How deep is dangerous?

[DevonDiver]

IMO, OW instructors are doing their students a disservice if they do not fully explain the difference between pausing breathing using muscles and closing of the airway.

I disagree.

I teach students NOT TO HOLD THEIR BREATH. Nothing more, nothing less.

If they try something clever like 'pause breathing' then they can end up DEAD.

Every scuba agency gives a very clear message about breath holding on scuba. It would be an act of idiocy to confuse this message - given the fatal consequences if someone gets it wrong.

It is nice that Charlie99 has his opinions on this - but the reality check of actually being responsible for the lives of real students has made ME much more careful of the 'facts' that I pass on to people - especially when they are inexperienced.

 

[Charlie99]

It is nice that Charlie99 has his opinions on this - but the reality check of actually being responsible for the lives of real students has made ME much more careful of the 'facts' that I pass on to people - especially when they are inexperienced.

Is one of these "facts" your assertion that the glottis cannot be voluntarily controlled?

 

[DevonDiver]

The only fact that anyone needs to know is that they don't hold their breath underwater.

I am not even going to debate 'glottis control' with you - as this is a public forum and people may read this and think that they'd like to give it a try. I, personally, wouldn't want to have a guilty conscience because I'd been acting big-headed on a public forum and this resulted in a newbie diver dying of a LOI.

If you really want to debate this issue - with an appreciative crowd - find yourself a slot on a Dive Medic Technician course (I'd recommend DDRC in Plymouth, UK or Adelaide, Oz) ... they deal with the results of bad diving practices all the time and, I am sure, would love to hear about your special techniques for getting nice photos etc etc etc etc

 

[DevonDiver]

Is one of these "facts" your assertion that the glottis cannot be voluntarily controlled?

We'll see.... how about you go diving this week....pop down to 20m and then ascend on a single breath - holding your breath, but keeping your glottis open?

 

[nereas]

Humming is taught in basic open water, in order to keep the glottis open during an emergency swimming ascent (ESA).

I myself have never had to try it in an actual emergency situation, fortunately.

Working with students has given me ample opportunity to practice and demonstrate it, which is also fortunate for me.

If the situation ever actually arises, hopefully I will keep my head clear and remember to do it.

I hope the same for others as well, although unless a diver becomes a D/M or an instructor, I suspect that many of the safety skills that have been taught become rusty if not totally forgotten. Most people when they dive recreationally do not practice any skills other than what they need to descend and ascend normally, and to swim underwater.

To decrease the possibility of gear malfunctioning, I always check my gear in advance, normally a few days before the dive as I am stacking it up, and then just before going into the water with it.

But even after all that, gear can always malfunction. This then necessitates safety drills and/or gear redundancy.

 

[Charlie99]

We'll see.... how about you go diving this week....pop down to 20m and then ascend on a single breath - holding your breath, but keeping your glottis open?

Been there. Done that.

Contrary to what you seem to think, a CESA from 20m is easy to perform, if done properly -- i.e. not breathing out, but simply keeping the glottis/airway open.

My comments on a practice CESA from 90' taking about 2 minutes to ascend:http://www.scubaboard.com/forums/1193170-post46.html

If your airway is open, any excess air just bubbles out. You adjust your buoyancy with lung volume, just like when breathing on scuba.

http://www.scubaboard.com/forums/330382-post59.html is an interesting report by one of the SB medical moderators on a CESA from 30 meters in a submarine escape training tower in the UK. It was on a single breath, and he took over 5 minutes to ascend the 30 meters.

Clearly, to do that slow of an ascent, one would have to maintain an open airway, but not actively breathe out or hum or "aaaaaah".

 

[Dr Deco]

Hello Neff:

[1.] As many posters have indicated, any ascent with a closed glottis is a very bad idea and can result in barotrauma. The published – and somewhat dubious - record is about three feet deep with a lung full of air. The reference is below.

[2.] As far as DCS and surfacing goes, I would guess that fast ascents within the NDLs would be permissible – well, “possible” is a better word. Tables have conservatism built in. I certainly would not make that any kind of regular practice. You state that this was a one-time event.

This applies only to NDLs. Decompression diving does not have such conservatism.

Dr Deco :doctor:


References :book:

Arterial gas embolism following a 1-meter ascent during helicopter escape training: a case report. Benton PJ, Woodfine JD, Westwood PR. Aviat Space Environ Med. 1996 Jan;67(1):63-4.

We present the case of a helicopter pilot who suffered an arterial gas embolism following instruction in the use of the Short Term Air Supply System (STASS) at a depth of 1 m of water. This is believed to be the shallowest depth from which a case of arterial gas embolism associated with the use of compressed air breathing apparatus has been reported.

 

[Neff]

Thanks Doc, and everyone. Yes ... with hindsight, I can see that the logical thing would have been to fin back down. I think my mind was more taken up with exchanging gases and keeping lung volume low. Well, despite my lucky episode, I still have a very healthy respect for the safety rules, especially since learning through this forum, that even very shallow depths can cause a problem. I did not know that.
Many thanks

 

[DevonDiver]

Sobering reading.........

An extract from…..Undersea and Hyperbaric Medicine, Vol 20, No2, 1993

Air Embolism With Bilateral Pneumothorax After A 5m Dive


I. Friehs, G.m. Friehs and G.B. Friehs

University Clinic of Surgery, Department of Thoracic and Hyperbaric Surgery, and University Clinic of Neurosurgery, University of Graz, Medicical School Graz, Austria.

Air embolism with bilateral pneumothorax after a five meter dive. Undersea and Hyperbaric Med 1993: 20(2):155-157.- After an emergency ascent from very shallow depth, a diver suffered a triad of symptoms after bilateral barotrauma of the lungs: air embolism with subsequent paraparesis, pneumomediastinum, and bilateral pneumothorax.

The two main causes for diving accidents while using scuba devices are DCS (caisson disease) and barotraumas of the lung with consequent air embolism. Inexperienced divers sometimes fail to comply with recommended ascent rates, especially in emergency situations. With breath holding or air trapping, the volume of air in the lungs inhaled at depth expands on ascent in direct relation to the decrease in surrounding pressure (Boyle-Marriotte’s Law). When the lung’s elasticity of approximately 100mbar is exceeded, the pulmonary parenchyma is damaged, sometimes resulting in pneumomediastinum and pneumothorax. Air bubbles entering the pulmonary circulation are transported into the arterial blood stream and cause neurologic deficits of differing degrees. Symptoms may occur as soon as the victim reaches the surface.

CASE REPORT

A 24 year old male, admitted to our hospital after a diving accident, reported that at a depth of only 5m he had planned and undertaken an emergency ascent. At a depth of 1m he held his breath rather than exhale. On reaching the water surface the patient complained of sudden onset of dizziness, paraparesis of the lower extremeties, and shortness of breath. On auscultation, a left side pneumothorax was noted. An x-ray taken in the local hospital confirmed the suspected diagnosis and revealed an extensive mediastinal emphysema. Chest drainage was instituted immediately, and the patient transported to our hospital by helicopter, flying no higher than 850m above sea level while breathing 100% oxygen. A subsequent x-ray in the emergency room showed the left lung was fully expanded, but an incomplete pneumothorax was diagnosed on the right……

DISCUSSION

As opposed to bends (caisson disease), lung barotraumas associated with diving is not dependant on time or depth. Barotrauma can occur even at a depth of 1 – 2 m. The main reason for this type of accident is panic emergency ascent by young, inexperienced divers. Divers should ascend to the water surface by continuously exhaling to compensate for gas expansion in the lungs. An intrapulmonary airway pressure that exceeds the pressure produced by the lung’s elasticity results in extraalvolar air leakage. The perivascular sheaths then mediate the air to the mediastinum, to the subcutaneous tissues, and to the intrapleural space. This explains the occurrence of mediastinal and subcutaneous emphysema. The rupture of lung parenchyma may also allow gas to enter small blood vessels, and anterograde migration of bubbles in pulmonary venules may then lead to arterial emboli formation. Possible platelet aggregation and other coagulation disorders induced by bubble surface and plasma interaction, followed by vessel occlusion and reduction of perfusion, lead to hypoxic damage of the organs supplied by these vessels. Resulting neurologic deficits range from bypesthia to decerebrate symptoms, to death in worst cases……

 

[lamont]

i was involved in trying to rescue a fatality here due to an OOG at 10 feet that resulted in a rush to the surface with a closed airway and barotrauma. it definitely doesn't take much.