DCS on air vs. DCS on Trimix

[PeCeDiver]

During a couple of discussions on deep air diving somebody mentioned that a deco related accident on Trimix is likely to be more fatal than an accident on normal air. Since I'm not trained/certified on Trimix, I don't know whether this is true or not. Can somebody shed some light on this statement? Is it perhaps related to the nature of the gas or the familiarity of the medical staff with Trimix diving (or lack thereof)?

Thanks.

 

[Dr Deco]

Dear PeCe Diver:

I do not the truth of this, but it has been said for decades that DCS problems appear more rapidly with helium in the breathing gas. The conventional explanation is that the high diffusion rate of helium causes the rapid growth of decompression gas bubbles.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[BigJetDriver]

PeCeDiver once bubbled...
During a couple of discussions on deep air diving somebody mentioned that a deco related accident on Trimix is likely to be more fatal than an accident on normal air. Since I'm not trained/certified on Trimix, I don't know whether this is true or not. Can somebody shed some light on this statement? Is it perhaps related to the nature of the gas or the familiarity of the medical staff with Trimix diving (or lack thereof)?

Thanks.

To add to what Doc Deco has already stated, we have the fact that most of the diving done with trimix will be deeper profiles, and the inert gas load will be higher than for other types of diving.

Most chambers will utilize the Navy Table Six as standard treatment protocol in any case.

 

[MonkSeal]

I've read that DCS cases with trimix in most cases are of neurological type. Does this have anything with fact that helium is "quick" gas and spinal cord is is considered as quick tissue. Can you put a more light on this issue ?

 

[Dr Deco]

Dear MonkSeal:

I do not have an explanation for the CNS cases predominating.

From field reports, more that half of the reported DCS cases are of the CNS type. This has lead some to believe that CNS cases predominate in open-water recreational divers (as compared to laboratory studies of recreational tables). I do not know the answer, but I suspect that there is considerable under recognition and under reporting of joint-pain DCS (“the bends”). Minor cases, such as are seen in the laboratory, and are not easily recognized by a diver in the field. There would be denial, attribution to some other even (lifting and getting a sore wrist), or the simple fact that most “bends” dissipate within a few hours (if minor).

If the pattern follows, trimix might well be similar to air in the biased reporting factor.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[BRW]

All,

The question of DCS incidence vs mix can't really be answered
because of depth limitations for mixes, lack of specific data,
depth dependences, and related concerns.

But one fact seems clear from the field, reported Wkshp
findings, deco and tech diving protocols, etc. And it's
simple -- Paul also alluded to it from his perspectives
and experience and I mentioned it in deep stop posts:

"Keep ppN2 As Low As Possible For All Diving And Depths"

Stats suggest as ppN2 goes up, so goes DCS risk. Period.

We have a sign in our locker room "God invented helium
for diving, the Devil invented nitrogen" We have marched to it
for 10 yrs without mishap. Here at C & C, we never dive
N2 mix fraction above 35%. Helium is the gas. And even for
short, shallow exposures in the 60 fsw range, usually with
repets, but not reverse profiles.

Regards,

Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Leader
ut: