Emergency ascent from depth -- how deep is this safe?
Bryan Penprase
If all else goes wrong at a depth of 30 feet, we were taught that
we can simply ditch the weight belt and other gear that may be tangled,
and then do an emergency ascent. We tested this in the pool, where our
instructor adjusted our BC for neutral bouyancy with weights, and then
we rocketed to the surface, while exhaling the entire way, with the arms
spread out to "slow the ascent". This was also a part of the open water
test, and we did this from 30' in a quarry.
My question is -- at what depth does this not become possible?? Assuming
that the diver is in a no decompression situation, wouldn't the ascent rate
from the emergency ascent at certain depths be so rapid that an embolism would
be assured, even if exhaling? Does anyone have stories about doing this from
deeper than 30' (and surviving?) What is the accepted wisdom on this point?
With the story of the man in Oregon dying from losing his weight belt, I have
been worry about what would happen in an emergency ascent from > 30'. Thanks
for the information.
Regards,
Bryan Penprase
PADI AOW, PDCI OW
penp...@stsci.edu
Ed McKenna
>Here is a question that has been bothering me for some time..
>If all else goes wrong at a depth of 30 feet, we were taught that
Jeez, I didn't have to ditch the weight belt when I did the ascent.
Actually, I don't think I would have wanted to either. When I did mine
for the open water test (PADI). I was at 40 feet. The instructor was
right in front of me ( an octopus away). I exhaled and swam up. Lots
more control, I would think than ditching the belt.
I've had to have a buddy re-attach my weight belt at 35 feet. Not
a great feeling. I sure wouldn't want to do it for an emergency ascent.
much prefer the swim.
Just my opinion.
Ed.
Just out of curiosity, can any instructors say whether ditching
the belt is really part of the requirement for openwater diver?
CDR Peter Kent
>that the diver is in a no decompression situation, wouldn't the ascent rate
>from the emergency ascent at certain depths be so rapid that an embolism would
>be assured, even if exhaling? Does anyone have stories about doing this from
>deeper than 30' (and surviving?) What is the accepted wisdom on this point?
>With the story of the man in Oregon dying from losing his weight belt, I have
>been worry about what would happen in an emergency ascent from > 30'. Thanks
>for the information.
The question you raise is extremely pertinent for free ascent escape from
sunk submarines. There are two issues (at least) that affect the likelihood
of survival with non-life threatening injuries. One is the time at depth
(in other words, what is your inert gas decompression load), and the other
is the existance of equipment that can help you make it to the surface
safely. With no gas load, (i.e. virtually explosive compression to depth
from the 1 ATA ambient pressure normally found in an undamaged submarine), and
using specialized hoods that keep your nose and mouth dry, and allow you to
take short breaths on the way up (even though you want to spend almost all
your time forcefully exhaling, you will run out of sufficient oxygen to retain
consciousness if all you do is exhale while free ascent surfacing from very
very very deep), the Royal Navy has demonstrated the feasibility of submarine
escape from approximately 600 feet of sea water!!! Of course all subjects
sustained ruptured ear drums, and many experienced squeezes of the sinuses
etc., but survial, without embolism, has been demonstrated. No bends either,
because the compression was explosive, and the decompression started immediatelyand kids, don't try it in your local quarry!!
As far as emergency escape from depth while recreational scuba diving, in
my opinion, you have to weigh the likelihood of drowing at depth. If I
was certain that I would drown if I attempted a controlled ascent, I would
take a chance on possible DCS or AGE and make for the surface while forcefuly
exhaling all the way up. Of course, if I was staying well within my
no-decompression limits, (as required by U.S. Navy regs for scuba dives), my
chances of DCS should be quite low, in spite of the accelerated rate of
decompression. My chances of AGE should also be quite low, because I
supposedly have passed a diving medical exam by a competent diving medical
officer, and will be observing proper technique for emergency ascent. Do I
recommend liberal use of emergency ascent proecdures? NO, NO, NO. Do I
advocate voluntary suicide rather than emergency ascent if that is the only
alternative? Absolutely not!
Disclaimer: The comments and opinions above are my own, and do not constitute
the policy or opinion of the U.S. Navy, or the Department of Defense. Peter
--
CDR Peter Kent, MC, USN
Program Manager, Diving and Submarine Medicine
Naval Medical Research and Development Command
E-mail: rdc...@nmrdc1.nmrdc.nnmc.navy.mil
Becky Hudgins
[stuff about practicing emergency ascents deleted]
>My question is -- at what depth does this not become possible?? Assuming
>that the diver is in a no decompression situation, wouldn't the ascent rate
>from the emergency ascent at certain depths be so rapid that an embolism would
>be assured, even if exhaling? Does anyone have stories about doing this from
>deeper than 30' (and surviving?) What is the accepted wisdom on this point?
My SO had to make an emergency ascent from a little over 100
feet on his first openwater dive. He tells it like this.
They had been at 100-110 feet for about five minutes, and
were starting to think about coming back up, when he spotted
an anchor and decided he wanted it. He was messing with it,
trying to work it loose, when he ran out of air.
He explains that this was 15 years ago, when standard dive
gear was a single-hose regulator and a Mae West. Nobody
had pressure gauges. A few had depth gauges (he didn't).
An octopus was unheard of. He did have a J-valve, but it
failed.
His buddy, oblivious, had already started up the line. Barry
(my SO) started to make a controlled ascent, trying to get
by on the occasional breath he would get as he ascended and
the air in his tank expanded. It wasn't enough. So he pulled
his CO2 cartridge, and ho-ho-hoed and away he goed. He thinks
he blacked out then. The next thing he remembers, he came
shooting up out of the water. Everything in his sinus cavities
had let loose, and he says he didn't have so much as a stopped-up
nose for months after that.
So he made it. Still, it's not something I'd want to do for s***s
and giggles. I should point out that he says he was dumping
everything, everything in his lungs (for as much of the ascent as
he remembers), and there was always plenty more where that came
from.
So, I believe you could make it up from 100 ft. for certain, if
you're lucky; maybe even 150'. If it came to that, I would
certainly take my chances.
Becky Hudgins
NAUI Divemaster #D-5088
David Duis
>we can simply ditch the weight belt and other gear that may be tangled,
>and then do an emergency ascent.
>
>that the diver is in a no decompression situation, wouldn't the ascent rate
>from the emergency ascent at certain depths be so rapid that an embolism would
>be assured, even if exhaling? Does anyone have stories about doing this from
>deeper than 30' (and surviving?) What is the accepted wisdom on this point?
I know one diver who did this from 130' in the tropics. I can't think
of a physiological reason why ascent rate should affect your chances
of embolism --- so long as your airway is not obstructed at any time.
So you should be able to ascend from any depth that your blood gases
will support (remember shallow water blackout?)
Where ascent rate becomes a problem is when you do have airway
obstructions. Obviously, the faster you're going, the quicker an
obstruction (like swallowing, pausing exhaling, etc.) will affect you.
Cheers,
Dave Duis NAUI AI Z9588, PADI DM 43922, EMT
du...@bent.esd.sgi.com Always check your Sources.
PS: I'm sure there's more to come on obstructed airways, but please
let's not have a rehash of the recent "breath-holding while diving."
Geoffrey Rutledge
(David Duis) writes:
> [stuff deleted ] ... I can't think
>of embolism --- so long as your airway is not obstructed at any time.
>So you should be able to ascend from any depth that your blood gases
>will support (remember shallow water blackout?)
> >Where ascent rate becomes a problem is when you do have airway
>obstructions. Obviously, the faster you're going, the quicker an
>obstruction (like swallowing, pausing exhaling, etc.) will affect you.
> >Dave Duis NAUI AI Z9588, PADI DM43922, EMT
While it is true that the rate of ascent does not affect your chance
of a cerebral air embolism when you keep your airway open, the risk of
embolism is not the only danger. There is a good reason to ascend
slowly, and more rapid ascents CAN get you into serious trouble,
especially on deep (>60 ft) dives. When you make a deep dive for a
short interval, you are putting larger amounts of nitrogen into the
blood - remember that the blood equilibrates with the nitrogen in your
lungs much faster than your tissues (muscle, bone, etc) equilibrate
with your blood. When you dive to 100 ft you are putting a relatively
large amount of nitrogen into your blood, but it will come out just as
quickly as it went in while you ascend. However, from deep dives at
the limit of the tables, it is essential that you ascend slowly to
allow this nitrogen out through your lungs. If you ascend too
quickly, this nitrogen bubbles out of your blood in larger size and
number of bubbles. You can detect these bubbles in your venous
circulation with a doppler ultrasound probe, and you can see them on
2D ultrasound images. Because the bubbles are not occuring in the
tissues other than the blood itself, they do not usually cause
symptoms.
When these bubbles develop in the venous plexus draining your spinal
cord,however, the blood may clot. This causes a venous occlusion, and
you may suffer a spinal hit.[ This can result in paraplegia - ie, the
loss of use of both your legs - and loss of the ability to urinate
and to perform normal sexual functions)]
The factors determining whether you suffer a spinal hit are numerous,
and include variations in the anatomy of your spinal venous plexus,
the degree to which your blood wants to clot (coaguability), and your
level of hydration. It _is_ possible to get a spinal hit even if you
are diving within the tables, and this possibility is increased if you
ascend too quickly.
The bottom line here is that a rapid ascent from depth really is an
emergency procedure that should be undertaken only when the other
options are worse (ie, when the other option is to drown). A corollary
is that if you like deep dives, you should plan your air to allow for
a slow ascent. Better yet, plan to take a 2-5 minute decompression
stop at 10 feet even if you are diving within the tables. It doesn't
hurt.
Geoff
CDR Peter Kent
> Because the bubbles are not occuring in the
>tissues other than the blood itself, they do not usually cause
>symptoms.
Geoffrey: May I call your attention to the relatively recent work of Drs.
R. Pearson, T.J.R. Francis, P. Pezeshkpour, and A. Dutka from the Naval Medical
Research Institute in Bethesda, and the work of Drs. J. Hardman and E. Beckman
at the University of Hawaii on the subject of the etiology of spinal cord
decompression sickness. These investigators developed rather convincing
evidence from experimental studies that show considerably different patterns
of appearance (and damage) to the spinal cord of a dog, depending upon
whether the animal was subjected to arterial embolism, or decompression
sickness. In quick summary, it appears that at least in the dog model, there
is essentially no evidence for venous gas bubbles as the primary event in spinalDCS. Rather, the first observable event appears to be the development of
gas filled space occupying lesions in the white matter of the cord. The
bubbles are autochthonous (they have formed in situ, as primary events).
This is in distinction to what is observed in the brain in CNS DCS.
Further research is ongoing to clarify the findings. The difference is
believed to be related to difference in vascular anatomy between the
two locations. Papers by these authors, on this subject, may be found
in the supplement to Vol 17 of Undersea Biomedical Research (program and
abstracts from the August 11-18 1990 meeting of the UHMS).
I do not believe that similar pathological studies have been performed
in inner ear, bone, or peripheral limb models of DCS as of yet. Therefore,
it may be premature to say that all DCS is mediated by venous bubbles as
the primary insult. Peter
Craig Campbell
>that the diver is in a no decompression situation, wouldn't the ascent rate
>from the emergency ascent at certain depths be so rapid that an embolism would
>be assured, even if exhaling? Does anyone have stories about doing this from
>deeper than 30' (and surviving?) What is the accepted wisdom on this point?
> Bryan Penprase
I know a diver who had an uncontroled ascent from ~130 ft while in
decompression mode (deeply). This was the result of a dry suit blowup. I
have heard a number of possible causes varying from unnoticed air expansion
in boots to stuck or bumped inflator valve. I make no attempt to explain
the incident.
This diver rocketed to the surface, and stayed there. His dive buddies could
not join or help him since they too were in decompression mode. It is not
clear whether the victim passed out or not. When his buddies finally reached
him, he seemed physically fine, and refused both medical treatment and
recompression. (Odd, since he is qualified to run a decompression chamber
and must certainly know better.)
Physically, the victim seems to have had no adverse effects from the
experience. Emotionally, however, he was extremely upset that the incident
happened. This is still an emotional memory for him (it happened a year or
more ago), so discussing it is uncommon.
The bottom line? All the tables and computer algorithms we use are models.
They work on statistics (more or less). Nothing is assured or guaranteed, be
it either good or bad. If I were facing drowning, I'd try to beat the odds.
Accepted wisdom? Hmmm...
How about, "Don't Panic"?
(Anyone accept that? :-))
craig
Peter Sander
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