The Quarter Turn That Kills 57

no_quarterAt least one diver won’t be spending the holidays with family and friends this year, thanks to the dangerous practice of opening a scuba tank valve all the way, only to close it back a quarter turn. According to an article in the Daytona Beach News-Journal, an Edgewater, Florida, diver perished October 9 with more than 140 bar/2,000 psi remaining in his tank. His valve, however, was only open one-quarter turn.

The same thing happened to cave-diving pioneer Sheck Exley over four decades ago. Exley was descending, head-first, into a narrow crack in what is now Wes Skiles Peacock Springs State Park. Exley had accidentally closed his tank valve all the way, then opened it a partial turn, as he was taught. His regulator still breathed fine at the surface but, upside down at 20 m/65 ft, Exley found himself starved for air.

Exley ended up surviving what had been a very close call, and made it a standard of practice in cave diver training to either open valves all the way or fully close them. This has become a standard of practice in tech diver training as well. For reasons passing understanding, however, it has not become a standard of practice in recreational diving.

Where Does This Come From?

It’s common in industries ranging from welding to HVAC to never fully open a cylinder valve. The concern is that, if you try to force open a valve that is already open, you may damage the valve. Well, guess what? If your acetylene valve is only partially open, you may not be able to weld. If your scuba tank is only partially open, you may very well die.

In shallow water, a partially open valve may still be capable of delivering sufficient gas. At depth, however, the same valve setting can leave a diver starved for air.

Forcing a tank valve past its normal stopping point in either direction is a bad idea — even though modern scuba valves are a lot harder to damage than people realize. Curiously, you never hear dive instructors say, “Close your valve all the way and then open it a partial turn.”

In the final analysis, valve damage beats being dead.

So What Should You be Doing?

So that you live to enjoy another holiday:

  • Open and close scuba tank valves only by turning them very gently. Stop as soon as you feel resistance. A valve turnwheel that does not turn easily requires service.
  • Make sure your valves are either all the way open, or all the way closed.
  • Be wary of well-meaning buddies and even dive boat crew checking your valve position for you. Even divemasters have been known to accidentally close a valve all the way, then open it a partial turn. Because this can work in shallow water, divers may not realize they are at risk until it is too late.
  • To help ensure your valve is open all the way, take several deep breaths from your regulator while looking at your pressure gauge. The needle or reading should hold rock steady. If it drops with each breath, your valve is closed. If it fluctuates with each breath, your valve is only partially open. Do not dive until the valve is open all the way.

The next time you run into an instructor teaching this archaic and dangerous practice, set him straight. Better to ruffle some feathers than to bury a dead student.

Please Note:

Since first posting this a week ago, I’ve received overwhelmingly positive response, the support of well-known authors Steve Lewis and Bernie Chowdhury, and found similar articles on the and Scuba Diving magazine websites. More importantly, friends and I have confirmed that NASE, PADI, TDI/SDI, GUE and, I’m told, BSAC all say “turn it all the way on” in their entry-level training materials. (I had one person insist that SDI says a half turn back, which is funny, because I produced the SDI Open Water Diver course video and know damn well what is in there.)

So, if you want to waste your time composing a reply that supports this dangerous, outdated practice, be my guest. I’ll just delete it.

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57 thoughts on “The Quarter Turn That Kills

  • Vincent Janelle

    We do this with rebreathers (at least, the way I was taught – recently), with the idea being that a boom scenario, it’s more important to save your gas (tiny tanks), and you should always be monitoring your loop.

    It makes me twitch every time I do it, however.

    • Edward hall

      Yes Vincent, that’s what they teach for re-breathers. We also as re-breather divers should ALWAYS have a second source of gas, most of the time in OC form, which should be open ALL THE WAY and tested at the surface. More and more re-breather divers are using in-line shutoffs on their bail out, deco, and deep-gas, tanks.

      Try the in-line shut offs, espc if you dive to 200+ etc, the likes of Tom Mount, and Peter Sotis use them and teach them.

  • Bernie Chowdhury

    **Great** post, Harry! Thanks! Hopefully, ALL divers and — especially — their instructors, will pay attention to this and make it standard practice in every facet of diving, whether tech, or rec.
    Again, thank you!
    Bernie Chowdhury
    Tech Instructor
    Author – The Last Dive

  • Craig Werger

    Good information in relation to open circuit diving. Having the valve all the way open will ensure it only turns one way in an emergency… Off

    When closed circuit diving however it is common practice to have the onboard oxygen valve only a couple turns open as it would never demand high flow.

    Safe diving,


  • john connor

    Thanks for this, I have been diving for 7 years, I have started tec basics, I always did the quarter turn trick after getting taught this way. NOT ANYMORE.

  • Gareth

    Let me see if I have got this right,
    you are worried that the diver turns valve the wrong way (closing it) when thinking its opening it, and then only “opens” it a quarter turn, so it looks fully on.
    Your solution is to fully turn valve and no 1/4 turn.
    So if we have same diver who does not know which way his valves opens he closes it fully (thinks is open fully)
    So he jumps in and gets 2 breaths on the surface as valve is fully closed. Is this your solution fully closed/fully open ?? He has still made the mistake.

    The REAL solution is that the divers needs to KNOW which way valves turns to open.

    • Admin Post author

      You can argue all day about what divers “should” be doing. In the final analysis, it’s irrelevant. As countless close calls and at least one documented fatality have shown, this is a mistake that real-world divers continue to make, no matter how well taught.

      As well-known author Steve Lewis, who has written material for several training organizations, says in his new book:

      This oversight has caused OOA panic in recreational divers resulting in death. One incident recently in Blue Springs, Florida resulted in a new diver dying with more than half a complete fill in his single tank. We can say that one trigger in this sad event was the silly, out-dated practice of open valve fully and then close a half turn. This asinine piece of diving lore has caused countless panicked ascents, and innumerable complaints to rental departments that “The regs you gave me did not work at depth.”

      Here are articles from and Scuba Diving magazine that echo what my article says.

      The fact is, every major training organization, in their technical diver training courses, teaches turning the valve on all the way. The problem is that we have too many recreational instructors out there who are too lazy to change what they teach.

    • Diiver

      This is rather odd. Diving for 20 years and teaching for 15: I’ve NEVER heard if such a ridiculous practice of 1/4 turn ON. This would cause spg needles to fluctuate during predive checks and starvation of air when tank is low (not empty).
      The method widely accepted is fully ON for air flow and 1/4 turn back so the valve is less likely to jam open from overzealous divers.
      Perhaps that practice got flipped somwhere??

      • Admin Post author

        You need to go back and re-read both the article and the comments from well-known experts such as Bernie Chowdhury, author of The Last Dive, and Steve Lewis, author of technical diver training materials for TDI, NASE and others. Also follow the links to the articles appearing on the and Scuba Diving magazine websites. Neither these experts nor the technical diver training materials published by all major training organizations condone turning a fully open valve back a quarter turn.

        By the way, I’m glad to see you’ve been teaching and diving as long as you have. Keep it up another 20 years and you may catch up to some of the rest of us (he says, tongue firmly in cheek). In reality, how long a person has been diving or teaching is meaningless if he hasn’t learned anything during that time.

    • colin fairhurst

      Hi the difference is if its a quarter turn open when you do your buddy check the needle of your gauge won’t drop fooling you into believing its on however at depth you won’t get enough air.The BSAC stopped this quarter turn nonsense about 30 years ago.Other training agencies still teach it.

      • Admin Post author

        Judging from some of the replies I’ve gotten, there are a lot of instructors out there blissfully unaware of what their own organizations recommend. Some friends and I spent yesterday evening surveying what appears in various agencies’ entry-level training materials. Here is what we found:

        • PADI: All the way on.
        • TDI/SDi: All the way on.
        • NASE: All the way on.
        • GUE: All the way on.
        • NAUI: Quarter turn back.

        Why is it the fact NAUI’s materials are out of date (and out of touch) doesn’t surprise me?

        • Stacy

          It does not surprise me the the NAUI manuals and instructions are outdated. I refuse to dive with anyone that is NAUI certified. They are not taught safe diving practices. They often venture off on their own leaving their dive buddy to fend for themselves. I wish all diving certifications were equal but they are not.

        • Eris

          Can you post a link to the PADI:all the way on? I’ve looked for it online and in my beginning instructions manual and don’t see it but would like to be able to produce it when I go diving next time and ask for “all the way on” instead. Thanks!

          • Admin Post author

            You will find the reference in either of the last two editions of their Open Water Diver manual. I don’t have either, so I can’t cite a page number for you.

            Divers Alert Network recently joined the ranks of major organizations recommending “all the way on.” Here is an article that talks about that.

  • Lloyd | Backpacking Scuba Diver

    This is one thing I love about the industry – so many techniques and so many opinions.

    I’m starting my career in diving in the near future and I’m glad I came across this article. Without a ton of knowledge and experience myself re scuba, I’d like to say I see both sides to this story.

    For one, a new diver – or, any diver for that matter – should be taught how to read his/her valve (as you mentioned), If the needle is fluctuating or dropping then something is amiss with the valve. I think safety/buddy checks are rushed most of the time (in my experience). And, I’ll admit, I’m guilty of this from time to time, but it’s not safe. From my understanding of what you’ve written, if a thorough check is done a diver should notice this issue before he/she enters the water.

    On the other hand, why not just avoid the issue all together. Open it full throttle and there won’t be an issue – other than the potential for too much stress on the valve. But how often does this actually happen – if ever – on well maintained equipment? Hell, is Tech Divers are practicing this it must be safe.

    I think as an instructor it would be wise to explain to your student both techniques and the benefits and hazards of each and let them decide. Just my opinion.


  • cavediver

    There is some substance, but the important thing
    to stress is *knowing* which way your valves open and close. That what’s saved Exley. And that’s what’s gonna make the difference the day the valves end up in an unexpected position – contact with the ceiling can make them turn and unless you know *exactly* what you are doing – it will become exiting…

  • Brian Higginson

    Load of rubbish, ive been diving 2 years and did 600 dives as a Dive Master last year with 550 in one lake and I was ok.. as a Dive master I know what’s best. If anyone needs training then get in touch

    • Admin Post author

      I don’t know which to be more impressed with, your vast experience (two whole years and a whopping 600 whole dives…in a lake), or the fact you are confident in telling every cave diving instructor, every technical diving instructor — not to mention PADI, TDI, SDI, NASE and GUE — that they are wrong for teaching this. It’s okay though. Forty years ago, when I had as little real-world diving experience as you do, I thought I was pretty hot shit, too.

      • Edward hall

        That’s whats really wrong with the dive industry. It’s also wrong with Flight Instructors as well.

        They all seem to think it’s about THEM. Look guys when you become an Instructor, it becomes about your students, NOT YOU!

        That’s kind of the the WORD INSTRUCTOR.

        Any idiot can breath underwater, even instructors. It’s a little different when you can NOT.

  • divergirl

    I read this article with interest.I am an instructor and was taught and have always taught the 1/4 turn back method and I agree this method taught on its own could be dangerous.
    However, please let me expand. ALL my students are taught this as part of their buddy check as an easy way of ensuring their tanks/buddy’s tanks are fully open,as new divers often struggle with which way a tank turns on, and so this helps. They are ALL also told emphatically that they must also breathe off their air whilst their gauges to look for a fluctuating needle, which tells them that the air is being restricted ie the valve is not fully opened and if the needle drops and does not return the tank is turned off. I also get ALL my students to learn the “leftie loosy righty tighty” phrase – simple but effective. The three methods taught together should remove the problems mentioned in the above article.
    Having read the article, however, i can see the argument against this practice if the other two methods mentioned above are also not taught and re-enforced and even this old dog is prepared to learn a new trick…
    Maybe, as someone mentioned above, the important aspect is to ensure everyone is taught which way the valves turn – simple but effective, as proven by Sheck Exley’s experience?

  • Tom Hlavac

    A valve that is in the closed position can cause a lot of trouble (potentially fatal) during rocky shore entries. I see a lot of newer, and some experienced, cold water divers (Pacific northwest waters where almost everyone is using drysuits) struggling at entry. If you step into the water and are heavy, and don’t have the air on to adjust quickly, a bad situation can occur just at the start of a dive. I have seen people panicking because they didn’t have their air on and are heavy in just a couple feet of water.

    I once had a client diving with a new (for the client) drysuit during a charter at Browning Wall. This diver had been sold a nasty used drysuit, too large in size, and during the “drysuit course”, the shop (apparently somewhere down in Seattle area) had simply added weight to her weightbelt and a couple 5 pounds weights to her BCD (these were attached so that they couldn’t be dumped easily. They probably wanted to sell the suit and a bunch of weights rather than take the time to properly instruct the diver. I had some premonition of trouble so made sure I was in the water first to be able to assist immediately on her entry off the swim grid. Sure enough, as soon as she hit the water she discovered she was unable to depress the inflator button on the drysuit, and that the BCD was too small to compensate for the weight – she started sinking like a rock. I grabbed on, stabilized her, wasted some time before I figured out her BCD was fully inflated, so swam her to the wall and settled us on a ledge, then inflated her drysuit for her a little. Took her back up, holding on tight as I could now assume she had no handle on her bouyancy. I don’t wear gloves so was able to depress the inflater button, after she had put her “cold water gloves” on, her finger was too wide and soft to press the stiff small inflater. Big learning point for me was to wear an oversize and well maintained BCD so that I can help in similar situations – rather than relying on the other diver’s gear (buddy’s drysuits can blow out and often divers have smallish BCDs, and nowadays there are several different inflater control types to be familiar with).

  • Luke Rogers

    This has made me think! I learnt through PADI and HSE part 4 training and as far as I can recall I was taught the quarter back turn trick?! Why this was I never fully understood, I assumed it prevented it from jamming?! I personally only cracked the valve back 1/16 of a turn anyway, just to prevent it from sticking!
    But, a jammed OPEN valve or a major mix up causing death, I think I will now adopt the all the way open approach!!
    On a recent dive trip in Zanzibar the dive crew insisted on setting up the tanks etc, when I started checking the valve myself them got really arsey with me! I was like look, my life…. my responsibility!!!! Can see how accidents happen!
    Thanks for the heads up!!! Luke.

    • Admin Post author

      What PADI recommends in their brand-new textbook is all the way on. Unfortunately, there are a lot of divemasters and instructors who apparently are not aware of this.

      • Mike Ross

        No kidding some DMs and instructors are clueless on this vital issue. This misinformed piece of bad instruction – turning the valve back – has survived for decades, and it will take decades to correct this misinformation, given the ossified mind-set of scuba instruction and those blockheads who will not conform their teaching to safe standards.

  • Carl

    I did the same thing myself whilst diving on a reef off Sharm El Sheikh when I was finishing off my BSAC Sport Diver. Didn’t realise the problem until we started against the current and I had to draw more air. The gauge kept dipping so I took up my buddy’s octopus and got the tank sorted by a third diver. It could have been a fatal mistake – thankfully I only got a bit of a kicking off the dive guide.

  • Brendon Rowe

    It’s about time somebody made this point. As mentioned above, all the arguements in world do not take away from the fact that you are not teaching or diving to your own qualifying bodies standards if you still use this achaic 1/4 turn back method (except NAUI apparently).
    It pevents jamming – if a valve jams shut, you service it, same applies in the rare case it jams open. Cylinder valves are made to excellent standards these days and are only on for couple of hours at a time, at most, unlike engineering valves which may be left on for years.
    1/4 turn on by mistake should be noticed in your checks – problem is 1/4 turn easily becomes 1/2 turn which won’t be noticed until depth. (Try it)
    All the way off by mistake gives less breaths before disaster – Now this WILL be noticed in your pre dive checks.
    One of my most experienced dive buddies fell foul of this practice after turning her cylinder on and then 1/4 turn back, after kitting up and carrying out her checks she waited for the signal to dive. Before jumping in the helpful skipper (with decades of diving and skippering experience) checked her valve, found it turned in both directions, and turned it the wrong way till it was off (thinking it was now fully on). Descending head first behind her buddy she made it to almost 30 metres before finding she had no air. A single cylinder meant no alternative, buddy heading away from her, no air to inflate anything. She survived by kicking hard for the surface. She just made it and managed to scream at the boat who got to her before she sank again.
    I occasionally still come across people doing this and always correct them and relate this story.
    And still some of them argue, I don’t get the obsession with unnecesary, outdated and unjustifiable practices. I guess nobody likes to be told they are wrong and old habits die hard.
    But I emplore you all to stop this potentially fatal practice, it has been written out of training manuals for a reason.

  • ScubaGrrl

    I dived with someone who was convinced that 1/4 turn was correct. I was completely puzzled and I questioned him about it on the boat – he was convinced he was right without questioning that I may have been taught something different as I was certified back in 2006. Of course, he was one of those guys who had to have the last word! Now I know this was a relic from his training 15 years ago, so I kind of get it. Still, part of being a safe and competent diver is learning to adjust and update your practices as standards change over time.

  • Leo Quartullo

    Had an incident ice diving a few years back that got me to purchase Vindicator knobs for all of my valves. When the person behind you while you’re sitting in the ice triangle “helps” by turning your valves OFF – AFTER you’ve already checked your inflator and regs for predive check – you (or at least I) found the investment well worth it. Anyone, diver or not, can clearly see RED or GREEN on your knobs. I feel much safer diving with them.

  • Henri

    It’s either open or closed…and I prefer mine open under water to be honest.

    Although the article is very nice written the comments show that many people Have different ideas which makes it even more interesting

  • Bob meadows

    I have shared your post and a great post it is !!!
    Been teaching this way fully on for years in both my Padi courses and all my Sdi / TDI courses
    Thanks for bringing up for everyone to think about maybe we can get all those old divemaster s to rethink their old ways !

  • Kenny Schneider

    Would Tank valve drills be to complex for open water students what about advanced students.
    I have trained beginning rebreather students to dive closing and opening valves to ad gas in some failure modes. are other instructors doing this?

  • Nicholas

    Ok, so I do like your safety argument for valves all the way on……. at least regarding safety. But idiots try to break valves *constantly*. I don’t have multiple decades of experience, but I’ve been doing this for a while now, and worked at over ten different dive operations – so I’ve seen a lot of broken and damaged gear, and plenty of stripped tank knobs. The fact that people just love to overtighten valves both open and closed leaves me wondering……… and it seems like no matter what you teach them they still do it. I explain in super explicit terms to new students that they should only tighten a regulator yolk knob with *two fingers* (the thumb and index finger) – I say it several times, and I show it several times, and the idiots still grab it with their whole fist and overtighten it half the time. So, I agree with you, but I guess I am writing in to ask you, or anyone else who is reading, what is a way, short of flunking a student who can’t figure out what “on” or “off” is, of getting people to internalize these two important points? 1. turn the tank on. 2. don’t overtighten things. I even once had a dive student, who was finishing a phD in quantum mechanics, turn my tank completely off for me during a buddy check. Should we be failing students who can’t figure this stuff out? what do people think? and can anyone offer some teaching tricks, because “righty tighty – lefty loosey” doesn’t work – people are too stupid to understand this stuff without a frame of reference. The only verbal cues that have been at all effective for me is to say to a diver who is behind me checking my tank, “turn the knob back towards you to turn the tank on”. (and I still crane my neck to watch to see if they are closing the valve) Anyone have any effective teaching tips? I hate to blame processed foods, television, and too much deodorant, but I feel like the world is too stupid to figure this stuff out. I mean, people really don’t know how to open a jar? if they can’t open a scuba tank, does that really mean that every time they want to open a jar of food they are guessing and turning it one way first, then the other, and simply waiting for the end result of the jar being open? and for the duration of their life they never actually internalized which way to turn it? they only learned to try both directions and hope it opens? …… think about that for a minute…….

    • Admin Post author

      I guess it comes down to the fact that, if you are going to teach the general public, you have to be prepared for the fact many otherwise intelligent (and not-so-intelligent) appear to suffer from a sort of dyslexia when it comes to telling clockwise from counterclockwise.

      The only advice I can offer (and this is far short of a total solution) is to avoid using the words left and right. Valves do not turn left or right; they turn clockwise and counterclockwiseanticockwise) — and only if you are looking at them from the end.

      Given that, despite our best efforts, people are going to continue to do this, it just underscores the importance of test breathing your regulator while looking at the pressure gauge.

      On a broader note, the main problem I see with diver training these days is that too many people make it through in the minimum time allowed. If 100 percent of your students complete training in the same compressed time frame as everybody else, then you are almost certainly certifying students who simply aren’t ready. In my experience, as many as one in three students really need to repeat one or more confined- or open-water training dives before being certified.

      Also, if any students repeatedly exhibits a behavior that could result in serious personal injury or death, you have a duty to not certify them until the behavior is corrected. To do otherwise puts you in an indefensible position.

  • Darlene

    Thank goodness I read this before getting into diving. I have never been in open water and I will be one day. Thanks for helping me learn this before a problem could have happened!

  • Retired diver

    This is a nice article, it raises awareness, and brings the practice up to date, I suppose – although I admit to always practising the 1/4 turn myself.

    I have to point out what I think is an error though (I trust someone will correct me if I’m wrong here). The 1/4 turn doesn’t come from fear of trying to force an already open valve open even more; it comes from the fact that, for SOME valves, when they are open and pressurised components shift slightly to take up any slack, allowing the valve to be turned open fractionally more before hitting the stopper than possible when not under pressure. As the tank empties the components “relax”, and can get jammed in the open position. Any diver who has found it difficult to close their valve after a dive has experienced this, and the amount of force required to released a jammed valve can certainly cause damage.

    Not all valves are designed in this way (though most that I’ve come across are), and of course safe diving practices must take priority, especially if it’s an effective way to affect accident rates.

    • Admin Post author

      Technical diving has been around for at least 20 years and cave diving longer than that. It has been a standard of practice in both cave and tech diving to fully open valves since the time of Sheck’s incident in the 1970s. During that time, there have been no widespread reports of valve damage or stuck valves as a result of doing so. Now it’s becoming an increasingly widespread practice in recreational diving — especially since this is what most training agencies recommend — and, again, no widespread reports of problems.

      I think you are basically right — at least in theory. However, just as neither hummingbirds not bumblebees should be able to fly, real-world experience does not appear to support the theoretical problem.

  • stuart knox

    After reading some of the comments and being new to scuba diving it amazes me that a simple arrow on the valve stating open/closed isnt used more.
    I marked my valve on my tank after i had made a couple of errors in the pool thankfully.
    Thanks for this artical and very informative, i just hope people take notice.

  • Neil DAvison

    There’s a bit of confusion over who says what here.
    PADI open water manual states: ‘open the valve slowly, all the way until it stops turning. (Note: it used to be common to open the valve all the way, and then close it a quarter to half turn. This isn’t necessary with modern valves, though it doesn’t hurt anything if someone does it).’ That’s straight from the manual. We wouldn’t allow any of our students to dive without having conducted a thorough pre dive safety check before every dive. This would identify a part open valve. Our students also wouldn’t be diving in an overhead environment until properly trained to do so.
    Conversely, the PADI equipment specialist instructor guide states:
    ‘b. Valve care and maintenance
    • Rinse under on/off valves with fresh water after use.
    • Turn valve on slowly, all the way on and then back slightly.
    • Turn valve off gently. Turning a valve off forcefully will cause damage to the seat.’
    Between courses, there is some discrepancy, but correctly trained new Open water divers will not experience these issues.
    The pre dive safety check is designed to identify issues such as these. Divers who disregard their training & pre dive procedures should not look to blame the semantics of valve opening. None of us are too experienced or clever to forget the basics.

    • Admin Post author

      Regarding PADI’s materials, you need to consider the date of publication. The Equipment Specialist instructor guide is, apparently the oldest and clearly conflict with the much newer Open Water Diver course materials. The Open Water Diver manual you quoted is now out-of-date, and has been superseded by a brand-new version that simply says to turn valves on all the way.

      As far as buddy checks solving all the problems goes, we as an industry need to collectively Wake the Fuick Up. We’ve been teaching this for 50+ years. It hasn’t made a difference. As well-intentioned as buddy checks are, they are simply not something that real people do.

      Worse, a well-meaning buddy (or divemaster) can as easily turn your air all the way off and open a partial turn as he can turn it on. The fact is, just as some people can’t distinguish red from black, there are people who simply can’t tell clockwise from counterclockwise. It doesn’t mean they weren’t adequately trained; it means the training they received failed to recognize this very human failing.

      The only way to truly ensure your air is fully turned on is to look at your pressure gauge while taking several deep breaths from your regulator. If the reading drops or fluctuates, your air is either turned off or only partially open.

  • Mike D

    Nice article, I found it after having a heated discussion on a boat in the Red Sea 2 weeks ago. I’m a mechanical engineer but DM in my spare time. A lot of misunderstanding regarding the ‘magic quarter turn’ stems from the old style ‘vertical’ valves which could indeed get stuck ‘on’ whilst supplying air to the first stage. This is because two flat faces mated flushly together when the valve was opened fully. That type of valve was used in the 70s – when the older generation of divers were learning to dive.

    Nowadays we use crossflow valves, which physically cannot get stuck open unless the person opening it all the way is the hulk, and damages it. They are designed specifically not to get stuck when supplying gas to the first stage.

    Those that advocate use of the 1/4 turn and saying that they check to see if the needle moves when breathing are missing the point entirely. When a diver is at depth, the external pressure changes the ability to supply air at the same flow rate as we descend. A 1/4 turn may look harmless (and needle might not move) on the surface, but at depth, and coupled with a piston regulator, the ability to supply air can be greatly compromised. This is why some divers that ascend in an out of air scenario notice that they can use their scuba unit again when shallower.

    If you need further explanation I recommend doing an equipment specialty course. A good instructor will be able to provide both types of valves (cut in half), in order to see how they work. You can also see the differences between a balanced diaphragm reg and a piston reg.

    Thanks for the article.

  • nemo

    Really great post, thank you. I’m an instructor, and was always taught to teach the half turn back. I never knew why, other than that sometimes the tank handle can get “stuck” a bit when it is all the way open, but who cares! Really, after the possible problems that can arise, as you described, I don’t know why I would ever suggest this practice again. Thank you so much!!

  • Mike Ross


    Thank you for the decades overdue correction of this hoary, unnecessary, and dangerous practice of teaching recreational divers to turn their valves back from the full-open position. The practice of turning the tank valve back from full open is unfortunately still being taught today in many highly respected scuba schools. Dive boat “Divemasters” often do this to divers behind their backs just as they are about to enter the water, with the diver clueless about what has been done to the valve.

    The nightmare scenario is reaching your minimum tank pressure at depth with the tank valve partially closed (either from you having done this yourself, or a divemaster or your buddy surreptitiously doing it), and having your buddy have a sudden catastrophic loss of air pressure from a high pressure O-ring blowing out. You’re now faced with not one but two divers attempting to breathe at perhaps at two, three or more atmospheres with a much lower, minimal tank pressure and your partially closed tank valve limiting the air flow to both of your regs. This could easily result in both divers over-breathing their regs, causing either panic or anoxia, and possibly not making it to the surface alive.

    Keep your tank valve either open or closed 100%, and don’t ever let anyone else touch your equipment except a trusted buddy with whom you’ve discussed and practiced your respective safety protocols.

    Your life and possibly that of a loved one is at stake.

  • Tim Gordon

    Just a note: with oxy-acetylene welding, the oxygen cylinder is always opened fully. The oxygen cylinder has a handwheel, just like a SCUBA tank does. The acetylene cylinder, in most cases, has no handwheel, but a square stem that is operated by a wrench that is fit over it. The wrench is to stay in place while the cylinder is being used (in other words, while welding) and it is only opened about 1/4 turn so it can be closed quickly in the event of a fire.

    I have yet to hear of any SCUBA divers breathing from acetylene cylinders…

  • Carlton

    1/4 turn is out of date but I can tell you this from someone that splashes lots of divers everyday from my commercial boat. Every time we walk a diver to the exit of our boat, we check the air valve to make sure its all the way open. When a diver opens his valve all the way can then cranks back a “hair” it’s very easy to tell the tank is on by a simple roll of the valve to its full open stop. We’ve had many divers crank our tank valve so hard open that we have trouble moving the valve. At that point I don’t know if its hard open or closed unless I really crank on it or have them take a few breaths before entering and looking at their valve. We generally have to service that valve soon after. We teach our students to always take a few breaths while looking at the gauge. We’ve had students while doing a buddy check turn off their buddies air. We’ve had an instructor make a decent to detach a mooring line on a wreck only to run out of air at 30 meters because they only cracked their tank open. Students do it out of ignorance; experienced divers do it for a different reason. Complacency. I am also a private pilot that has a written check list for may preflight inspection. It’s been used so many times that I sometimes think I checked something that I didn’t really check because I became complacent. Flying can kill you as quick as diving.
    In my opinion it isn’t the 1/4 turn that kills, its complacency that kills. Cave divers and technical divers are much more experienced than an new OW diver. The safety record for new divers is pretty good give all the newness. It seems its after they’ve done long enough to become complacent, the accident rates climb. This is not just a scuba phenomenon, Its part of human nature.

    Complacency kills.

  • Lance Wagner

    If I read this story a year ago i would have called it irrational except that it actually happened to me. Not sure how or why but i found myself at 80 feet and felt like i was sucking air through a straw. I thought it must have been regulator or first stage failure of some kind. As i got to shallower depth it breathed normally again. I still thought it had to be gear issues until someone mentioned this could have been the issue. I always open my valves all the way and back it just until it’s no longer tight… not more than an inch. By the way I’m not an Amateur diver. I’ve been diving commercially for over 20 years.

  • Ben J. Farrar

    Ohhh shit yeah i agree entirely. I work in the holiday diving business where i direct dive cruises and 99% of the divers i have never met before so god knows what they have been told. The majority were trained 5-10 years ago so most think turn back half a turn is how to open a tank. I & my dive team always tell our divers when they are onboard the speed boats and before we cast off from the liveaboards to A] make sure that they have their mask, computers and cameras (we look after their fins, weight belts and scuba units) B] to check that their air is on fully by breathing from the reg (some purge it) and C] most important is to look at the pressure gauge for needle movement. But it is not always possible to actual see the diver looking at their gauge when they are checking their air on a speed boat. Some guests (mainly group leaders) complain about our repetiveness but when i explain i have personally saved one panic diver bolting to the surface from 20m (no joke) with mask and reg removed because of the back half turn technique and evacuated another diver who although not in my dive group but was actually buddied with his instructor and both of whom were still under my care, again the reason for the problem started with the back half turn rule, they agree. Both of the divers by the way made a full recovery but tried and failed to blame me / dive guides / boat crew of negligence. So since those incidents i brief all my guests / students on is fully ON and off is fully OFF so please turn on your tanks yourselves just before you put on your eqt. Four years later (touch wood) i have never had a repeat incident and it is amazing how many divers ask why not go back half a turn.
    ****If you want more details (without names of course) of the incidents for you to use as examples please ask me.****
    Dive Safe. Live Safe. Enjoy Life.

  • David Rhea

    Also to be noted, make sure your configuration, buoyancy, trim and skills allow you to reach your vavle/valves. If properly trained and diving in an overhead environment, always check your valves ( do a flow check) anytime you bump the ceiling.