Oxygen Dose Calculations

[BRW]

All questions about oxygen dose can be answered
directly by simple calculations and bookkeeping
of hypothetical dose.

It's pretty straightforward and tech divers
have to do it all the time.

1) -- for CNS dose, divide all your actual
exposure times at any given ppO2 by
the NOAA limits (somebody included them)
and sum the fractions. Sum must be LESS
than 1 for safe CNS dose. If your ppO2
at any given level is less than 0.50 atm,
it doesn'r contribute to the sum. For
repets, the total dose should sum below
0.85 roughly across all repets.

2) -- for full body dose, take the differences
between actual ppO2 and 0.50, divide
each difference by 0.50, and then
multiply by the time at each level
in minutes (liberal). Sum these
operations across whole dive profile.
If any level ppO2 ie less than 0.50 atm
it doesn't contribute to the sum.
This full body dose must remain below
1400 OTUs as a dose point in one day.
Full body oxygen is thought to decay
away with 90 minute halftime.

Technical Diving In Depth has it and other
details -- pp 89 - 94 -- and graphs. So do
most Agencies like IANTD, ANDI, NAUI, TDI etc
in their tec manuals.

 

[Dr Deco]

Thanks, Bruce, for the information on the calculation of oxygen toxicity doses. I am sure that it will be helpful to the readers.

I do not have sufficient familiarity with this topic to give much detailed information.

Mike Powell (Dr Deco)=-)

 

[The Iceni]

Originally posted by BRW


1) -- for CNS dose, divide all your actual
exposure times at any given ppO2 by
the NOAA limits (somebody included them)
and sum the fractions. Sum must be LESS
than 1 for safe CNS dose. If your ppO2
at any given level is less than 0.50 atm,
it doesn'r contribute to the sum. For
repets, the total dose should sum below
0.85 roughly across all repets.

I am confused, Bruce.

While I can well understand the usefulness of the NOAA tables for whole body toxicity, as this clinical syndrome appears to be strictly dose related, I remain confused about the usefulness of the published NOAA tables for CNS limits.

Now. I readily admit that am very much an amateur but the following features of CNS oxygen toxicity tend to convince me that the published NOAA tables fo CNS toxicity are not as uselful as those for whole body toxicity.

For CNS oxygen toxicity;-

1) There is considerable variabiliy in sensitivity from individual to individual.

2) There is considerable variability from day to day and with time of day with any single individual, so much so that the Royal Navy abandoned its screening programme for susceptibel individuals in diver recruits.

3) Carbon dioxide is implicated in the pathogenesis of acute CNS oxygen toxicity so circumstances where there is a build up of CO2 such as heavy work load and poorly functioning equipment are likely to precipitate acute CNS toxicity even within table limits.

4) Stress, dark, immersion and cold worsen the risk.

5) An increasing number of amateur British technical divers appear to be disreagarding the published limits without any adverse consequences deciding for themselves the limits to use on each dive.

Any ideas?

 

[BRW]

Yes, CNS clock and OTU limits in NOAA tend
toward conservative. Especially in the real
world of diving.

Not to dismiss the protocols sketched on
previous post, which are standard "lessons" for
mixed gas divers ala Agencies, tech divers all
over certainly exceed the clock and OTU limits
all the time. Here are three with some number
estimates. And WKPP guys, jump in, if you are
out there.

1) -- our Counterterror Team dives on OCs and
RBs can run at ppO2 in the 1.6 - 1.8 atm
range (because we need NOT to deco hang
our 4 man teams). We run a CNS clock above
1.5. Our pulmonary score exceeds 1000 OTUs
daily for 3 - 4 days. No oxtox probs.

2) -- WKPP dives are much more spectacular.
After a 5 hr exposure at 300 fsw on trimix
and some 4 - 6 hours deco, they enter a
habitat at 30 fsw and breathe pure O2 for
a few hours, detox on back gas (or what
is ever around) every 20 -30 minutes or
so. Just at the bottom, the CNS clock is
above 1.5, and OTUs are near 500. On the
way up, these triple. And in the habitat
these double again -- neglecting some
detoxing. Bottom line -- CNS clock hits
8.2, and OTUs score 1600. This is why
we consider WKPP divers the most elite
around. Even SEALs don't come close.

3) -- The USN (Thalmann) tested for CNS oxtox
at 1.6 and 1.8 atm ppO2 level, and found
no real probs for taking divers at 1.8 atm
out to the O2 limits for 1.6 atm.

Bottom line -- oxtox data has gaps and much
not understood in mechanisms. Is worse off
then deco theory -- even "half correct"
Haldane. But for now, the NOAA stuff is OK
for general consumption because it's benign
in the absence of correcting knowledge.

Bruce Wienke

Program Manager Computational Physics
Counterterror And Countermeasures Dive Team Ldr

 

[chuckrt]

I have to admit this is a very interesting thread. I have learned some very interesting and informative data.

chuckrt

 

[The Iceni]

Originally posted by BRW
Yes, CNS clock and OTU limits in NOAA tend
toward conservative. Especially in the real
world of diving.

. . . We run a CNS clock above
1.5. Our pulmonary score exceeds 1000 OTUs
daily for 3 - 4 days. No oxtox probs.

. . . And in the habitat
these double again -- neglecting some
detoxing. Bottom line -- CNS clock hits
8.2, and OTUs score 1600. This is why
we consider WKPP divers the most elite
around.

Bruce Wienke

Many thanks, Bruce, for your informative answer, which seems to confirm that CNS oxtox is not as clear cut as whole body toxicity.

I can imagine that a UPTD dose of 1600 is not so bad since this only just exceeds the daily recommendation of 1440, developed for long term treatment.

However, can you explain what you mean by CNS clock hits 8.2? I realise this does not mean a pp O2 of 8.2 bar. Does this mean they exceed the 24 hour CNS limits by a factor of eight?

Sorry to be a pain.

Kind regards,

 

[BRW]

Paul

The sum of all level exposures from 300 fsw/300 min thru
deco and then surfacing totals 8.27 (ratios of exposure times
at some ppO2 divided bt NOAA limits for exposure times all
summed for their bottom mixes, deco gases, and pure O2
in habitat) is 8.27,

If you want, I will post a sample profile with bottom mix,
gas switches, deco profile, OTUs at each level, CNS clock
at each level, etc. The calculation is a standard RGBM (used
by tech diving extensivlely these days and we have been
using it for 8 yrs). Deep stops are natural to RGBM dual
phase model calcs, not juxtaposed on Haldane schedules.
The deco run time for RGBM is 10 hrs, while the deco time
is 20 hrs for Haldane. And RGBM staging is done safely.

I am headed out for 10 days, but I will try to ship that
info to Ladydiver@cox.net when I get a chance today.

She graciously received and tallied RGBM pdf info for this site
(which can probably be accessed thru FTP).

Bruce Wienke

Program Manager Computational Physics
Counterterror And Countermeasures Dive Team Ldr

 

[Piscean]

What is/who are the WKPP?

 

[Dr Deco]

Piscean:

WKPP stands for the "WOODVILLE KARST PLAIN PROJECT." It is a group of divers dedicated to cave exploration. They are noted for having developed some vary interesting techniques for deep diving.

"Karst" refers to a type of limestone formation in which cave formation is possible. It is common in Florida and in the Yucatan region.

Dr Deco :doctor:

 

[The Iceni]

Originally posted by BRW
Paul

The sum of all level exposures from 300 fsw/300 min thru
deco and then surfacing totals 8.27 (ratios of exposure times
at some ppO2 divided bt NOAA limits for exposure times all
summed for their bottom mixes, deco gases, and pure O2
in habitat) is 8.27,

If you want, I will post a sample profile with bottom mix,
gas switches, deco profile, OTUs at each level, CNS clock
at each level, etc. . . .

Bruce Wienke

No need to send me the profiles as I think I understand exactly what WKPP are doing, which leads to the obvious question.

What is it about their diving practices that alows them to exceed the NOAA CNS limits by a factor of eight times normal recommended limits or 800%?

Could it perhaps be a combination of;

1) A very relaxed form of diving with state-of-the-art scuba equipment so there is little or no build-up of CO2.

2) Expereinced and skillful divers with meticulously planned and executed dives to reduce, if not to completely eliminate, all forms of stress.

3) State-of-the-art lighting equipment and crystal clear water, again reducing stess.

4) Decent insulation reducing the effects of cold

5) Dry stages to reduce the effects of immersion.

6) They must all be extremely cardiovascularly fit.

7) They are obviously enjoying themselves!

If so, this suggest that CNS oxygen toxicity is greatly inflenced by these factors. I find this fascinating!

Thanks Bruce, for your patience. I hope the op goes well. :royal: