seahunt's DIRt on the DIR Demo.

[ Follow Ups ] [ Post Followup ] [ California Scuba Diving BBS ] [ FAQ ]

Posted by seahunt on March 05, 2001 at 16:02:01:

I did go into their lair and hear their siren song.
I demanded the truth and made sour notes in their
song, but they would not tell their secrets. Till
the very end I tortured them and flayed at them.
They struggled and sweat as I squeezed and squeezed
harder. Then, just before I gave up from weariness,
in desperation, one of them weakened and some truth
came out. It was an uneasy truth, but still
truth with all it's blinding power.
So who spilled the beans and how?

This one might be long, but it deserves it. Actually, I will try
to cut it down some, because there is a fair amount of content for this
essay. Besides, the screen writers are on strike and who knows what I
can parley this into. Further on, there is a juicy little DIR tidbit
for you.
It certainly was interesting meeting some of the people I only
know from the web. Obviously it was a bit rushed to figure out who
all of the players were, but it was fun trying. I hear that Michael
Kane lost a buck.
I went to see what info I could pick up and to clarify or
challenge some DIR concepts that seem funky. It was a 3 1/2 hour
talk, mostly by Jerrod Jablonski. Have you ever tried to talk that
long. It's tough. Before the talk, there was a VCR tape running
showing cave exploration. It was remarkably beautiful and answered
one question I have always had about the appearance and size of the
At the beginning of the talk a tape was shown that was very
interesting along with a discussion given by the guy who pulled that
Air Force guy out of the mine north of LA. The tape was the recording
made by the diver before he died. Given what we were told, he was on a
bit of a suicide mission when he went into the mine, though what killed
him, breathing bad air in the mine, was actually a hazard that the diver
was quite aware of. Why he died... good question. Eerie tape though,
especially when the camera fell into the mud as the diver died.
Really, though the discussion was hours long, DIR is very technical
and a presentation like this is only going to cover so much, but it was
mostly along the lines of what you hear and see on the net if you look.
Now I went to this demo based on the promise that I would get a
description of the DIR manual deco calculation methods. I was also curious
about how DIR would apply to CA diving in general as well as some specific
issues like the deco calcs that I wanted cleared up. Remember, the DIR web
sites are not very informative and who knows exactly where what the local
DIR contingent tells us is going to fit.
One of the things I was curious about was how knowledgebale Jerrod
was about California diving. Since he claims that DIR is completely
applicable to CA diving, a lack of knowledge could be a mark against
his arguements. Local knowledge would tend to support his arguements.
Well, it turns out he knows basically nothing first hand about CA
diving. He talks about NITROX on charter boats and doesn't have any
idea how limited that option is. He had no idea that deco diving is not
what we call sport diving. One person mentioned that the waiver we all
sign contains an agreement not to do deco dives. There were a few other
points, but they all pointed to a very weak knowledge of CA diving.
He can claim this is about rec, but it's mostly tech. Talk to me about
helium, decompression or stage bottles and you aren't talking CA sport
diving. That's not a huge issue, but it is annoying.
Another main point I wanted cleared up was about using steel tanks
with a wetsuit in the ocean. This issue would further clarify something
about the issue of DIR adaptability in general. Well, you gotta figure
that Jarrod is really not there to talk to people that disagree with him
anyway. He waffled enough, that I couldn't get a clear idea what he
thought. It was bad, but it was sorta OK. I dunno, he could have well just
have been disgusted answering tough questions for me. Later, I continued
this question with (I think) the representitive from Halycon and when
pressed he had a very interesting view... Of ourse that doesn't mean it
is the DIR view, but... He asked me about my buoyancy in general.. I
float like a cork. He said that in that case, it might be reasonable
for me to use a single steel tank. If that is the official DIR line,
then it means that DIR is potentially adaptable... Also, it brings up
a very interesting issue about buoyancy and how nice it would be if the
dive company engineers would come up with better designs for ditchable
weights. Really, the answer to my question was not about the steel tank,
it was an issue of buoyancy, part of which is the type of tank used...
if that is the DIR line... Note that the local DIR contingent never
viewed the issue this way.
Then the biggy, manual deco calculations.
To explain this, I'm going to have to clarify some definitions used
here. A decompression theory is called a model. It can be a table, a
computer, a calculation or one other thing. A method is the sampling of
time and depth to be put into the model to get a (best) guess/calculation
of the immediate deco situation/solution or call it a 'location'. A target,
would be a desired deco location in a model. Perhaps no deco is the target
or some particular planned decompression obligation. A computer does both
data sampling and calculation, so it is both method and model. A location
may or may not be a target, but it is the value used to carry over
between repetitive dives. Pay attention, cuz you will be tested on these in
the future.
So I'm doing what I can to ask Jerrod for clues to either method or
model. I had asked for a demonstration of some element of the DIR method
of deco calc. I offered examples of dives that could test a method and
or model. Remember Terry's post of just a bit ago, where his description
was very similar to standard table deco calculation methods. I used a dive
at the west end of San Nic as an example that might well test what Terry
had written. I got little information and almost nothing I could make
sense of. Notably, what I did hear, was about method and not model. It
appeared that the DIR way definately did include depth averaging, a
no no in many circles. It also talked about notebook computers on a
boat for modeling... computers love salt water. Also, it was obviously a
method based on repetitive experience, which right off makes it a bad idea
for newbies (and not appropriate for casual divers either). They also talked
a whole lot about knowing deco theory (models).
I didn't get enough info to make any sense of anything meaningful,
which in a way was a bit curious. Well, it was late, people had to go,
no progress was being made. I ended up outside talking to Terry. He was
fairly frusterated and near to getting excited. I get people that way.
Heck he was about to spit. Then he geeked. No not an anhuerism. He spilled
the beans. He actually said a fact... Well, I can do a lot with a fact
and this one had a certain fascination to it. If I wanted to, I could
make up a whole story about that fact jack... so I'm gonna... and it
deserves a pulitzer for imagination. Heck, it might even have some truth
to it.
What Terry said was an interesting. He said that since any
computer was using a model that could be the same as the model in a
table, if the table and computer didn't agree, then the error was in
the sampling the diver used for the table. As far as I know, that is
generally true, but we know that we get far more bottom time with a
computer, so it must have to do with the method used by the diver
using the tables as their model. We know this is true, because all
(all standard) tables were designed for the diver to calulate using
the deepest part of the profile. There are other biases built in as
So what would happen if a diver tried to match the computer for
accuray? Say a diver noticed this discrepancy and decided to overcome
it. (I think this is almost how the DIR idea got formed, but they used a
measurement model, not a table model) This leads to some interesting points
and also hints at a few things not mentioned at DIR demos. Also, it may mean
that I can describe this easier than the DIR folks, because they reached
these conclusions by a different, more difficult way. I can use a simpler
description to get to the same place.
Since I had pretty good information about the dives at San Nic
and they were a good test case, I figured I could make a comparrisson
where I used the same model, but different methods to do deco. To test
this, you would need a computer and tables that used the same deco
model. To at least look at this, I did a bit of number juggling to see
if I could fit my computer done test dive into a table. Even if the
models were not identical, I should be able to get similar answers with
a bit of massaging... I couldn't, but that just means that the methods
between the diver and the computer were vastly different. Fasinating.
At this point, the issue of DIR deco claims rest on method, not
model. If you could make your methods as accurate as a computer, you
you could do deco calculations that would match a computer using the
same model, regardless of model. Here comes Frank Farmer's question
about whether a computer would be just as good as DIR methods if it
had as good a model. If I'm making up this story correctly so far,
it would. Apparently, the new Sunto Viper, does use (near) the same model
that Jerrod is using currently. (1)
So what about these mystical methods? Well, this is an interesting
point. Actually, theoretically it should be possible. Not easy, not
always accurate and perhaps difficult to learn, but not impossible. This is
where you really see where the DIR desription of things is horrible,
but probably for a different reason that I will mention later. I was
looking for something complicated related to deco theory. Actually,
they keep calling it deco theory, but it is gas laws that they are
taking advantage of. (They should mention this) Gas laws are linear in
respect to temperature, pressure and time. That is a much simpler problem
of methods than are the calculations of a deco model. It is simply a few
parellel analog calulations. With practice, humans can do those very
accurately. It is like estimating measures on a line. If a person works at
it and uses a ruler to check their estimates, they can become very accurate
estimating measures 'by eye'.
One other point mentioned by Jerrod fits in here somewhere. He
mentioned a bottom timer that recorded a profile of the dive (that's
the method). Then this data would be plugged into a notebook/palm
computer for deco calc after the dive (that's the model). Apparently,
this gave the ability, using appropriate deco software, to use different
models on the same data. Also, this would be a good teaching tool,
because, take my example of a dive on Eagles Reef, this could give the
information a diver would need to learn how to estimate the depth to be
used in whatever model they did use. While I have done a lot of
different dives there, the average depth of the dive is probably fairly
consistant... (though what it actually is is the trick to figure. A depth
recorder and some SW could do it)... and the time would be known by the
timer. Really, this is simply using a computer to make a deco calculation.
It's just that the computer is not in the water and so different models can
be used and the different individual models can be adjusted. It sounds like
a great research tool.(2)
So what I've said up to now is that the DIR deco calculations
are done by using a different method. The problem is how do you learn to do
the methods as accurately as a computer. In this story, I will say that it
is by using a computer to tell a diver what their location is and learn
from that. When your manually calculated deco location matches the computer
generated deco location, both using the same model, then the manual methods
are equivelent to the computer method. Given that the problem, depth
averaging, should not be that difficult, this is feasable. Of course, in
this scenerio, you are just trying to learn to imitate a computer... not a
super important goal. But what if there is one more DIR ommision that I can
write in to my story? What if the model/table is different too, as well as
the method?
Now, this Viper deco computer is supposed to use the same algorithms\model
that the DIR folks are currently using... when they use any model that uses
calculated deco locations (3). What if they actually aren't using calculations
at all? Thinking back to what Jerrod actually did say, would it be that the
model they are ultimately using is actually doppler tests? What if they
don't calculate decompression status, they measure it? Well, it sure would
explain why I could never get an answer to the question of what the
model/table was that they were using. It would also work to reduce the
number of DCS hits a person could get learning this method...
OK, so where does this leave us?
DIR does have a valid manual method of calculating deco obligation in
terms of depth and time. It should be workable because of the simplicity of
the gas laws involved, not because of trick deco calcs. Some people could
never learn this method, but if a diver was devoted enough, and many are,
this calculation method could be learned using a computer for verification
or calibration of the estimate. The difficulty of using this method would be
different in different dive areas.
(4)It appears that using a computer based on the same algorithm/model
would serve the same function as far as providing a deco solution/location.
This would always be true to a certain point of nitrogen buildup. Past that,
using actual measurements from doppler analysis as your model, would show
pretty much the exact deco solution/location.. with no calculation and
likely it would take into account variations in individual physiology.
Something no other model can do. Now, Jarrod did mention not to try
this in your own home.
So as far as I can see what DIR manual deco calculations are, DIR does
have a method, depth averaging, that seems reasonable. They use two models.
One model is basically (the best available, still being tested) tables and
the other is actual measurements based on doppler detection of gas bubbles
in the system. If that is so, it really should be admitted to and explained
as a research method. I assume that one of Jarrod's major projects is using
doppler studies (model) to validate and tune the (latest greatest)
table/model... Then we can all use it in a computer.
Remember, this is just a story I made up from the tidbits and
the one fact that I heard. Is it DIR? I think so. I numbered some (4) points in
parenthesis so that any clarifications could refer to points by number. (I'm
especially interested in if a computer using the same advanced model would
give the same results as the manual calc method). This story fits the facts
and explains why we can't get a description of it. You can decide if you
would want to use it or not.
Note that if Terry's little fact is true, that does not speak very
well of the the sophistication of dive computers. If he is right, which I
sorta think he is, those are some dumb programs with a lot of room for
improvement. There are a few other issues raise here that could use
closer examination, but I think they are as I have said and support the
method described. Actually, though it might surprise him, I do appreciate
Terry May's efforts, cuz he's the only one that really tried to come up
with an explanation and finally he gave me enough information to come up
with this story, which might actually be what he meant.

Enjoy the diving, seahunt
PS. After all that, even if I am wrong, I don't want anyone claiming I
didn't give a serious try to figuring out what DIR is up to. If points
are wrong, clarify them... As I said this is just a story I made up
from the little I could find out. If you figure it's all wrong, then
after going to the demo and doing all this to figure out what was meant,
I really do figure that I am owed an explanation. Note that I have tried
to give as good an explanation as possible, with the minimum of evaluation
past basic feasability.
Can anyone else make up any good stories that fit what little we've
been able to find out about DIR deco calcs?

PPS. RaiderKarl... Dive your plan, plan your dive. That is what they teach you in your first class... Did you ever get past that.

PPPS. Per MHK last post... I'll have to look at that closer, but why didn't you say that before. Much of that is what I guessed, though you made no mention of the doppler. I will analyze the post when I get the time... Though I found out from Terry's post something and that suggested that a sawtooth profile was not a good test for DIR methodology and that deep square dives would be better, hense the change in questions.

Follow Ups:

Post a Followup




[ Follow Ups ] [ Post Followup ] [ California Scuba Diving BBS ] [ FAQ ]