals with the scuba diver’s “mechanical gills”, or the scuba tank. Here, I am to explain how long a tank of compressed air will last so the scuba diver may know when to end his/her voyage. I researched for accuracy. Accuracy is good. But then, I stumbled upon this equation: 3000 psi / 14.7 psi = 204.08. For the sake of helpful simplicity, I have chosen not to go to mathematical territory and will try to be as accommodating as I can with the use of shallow words.

The most common and average scuba tanks hold about 80 cubic feet of air at a rated pressure of 3,000 psi. The average scuba diver will consume about a cubic foot of air every minute. So, that’s 80 cubic foot of air being used up at a rate of one cubic foot per minute. That would mean that the average tank will last about 80 minutes if used by the average diver. Aha! My high school diploma is proud of me.

Notice the overuse of the word, “Average” in the previous paragraph? Yeah, me too- I wrote it. My point is, the outcome of the numbers above is not absolute. The time a diver is allowed to stay underwater varies within the diver himself. If the scuba diver has the lungs of a young person like Justin Beiber, an average scuba tank will be more than enough. But, if you’re size is anywhere between Robert Downey Jr. and The Incredible Hulk, a larger tank is advised.

The Physical Aspects

Now that we’re shifting from the technical to the physical aspects of the scuba diver’s time limits, it would be safe to assume that we’d be able to breathe normal again by taking a step down intellectually, yes? No. As I was researching facts about this point of my article I came across with this:

Diving time limit formula

What the hell is it? Don’t ask. Please.

So where was I? Oh yeah. The human lungs are used to breathing oxygen. Our scuba tanks are not composed of pure oxygen. It is a mixture of gases. These gases aren’t dangerous. But when the scuba diver breathes too much of it underwater, he/she might contract ailments such as decompression sickness, nitrogen narcosis, oxygen toxicity. I don’t know what exactly they are, but the words, “sickness”, “narcosis”, and “toxicity” scare me.

Also, diving in shallow waters allows you to dive for a longer period of time because the shallower you dive, the less air is compressed. And remember, the human body is subject to hypothermia. This possibility is dependent on the choice of your dive spots. Go Scuba Diving in Palau this summer and you’ll be just fine. Try diving in Antarctica during the winter and you’ll be the homo sapien discovery after the next ice age.

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  1. When I went scuba diving in Thailand, my tank went down quicker than average. The guide who I went with said that it was because I was nervous. Since it was only about my second time using scuba equipment I guess I was somewhat frightened. He says that in that state you can breathe more quickly using up more in the tank.

    • Usually scuba diving is a nerve wracking and exciting experience the first or second time around. I wouldn't be surprised if you consume the air in your tank faster than the average diver. I'm sure you last a lot longer under water now Steve 🙂

  2. Nope, the human lungs are NOT used to breathing "pure oxygen". They are used to breathing the air in our atmosphere…which is the same air that is in our tanks. It is a mixture of gases.

    • Thank you for the correction Steve. Updated the article.

    • Yup your "average air" would be roughly 79% Nitrogen and 21% O2. Pure O2 can cause oxygen toxicity (surface, 1 ATM) in 2-3 hours. Which is why breathing it underwater would be even more dangerous!

  3. "I don’t know what exactly they are, but the words, “sickness”, “narcosis”, and “toxicity” scare me."

    Educate! don't fear the unknown!! 😉

    It is awesome to see interest in the physiological and physics side of diving but I wouldn't mind throwing in my two cents. I'm by no means a dive medicine professional but I do engage in decompression diving and recreational instruction so some of your fears are rather easily alleviated.

    Oxtox (oxygen toxicity) for regular air (21%) begins to be at risk around 200 feet (well beyond the recreational limit and a depth most divers have no interest or ability to visit). I say begins to be at risk because there are several factors depending on how conservative or not you plan your dives. So for most diving I wouldn't be concerned at all about oxtox, you're more likely to get this in the hospital when being administered oxygen ;).

    You know some people like to get "narc'd" (nitrogen narcosis). Your reasoning for why it happens though is a little off. It isn't because of the amount breathed. For example, you could breath compressed air at a shallow depth all day long (assuming you had spare tanks) and never experience narcosis. Narcosis comes from the narcotic effect of increased partial pressures of nitrogen. Basically you need to be getting lots of it in single breaths. Depth (pressure) causes it not dive time. If you experience symptoms at 100 feet then generally you will always experience symptoms at 100 feet regardless of dive time (and hey some people pay good money for a buzz!).

    Decompression sickness is probably the most likely serious ailment of those you listed and the stat for occurrence in trained divers diving within their trained limits is in the 1 per 10,000 dives range (not very likely 😉 )

    I would only like to add one other thing. DCS (decompression sickness, bends, what have you) is an issue based around bottom time NOT how much gas you use. If I use half as much air as the next guy but we both stay at certain depths too long we are both equally at risk (if we do not follow the proper dive plan of ascending and making decompression stops, again well beyond the scope of your average dive training). Other physiological factors play a greater role than amount of gas consumed. For example, someone huffing and puffing down a tank quickly is not necessarily absorbing all the gases they are using, they are simply breathing too much.

    Decompression theory is a constantly evolving science. It can be as simple as follow the rules and as advanced as record breakers reaching near 1000 foot dives.

    Your average diver for 80 cubic foot tank though seems right. I use 63 cubic foot tanks with my students in the pool and during their first few days of training we routinely do 45-60 mins underwater coming up with reserve air. This is less than 20 feet though (depth makes you consume air faster of course) but you would be surprised how many giant guys use very little air and how many tiny people use tons!

    The biggest factor in determining how long a diver can stay down is really how much training, gear, and time he wants to spend. The record single dive time is 48 + hours if I recall! Sorry for so much information you probably didn't want but I just love this stuff!

  4. Richardnz says:

    Age has nothing do do with air consumption. Fitness and experience are the major factors. How physical the dive is and how deep the dive is also have a major impact. There is a formula based on your surface breathing rate that will let you know roughly how long you will last at any given depth.

  5. hey guys
    i doing research about in deep so i could find how long the diver need to stay in cerain level when coming back to surface?
    i really will be thankfull if i could fine my answer through this website.

    • Hi Zaki,

      To be on the safe side, a diver should do what is called a decompression stop after all but the most shallow of dives. This is usually around 3-5 minutes at a depth of 15 feet. The length of the stop, and rate at which you can ascend to the surface depends on a lot of things, particularly the time and depth of the dive (or dives) that you've done before. The best way to accurately assess the length of your deco stop is using a personal dive computer. It's important to always make sure you have plenty of air so you can safely complete the stop (air is used much faster at greater depths, or in general by less experienced divers who may not have the same kind of control over their buoyancy).

      Hope that helps a little.

  6. Cold plays a huge factor too i find. As a trainee, i used nearly twice the amount of air when the water temp was only 5 deg and i was in a semi dry than i did pool training or in the mediterranean.

  7. veritanuda says:

    All the comments above are interesting but I would like to make the point why we , as land mammals, are not adapted to the sea even with our funky technology. Truth of the matter is the deeper we go the higher pressures we are subjected to, 1 cubic meter of water weighs 1 tonne, ergo it does not take too long before you have massive pressures contracting on you. Because of these pressures the density of your breathing changes as the air in your lungs is also compressed you need to increase the density of the air that you breath. The longer you dive the higher amounts of gases you absorb and this is what leads to oxygen toxicity. I think @Chris has covered most things but the bottom line is we are not evolved to spend vast amounts of time underwater, unlike a whale 😉
    That being said though, there are areas of technology that could have an impact on human survival in extreme circumstances. I am thinking bio-nano tech might well discover ways to scrub our bodies of excess gas in real time. This combined with suits that are thin yet strong enough to cope with pressures will bring a whole new experience to diving. I know it sounds Sci-Fi.. but really it is closer than you think. 🙂

    Cool discussion though 🙂

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