"Over-breathing your reg"?

[Trimix2dive]

huh??

You need to switch from you snorkle to your regulator well before you reach 60 feet from now on.

 

[Thalassamania]

Akimbo's got it right.

 

[Akimbo]

It is possible to overbreath a regulator. I did it once on a working dive trying to drag 30 feet of chain and 150ft of 3/4 rope along the bottom at 130ft during a wreck salvage job. This was back in the late 1980s and the reg was probably 20 years old then. That experience is why I have nothing but ScubaPro MK20s now. I know there's no way I can overbreath one of them. So maybe it isn't a concern under normal diving conditions with modern regs, but that doesn't mean it's never happened.

I completely agree about performance of older regulators. This post may provide a perspective to anyone interested in the subject:

http://www.scubaboard.com/forums/5195415-post51.html

 

[RogerAGrimes]

The term "overbreathing your regulator" is supposed to refer to reaching a respiratory rate that the regulator simply can't provide. In practice, this is all but impossible. What DOES happen is that, as a result of overexertion or anxiety, the diver raises his respiratory rate. Given that regulators -- even the best ones -- increase work of breathing, as the diver reaches a less efficient ventilatory pattern, CO2 climbs. The diver feels anxious and short of breath because the increased CO2 causes an increased ventilatory drive. The obvious conclusion is that the regulator isn't delivering enough air, when in fact, it's delivering everything that is asked for.

Heavy exertion is always something to be avoided on scuba. If you ever get the feeling that you just aren't getting enough air, STOP and rest. If that means grabbing a rock to stabilize yourself, do it. High CO2 heightens narcosis, causes anxiety, and predisposes to panic. Stopping, breathing quietly, and thinking can prevent accidents.

This is great advice on all points. Many years ago I experienced my first underwater panic attack caused by over exertion which led to "overbreathing" my reg. The symptoms were exactly as stated, I started breathing very heavily and frequently, I got super anxious, near panicked, and felt like I could not get enough gas. I remember sitting there at 130 ft with my wife and trying to think myself out of my panic attack. I logically thought that if I truly was not getting enough air (as I was feeling), then I would have been unconscious ...so obviously it was just my head playing tricks on me. But then the panic won out. I wanted nothing more than to jet to the surface, pull my mask off and my regulator out of my mouth and breath "fresh air". But I didn't. I went to my wife and called the dive and we went up slowly.

Since then, I've learned to be hyper aware of the overexertion issue (which often occurs in heavy current or malfunctioning equipment situations). When I feel myself starting to over exert or breath hard, I just hook a finger on some underwater object, focus, and relax for 30-60 seconds. It works every time.

And I know that when I'm in better shape (less fat and doing a lot more hard aerobic exercise out of the water) that I never get panicked or over exerted in the water. I know the problem is me and not my reg. In fact, when I feel overexerted, I purposefully breath slower, which calms me down and stops the C02 buildup that isn't needed anyway.

 

[JB]

I think one has to be cautious about interpreting gas flow when evaluating regs. Most regs can deliver upwards of 600 l/min of gas flow. The minute volume of someone taking 60 x 3 liter breaths per minute is only 180 l/min (and this is physically impossible to do, hence the Navy testing standards of 62.5 l/min). So superficially reg design is overkill and no-one could possibly come close to that minute volume and overbreath a reg.
The issue comes down to peak inspiratory flow. On a maximal effort inhalation the peak inspiratory flow for an indevidual is a little less than their peak expiratory flow, so for me about 500 l/min (just for an instant). If the reg does not deliver more than that, just for an instant, there will be a sensation of obstruction to air flow. In surface closed circuits this is overcome by having a reservoir bag.
As long as the maximal gas flow is more than your peak inspiratory flow it is impossible to overbreath a reg.
On the second issue, when you hyperventilate the CO2 actually goes down, and this happens in anxiety and can happen with exercise. In this situation the sense of dyspnoea is central in origin and bears no relationship to respiratory mechanics or blood gas values. The consequences are chest pain, acral paraesthesiae, a sense of impending doom, and can cause loss of consciousness from cerebral vasoconstriction. Panic is panic and no regulator is going to stop you panicing, or make your panic less!

 

[knowone]

Thanks JB. I think some people are intent on defying Anon.

 

[blue steal]

Thanks JB, you sound like my boss who is a Pulmonologist.

 

[Akimbo]

I think one has to be cautious about interpreting gas flow when evaluating regs. Most regs can deliver upwards of 600 l/min of gas flow. The minute volume of someone taking 60 x 3 liter breaths per minute is only 180 l/min (and this is physically impossible to do, hence the Navy testing standards of 62.5 l/min). So superficially reg design is overkill and no-one could possibly come close to that minute volume and overbreath a reg.
The issue comes down to peak inspiratory flow. On a maximal effort inhalation the peak inspiratory flow for an indevidual is a little less than their peak expiratory flow, so for me about 500 l/min (just for an instant). If the reg does not deliver more than that, just for an instant, there will be a sensation of obstruction to air flow. In surface closed circuits this is overcome by having a reservoir bag.
As long as the maximal gas flow is more than your peak inspiratory flow it is impossible to overbreath a reg.
On the second issue, when you hyperventilate the CO2 actually goes down, and this happens in anxiety and can happen with exercise. In this situation the sense of dyspnoea is central in origin and bears no relationship to respiratory mechanics or blood gas values. The consequences are chest pain, acral paraesthesiae, a sense of impending doom, and can cause loss of consciousness from cerebral vasoconstriction. Panic is panic and no regulator is going to stop you panicing, or make your panic less!

Your analysis does not take into consideration the inhalation curve or the residual gas volume of the hose itself — effectively a reservoir. Even though the volume of the hose is minute, it is about four atmospheres above ambient. The momentary "over-breathing" you describe has been found to be undetectable by the diver. As I recall, a 30%+ IP pressure drop had to last more than a quarter second to be detected by the test subjects.

In the end, the ANSTI breathing simulators used in EN-250 and USN tests mimic the human breathing cycle awfully close. As a result, any detectable performance anomalies are recorded.

 

[Seadeuce]

Forgive me for being late on entering this discussion, but I feel there is a relevant point to be made.

The OP asked about how and if overbreathing a reg. could happen. The replies have explained - to some extent - the answer to his question. Rather than get all technical about regs and the mechanics of breathing I respectfully suggest that, if such a perceived problem were to occur, then pressing your reg purge button SLIGHTLY will accomplish two things:

(a) Overcome the breathing resistance needed to "crack" the valve's diaphragm each time you breathe;

(b) Supply an immediate psychological placebo in that you will realise all the air one needs is immediately available, hence overcoming the "escape to the surface" syndrome most people get with such an experience.

It works every time, allowing the "Stop, Think, Act" philosophy to be carried out with less anxiety - and more air!

If you want to test this theory, then "sprint" awhile when next you're on a dive. Then, as you begin to pant a bit, try the above.

Have been doing it for years where necessary, and always inform any students.

It can be a lifesaver.

Cheers,


Seadeuce

 

[Stu S.]

For years I used a 1970's Healthways Scuba Star regulator. It was the cheapest one sold at discount stores. At 145 feet down, it delivered air aplenty. On those NC submarine dives, there was always more air than needed. If that thing worked, a recent regulator should have more than enough flow for any diver.

You can overbreathe your body due to the situation you are in. Overbreathe a modern regulator? Probably not.