Of course no one else on rec.scuba could teach Curtis anything about
diving since he knows everything about everything.  (Even though he
apparently still doesn't understand that he can't do typical
recreational dive profiles as I've described without a dive computer)

But don't bother explaining yourself or attempting to contradict
anything you quote - just make your typical snide remarks and pretend
that we think you're really very impressive for diving in mudholes in
GUE-clone team formation.

Precisely why I read rec scuba for entertainment purposes only, not for
serious learning.

Curtis

 In perfect conditions, during a relaxed dive.

 A SAC rate doesn't have anything to do with how long a tank -actually-
lasts.

 It has to do with how long a tank -might- last, under absolutely ideal
conditions.

 I use the SPG.

 In my world, the SAC rate is virtually useless.

   Beg to differ.

   Although the specific numbers may not be important, knowing how long a
tank will last is.

Curtis

On Wed, 10 Feb 2010 08:08:48 -0800 (PST), John Van Ostrand

Which shows how unnecessary that knowlege is.

Does anyone foresee dive technology getting to a point where much more
limited skill is involved?

We have it easier than the last generation of divers. We have SPGs and
computers and such. Most divers have no idea of their SAC rate, most
just follow the DM.

What's the next innovation that will remove yet another critical skill
from diving?

Why, necessarily?  If one diver continually runs short on air and his
buddy continually returns with more air than the recommended minimum,
assuming only one size tank is available such as at the standard
resort setting, what's the harm in balancing out the air a bit if it
can prolong the dive by another few minutes?

Awareness. Awareness. Awareness.

You don't dive a profile waiting for a bell to ring like you're a
three minute egg. You don't suck your air down to 500 or even 750 psi
at 100 fsw before you decide, oops, it's time to head for the surface.

You plan your dive. You dive your plan. Departure from the plan may or
may not call for an abort of an open-water dive in a tourist group
situation but a low-air situation certainly shows a lack of awareness
of a number of factors and calls for re-training if it occurs more
often than rarely.

It's perfectly OK to be aware of your air consumption at depth and to
be calm about it. Awareness of it will calm you down because you will
know that you will not miss a decision point about when to turn around
or when to start your way up to your safety stop. A sharing air
situation is an abort condition for both buddies, not a method of
continuing the dive.

Exactly.  Which is why I proposed a device that is small, passive, out
of the way and would fail passively as well.

Would still be a reminder to anyone to check their gauge when it popped
if they were in a bad habit mode.

Certainly people are adding transmitters for their computers.  That is
is definitely not "simple".

Considering gear some people bring with them that could cause
distraction, photography being an easy example, such a device seems well
warranted.

KISS principle applies.

I dived with a HyperAqualand on my wrist. It beeped incessantly with
rate of ascent warning if I so much as moved my hand up in the water
column. Every diver I was with could hear it. Except me. I had to
strain to hear it. Hooking it to a D-ring made it less annoying for
others but I still couldn't hear it. One extra gizmo I didn't really
need.

I wear my hoseless computer for all dives but I still carry the SPG
and hose console in my kit in case of hardware failure. Nothing would
be worse than being on a trip and having a computer or transmitter
fail. At least with an SPG I can still dive on tables.

As for your cockpit redundancy analogy, all those gauges to scan and
read and commercial pilots still are bored to death in the cockpit.
Those gauges don't mean a thing when the wings are falling off or
you've busted your elevator jack screw trying to "troubleshoot" a
problem.

The key is awareness. You don't have to stare at the console for the
whole dive, it's OK to look at the scenery but a periodic glance at
your gauges will tell you instantly how your consumption is going to
affect your dive.

It seems (to me) that it would be simple enough to add a mechanical
device to the first reg. that "pings" (plonks, thuds, whatever) when a
certain pressure is reached without otherwise being part of the airflow
control.

"Douglas W. \"Popeye\" Frederick" <Popeye8...@gmail.com> wrote:

Agreed.   In part because early regs weren't balanced.

And what's also important to note is that the mathematics by which
130fsw also works out to be 1 ATM PPO2 was revisionist bullshit that
came much much later as an attempted "justification" of the 130fsw
value by the Recreational Agencies.

With pictures with diagrams and circles and dates.

In the early days, we also didn't have 3000psi tanks - a full steel
was ~2200 (if no plus rating).   As such, a 1000psi rule would have
been half the tank.

Similarly, the lack of an SPG made the J valve ... and its spring
setting .. your reserve.  Given that unbalanced regulators tend to
breathe like crap below ~250psi, a setting of 500psi for the J valve
would give you a warning starting at around 750, whereupon its release
would give you "enough" time to get up from ~100fsw.

Naturally, there's also stories of divers who accidentally tripped
their J and while still deep, sucked it dry, flipped, and then got a
surprise of no reserve.

-hh

IIRC, there's a gear related military history significance about the 130 ft
mark- something about older regs' breathing characteristics going to crap at
that depths, and it just became an arbitrary rule-of-thumb.

 ESG will be along to explain that coherently.

 I think that's true.

 They gotta set a limit (for me to ignore) somewhere, and 750 or a grand
would be too much.

 I've put that paradigm to many good uses. :-)

My opinion:

500 PSI is about 350 PSI usable before breathing gets harder, depending
on the regulator in use.  350 PSI is about 12% of a tank of air in an
3000 PSI tank, a bit over 8 cubic feet for an AL80.  As margins go, 8 CF
is a bit thin at 130' (let's say a bit over a minute of moderate
exercise), but it beats "nothing" by a mile and it would probably be
hard to talk recreational divers using singles into greater margins.
I'd rather be more conservative, personally, but I also carry a lot more
gas than the average recreational diver and I don't dive singles without
a 20 CF pony.

Pretty significant narcosis sets in around 140' on air or Nitrox, at
least for me on most days.  At least some of the agencies that certify
for Trimix recommend an equivalent narcotic depth of 100' on deep dives.
 I'd prefer to limit depth for air or Nitrox to about 150', but if the
dive is complex or long I'd want Trimix or to stay shallower.

Another way to look at this (thanks, Popeye, for your "where are the
bodies?" post a year or two ago) is to observe that those who obey these
limits don't seem to die very often.  There is a pretty broad body of
experience that say these rules are "conservative enough," in other
words, in light of current training standards and diving with a buddy.
So while these margins make me nervous for the average recreational
diver who dives once or twice a year, they seem to be working reasonably
well.  YMMV...

I know it's been discussed before. But I'm getting into a discussion
on another forum with some one about the history of those limits. And
whether or not they are arbitrary or not. And if they have any real
basis as being safer than say any other number.

So anybody care to refresh my memory on the history of those numbers?