Holding a panicked diver down

[brnt999]

I have a question to the experts. When we dive we make decisions based on risk calculations. For example it is possible we could be attacked and eaten by a shark. We calculate the probability/risk as low and we dive.
Do we know what the probability is of getting an air embolism by holding our breath and rapidly ascending? We have numbers of fatalitities that die of an air embolism but do we know how many rapid ascents there are with the breath held that don't result in an air embolism? If there were a million rapid ascents with breath held and there were 5 deaths or injuries then the probability is relatively low. That doesnt mean we wouldnt still strive to dive safely and not hold our breath, but we might use this risk calculation when make other decisions. For example we might weigh the risk of holding down a panicked diver against the risk of not holding them down. So my question is--do we know the probability of suffering an air embolism on a rapid ascent with the breath held?

 

[Steve_C]

A long long time ago I was a WSI and did some life guarding. For panicked swimmers we were taught to approach low, turn them, then come up behind much like has been suggested above. If something went wrong, then we were taught to go down since the swimmer wants to go up. My question is if a panicked diver is similar? Its not as clear since you have something they might want, like air, but if they are wanting to go up maybe it is similar. Any comments out there? Perhaps it depends on the cause of the panic?

 

[DevonDiver]

So my question is--do we know the probability of suffering an air embolism on a rapid ascent with the breath held?

I'm not sure of a statistical answer. There is a mathematical one though - Boyle's Law. That law is quite definitive about the effects of pressure, ascent and closed air spaces.

Bear in mind that air embolism is just one of several possible lung over-expansion injuries from a breath hold ascent.

 

[Diver0001]

Do we know what the probability is of getting an air embolism by holding our breath and rapidly ascending?

If you're deep enough the chance is very high and the chances of dying from that injury are also very high. Moreover people who survive it often have resulting brain injuries. If I'm not mistaken there is a DAN report, which I don't have handy at the moment, that shows drowning and AGE as the two most common injuries causing avoidable fatalities. IIRC, depending on whose statistics you read, panic is related to 40-60% of accidents and the onset of panic (and the triggers for the vast majority of accidents) is *usually* due to the diver being confronted with something unexpected, such as LOA, OOA, sudden poor visibility or buoyancy problems.

We have numbers of fatalitities that die of an air embolism but do we know how many rapid ascents there are with the breath held that don't result in an air embolism?

If you are deep enough when you initiate it then the chances of a breath-hold ascent causing some kind of lung over-expansion injury are 100%. It's extremely dangerous and often deadly.

If there were a million rapid ascents with breath held and there were 5 deaths or injuries then the probability is relatively low. That doesnt mean we wouldnt still strive to dive safely and not hold our breath, but we might use this risk calculation when make other decisions.

I understand what you're trying to say (I think), which is that risk is a calculation of "chance" times "effect". In the case of a breath hold ascent, my opinion is that you can boil down this calculation to "100% * effect" because the chances of NOT having a lung barotrauma of some variety from a breath hold ascent, especially when initiated from sufficient depth, is pretty much negligible. If we believe statistics, then it's a safe bet that your chances of surviving and making a full recovery from a breath hold ascent are poor.

For example we might weigh the risk of holding down a panicked diver against the risk of not holding them down. So my question is--do we know the probability of suffering an air embolism on a rapid ascent with the breath held?

I understand what you're trying to say, which is that holding down a diver also entails a risk, namely a risk of drowning, and that this risk should be weighed against the risk of severe injury or death due to a breath hold ascent.

To my way of thinking you're looking at the world in black and white (hold them down or don't hold them down) and you're missing the big picture.

In the cases of divers I've seen to date in full-blind-panic making a clawing scramble to the surface they retained the regulator in the mouth and were panting, as opposed to holding their breath. In those cases I believe, as I said above, that controlling the ascent and "assisting" them to the surface is probably all you can really do.

If, for some reason, they are holding their breath and you can slow down that ascent to some degree then they'll eventually start breathing again on their own and by tackling them you are in a position to poke or shake (or whatever works) them into snapping out of holding their breath if that's what they're doing.

Basically, what you appear to be hearing is that there is some kind of "best practice" that says "hold them underwater", but among all the instructors I know the "best practice" is to do whatever it takes to stop the diver from injuring or killing themselves.

Since you like algorithms, what you want to do, and in the order of importance is the following:

1) if the diver has spit out the regulator due to panic then you must get a regulator back in their mouth immediately. In practice this is going to mean grabbing on to them and literally stuffing a regulator in their mouth with the purge valve slightly depressed so it's clear if they inhale first. These divers are at the highest possible risk of either making a breath hold ascent or drowning if you don't do something and this is the case where assisting them immediately and firmly is going to make a difference between life and death.
2) if the diver is holding their breath and they have a regulator in their mouth then make them start breathing again.... In practice this is going to mean you need to tackle them and either do something to snap them out of it and/or somehow delay the ascent until the body takes over and breathing starts again. If you don't do this then they run a severe risk of developing a lung barotrauma with all of the nasty consequences.
3) if the diver is ascending too quickly but you can see they are breathing then do what you can to slow it down to some kind of controlled speed so you have time to respond if they make matters worse by spitting out the regulator or holding their breath, etc
4) if *possible* try to convince them to stay under water and sort it out.

Or put more succinctly,

1) regulator
2) breathing
3) ascent speed
4) get control back

or even more succinctly in terms of priority

A - air (regulator in mouth and victim is breathing)
B - buoyancy (ascent speed under control)
C - control (help the victim to regain their composure). This is also an interaction so you could think of C as "communicate".

R..

 

[Tigerman]

...
what if that diver drowns?...would you have second thoughts about your decision?
...

In short. No.
Then of course theres the question of why they would drown in the first place, I dont think anybody is speaking of just pushing people to the bottomn and keeping them there without ensuring they have gas to breathe for the next couple of hours..

Leaving the diver alone is your choice of word. I spoke of holding the diver down vs assisting them safely to the surface.

And you think I speak of holding the diver down for a couple of hours? The entire objective of holding the diver down is assisting them safely to the surface - which is pretty hard to do if they get decapitated by a boat in the process..

 

[DevonDiver]

If you're deep enough the chance is very high

With respect to depth, I read an article (I believe it was from DAN) that the shallowest recorded lung over-expansion injury occurred from 0.3m (swimming pool).

If you are deep enough when you initiate it then the chances of a breath-hold ascent causing some kind of lung over-expansion injury are 100%. It's extremely dangerous and often deadly.

The average residual volume (the air that remains in your lungs, even after a full exhalation) is ~1.2 litres. Total lung capacity is circa 6 litres. So, any ascent from 40m, even with completely "empty" lungs is going to cause an injury. Most people would struggle to vent their lungs down to the bare residual volume anyway.

Starting the ascent, whilst breath holding, with any surplus air in the lungs will cause air expansion in line with Boyle's Law - bringing about injury from much shallower depths - related to whatever the lung contents vs. lung volume might be. If the lungs were nearly full, an injury would occur at remarkably shallow depths.

From wikipedia:

[TABLE="class: wikitable"]
Average lung volumes in healthy adults^[7][TR]
[TH="bgcolor: #F2F2F2, align: center"]Volume[/TH]
[TH="bgcolor: #F2F2F2, colspan: 2, align: center"]Value (litres)[/TH]
[/TR]
[TR]
[TD="align: center"]In men[/TD]
[TD="align: center"]In women[/TD]
[/TR]
[TR]
[TD]Inspiratory reserve volume[/TD]
[TD="align: center"]3.3[/TD]
[TD="align: center"]1.9[/TD]
[/TR]
[TR]
[TD]Tidal volume[/TD]
[TD="align: center"]0.5[/TD]
[TD="align: center"]0.5[/TD]
[/TR]
[TR]
[TD]Expiratory reserve volume[/TD]
[TD="align: center"]1.0[/TD]
[TD="align: center"]0.7[/TD]
[/TR]
[TR]
[TD]Residual volume[/TD]
[TD="align: center"]1.2[/TD]
[TD="align: center"]1.1

[/TD]
[/TR]
[/TABLE]
[TABLE="class: wikitable"]
Lung capacities in healthy adults^[7][TR]
[TH="bgcolor: #F2F2F2, align: center"]Volume[/TH]
[TH="bgcolor: #F2F2F2, colspan: 2, align: center"]Average value (litres)[/TH]
[TH="bgcolor: #F2F2F2, align: center"]Derivation[/TH]
[/TR]
[TR]
[TD="align: center"]In men[/TD]
[TD="align: center"]In women[/TD]
[/TR]
[TR]
[TD]Vital capacity[/TD]
[TD="align: center"]4.8[/TD]
[TD="align: center"]3.1[/TD]
[TD]IRV plus TV plus ERV[/TD]
[/TR]
[TR]
[TD]Inspiratory capacity[/TD]
[TD="align: center"]3.8[/TD]
[TD="align: center"]2.4[/TD]
[TD]IRV plus TV[/TD]
[/TR]
[TR]
[TD]Functional residual capacity[/TD]
[TD="align: center"]2.2[/TD]
[TD="align: center"]1.8[/TD]
[TD]ERV plus RV[/TD]
[/TR]
[TR]
[TD]Total lung capacity[/TD]
[TD="align: center"]6.0[/TD]
[TD="align: center"]4.2[/TD]
[TD]IRV plus TV plus ERV plus RV

[/TD]
[/TR]
[/TABLE]
Further to this, many people would expect to receive some form of physiological warning of an imminent lung injury. That's a false expectation - the lungs contain relatively sparse nerve sensors for pressure/pain. The first indication that most victims receive is the burst lung itself - typically reported as a sensation like being punched hard in the chest. Symptoms manifest very shortly afterwards.

 

[redacted]

In short. No.
Then of course theres the question of why they would drown in the first place, I dont think anybody is speaking of just pushing people to the bottomn and keeping them there without ensuring they have gas to breathe for the next couple of hours..

This is basically what happened in another thread: http://www.scubaboard.com/forums/accidents-incidents/449366-write-up-near-death-monterey.html

And you think I speak of holding the diver down for a couple of hours? The entire objective of holding the diver down is assisting them safely to the surface - which is pretty hard to do if they get decapitated by a boat in the process..

Why do you choose hours when minutes will do the job nicely. I have to wonder why you choose to describe this as "hold them down" rather than "assist them to avoid the hazard". I feel it depicts a dangerous attitude. My wife's first scuba instructor told the class on the first day that all problems were solvable UW and he would stand on anybody's tank and hold them down if they attempt to surface. He put the OW class off badly enough that he was replaced before the next class. It is not the act as much as the attitude that I find alarming.

 

[dumpsterDiver]

With respect to depth, I read an article (I believe it was from DAN) that the shallowest recorded lung over-expansion injury occurred from 0.3m (swimming pool).



The average residual volume (the air that remains in your lungs, even after a full exhalation) is ~1.2 litres. Total lung capacity is circa 6 litres. So, any ascent from 40m, even with completely "empty" lungs is going to cause an injury. Most people would struggle to vent their lungs down to the bare residual volume anyway.

Starting the ascent, whilst breath holding, with any surplus air in the lungs will cause air expansion in line with Boyle's Law - bringing about injury from much shallower depths - related to whatever the lung contents vs. lung volume might be. If the lungs were nearly full, an injury would occur at remarkably shallow depths.

From wikipedia:

[TABLE="class: wikitable"]
[TR]
[TH="bgcolor: #F2F2F2, align: center"]Volume
[/TH]
[TH="bgcolor: #F2F2F2, colspan: 2, align: center"]Value (litres)
[/TH]
[/TR]
[TR]
[TD="align: center"]In men
[/TD]
[TD="align: center"]In women
[/TD]
[/TR]
[TR]
[TD]Inspiratory reserve volume
[/TD]
[TD="align: center"]3.3
[/TD]
[TD="align: center"]1.9
[/TD]
[/TR]
[TR]
[TD]Tidal volume
[/TD]
[TD="align: center"]0.5
[/TD]
[TD="align: center"]0.5
[/TD]
[/TR]
[TR]
[TD]Expiratory reserve volume
[/TD]
[TD="align: center"]1.0
[/TD]
[TD="align: center"]0.7
[/TD]
[/TR]
[TR]
[TD]Residual volume
[/TD]
[TD="align: center"]1.2
[/TD]
[TD="align: center"]1.1

[/TD]
[/TR]
[/TABLE]
[TABLE="class: wikitable"]
[TR]
[TH="bgcolor: #F2F2F2, align: center"]Volume
[/TH]
[TH="bgcolor: #F2F2F2, colspan: 2, align: center"]Average value (litres)
[/TH]
[TH="bgcolor: #F2F2F2, align: center"]Derivation
[/TH]
[/TR]
[TR]
[TD="align: center"]In men
[/TD]
[TD="align: center"]In women
[/TD]
[/TR]
[TR]
[TD]Vital capacity
[/TD]
[TD="align: center"]4.8
[/TD]
[TD="align: center"]3.1
[/TD]
[TD]IRV plus TV plus ERV
[/TD]
[/TR]
[TR]
[TD]Inspiratory capacity
[/TD]
[TD="align: center"]3.8
[/TD]
[TD="align: center"]2.4
[/TD]
[TD]IRV plus TV
[/TD]
[/TR]
[TR]
[TD]Functional residual capacity
[/TD]
[TD="align: center"]2.2
[/TD]
[TD="align: center"]1.8
[/TD]
[TD]ERV plus RV
[/TD]
[/TR]
[TR]
[TD]Total lung capacity
[/TD]
[TD="align: center"]6.0
[/TD]
[TD="align: center"]4.2
[/TD]
[TD]IRV plus TV plus ERV plus RV

[/TD]
[/TR]
[/TABLE]
Further to this, many people would expect to receive some form of physiological warning of an imminent lung injury. That's a false expectation - the lungs contain relatively sparse nerve sensors for pressure/pain. The first indication that most victims receive is the burst lung itself - typically reported as a sensation like being punched hard in the chest. Symptoms manifest very shortly afterwards.

I was taught a long time ago (not sure where) that this type of analysis is wrong. When I was 13 and preparing to do the mandatory free ascent from 60 feet, I was terribly worried about no exhaling enough, so I did the same math and figured if I just exhaled on the bottom and swam up, then the lungs could not be overfilled. It was explained to me that there were many cases where students suffered AGE, but the instructor was able to verify that they had exhaled or were exhaling on ascent . It was my understanding that assuming the lungs are two balloons (as done in your calculations) is not a valid model. What can occur is that when a person exhales hard, and contract the chest etc, it can cause portions or pockets of the lung to be closed off.. this allows (isolation) of portions of the lung allows pockets of the lung to be overpressurized even though the total lung volume is not excessive. So this whole idea supports the idea that the ascending diver needs to be relaxed and keep the airway open and slowly and constantly venting the lungs.

 

[Diver0001]

. this allows (isolation) of portions of the lung allows pockets of the lung to be overpressurized even though the total lung volume is not excessive. So this whole idea supports the idea that the ascending diver needs to be relaxed and keep the airway open and slowly and constantly venting the lungs.

Yeah, I've heard of a spontaneous pneumothorax occurring in some smokers. I'm not sure but it sounds like this is what you're describing.

R..

 

[DevonDiver]

I was taught a long time ago (not sure where) that this type of analysis is wrong. When I was 13 and preparing to do the mandatory free ascent from 60 feet, I was terribly worried about no exhaling enough, so I did the same math and figured if I just exhaled on the bottom and swam up, then the lungs could not be overfilled. It was explained to me that there were many cases where students suffered AGE, but the instructor was able to verify that they had exhaled or were exhaling on ascent . It was my understanding that assuming the lungs are two balloons (as done in your calculations) is not a valid model. What can occur is that when a person exhales hard, and contract the chest etc, it can cause portions or pockets of the lung to be closed off.. this allows (isolation) of portions of the lung allows pockets of the lung to be overpressurized even though the total lung volume is not excessive. So this whole idea supports the idea that the ascending diver needs to be relaxed and keep the airway open and slowly and constantly venting the lungs.

Absolutely - my purpose was merely to underline the inevitability of lung over-expansion, whilst breath holding on ascent. I've met some divers who believed that a full exhalation would keep them safe from over-expansion, in every case they had forgotten, or were unaware, that the lungs retained a significant residual volume that subsequently expands. I wanted to get that fact clear from an early stage in the debate.

Keeping the airway/lungs open, through continual breathing is critical. There's also plenty of documents stating risk of lung injury from 'trapped pockets' due to other reasons - smoking, congestion, asthma etc etc. My assumption would be that breath-holding, even from empty lungs, should increase the risk of those occurrences also.