Holding your breath

[windapp]

Holding your breath with your airway open is only dangerous if you are so panicked you can't remember to exhale. Holding your breath with your glottis closed can kill you from four feet of water. This is why novice divers are taught a simple mantra, "Never hold your breath." If you don't have enough presence of mind to keep your glottis open AND allow expanding gas to escape if you ascend, you are in tremendous danger.

You can't not exhale with an open airway on ascent. Physics won't allow out. The problem with panic is that we naturally close our airway in that situation.

 

[dfx]

Also remember that the volume change is proportional not linear. Holding your breath at 100 feet and rising to 95 feet is different than holding your breath at 5 feet and rising to the surface. The volume change from 100 feet to 95 feet is small compared to the change from 5 feet to the surface. Boyle's law.

Volume changes yes, pressure change no.

This is the pressure at the various depths:

0 feet = 14.7 psi
5 feet = 16.9 psi
95 feet = 56.9 psi
100 feet = 59.1 psi

With a lung volume of 6 liters and a lung full of air, going from 5 ft to the surface those 6 liters of gas would expand to 6.9 liters. Going from 100 to 95 feet, they would expand to 6.2 liters.

However, the pressure differential would be the same, 2.2 psi in both cases.

I'm not sure which one of the two is relevant, but I would assume it's the pressure that makes the lungs rupture.

 

[windapp]

Volume changes yes, pressure change no.

This is the pressure at the various depths:

0 feet = 14.7 psi
5 feet = 16.9 psi
95 feet = 56.9 psi
100 feet = 59.1 psi

With a lung volume of 6 liters and a lung full of air, going from 5 ft to the surface those 6 liters of gas would expand to 6.9 liters. Going from 100 to 95 feet, they would expand to 6.2 liters.

However, the pressure differential would be the same, 2.2 psi in both cases.

I'm not sure which one of the two is relevant, but I would assume it's the pressure that makes the lungs rupture.

The answer to your question is both. However, it is mostly the volume difference.

Your lungs will expand until there is no longer any room to expand. Then they will be injured by the pressure that is trying to expand them beyond that point. My understanding is that the additional pressure beyond that maximum expansion point does not have to be much to cause serious/fatal injury. So...

If your longs are halfway to maximum at 95 ft, and you ascend to 55 ft while holding your breath, you live. In the same situation if you ascend from 40 ft to the surface while holding your breath, you most definitely die.

!!!!Note: Do not try this. You have no way of knowing exactly how full your lungs are.!!!!!

The rule should read: "Never close your airway. The best way to accomplish this is by continuously breathing, or in the case of a CESA, by making a continuous sound. If you stop breathing, for example to take a picture, or to help with your descent, you must be always aware of the state of your airway, and be absolutely sure that it is open"

 

[TSandM]

I do not believe it is constructive to give people misinformation.

We do not teach "open glottis" to our OW students. We teach them, "Never hold your breath." It's simple and easy and ingrains the important idea, and I even try desperately to remember to make little bubbles whenever I am doing skills in the pool that involve having a regulator out of my mouth.

However, if someone is intelligent enough to ask the question, "Is it dangerous to exhale and hold it on descent?", I am not going to tell them yes, because that's misinformation.

If someone asks the question here, I am not going to give them an incorrect answer. I will give them a complete answer, which I believe I did, including the circumstances where it is dangerous, and the anatomic basis for the problem.

This is much akin to the threads where people won't answer questions about decompression, because they're afraid someone will take the information and hurt themselves with it. I will not advise someone to hold their breath as a novice diver, and I will not advise someone to do staged decompression diving without training. But I don't think there is anything wrong with giving an inquiring mind the information it is looking for, so long as that information is both accurate and complete.

 

[Peter Guy]

Andy -- got to go with Lynne here -- Accurate information is better than inaccurate information. I want (actually I need) my students to understand what is going on so that they can comprehend WHY the rules are "the rules." Knowing a rule without understanding it can be just as dangerous as not knowing it at all.

 

[TMHeimer]

The fact is that, unless you hold your breath WHILE ASCENDING, no harm will come to you. Many of us hold our breath for periods of time, especially when taking pictures -- but you have to have sufficient situational awareness to be absolutely SURE you are not ascending while doing so. And you have to learn to hold your breath while keeping your airway open.

Yeah. A problem can be one I just had with a student. He had no idea how to keep the glottis open without exhaling. Of course, he had all sorts of problems with anything to do with mask off breathing. I guess saying never hold your breath is a fail safe thing for this guy. It would be interesting if there were some kind of instruction (such as you later gave) to help these folks. It would be good if these students knew what's going on in there before starting scuba.

 

[Frosty]

Hey folks help me out here on this one.

Hold breath going up -simple math says you are in a power of hurt.

Hold breath in a hover -mehh no issue I can see as long as you don't go up or down air volume has no change


Hold breath going down -Near as I can figure the worst case senario is a collapsed lung due to the exact oposite effect of holding breath going up. same math says I'm right
Or is my thinking foooey ??

 

[DevonDiver]

Hold breath in a hover -mehh no issue I can see as long as you don't go up or down air volume has no change

Lets be realistic about most diver's ability to hover... +/- what depth variation?

Now... let's consider how they hold their breath.... held with lungs empty... held with lungs partially full....held with lungs at max capacity?

At what depth... with what pressure differential per depth unit of fluctuation as they hover?

Lungs at max capacity - full inhale - plus what variation of pressure on their imperfect hover?

Hold breath in a hover?.....I see issues here.....

 

[AfterDark]

I've been holding my breath hovering while taking pictures, shooting a fish, waiting for a bug to crawl out of its hole for more than a few of decades now and never have had an issue. I think DD you and others in vacation locations that lead dives get a somewhat lopsided view of the “average” diver.
Everyone one I dive with here in New England has good buoyancy control, above average going by your description of average. We are in the basic section and I do understand the need to impress on new divers the absolute deadly danger in hold ones breath but, never is a strong word. Do students keep breathing when practicing air sharing switching from primary to secondary? Or their buddies regulator? Do they do ditch and donning during OW? If so do they keep breathing? I think the answer to these has to be no they hold their breath, So even before they hit the ocean the average student has held his or her breath at least long enough to switch regulators.

 

[DevonDiver]

I think DD you and others in vacation locations that lead dives get a somewhat lopsided view of the “average” diver.

Bear in mind that I was a 'cold-water diver' for more than a decade before I abandoned that misery for the tropics

Given that the vast majority of divers do train in 'vacation locations'...and given that the vast majority of them only dive on vacations... it does make a compelling case for what the 'average' is. I don't want to get into a cold-water versus warm-water spiral... that's nonsense... but divers who do dive in their home location gain more experience and ingrain skills better due to the higher frequency of their diving. In that sense, they are probably much more skilled than the 'average'.

For perspective on 'average' - there's a single dive school (sausage factory) on Koh Tao, Thailand that certifies more students per year than the whole of PADI UK. I've heard it discussed that the dive shops on Koh Tao (a tiny 7km long island) had considered forming their own agency. Based on their annual certifications, it would have made them the second or third biggest certifying agency in the world (after PADI globally...and maybe SSI).

We are in the basic section and I do understand the need to impress on new divers the absolute deadly danger in hold ones breath but, never is a strong word.

Do you tell your infant kids to 'never go with strangers'.... or do you sit them down for a few hours and impress upon them a matrix of decision-making criteria to identify which persons they may allow to lead them away?

We know that they will develop those criteria over time and with experience. However, we appreciate the benefits of an equivocal message in the interim.

Do students keep breathing when practicing air sharing switching from primary to secondary? Or their buddies regulator? Do they do ditch and donning during OW? If so do they keep breathing? I think the answer to these has to be no they hold their breath, So even before they hit the ocean the average student has held his or her breath at least long enough to switch regulators.

Incorrect. Students aren't told to 'keep breathing'. They are told to 'never hold their breath'. That is why instructors emphasize the need to 'blow bubbles' whenever the regulator is removed from their mouths. Exhaling continually is not holding the breath...

Again... another good example of why a K.I.S.S. approach to critical safety matters can prevent harmful confusion. If even an experienced diver like AfterDark can get confused about such basic principles, then there is a strong argument for not over-complicating safety messages.