Been to Koh Tao, should I go to PERHENTIANS?

Stef wrote:
> "Reef Fish" <Large_Nassau_Grouper@Yahoo.com> wrote in
> news:1122918742.501048.298150@z14g2000cwz.googlegr oups.com:
>
>
> >
> > Why did you get PADI certs from THREE schools?
>
> To learn in different environments, OW and AOW were in the Red Sea, RDC
> and DM were UK shorebased and offshore boat diving, lately I've been
> doing a lot of inshore stuff. Different instructors with different
> backgrounds... none of them were bad, I just wanted to spread experience.
>
> Before you ask yes I am (now) spreading agencies as well, I wanted to
> become competent as a diver first and I don't believe for one minute that
> that is agency dependent.

"It's NOT the agency, but the INSTRUCTOR that matters" is the
universally
accepted truism for OW-I training, that has been said for over a decade
in scuba forums.

The Nitrox-I course is a conspicuous exception, at least in the USA.
When PADI has its own Manual prescribed for the course, and it contains
NO gas theory, no conversion formulas, virtually no vital knowledge
except some trivia related to EAN32 and EAN36, most PADI instructors
do not have the course material to teach more.

That's how I got a shocking contrast from a Nitrox-I course (and
witness several of them taught on liveaboards) by PADI, and the
SSI course I had, from Gilliam's book.


> > Did ANY of them teach you any of the relevant gas laws? How to
> > compute the MOD and EAD from PPO2s? Did any even talk about
> > PPO2 different from 1.4 and 1.6? Did any bring in the Time of
> > Exposure as one of the critical elements of EAN diving?
> >
>
> Yes (for all of the above) the one I did my Nitrox cert with.

Not surprising for the more advanced Nitrox courses, but does PADI
use different Manuals (textbooks) for Nitrox I in the uk? Was it
a PADI Manual or a non-agency affiliated book?


> >> Before this gets horrendously off-topic I'll ask my next question in
> >> rec.scuba.
> >
> > LOL! "Hi folks. I am a Pom from the other side of the pond. Can
> > I carry a gun while diving with Nitrox?"
> >
> > That should get you lots of On Topic stuff there.
>
>
> Wouldn't that be au.rec.scuba? I didn't think we were called Poms in the
> US, or maybe I'm mistaken?

You're not mistaken. Most US divers wouldn't know what a Pom is if
their lives depended on it. I learned it from my Aussie, as well as
BRIT diving friends. There are even interesting etymology of
the term "pom", but that would be really OT.

-- BOb.

In article <Sd5Ge.18354$aY6.9742@newsread1.news.atl.earthlink .net>,
leebell@ix.netcom.com (Lee Bell) wrote:

> > In article <TovFe.9410$oZ.1597@newsread2.news.atl.earthlink.n et>,
> > leebell@ix.netcom.com (Lee Bell) wrote:
> >> It varies with the mix and with your willingness to push your luck.
> > In
> >> the past, a partial pressure of Oxygen equal to 1.6 atmospheres was
> >> considered safe enough. Currently the standard is 1.4 atmospheres.
> > At
> >> 1.4, the MOD for 32% is 111 feet salt water, for 36% is 95 feet salt
> >> water and for 21% (air) is 187 feet salt water.

So when divers are trying to break depth records they are working on their
own theoretical tables ? or are the tables relevant for depth's not yet
achieved ?
And.....would they use nitrox or air to get down to the MOD (187ft ? yes i
understand they can only do 187 on air) and then ???? to descend down to
their required depth. Coming up from that depth they would use ?????? the
same as they did below the 187 ? and from 187 up they would be using
higher % of nitrox ? and at the higher PP of 1.6 ? to do their deco stops.

Dave Morgan @ Work in the UK
Take out the "goes diving" bit....
Trip photos on line at www.morg.co.uk

<morgand@cix.compulink.co.uk> wrote

>> I live in south Florida. I mean that the only thing I wear for most
>> dives is a Speedo bathing suit under a lycra dive skin. I own, and
>> sometimes use, a 3mm wetsuit, but I don't wear it often.

> Christ......the only time i dived Florida (out of Key Largo) the water was
> positively "cool"......it was January though.

It's cool for me too. The fact is, though, when you're no more than a half
hour from a dive, any time of the year, you tend to get picky about
conditions you dive in. It has to be a pretty special dive to get me in the
water during the winter.

>> My wife is not as experienced as I am, so I usually do a bit better,
>> but not always. It's close. I don't know why women are easier on gas
>> than men, but it certainly seems to be true.

> They just like everything to last longer...........men.........well, they
> just want to do it (dive that is) and go to sleep.

They're spoiled.

Lee

"Reef Fish" <Large_Nassau_Grouper@Yahoo.com> wrote in
news:1122949156.469326.215400@g43g2000cwa.googlegr oups.com:

>
> "It's NOT the agency, but the INSTRUCTOR that matters" is the
> universally
> accepted truism for OW-I training, that has been said for over a
> decade in scuba forums.

I've never countered that statement and never would.


>
>> > Did ANY of them teach you any of the relevant gas laws? How to
>> > compute the MOD and EAD from PPO2s? Did any even talk about
>> > PPO2 different from 1.4 and 1.6? Did any bring in the Time of
>> > Exposure as one of the critical elements of EAN diving?
>> >
>>
>> Yes (for all of the above) the one I did my Nitrox cert with.
>
> Not surprising for the more advanced Nitrox courses, but does PADI
> use different Manuals (textbooks) for Nitrox I in the uk? Was it
> a PADI Manual or a non-agency affiliated book?
>

It was (and is, I've just dug it out) a PADI manual, I don't know if it's
any different to the manuals used in the US except that it's the metric
edition.

I'm guessing you'd search for it by the Congress Card number? 95-072885
Or the ISBN is 1-878663-21-6

All of the relevant formulae discussed in this thread are there as is the
24 hour time of exposure; the style of the manual is pretty basic, but
then I've yet to read a PADI manual that doesn't read like a childrens
story.
The gas laws are a glaring ommission (aren't they covered in OW-I
though?), other than that I'd say that they have this thread pretty well
covered.




There are even interesting etymology of
> the term "pom", but that would be really OT.


And that changes Usenet how exactly???



--
Stef the pragmatist

Hope for the best
Plan for the worst

Sometimes the glass is half-full; most of the time I’m waiting for a
refill.

<morgand@cix.compulink.co.uk> wrote

> So when divers are trying to break depth records they are working on their
> own theoretical tables ? or are the tables relevant for depth's not yet
> achieved ?

"Tables" isn't as clear a term today as it once was. Technical divers often
create custom tables on a land based computer. If gas transfer theories are
accurate, and they've been pretty thoroughly tested by now, then they can be
applied to depths and times beyond what most divers would even consider.
There probably are a host of other factors involved. That's why they call
it technical diving.

> And.....would they use nitrox or air to get down to the MOD (187ft ?

No. Nitrox is not a deep gas. They would use some other mix. The most
common deep gas uses helium to replace some of the oxygen and nitrogen.
Very deep water gas contains less nitrogen and less oxygen than air.

> yes i understand they can only do 187 on air)

You understand incorrectly. Lots of people have gone past 187 feet on air.
Divers used to accept a PPO2 of 2 ata. On air, that translates to a MOD of
281 feet. Even today, a PPO2 of 1.6 is acceptable under certain conditions,
yielding a MOD of 218 feet. Finally, because the oxygen toxicity has a time
aspect, quite a few people have done very short duration spikes to depths
well beyond 187 feet.

Some of us think that somebody is crazy for doing such dives when there are
safer alternatives, but most of us have been called crazy at one time or
another.

> and then ???? to descend down to
> their required depth. Coming up from that depth they would use ?????? the
> same as they did below the 187 ? and from 187 up they would be using
> higher % of nitrox ? and at the higher PP of 1.6 ? to do their deco stops.

It's not unusual for exceptionally deep divers to use a bottom gas, a travel
gas and one or more deco gases. The gases used at each stage of the dive
depends on the depths involved and the diver's preferences for travel and
deco gases.

Lee

On Tue, 02 Aug 2005 05:55:51 -0500, morgand@cix.compulink.co.uk wrote:
> So when divers are trying to break depth records they are working on their
> own theoretical tables ? or are the tables relevant for depth's not yet
> achieved ?

Decompression tables are generated using an algorithm. These days the
algorithm is run on a computer; some of these in real time (as in a dive
computer).

The algorithm is based on one of many models that attempt to predict
what is happening inside the body with respect to gas absorbtion and
elimination. Some of these models are well tested for a certain range of
profiles.

The various models may specialize; some used by navies and commercial
operations allow for surface decompression (surface relatively quickly and
complete the required decompression in a chamber), and some specialize in
saturation profiles. They are probably well-tested, and proven reliable, when
applied as intended.

Modern recreational dive computers are well tested within recreational
profiles, and have proved to be fairly reliable within those profiles.

Models will generate a profile for virtually any dive. But using a model
outside its well-tested range means taking more risk.

I guess you could say using even a well-tested model, but applying it outside
its well-tested range, is using a "theoretical" table.

But really, they're *all* theoretical. We don't know if the models are right,
but that isn't what matters - they produce useable results, at reasonable
cost.

> And.....would they use nitrox or air to get down to the MOD (187ft ? yes i
> understand they can only do 187 on air) and then ???? to descend down to
> their required depth. Coming up from that depth they would use ?????? the
> same as they did below the 187 ? and from 187 up they would be using higher
> % of nitrox ? and at the higher PP of 1.6 ? to do their deco stops.

I think you're asking if different gasses are used during a deep dive.

Breathing gasses can be optimized for a depth range. One can choose a gas
based on several factors, including MOD (oxygen issues), and acceptable
narcosis risk. Personal risk tolerance also enters into the choice.

A very deep dive might employ many different gasses. Gasses used during
descent, but not at final depth, are sometimes called "travel" gas. During
ascent, they are called "decompression" gas.

Such a dive does not necessarily use these gasses symetrically (same gasses in
same depth ranges on descent as ascent). Some divers will tend to be much more
conservative with respect to oxygen issues (MOD) on descent; they'll use
1.4ATA (or lower) to govern the MOD during descent and at the bottom, and a
higher threshold (typically 1.6ATA) on ascent. The reasoning behind doing so
is (a) supposedly one isn't "working" during decompression stops, and (b)
there is a desire to flush inert gasses (nitrogen and helium) as quickly as
possible during ascent, which using the higher PPO2 helps to accomplish.

--
Art Greenberg
artg AT eclipse (remove this) DOT net

In article <uTIHe.1824$ns.187@newsread1.news.atl.earthlink.ne t>,
none@none.invalid (Art Greenberg) wrote:

> *From:* Art Greenberg <none@none.invalid>
> *Date:* Tue, 02 Aug 2005 11:34:50 GMT
>
> On Tue, 02 Aug 2005 05:55:51 -0500, morgand@cix.compulink.co.uk wrote:
> > So when divers are trying to break depth records they are working on
> > their own theoretical tables ? or are the tables relevant for
> > depth's not yet achieved ?
>
> Decompression tables are generated using an algorithm. These days the
> algorithm is run on a computer; some of these in real time (as in a dive
> computer).

Ok.....

> The algorithm is based on one of many models that attempt to predict
> what is happening inside the body with respect to gas absorbtion and
> elimination. Some of these models are well tested for a certain range of
> profiles.

Leaving aside the "fact" that everyone is different, what gets me drunk is
probably not what gets you drunk (not that i am suggesting you do get
drunk)........the "models" have been based on many trials and
experiments........


> The various models may specialize; some used by navies and commercial
> operations allow for surface decompression (surface relatively quickly
> and
> complete the required decompression in a chamber), and some specialize
> in
> saturation profiles. They are probably well-tested, and proven
> reliable, when
> applied as intended.

OK.....

> Modern recreational dive computers are well tested within recreational
> profiles, and have proved to be fairly reliable within those profiles.
>
> Models will generate a profile for virtually any dive. But using a model
> outside its well-tested range means taking more risk.

Agreed.......

> I guess you could say using even a well-tested model, but applying it
> outside
> its well-tested range, is using a "theoretical" table.

OK.....

> But really, they're *all* theoretical. We don't know if the models are
> right,
> but that isn't what matters - they produce useable results, at
> reasonable
> cost.

They're as right as they can be at this moment in time though ?

> > And.....would they use nitrox or air to get down to the MOD (187ft ?
> > yes i
> > understand they can only do 187 on air) and then ???? to descend
> > down to
> > their required depth. Coming up from that depth they would use
> > ?????? the
> > same as they did below the 187 ? and from 187 up they would be using
> > higher
> > % of nitrox ? and at the higher PP of 1.6 ? to do their deco stops.
>
> I think you're asking if different gasses are used during a deep dive.

I think i was asking for the answer to be specific......what would they
use to get to their MOD.......
What would they use below that.........but i think that was answered.

> Breathing gasses can be optimized for a depth range. One can choose a
> gas
> based on several factors, including MOD (oxygen issues), and acceptable
> narcosis risk. Personal risk tolerance also enters into the choice.

So different divers would not allways use the same mix's.......


> A very deep dive might employ many different gasses. Gasses used during
> descent, but not at final depth, are sometimes called "travel" gas.
> During
> ascent, they are called "decompression" gas.

OK.....


> Such a dive does not necessarily use these gasses symetrically (same
> gasses in
> same depth ranges on descent as ascent). Some divers will tend to be
> much more
> conservative with respect to oxygen issues (MOD) on descent; they'll use
> 1.4ATA (or lower) to govern the MOD during descent and at the bottom,
> and a
> higher threshold (typically 1.6ATA) on ascent. The reasoning behind
> doing so
> is (a) supposedly one isn't "working" during decompression stops, and
> (b)
> there is a desire to flush inert gasses (nitrogen and helium) as
> quickly as
> possible during ascent, which using the higher PPO2 helps to accomplish.

Yes, i understand that.........

Thank you........i thought you said all that very well.



Dave Morgan @ Work in the UK
Take out the "goes diving" bit....
Trip photos on line at www.morg.co.uk

>> Breathing gasses can be optimized for a depth range. One can choose a
>> gas
>> based on several factors, including MOD (oxygen issues), and acceptable
>> narcosis risk. Personal risk tolerance also enters into the choice.
>
> So different divers would not allways use the same mix's.......

Maybe yes, maybe no. Quite often, personal risk is a function of training.
Most divers, for example, use a PPO2 limit of 1.4 because that's what
they've been taught is safe. Many deep divers use an equivalent nitrogen
depth or END of 100 feet because that's what they've been taught is safe.
Two people planning the same dive, are likely to use the same personal
limits and, therefore, the same mix of gases. Divers working as a team,
including a buddy team, are also likely to use the same gases for their
dive. It simplifies things if/when there is a need for one diver to share
gas with another.

Lee

morgand@cix.compulink.co.uk wrote:
> In article <uTIHe.1824$ns.187@newsread1.news.atl.earthlink.ne t>,
> none@none.invalid (Art Greenberg) wrote:
>
> > *From:* Art Greenberg <none@none.invalid>
> > *Date:* Tue, 02 Aug 2005 11:34:50 GMT
> >
> > On Tue, 02 Aug 2005 05:55:51 -0500, morgand@cix.compulink.co.uk wrote:
> > > So when divers are trying to break depth records they are working on
> > > their own theoretical tables ? or are the tables relevant for
> > > depth's not yet achieved ?
> >
> > Decompression tables are generated using an algorithm. These days the
> > algorithm is run on a computer; some of these in real time (as in a dive
> > computer).

I missed all of this subthread until now.

You asked about "divers trying to break depth records", and what Art
said couldn't be further from the truth!! They DON'T use algorithms
for their SPECIAL decomp tables. Dr. Manion, the world record
holder of AIR depth on open-circuit scuba, 525 ffw, used the
Aladin dive computer only as a DEPTH GAUGE and it was the depth
recorded on his computer that was accepted as the World Record, on
May 23, 1994 -- the day I was with him in Nassau, Bahamas during
his PRACTICE dives for an intended record-breaking dive on a
future day (that was cancelled because Bret Gilliam, the world
record holder then, had conceded that Manion's record was not
worth the risk for anyone to break, not even by Manion himself).

Manion's decompression tables were based SOLELY on his own
M.D. experience (and microbubble measuring instrument), AND what
he learned from Sheck -- who dived at MUCH greater depth with
mixed gases. Sheck's tables were ALL custom tables devised by
himself, via trial and error.

It's true that some LATER dive computers used some algorithms
that made use of some ELEMENTS of their tables, those are used
by the latter generation of techdivers who were NOT out to
break any records!
>
> Ok.....
>
> > The algorithm is based on one of many models that attempt to predict
> > what is happening inside the body with respect to gas absorbtion and
> > elimination. Some of these models are well tested for a certain range of
> > profiles.

That is an accurate statement about the history of how dive computer
algorithms came about and are continuously revised and tweaked.

There are TONS of posts on dive computers and dive computer algorithms
that dealt with this aspect of it.

The point I always emphasized was, and it, that the best-known
algorithms
were based on the THEORY of gas diffusion, solved by differential
equations, on HYPOTHETICAL compartments of "tissue groups" which NOBODY
knows what's what in real humans.

They seemed to "work", and so they were used -- and as time went on,
when relevant "data" from human divers came in, there were more
relevant REAL information, but still proxy for THEORY, but with a
more solid empirical basis for support.

Most of the newer TOYS now have buttons for "tweaks", setting your
own "conservatism" or wotnot, which is just a euphemism for technical
BS!

> Leaving aside the "fact" that everyone is different, what gets me drunk is
> probably not what gets you drunk (not that i am suggesting you do get
> drunk)........

That's a VERY good point to note! They ain't YOU, and you ain't them!
I use that line mostly for "medical advice" that is ALWAYS
inappropariete
for anyone to give in scuba forums, without being an M.D. AND have
physically examined the diver in question.

Of course everybody gets drunk if one DRINKS too much (for that
person's
limit). I am one who NEVER got drunk, on land or in my depth bounce
dives to below 200 fsw. NEVER even felt perceptively different from
diving at 80 fsw, say. The reason? I don't drink, except for a
very occasion social sip, in what we call NEDfests (meeting of
NEDs - Network of Egghead Divers). In water, because of the SHORT
times of exposure and my motto, "Know YOUR limits and dive WITHIN
them", almost all of my deep bounces are no-deco dives, except a
few that required a minute or two, of essentially "safety stop".


> the "models" have been based on many trials and
> experiments........

See the above. Only THEORY and post-hoc experiments to validate the
usefulness of the algorithms in common ranges by the "average" diver.
>
>
> > Modern recreational dive computers are well tested within recreational
> > profiles, and have proved to be fairly reliable within those profiles.

Actually most of them have NOT been adequately tested by humans.
Most of the divers who used them do NOT reqularly dived to the LIMITS.
Most dive well within the NDL limits, and so, that absence of a
large number of DCI or DCS incidents only meant the testing profiles
are not sufficiently extreme -- to be considered if it were done
in a "controlled experiment" of various depths and durations.

The only algorithm that had been EXTENSIVELY tested, over millions
and millions of dives, by recreational as well as professional divers,
was the ORCA algorithm of modified Haldanean model, by Karl Huggins.

If you go to the groups advanced search option of google, and
specify "Karl Huggins ORCA" as the keywards for search, and "reef fish"
as the author, you'll get SIX threads over the years, covering
various aspects of the dive computer issues, relative to ORCA.

That's the algorithm used in EDGE, SkinnyDipper, and later models
of ORCA. It's a SIMPLE model. No bells, no whistles, no tweaks,
no setting of any kind, but a RELIABLE gadget I've used in nearly
ALL of my dives. That's also one reason I don't dive below
200 fsw often, because it goes out of range at 200 fsw.
But I BET I have more dives at max depth of 199 fsw than anyone
else. It's not all that eaxy to stop exactly at 199 fsw either,
unless you're perfectly sober, and have perfect buoyancy control!

>
> > But really, they're *all* theoretical. We don't know if the models are
> > right,
> > but that isn't what matters - they produce useable results, at
> > reasonable
> > cost.
>
> They're as right as they can be at this moment in time though ?

Both you comments are correct, as I stated the case more precisely,
with reference to gas diffusion multi-compartment differential
equations modles.


> > A very deep dive might employ many different gasses. Gasses used during
> > descent, but not at final depth, are sometimes called "travel" gas.
> > During
> > ascent, they are called "decompression" gas.

BUt those are WAY OUT of the realm of recreational diving. Sheck's
short dive (written up in UNDERCURRENT) required 37 bottles of
decompression gas, over many, many hours.


> Dave Morgan @ Work in the UK
> Take out the "goes diving" bit....
> Trip photos on line at www.morg.co.uk

I think somewhere along the line of this thread, you asked if Nitrox
was suitable for "deep dives". The answer given by Lee was a very
poor one.

If anything, Nitrox is a SHALLOW DIVE gas! For deep and long dives,
one gets into technical diving, the NOBODY uses Nitrox, but gases
that uses various mixes of inert gases.

-- Bob.

In article <OyMHe.9222$6f.5129@newsread3.news.atl.earthlink.n et>,
leebell@ix.netcom.com (Lee Bell) wrote:

> *From:* "Lee Bell" <leebell@ix.netcom.com>
> *Date:* Tue, 02 Aug 2005 15:45:50 GMT
>
> <morgand@cix.compulink.co.uk> wrote

> > I have seen divers doing 100m on air in that old quarry i post a link
> > to yesterday),i
> > was trying to ask what would they use to get to their MOD . . .
>
> It's not their MOD, it's the gas's MOD at their chosen PPO2 and N2
> equivalent limits. If you plan on diving to 300 feet, you'd be using
> something with less than 21% oxygen and less than 78% nitrogen.

With regard to "their" MOD.......surely it IS their MOD, what I'm implying
is..............take two divers.......identical gas mixes, each of those
divers would have different MOD's. Or am i assuming incorrectly, that just
because the MOD for air or 21% at PP 1.4 is 57m and divers can and do go
well beyond that it does NOT apply to mixed gas diving ?

> > We did 60m in Chuuk on air and felt fine......
>
> I'm sure you did feel fine. You were almost certainly narced to the
> gills.

I dont think so.......i dont think either of us were.

> Whether you tell people about it or not is really not the issue.
> Whether you're around to tell them is.

What I'm saying is.......telling all the kids about the Bogey Man and to
be carefull walking in the woods after dark will only have them all
running home saying they have seen him.


Dave Morgan @ Work in the UK
Take out the "goes diving" bit....
Trip photos on line at www.morg.co.uk