Forget The Sharks: How 47 Meters Down Fails Dive Science

By Christie Wilcox | June 23, 2017 12:12 pm

6605799dba35561938a0ab69287af9d8This is a guest post by Jake Buehler, who just so happens to be an AAUS certified scientific diver as well as a science writer based in the Seattle area. He blogs over at Sh*t You Didn’t Know About Biology, which is full of his “unrepentantly celebratory insights into life on Earth’s under-appreciated, under-acknowledged, and utterly amazing stories.”


Summer is finally here in the Northern Hemisphere. The days are long, the weather is warm, and the water is inviting. It’s also time for our annual lesson from popular culture that this refreshing invitation is a lie, and that the only thing the sea offers us is electric, blinding terror. Yes, summer inevitably means the advent of a new crop of shark-based survival horror flicks.

This summer, much like the last with “The Shallows”, movie-going audiences will be treated to another shark-centric screamfest: “47 Meters Down.” The British-American film—starring Mandy Moore and Claire Holt—opened in U.S. theaters last weekend. Recent, somewhat ubiquitous trailers for the film outline its terrifying premise: while vacationing in Mexico, a pair of sisters goes cage-diving with great white sharks, only to have the winch suspending their protective cage fail, sending them plummeting 47 meters down to the ocean floor, from where they must escape to the surface before the swarm of sharks—or their dwindling air supply—does them in. It is no doubt that just like with “The Shallows”, we will again be reminded that the persistent blood lust of horror film sharks is altogether different from what science tells us about the behavior of their real-life animal counterparts. But the film and overall premise of “47 Meters Down” commit a litany of science inaccuracy sins completely unrelated to sharks. Frankly, the movie fails spectacularly when it comes to portraying the biology and physics at play during SCUBA diving (which is kind of amazing, actually, considering how much of the film’s plot is directly rooted in the consequences of being underwater). Being a trained AAUS scientific diver, dive science is an area I know a little about, so I made the commitment to sit through “47 Meters Down” so you wouldn’t have to, all to separate the reality of how diving works from…well, whatever it is that the movie plopped out.


The backdrop of the haline horrorshow plays out like this: sisters Lisa (Mandy Moore) and Kate (Claire Holt) are on vacation in Mexico. Lisa reveals that the idea for the trip was largely spurred by her recent breakup with her boyfriend, who left her because he got “bored” with her and their relationship. What better than a spontaneous trip down to Mexico to prove him wrong? Kate attempts to brighten her sister’s spirits by taking her out drinking and dancing until the wee hours of the morning. In doing so, the sisters meet some local men who tell them about cage-diving with sharks, convincing them to join in the next day. Lisa is terrified of the idea—both beforehand and the next day when they actually make it out to the boat—but Kate reminds her that posting cage-diving photos on social media is a surefire way to cultivate jealousy in her ex.

The cage-diving operation is beyond sketchy (something explained away by one of the local men as “it’s Mexico *shrug*”). The captain of the boat and this whole cage-diving outfit is Taylor, portrayed by a curt, sun-withered Matthew Modine—a man heading an alarmingly rusted and worn down vessel, and wholly unconcerned with whether or not the sisters actually know how to dive in the first place (Kate has some dive experience, but Lisa has absolutely zero, despite telling him otherwise).

As the sisters gear up and prepare to descend in the cage, great white sharks start to circle the boat, exciting basically everyone other than super-skeptical Lisa, burdened with the heavy hand of foreshadowing. Some of them are huge, as much as 28 feet in length, according to Captain Taylor (which is waaaaay bigger than any recorded great white shark in real life). Eventually, after a very short safety briefing from Captain Taylor, Lisa and Kate sink just below the surface in the cage, marveling at the shimmering schools of scombrid fishes, and the giant, toothy stars of the event. The two sisters converse with each other (and Taylor up top) using a comm system embedded in what appear to be the most incredible, top of the line full-face masks ever (more on that later), sharing in the excitement. Soon, Lisa decides that she’s had enough shark-induced adrenaline for one day, and that they need to be pulled back up. Of course, the Murphy’s Law of horror flicks like these kicks in immediately, and the winch suspending the cage busts, sending them rocketing down to the ocean bottom. It is at this moment that the movie starts sharing “alternative facts” about what happens at depth, which I have broken up below.


Under Pressure

Once the cage begins to plummet to the seafloor, Lisa and Kate begin to experience increasing pressure. As more and more seawater stacks up above them as they sink, the pressure exerted on their bodies by all this water goes up. Every 10 meters or so of seawater produces the same amount of pressure as the entirety of the Earth’s atmosphere at sea level. So, at 10 meters down, a person experiences 2 atmospheres of pressure. 20 meters down, it’s 3 atmospheres, and so on. All that squeezing doesn’t do a whole lot to your solid, fleshy parts—but it does a lot to air spaces. Gas is compressible, and as the pressure mounts, the air-filled sinus cavities, interior parts of the ears, inside of the mask, and lungs are all impacted.

In SCUBA diving, one of the first things you learn is how to combat this pressure upon descent using equalization techniques. This is particularly important for the ears, because if you reach a mere several meters down and fail to equalize any of that pressure pushing in, you can be dealing with a serious amount of pain, ruptured eardrums, and even irreversible hearing loss. The only real way to avoid discomfort is to descend slowly and equalize as you go, and by slowly, I mean half a meter at a time.

Lisa and Kate do not descend slowly. The cage they are trapped inside of hurtles towards the bottom at a rate that made me wince in sympathy for their poor, doomed air spaces. Once on the bottom, Lisa is shown to have a minor bloody nose, which is the extent to which either of them have any adverse effects from the pressure (also known as “barotrauma”). Increased pressure in the sinuses can definitely cause blood vessels to pop, and this can even happen under normal descent conditions. But because the two sisters are using full face masks and not “conventional” half masks, barotrauma in the sinuses and within the air space of the mask is essentially impossible (the constant flow of air into the full face mask keeps the interior pressure regulated with every breath).


Had Lisa and Kate been wearing conventional masks, it’s likely their free fall to the bottom would have resulted in a catastrophic, excruciating degree of “mask squeeze”, where the outside pressure of the water crams your mask into your face, causing nasty, extensive bruising and your eyes to turn the color of merlot, making you look like Qyburn just brought you back to life. Rather than mask-associated barotrauma, it is far more likely that Lisa and Kate would have blasted out their ear drums after rocketing down to more than five atmospheres of pressure, flooding their ear canals, hitting them with a bout of vertigo and persistent deafness. But, all they have to show for their extremely fast descent is a single barotrauma-induced leaky blood vessel in precisely the wrong location.

As they fall to the bottom, there’s a dramatic shot of the display face of a wrist-mounted dive computer cracking, illustrating the extreme depths and pressure Lisa and Kate are plunging towards. Wrist-mounted dive computers are basically high-tech watches designed to relay information to the diver about the environment (current depth, temperature), how long they’ve been below the surface, and other important info. These devices are flat-out rugged, often outfitted with tough displays made out of scratch-rebuffing mineral or sapphire glass, and rated to accurately register depths of 100 meters or more (like the popular, no-frills Geo 2.0 computer put out by Oceanic). These depth ratings? Yeah, they aren’t for the structural integrity of the display or the body of the computer; they’re for the pressure sensor. A computer that starts to inaccurately register depth at 100 meters might eventually fail to be waterproof somewhere below that point, but acrylic or specially tempered glass crushing like a Jolly Rancher under a boot heel? If this could happen to a dive computer at all, it wouldn’t happen at 47 meters, and if Lisa and Kate were actually exposed to a hyperbaric environment capable of such a feat, an obliterated inner ear would be the least of their worries.

47 meters down 2

Every Breath You Take

Once Lisa and Kate are down at 47 meters, the dire nature of their situation becomes clear. Strapped to their backs are air tanks, filled with compressed air that they are currently breathing—a tragically finite resource. These tanks appear to be a variety pretty standard in the SCUBA world: “aluminum 80s”, named for their composition and the fact that they are rated to hold 80 cubic feet of gas. This registers on a pressure gauge as about 200 bar when full (or for imperial folks, a little over 2900 psi). The pressure in the tank, expressed as a number in bar or psi, is a ticking clock on any dive. It is the most obvious limiting factor in a dive, and everything you do underwater fits into a plan to manage your air supply, so that you come up to the surface alive.

Being stuck in a rusty cage, surrounded by inexplicably murderous wildlife provides a major wrench in that plan.

The film is quite aware that the more time the characters spend underwater, the lower their air reserves get. But what “47 Meters Down” completely and spectacularly ignores is that, with SCUBA, depth is incredibly relevant to the rate of air consumption. With increasing depth and increasing ambient pressure, the air you breathe on SCUBA becomes more dense. But because the volume of your lungs doesn’t change, you end up using a greater volume of your overall air supply with every breath, the deeper you go. With every additional atmosphere of pressure, the air you breathe is compressed to half the original volume. So, at 2 atmospheres (about 10 meters below the surface), your lungs take in air that is twice as dense as it would be at the surface, meaning you will go through your air twice as fast. At 47 meters down, a person is experiencing 5.67 atmospheres, which means they blaze through their air at nearly six times the rate they would at the surface.

This relationship between depth and relative air consumption rate is not possible to get around, and the fact that Lisa and Kate are so damn deep makes just about everything they do in the film underwater either physically impossible or fatal in the real world. To really illustrate why this is the case, we need to get an idea of how long a diver can be expected to last on a tank of air at 47 meters depth. The base level of air consumption (often shared as a surface air consumption (SAC) rate, which is the cubic feet used per minute at rest at the surface) can vary quite a bit between people, and can be influenced by physical attributes like fitness (less conditioned divers might blow through air faster) or body size (bigger folks tend to need more air, unsurprisingly), or dive experience, as a familiarity and comfort with diving can increase air use efficiency. Some people, for unclear reasons, just manage to use very little or large amounts of air (I’m one of the latter; I can drain a tank like no one’s business). Temporary factors like stressful or tiring dive conditions can decrease efficiency on a given dive. A pretty normal SAC for a comfortable, experienced diver can be ballparked at 0.5 cubic feet per minute, meaning that a full aluminum 80 tank could theoretically last 160 minutes at the surface. At 47 meters, it would take about 28 minutes to drain the tank to empty…not considering the time breathing on the tank before and during descent, or leaving enough air to get back to the surface.

Again, this is a calm, resting, experienced hypothetical SCUBA diver. Lisa and Kate, to put it lightly, are none of these things. They spend huge chunks of time panicking, screaming, and swimming as fast as possible away from ravenous great white sharks (an action, I might add, that is made all the more difficult due to neither of them even wearing fins). At one point, Kate is engaging in multiple feats of strength in an attempt to free her sister from the cage, which is a level of exertion that cannot be kind to her overall air reserves. Not long before this, Kate advises her terrified and hyperventilating novice diver sister to breathe slowly and regularly to conserve air—not that any benefit from this is realized when the two of them are executing a continual Cross Fit workout at depth. We can give a very conservative estimate that the insanely strenuous and stressful conditions would give Lisa and Kate at least the equivalent of an SAC of 1.0 cf per minute (for some reference, I’m a big dude who has had mildly stressful dives while relatively inexperienced that came out to an SAC of about 0.9). At this rate, Lisa and Kate would empty their bottles in less than 15 minutes…not even considering all the time they spent in the cage at the surface. In the real world, Lisa and Kate would never have the opportunity to flee from the hoarde of sharks. They would run out of air and asphyxiate long before having the opportunity to escape from the cage. The movie would run about as long as the sequence of previews that came before it.

“47 Meters Down” doesn’t help this dramatic miscalculation when it brings up their remaining air pressure multiple times throughout the movie. In one moment, Kate estimates that 80 bar will last 20 minutes at their 47 meter depth. She is wrong. Under ideal conditions (where SAC is 0.5 cf per minute), that might get her 11 minutes. Realistically, it’s probably half that amount of time. Of course, what follows is the bulk of the movie, arguably longer (even accounting for some attenuation of the duration of events) than her own exaggerated number, and definitely not a handful of minutes. Long after this point, Lisa gains access to a second air tank, but even under the most optimistic scenario, there is just no way she’d last long enough on the first one to enjoy it.


Straight Up

A third conflicting factor severely messing up Lisa and Kate’s dive—you know, outside of the sharks and the rapidly draining air supply—is the risk that comes from coming up to the surface too quickly. The culprit is nitrogen, which makes up nearly three-quarters of the composition of air, and is normally inertly inhaled and exhaled as our physiology focuses on the “good stuff” (oxygen). At depth, all that compressed nitrogen gas dissolves and accumulates in the blood and tissues. All of that is all well and good, but when the dive is over and you head to the surface, the pressure drops, and all those dissolved nitrogen bubbles are free to expand in a process not all that different from the carbonation fizzing in a freshly-opened soda bottle. If you come up at a pace slow enough to let your tissues off-gas their nitrogen load, everything is golden. But if you come up too fast, you can get nitrogen bubbles forming in your tissues as they decompress, causing “decompression illness” or “the bends.” DCI can range from transitory discomfort or pain, to a life-endangering emergency, and it’s often hard to tell which it’s going to be until the symptoms emerge. If decompression is handled poorly enough, a diver can have nitrogen bubbles forming and lodging in arteries. This “arterial gas embolism” can be acutely deadly. It’s not just nitrogen bubbles that can be a problem for ascending divers: as the pressure drops, the air being pushed in and out of the lungs swells in volume. Moving upwards slowly while breathing avoids any issues, but shooting to the surface or holding your breath while swimming upwards can cause the lungs to over-expand and burst, sending gas into the bloodstream, causing an arterial gas embolism on its own. For these reasons, safe ascent is drilled into trained divers’ heads, and a “decompression stop”—where the diver finishes a dive by hanging out a few meters down for a couple minutes to give the nitrogen more time to fizzle on out of the tissues—is very commonly incorporated into even relaxed, shallow dives as a safety precaution.

DCI/the bends is bad. It is worth avoiding at every turn. At best, it is painful and debilitating, and at its worst, it can kill you. What it isn’t, though, is an automatic death sentence, which is what “47 Meters Down” seems convinced of.

Shortly after Kate escapes the cage, she swims towards the surface a bit (up to 40 meters) so she can get in range of the boat, allowing her to use her mask communications system to notify Captain Taylor that they are still alive down there. Kate tells Taylor that she has 55 bar left (that’s only one-quarter of a tank!). Taylor then advises Kate and her sister stay down in the cage at 47 meters and wait until they can pull the whole thing up somehow, because if they go to the surface while fleeing the sharks, they will get the bends and they will DIE! This is a ludicrous flipping of priorities. Yes, decompression illness can be dangerous, even fatal in some cases. But you know what’s 100% fatal? Not having any air to breathe. Taylor advising Kate and Lisa to sit tight at 47 meters and race through their air rather than take a risky ascent is like your doctor telling you to stop drinking any and all water because there might be lead in it. Yes, technically lead poisoning is not ideal, but perishing from dehydration is quite a bit worse.

The ultimatum given in “47 Meters Down” for avoiding the bends (and a guaranteed, awful death, apparently) is that Lisa and Kate need to do a decompression stop for 5 minutes at 20 meters down. If they do that, Captain Taylor claims over the comm system, then they are in the clear. If they don’t do this, then “nitrogen bubbles will form in your brain and you will be dead.” As a precaution, it sounds nice, but after spending something like 45 minutes of film time (somehow) at 47 meters, a single safety stop at twenty meters isn’t likely to reduce the risk of decompression illness much at all. “Deep”, 120 or 130 foot dives using normal air mixtures that last for half that amount of time would need multiple stops at shallower depths to help facilitate decompression of gases. Captain Taylor’s obsession with decompression safety also immediately, and hilariously, falls apart when, during a scene where the two sisters are on their way to the surface and finishing their five minute, 20 meter decompression stop, he tells them to swim upward as fast as they can to the surface as soon as the stop is complete! The closer you get to the surface, the more dangerous rapid ascent becomes, because at shallower depths is where the bulk of the compression and expansion of the volume of gases occurs. Suddenly jumping up from 80 to 70 feet down isn’t nearly as dangerous as sprinting up to the surface from 10 feet down. Darting to the surface after an insufficient decompression stop is actually the worst possible way to avoid getting the bends. So after an entire film of fixation on avoiding the bends, Captain Taylor tells Lisa and Kate to do something almost guaranteed to cause decompression issues.



When Captain Taylor floats out the idea of sending down extra tanks to the two sisters, he mentions that using a second tank will increase the risk of “nitrogen narcosis”, and that they would need to be careful and evaluate each other’s behavior for concerning irregularities. Nitrogen narcosis—also called the “rapture of the deep” and the “Martini effect”—is a real phenomenon. It’s an effect of diving on a normal air mixture that typically doesn’t become noticeable until at least 30 meters down. The mechanism of the narcosis isn’t entirely understood, but it is assuredly a consequence of high partial pressures of dissolved inert gases (nitrogen and noble gases like xenon and argon) in the body of the diver. Narcosis has been likened to alcohol intoxication, or being under the effects of an anti-anxiety drug, and can range from a slight dulling of senses and judgement, to severe confusion in some people. Whatever narcosis is, it is not what is portrayed in “47 Meters Down” at the end of the movie.

Nitrogen narcosis is depicted as a long, complex, “waking dream” style hallucination experienced by Lisa while she waits in the cage for help. Viewers discover that a highly-involved escape and rescue sequence is entirely imagined by a stationary Lisa, unbothered and lost within an episode approaching psilocybin mushroom trip levels of severity and duration. While nitrogen narcosis hallucinations can occur at the kinds of depths Lisa and Kate experience in the movie, sufferers aren’t transported to fully-formed, alternate realities. For most divers that experience narcosis, the effects are more akin to mild to moderate cognitive impairment, not the impact of powerful hallucinogens. Personally, I’ve experienced nitrogen narcosis on several occasions when diving at around 30 meters; it manifested mostly as difficulty keeping track of time (which can be dangerous while on a deeper dive), forgetfulness and slight disorientation, and problems effectively communicating with my diving buddy.

Narcosis is strongly associated with depth. The effects dissipate very quickly if a diver moves towards the surface. Captain Taylor’s claim that nitrogen narcosis becomes a risk with using a second tank isn’t quite correct; if narcosis was going to be an issue at 47 meters (which it likely would be), it would have been impacting Lisa and Kate long before that point. A second tank leading to more gas saturation would have far less impact than, say, descending five or six meters.


Of course, it should go without saying that the depiction of shark behavior is all wrong, too. Just as with “The Shallows”, there’s no way great whites would behave like this, even if they were offered up a couple of completely clueless, tasty humans. But that doesn’t even matter in the grand scheme of things; if this movie were true to life, Mandy would never have gotten the chance to worry about the sharks.

“47 Meters Down” exists in a world where much of the physics and biology of diving don’t apply, from how air consumption works at depth, to the effects of unmitigated pressure on the inner ear. The survival of the two main characters to the point of dealing with the threat of the great white shark swarm at all is only possible due to the suspension of essentially the entirety of dive science. Perhaps, if you consider it a science fiction movie rather than a horror flick, you can suspend disbelief long enough to make it through the film without groaning audibly at the sheer impossibility of it all.

Then again, based on the reviews, it’s probably not worth trying.


Film scenes credit: Entertainment Studios Motion Pictures 

CATEGORIZED UNDER: More Science, select, Top Posts
  • Uncle Al

    the only thing the sea offers us is electric, blinding terror
    Assassinated by affluence? Think of it as evolution in action.

  • Erik Bosma

    Great analysis but reading it all would probably take just as long as watching the movie. A little too great maybe. I admit I skipped through a lot of the article.

  • Josh Mellor

    Spot on analysis! I had similar thoughts watching this. I was taught while going through a commercial diving program that in the event of an emergency it is better to get to the surface bent than not at all. Granted we were trained for decompression dives, and were very accustomed to the inside of a decompression chamber which in a commercial application, we always had access to one. In short this movie was ridiculous.

    • Doug Arnold

      Ahh, the joys of surface decompression! Nothing like having to beat the clock like your life depended on it! 😉

  • Aggie✓ᵛᵉʳᶦᶠᶦᵉᵈ

    I’m completely clueless about diving but this movie seemed to defy common sense the whole way through. Great write up!

  • Casey C

    as trained divers, my dad and I wathed this movie just for laughs, and boy did it provide them! we drove my non-diver friend bonkers, but even she could recognise the lack of logic or common sense with some of it!

    • DisFan

      I plan to wait for it to be on Netflix or Amazon, then have a movie night with my daughter! Popcorn, laughs, ridicule!

    • Nes D

      the movie was made for non trained divers, some people dont know, actually millions, movies are not science documentaries, I wonder if you laugh at all movies, do you laugh when you see horror movies? because the monsters are not real as a train diver can you tell if they are real?

      • Casey C

        its almost like the huge ‘laughable’ mistakes are easily, EASILY fixed with little to no interference with the plot. There is a saying, people will swallow a huge lie and choke on a small one. if you want people to buy into aspects of your plot, it helps when things around it are accurate. increasingly movie goers expect that. and yes, of course I laugh at horror movies. so do most people.

        • Nes D

          Can you see? you laugh at all movies because you are having fun, thats the purpose of a movie. Next time you should advice hollywood when they make another Transformers movie. I am a computer´s technician but I enjoyed the Hackers movie even with all the obvious mistakes, I didnt pay attention to that. in both cases they just wanted to bring a good story, thats all.

          • Milos Radojevic

            Laughing at the movie doesn’t necessarily means that movie is good. For example, I don’t like fiction that much, and so many Hollywood movies are fiction, BUT NOWHERE is that written in their description, like this one. And that irrational screaming and breathing, and then ‘doing work’ in the sea ground. People that panic this way are not capable of opening cage, not getting outside.

        • fake_off

          Do you just troll the internet looking for comment sections where you can make yourself look smart? Because it is working.

      • Pei Lee

        I enjoyed the movie, thankfully I’m not a scuba diver so I wasnt trying to pick on details. Doesn’t mean I fell for it hook line n.sinker, pun intended. Just happy I watched a good movie!

        • fake_off

          Then you watched it wrong. The point of this movie is to show how smart you are about science

      • Holden McGroine

        This is not a fiction movie, so it cannot be compared with Transformers. Exaggeration of events is one things, totally faulty premise is another. There should be some plausibility in the plot of a movie based on its settings.
        And why would one laugh when watching this movie? It’s not a comedy. Unless it is so ridiculously unfeasible in the plot settings.
        Many of you never thought of the effect of the pressure in diving, it’s because you don’t know better, and this is not an excuse. Others aren’t close with logic. Hence the abundance of nonsensical comments.

    • Meowmeow

      Star Wars is completely unscientific. Does that mean you can’t enjoy it?

      • CC

        The sanctimony of this article and many comments is astounding. These guys must be super fun at parties… And especially on movie nights… 😒

      • Stella

        This is NOTHING like Star Wars. Not even in the slightest!

    • fake_off

      It must take some real smarties to see a b horror movie has some logical or scientific flaws in it

  • Eletruk

    Not being a diver, but know a little about physics, isn’t there another issue with the air use? Being 47 meters down means about 5.67 bar or 82 PSI, so wouldn’t that be the zero point? When pressure in the tank is equal or less than the outside pressure, gas no longer leaves the tank. So all the movie showing the dwindling air seems to ignore the fact that additional pressure is needed to breath air out of the tank. Or is it that the instruments show relative pressure?

    • Jonny Sage

      Yes, I noticed that too. They wouldnt be able to pull air out of the tank once it dropped below the outside pressure.

      • Doug Arnold

        While that is true, SCUBA tanks are normally filled to at least 3000 PSI, which would equate to a depth far beyond the limits of SCUBA divers. Every 10m of water depth ads another 14.7 PSI. So, by my calculations, it is well over 200m. You’d probably run out of air before even getting to that depth (plus you’d be dead if the tanks were filled with air…breathing air past 50m is actually dangerous due to the concentration of oxygen)

        Commercial offshore divers (saturation divers who live at depth) have a ‘bail-out’ bottle on their backs (their gas is coming to them through umbilicals) where if the main gas source cuts out, they have a backup to get them back to the bell. When I was training to be a commercial diver, we figured out how much gas a diver would have at about 200 or so metres down. They would have about 6 breaths to get them back, even though the bottle is charged to over 3500 psi

        • Ben Wilson

          Oxygen toxicity is not a factor at 50m on air. Nitrogen Narcosis is. The recreational limit has been set at 130′ because of narcosis.

          • Doug Arnold

            But the commercial diving limit on air in accordance with accordance with IMCA has been set to 50m because the partial pressure of O2 limit for commercial diving is 1.3 ata, as O2 is seriously toxic at around 2.0 ata. Mixed gas is used beyond 50 m due to NN, but 1.3 ata O2 in your gas mixture is the safety limit which is also a factor. You could be narced to the hilt but you’d still have a helmet on so you’d still have gas, but that’s of little consequence if your gas mixture is toxic due to O2 toxicity.

          • tlweb

            disqus_nf1eKVW1lO what

  • Kawthar Bakhach

    Aw come on. This movie was great. You’re all a bunch of party pooping peabodies.

    • dwp4you

      The movie SUCKED!

      • Stella

        Yes, finally a factual comment! Personally, I think this should have been narrated by one of the sharks, describing how the intelligent behaviours of humans are proven to be nonexistent and how much complete idiots starve for attention.

        • fake_off

          So…you think that this one person’s opinion is…a fact? Or just factual somehow? What do you think facts are?

  • Wiwin


  • Wiwin


  • Jonny Sage

    Some other things i noticed.
    They didnt have fins on, so swimming would not be easy.
    The trained diver swapped tanks under water, which would be difficult, and impossible for the untrained diver, not to mention taking off BC, putting a tank in it, and putting it back on.
    Navigating to the flashlight and back would be impossible without a compass. Holding depth without adjusting BC, especially for untrained diver, would be impossible.
    The time they spent under water would require much longer deco time, possibly multiple stops at shallower depths.

  • Doug Arnold

    Not having watched the movie, all diving movies tend to forget physics for the sake of a movie. As a former commercial diver and diving instructor, The Abyss is quite funny for its ‘artistic liberties’ 😉

    Now, DCI (either Type I or Type II) is a danger, but it is not the same as an AGE (arterial gas embolism, or an air embolism, which is what a SCUBA diver would experience, as they are only breathing air), which is caused by an over-expansion of the lung tissue that forces air (or the breathing gas) into the arterial system, and likely lodging in the brain, causing unconsciousness within minutes. This is easily prevented simply by never holding your breath underwater while making an ascent, which is why this is drilled into you even in a basic diving course.

    As for deco limits, going to 47metres woudl give you a no-deco limit of less than 5 minutes, so if they are down there for 20 mins or more, they are in for a very lengthy deco schedule (trust me, I’ve been there!). Depending on the schedule they use, they would probably need at least another tank just for the deco.
    If they chose to do an emergency ascent from 47 metres after being down there for so long, even if they didn’t run out of air on the way up, they would be bent like pretzels and would probably be in a serious amount of pain until they made it to a hyperbaric chamber. Surface decompression is used by commercial divers, where they are technically bent when they get to the surface, but they have 7 mins (ie you are using the Canadian Forces tables) to get from a depth of about 10 m, up to the surface, and then back into a chamber to go back to 10 m breathing pure oxygen. I’ve done this and it takes a lot of teamwork to rigourously sticking to the clock. The advantage of this is that you spend less time doing in-water decompression. As for the two characters, sure they could try the ascent, but probably within 5 mins of surfacing they’d be wishing they were dead!

    Nitrogen Narcosis affects people differently, sometimes not at all. Despite having gone down to 50 m myself (both in the water and in a hyperbaric chamber), i can’t really say I’ve ever felt intoxicated (or ‘narc’d 😉 ), but I’ve seen some people totally lose it. However, being narc’d has led to a number of divers suddenly thinking they either don’t need their reg, or the fish they’re looking at could use it, and they end up drowning.

    Oh well, why let the facts get in the way of a good story. I’ll still watch The Abyss, even though there are more holes in it than a block of swiss cheese!

  • Sarah Woerner

    I’m trying to figure out if it is rope or wire that is holding the cage up… Does anybody know for sure?

    • Msosostris

      There was a chain originally, then they attached to a “secondary winch” with what seemed more like rope.

      • Robert Clark

        It was spun metal cable, I think what they went for is it was so rusty and worn out it started breaking.

  • Sujeidy

    Gotta remember it is a movie, is for entertainment. There hasn’t been one shark movie that doesn’t exaggerate things if I wanted to see a real shark’s behavior or learn how to dive I would watch animal planet or go to the classes. It’s not realistic but that’s the point.

    • fake_off

      No successful movie has ever been made for entertainment purposes. Real movies–good movies–are incognito science lessons whose main purposes are to show smart people that they get smart things about science

  • Tricia Barker

    Can someone explain to me how they could hear one another underwater with no headphones and ears open to the water ? Magic?

    • James

      The make headsets that go in front of your ears and the vibrations allow you to here.

      Just google “headphones that don’t go in your ear” and you will find some.

      I have a set and love them.

      • Tricia Barker

        Thank you! I googled and could not figure it out. I feel much better about the movie now hahaha!

  • Phil Bennison

    My favourite issue was when the second tank arrives and it has an A-clamp fitting. her tank has a din fitting yet when she swaps tank the tank is suddenly a din. Maybe a kindly shark popped down with an Allan key and removed the insert 😂😂

    • Stella

      Thank you for the best comment I’ve read so far!😀

      • Phil Bennison

        Thanks 😊

      • fake_off

        Your standard for good comments is even lower than my standard for good movies.

  • D淡定D

    It is good to read some science stuff behind diving. The movie is still fun to watch.

  • Norman Railton

    Funniest part to me was the comms. They had no earpieces or headsets that I could tell, and could hear everything just fine

    • Creepy Green Light

      Nice point! I just read that today on IMDb. I didn’t notice that the first time I watched the movie. Watching it again right now with my daughter.

      • fake_off

        What makes it a nice point? Its general inaccuracy?

        • Creepy Green Light

          Fake_off – don’t be a jag off. And get your panties out of a knot while you’re at it.

    • Ben Wilson

      There was a buddy phone in their right ear, and the microphone is usually built into the skirt in the mouthpiece area.

      • KaraMarika

        You could see the mouthpiece inside their mask, to our right, their left. It was a little circle microphone to speak into. I think it is pretty common knowledge that scuba masks that you can communicate with others through exist. I have seen them used on many different shows, most notably on Josh Gates’ newer shown, which I believe is called Destination Unknown.

  • Meowmeow

    It is a fun thrilling movie. Why don’t you get the stick out of anus and just enjoy the film?

    • Stella

      Fun and thrilling as in you must be easily amused.

      • fake_off

        You seem like a really good person.

  • Schatzie’s Earth Project

    SO interesting how you fail to mention that this guy, Jake, is your boyfriend. Convenient, no? That same guy tried to totally scam me a year or so back, feigning all kinds of ignorance, not saying that the blog he was referencing to me on my blog was run by HIS girlfriend. So I guess that means you’re perfect for each other in your deceptive representations.

  • Máté Fekete

    There’s only one issue that still bothers
    me…isn’t it supposed to be excruciatingly cold down there? (Just to put another
    wrench in their odds of surviving..)

  • Máté Fekete

    There’s only one issue that still bothers
    me…isn’t it supposed to be excruciatingly cold down there? (Just to put another
    wrench in their odds of surviving..)

    • Ben Wilson

      Not really. At 47 meters it should be only a degree or so colder than at 10 meters.

    • fake_off

      I like the cut of your jib. Movies should only be greenlit after rigorous scientific scrutiny.

      • Máté Fekete

        as a non native speaker, i might not get the joke or the irony if there’s any.. but thank you i guess?

  • xjonsson

    As a movie if you suspend science, logic and reasoning for 90minutes then its watchable but if you are a diver holy hell this made me laugh so hard. You made some great points but there is one i feel you forgot that honestly i think would have killed them pretty quick.

    Neither of them have weight belts, if you have tried diving with even a slightly wrong weight in salt water you will know that if you go up a little bit the air expands making you go up faster, making even more air expand and you have an uncontrolled ascent. The blonde haired girl when going up to 40m to radio in would have shot straight to the surface if she hadnt put rocks in her BCD.

    As a how they could have made the movie work: they might have just about made the science cut if they called the move “18 Meters Down”

    Lisa and Kate would have had their highest chance of survival doing controlled stops up to the surface and completely forgetting about the sharks and just pray they had enough gas.

    • Zakaria Zaki

      thanks for this interesting information

    • MH

      That’s what I noticed too! Maybe at the higher depths they wouldn’t need weights, but they would rocket once they start ascending.

      And yes, no need to go all the way to 47 meters (not like most of the American watching public knows how deep that is anyway). The fact that they went into dive more than 40-50 feet when totally unprepared and surrounded by sharks would have been enough.

      I’m wondering if any other divers HATED when Kate explained the BCD inflater valve as putting air in if you want to go up and letting air out if you want to go down. NO NO NO.

  • Karate and Caviar

    Gosh, I loved your review. There are so many errors in that movie, it’s unbelievable. You would think that the director works with a professional diver who actually sense-checks the plot.. But already in the first few minutes I thought how can these girls be so stupid and naive.. Oh, well at least it was entertaining.

  • SavaShip

    I’m not really defending this bad movie… but you sir wrote an entire segment of the unrealisticness of certain events that were entirely hallucinated by a girl with no diving experience, so it actually plays against your complaint that it was inaccurate… of course it was inaccurate, it was in the brain of an untrained diver.

    • CC

      Exactly this. Some people just feel the need to exert their knowledge and prove others wrong, while missing huge points and bits of information. Just enjoy the movie and find a less bitter way to point out inaccuracies.

    • Ben Wilson

      Untrained or not, her symptoms are not in line with her likely condition.

      • SavaShip

        Hallucinations are indeed one of the effects of Nitrogen Narcosis… again, not defending this movie, but this specific portion is not really what was wrong with it.

      • fake_off

        Someone hire this guy as a dive science consultant on the sequel

  • Vanessa Hajian

    The main reason I love scuba diving is for the adventure, you don’t know what it may happen or what you may find below the water surface. In the past years I’ve taken a lot of pictures which I store in the logbook, along with all my diving logs. It’s cool that I can also search new dive spots or even add my own.

  • CC

    You do realize the race to the top was hallucination in the movie? The Captain was hardly obessed with decompression safety.

    I like learning to science and truth behind things occurring in movies and comparing them to what is shown in the movie…but… This entire article is so negative and has such a snarky sanctimonious tone that it was hard to enjoy. It’s a movie. It’s supposed to be an escape and about impossibilities and fun to watch. There’s a way to dissect fact from fiction without being so bitter lol simmer down.

    I enjoyed the movie while realizing it was probably full of impossibilities. I wanted to see if some of my hunches were right, but I wish I found a different article to confirm this. Sheesh.

    • Liderc

      I agree with this 100%. I came here looking to find out the faults in their diving science.

      But this article’s author sounded so bitter and sanctimonious that I no longer even wanted to learn more about scuba diving specifics.

      So, well done writer, you turned away someone who was actually looking to learn more about the science of scuba diving.

      Also, everyone already knows great white sharks don’t behave this way in real life, so even that part was pretty pointless.

      I enjoyed the movie for what it was, 90 minutes of time to waste and have a few scared jumps.

      • fake_off

        > I came here looking to find out the faults in their diving science.

        Time. well. spent.

      • Jen Norton

        That does not really matter the writer of this article missed the most important part. CNS clock when the body hits a 1.6 PO2 count you convulse and blackout (you basically sieze underwater) when a diver hits the 1.6 PO2 and is not wearing a full face mask they suck salt and stop living.
        At 150 you would be sucking salt on a standard compressed air tank.
        I have seen people get tunnel vision going over a rail at 130ft there is a stupid thing called the navy dive tables and 130 is on that list but these are people in top fit shape used to build theses TBT ABT tables.
        If you know math and science this movie will defy both only a person without a technical background could truly enjoy it without ripping it to logical shreads.
        Point is the movie would have been over 3 minute after the cage hit the bottom. Unless they spent the rest of the movie from the surface to recover the two bodies and the cage.

        • Dianna Burkholder

          We just dove to 143ft, and many others do the same in the Blue Hole in Belize. Granted, we could only spend a few minutes at that depth, but it’s by no means some instant death sentence.

          50 meters is only PO2 1.26. They would only have had an issue with PO2 with Nitrox.

    • KaraMarika

      I did not find the article to be as grating as you did at all. When you are an expert in something, it really amplifies your annoyance when movies/TV shows don’t bother to get an expert of their own and make sure there is some solid accuracy in their production.
      For example, I consider myself to be an expert on figure skating and while I enjoy every movie that revolves around the sport, it is very annoying when they use spotlights in major competitions or make it out like it is anywhere within the realm of possibility to do a bounce spin into a throw, which the male partner then somehow is able to catch (thanks a lot, Cutting Edge).
      So the frustration with the huge amount of glaring errors and impossibilities is obviously painful for the experts to watch. As the movie is going, we do not know that the dramatic rescue scene is (spoiler alert)….
      A hallucination. That information may have been gleaned from the foreshadowing, but it is not revealed until the end.
      And yes, the captain is obsessed with decompression sickness (the bends). He tells the women repeatedly to stay put and not swim up to the top rapidly because THEY WILL DIE!, which isn’t even completely true. As the writer stated, they can die, but it is not a guarantee.
      Basically it looks like the writers did a cursory Google search about diving and went with bare bones info for this movie. I have never gone diving in my life and I even know enough about it from various sources throughout my life to see all of the errors that he pointed out. It is pretty sad when even a novice can see the problems quickly.
      That being said, it ended up being pretty good. The beginning was VERY slow, but it picked up and got pretty good (if not predictable at times). The ended was a little annoying for me because I would have liked to see it finished out more. Did she get back with the BF? Did she decide she is better off without him and turn over a new, adventurous leaf? Did she become so terribly depressed that she became a recluse? Come on, give us something. Or was the second rescue all a hallucination too and she died there?

      • fake_off

        You didn’t find the article as grating because you are clearly just one of the few people in the two percent of humans as smart as the author

        • Linnéa Tyseng Nicander

          Smart has nothing to do with it, it’s all just about knowledge. Knowledge does have a tendency to ruin movies imo. I have no diving education but I’ve picked up a little bit about the bends. That’s what led me here.
          In the movie:
          1. In the cage it was OK to just haul them up ASAP but swimming up they’d get the bends, as if the cage was pressurised?
          2. The constant repition of the phrase “You’ll get bubbles in your brain and die” – that just sounded like the biggest hoax. It got me enough that I had to pause during the ascent and google this. I wish they’d just used “you’ll get the bends”, instead of that phrase and I’d have been able to finish the movie before googling.

          Then again I’m a cynic, and I’ve heard a bit about the bends. I’m likely to completely overlook obvious stuff in a movie about space ships. So, yeah knowledge.

  • Bosić Luka

    All though the film Lisa and her sister are communicating through “radio communications”, but, where are their “headphones”, “earbuds” in/on their ears? They can’t really hear through water can they?

  • Ben Wilson

    The author was correct about many things, BUT, he was slightly incorrect about one thing. The term for the bends is Decompression SICKNESS or DCS, not DCI. The bubbles he refers to causing an arterial gas embolism or AGE would definitely be from DCI, however that is not the bends and not due to nitrogen. An AGE is caused by holding your breath as you ascend, which is DCI, but not necessarily DCS.

    Decompression SICKNESS is caused by excess nitrogen. “The Bends”

    Decompression ILLNESS is a term used for both lung over expansion and DCS. Reason being is that we treat all dive related injuries of this type in the same way.

  • Stella

    I’m sticking to my opinion before I speed-watched this horribly acted, erroneous piece of video. The girls should have died for being such moronic idiots! Mandy is at her very best at showing how little she knows about acting.

    • Liderc

      And I’m sure you’re just amazing at your job, while she enjoys her millions of dollars for playing pretend on screen.

      And I don’t even like Mandy Moore, so just imagine what I think of you now that you’ve spoken this way about someone you don’t even know.

    • fake_off

      I get why you have such rigorous standards for intellectual honesty, seeing as how you form your opinions on movies based on “speed-watching” them

  • Turtles Run

    It is a movie, not science class

  • Lauren Kites

    But were you entertained? That’s the purpose of a movie.

    • fake_off

      No, the purpose of a movie is either (1) to learn science, or (2) for the screenwriter to confirm how smart you are by writing a scientifically accurate story

  • Lauren Kites

    Oh lets not forget the sharks. To see how ferocious and scary great whites are in the waters off of Mexico pay a visit to explore dot org and click on Oceans and then click on great white shark meditations. Yes meditations that should give you an idea. Seriously watch it its cool.

  • Michael

    Thanks for the informative article. I wasn’t expecting the movie to be perfectly realistic but was wondering how close or not it came.

    Question about the mask and the comm: were they realistic at all? The clarity? The 40 meter range to the surface? You imply they are ultra high tech – as in not yet invented, or just too nice/expensive for the rust-bucket boat? And is there a drain feature they seemed to use when taking the mask off/on under water?

  • fake_off

    It’s weird no one has pointed out that the obvious, central point of this article is for this guy to show off how smart he is, but only an idiot would take this movie this seriously

  • Joy Miles Gimbel

    The preposterous science is laughable literally, but listening to captain stupid makes me hope they don’t make it.
    It’s a cheesy horror flick so whatever but I hate the stereotype of evil shark against man given they’re endangered? Hated it even more in the see only if you enjoy Blake Lively’s body in the shark as personal enemy in The Shallows, which was highly rated for no other reason #sharkconservation

  • Raphsters

    I’m super late to the game, but had to comment about the fact that they’re also not wearing adequate wetsuits. At that depth hypothermia would catch up quickly, don’t you think?


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About Christie Wilcox

Dr. Christie Wilcox is a science writer based in the greater Seattle area. Her bylines include National Geographic, Popular Science, and Quanta. Her debut book, Venomous, released August 2016 (Scientific American/FSG Books). To learn more about her life and work, check out her webpage or follow her on Twitter, Google+, or Facebook.


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@NerdyChristie on Twitter

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