To fly or not to fly?
Treehorn
dives in the morning, when I am flying to Trinidad at 10 pm that night.
He implied that it will only be a little island hopper that this made a
difference. He said as long as I was not jumping on a international when I
got to Trinidad that I would be ok.
I will only be doing shallow beginner dives for two days (three days if I
dive on the day of the flight).
Is there a difference between a short trip on a small plane vs. a trip on a
international jetliner?
How much would dive depths play into my decision? What other factors are
there to consider?
I will be diving with a Suunto Cobra but from what I can tell the minimum
no-fly it will give you is 12 hours from the last dive. It also says in the
manual that this number is calculated based on a comercial jetliner at 2400m
or 8000ft.
I don't want to take any chances just because some dive shop wants to make
an extra $50 off me before I leave the island but on the other hand this guy
has years and years of experience and it would be nice to get in some extra
dives in my short window of opportunity.
Shold I play it safe and not dive the morning of my flight? Maybe I sould
pass on the last morning of dives and see some of the other sights on the
island.
Thanks
-Andrew
Leon Phelps
news:i8ji7.24738$f01.6...@news3.rdc1.on.home.com...
This is not advice but actually more questions for some one that knows.
Wouldn't a lower flight of say 5000 to 8000 feet be just as risky as one at
30000feet for the reason that the cabin pressure is maintained at the
equivalent of the lower altitude?
Randy
exped...@hotmail.com
"Fear is the path to the dark side,fear leads to anger, anger leads to
hate,hate... leads to suffering"
Yoda
Rich Lockyer
<DELETEabu...@home.com> wrote:
>I will be diving with a Suunto Cobra but from what I can tell the minimum
>no-fly it will give you is 12 hours from the last dive. It also says in the
>manual that this number is calculated based on a comercial jetliner at 2400m
>or 8000ft.
Yes, it is based on 8000 feet. This short island-hop... is the
aircraft pressurized? How high will it be flying? Taking a Cessna up
to 10,000 for a 1/2-hour hop would be more risky than taking an
international flight in a 757.
>Shold I play it safe and not dive the morning of my flight? Maybe I sould
>pass on the last morning of dives and see some of the other sights on the
>island.
That's the smartest thing to do. I find that, with all of the packing
and getting ready to go, I've got enough on my mind already. I've
done some snorkelling on departure-day, but generally, it's a day to
relax and make sure that nothing is left behind.
--- Rich
http://www.geocities.com/richlockyer/compindex.html
Rich Lockyer
<exped...@hotmail.com> wrote:
>This is not advice but actually more questions for some one that knows.
>Wouldn't a lower flight of say 5000 to 8000 feet be just as risky as one at
>30000feet for the reason that the cabin pressure is maintained at the
>equivalent of the lower altitude?
True, with one caveate... if you're at 30,000 and there is a sudden
pressure loss, you're going to be in DEEP trouble if you've violated
no-fly. Most passengers in that situation DO fizz to a degree, but it
is mostly subclinical and the O2 provided controls the situation.
Believe it or not, the Air Force has more experience with DCS than the
Navy.
--- Rich
http://www.geocities.com/richlockyer/compindex.html
Vegard Kjenner
your last dive, and you ex. have to decompress on the way up. Then you must
wait 24h....Not to cool to miss your flight and so on. Just relax and enjoy
your last day.
"Treehorn" <DELETEabu...@home.com> skrev i melding
news:i8ji7.24738$f01.6...@news3.rdc1.on.home.com...
Lee Bell
> I was recently told by a dive shop in Tobago that I am ok to do a couple
of
> dives in the morning, when I am flying to Trinidad at 10 pm that night.
> He implied that it will only be a little island hopper that this made a
> difference. He said as long as I was not jumping on a international when I
> got to Trinidad that I would be ok.
He hasn't told you enough for you to understand. The recommendation is for
a minimum of 12 hours between your last dive and your flight. Note this is
a minimum. Multiple days of multiple dives suggests a longer period may be
appropriate as does one or more deeper and/or decompression dives during the
series. What the shop is counting on is that some small planes,
particularly those that service dive operations, maintain a low altitude on
shorter flights specifically to reduce the risk of DCS for customers who
have been diving. While this could certainly reduce the risk on one end,
flying less than 12 hours after diving increases it at the other.
Since the no fly time is, in my opinion, based on knowledge that a risk
exists without the hard data to effectively define that risk, I tend to be a
bit conservative. Then again, I also tend to dive deep, long and often. I
generally plan my last dive at least 24 hours before any planned flight and,
on occasion fudge a bit when I know the dives will be realatively shallow.
I never fudge enough to cut the time to less than 12 hours or, for that
matter, even close.
The risk is not clear and it's your risk to take. My choice would be to say
"No Thanks".
> Is there a difference between a short trip on a small plane vs. a trip on
a
> international jetliner?
Normally yes. Most commercial jets are pressurized to a specific, known
altitude equivalent and fly high enough that the external pressure is
considerably lower. There is risk from the reduced pressure set for the
cabin and less likely but more serious risk if the cabin loses pressure.
Many small planes are not presurized. They fly at alitudes where ambient
pressure is adequate for human needs. If they fly low, this can be a higher
and, therefore safer pressure than what is experienced in a larger jet. If
they fly high, it can be less. In short, the risk is variable depending on
altitude.
> How much would dive depths play into my decision? What other factors are
> there to consider?
The key risk issue is nitrogen in body tissues. Depth, number of dives and
duration of surface intervals, including the one since the last dive in a
series all play a part in determining the nitrogen load.
> I will be diving with a Suunto Cobra but from what I can tell the minimum
> no-fly it will give you is 12 hours from the last dive. It also says in
the
> manual that this number is calculated based on a comercial jetliner at
2400m
> or 8000ft.
I'd ask myself why, if I trust my computer to help control risk while I am
diving, would I want to stop trusting it when it tried to control risk after
diving. There are those that know enough to make such decisions independent
of a computer, common practices, etc. I'm very experienced, but not that
experienced. You have to decide how confident and competent you are for
yourself, but I think you already know the answer to this one.
> I don't want to take any chances just because some dive shop wants to make
> an extra $50 off me before I leave the island . . .
You've got your mind right so far.
> . . . but on the other hand this guy has years and years of experience . .
.
I'll bet you're wrong. I'd bet that he has very little experience diving in
the morning and flying in the evening and I know he has no experience making
life and death decisions for you. You know he's biased.
> . . . and it would be nice to get in some extra dives in my short window
of opportunity.
How much are you willing to risk to get them?
> Shold I play it safe and not dive the morning of my flight? Maybe I sould
> pass on the last morning of dives and see some of the other sights on the
> island.
Maybe.
Lee
Lee Bell
> This is not advice but actually more questions for some one that knows.
> Wouldn't a lower flight of say 5000 to 8000 feet be just as risky as one
at
> 30000feet for the reason that the cabin pressure is maintained at the
> equivalent of the lower altitude?
So long as the cabin retains pressure, yes. While very uncommon, there have
been cases of lost cabin pressure. Such a sudden drop in pressure places
everyone at risk and anyone with an increased level of nitrogen in the
system at proportionately higher risk.
Lee
M. Carter Brown
Just to be safe... Everyone's body is different. I knew someone who flew
within that 24 hour time period and ended up having to go to a decompression
chamber later. I guess it was pretty painful and also lucky since it was in
her head... she never regained total hearing in one ear. I.E. It's not
worth the risk..
I was fine mostly because I'm on the leaner side and don't have much fat on
my body. If you're a woman or overweight, I would definately wait. (I'm
not being sexist or anything here). It's a fact that fat will retain
nitrogen for a longer period of time, therefore if you have more on your
body, and women naturally do, then 24 hours please. If your confident, in
good shape, and did not do a deep dive, i.e. ~ 30 - 40 feet only, then if
you wait 12 hours you "should" be ok, but is that last dive really that
important?
Carter Brown
Divemaster #88533
Charlie Hammond
>I was recently told by a dive shop in Tobago that I am ok to do a couple of
>dives in the morning, when I am flying to Trinidad at 10 pm that night.
>Is there a difference between a short trip on a small plane vs. a trip on a
>international jetliner?
Jets tend to maintain cabin pressure at the equivalent of 8000ft, even though
the fly at 3-4 times that height.
Smaller prop planes tend to fly at or below 4000 feet, but the CAN
fly higher! Lower altitude flights should mean that you can fly
sooner after you dive.
>I will only be doing shallow beginner dives for two days (three days if I
>dive on the day of the flight).
>
>How much would dive depths play into my decision? What other factors are
>there to consider?
For flying consideations, length of dive may be more important than depth.
Long shallow dives may require longer wait times that short deep dives.
>I will be diving with a Suunto Cobra but from what I can tell the minimum
>no-fly it will give you is 12 hours from the last dive. It also says in the
>manual that this number is calculated based on a comercial jetliner at 2400m
>or 8000ft.
If your computer says it is save to fly at a cabin alttityde of 8000ft,
then it is certainly safe to fly at 4000ft. This assumes you believe
the computer -- which is your decision.
>I don't want to take any chances just because some dive shop wants to make
>an extra $50 ...
>Should I play it safe and not dive the morning of my flight?
I have flown to 3500 ft 12-18 hours after diving. I DO NOT RECOMMEND THIS,
but I would probably do it again.
You are looking at maybe 10-12 hours or maybe less from dive to fly.
I woudl be concerned about that.
--
Charlie Hammond -- Compaq Computer Corporation -- Pompano Beach FL USA
(hammond@not@peek.ppb.cpqcorp.net -- remove "@not" when replying)
All opinions expressed are my own and not necessarily my employer's.
George Cathcart
> For flying consideations, length of dive may be more important than depth.
> Long shallow dives may require longer wait times that short deep dives.
Nitpicking here, but ...
For any consideration, the two variables of length (time) and depth have to both be considered. A long shallow
dive can yield the same pressure group (for those who are still familiar with dive tables) as a short deep dive.
It's the pressure group -- which is a measure of the residual nitrogen in your system -- that matters.
--
George Cathcart
"If this were a logical world,
men would ride side-saddle."
--Lt. Gen. Frank Sackton
U.S. Army (ret.)
jim frei
> I was recently told by a dive shop in Tobago that I am ok to do a couple of
> dives in the morning, when I am flying to Trinidad at 10 pm that night.
{snip...}
> Shold I play it safe and not dive the morning of my flight? Maybe I sould
> pass on the last morning of dives and see some of the other sights on the
> island.
you just answered your own concerns. there will always be another
day for diving.
--
jim frei
stormwater services group, llc
raleigh, nc
office: 919.816.0661
mobile: 919.819.4229
http://www.stormwatergroup.com
Lee Bell
> > For flying consideations, length of dive may be more important than
depth.
> > Long shallow dives may require longer wait times that short deep dives.
> Nitpicking here, but ...
> For any consideration, the two variables of length (time) and depth have
to both be
> considered. A long shallow dive can yield the same pressure group (for
those who are
> still familiar with dive tables) as a short deep dive. It's the pressure
group -- which is a
> measure of the residual nitrogen in your system -- that matters.
Forgive me, but I really enjoy it when someone nitpicks and gets it wrong,
as you just did. It is not the pressure group that matters, its the level
of nitrogen remaining in the most saturated body tissue that matters.
Charlie is correct. A longer shallower dive is more likely to be a problem
than a correspondingly short one that results in the same pressure group.
Here's why. Body tissues don't absorb and offgas nitrogen at the same rate.
Some tissues do so much faster than others. A short, deep dive loads the
faster tissue first but may not load slower tissues significantly. These
same fast tissues offgas faster as well and may not require a long surface
interval before flying. On a shallower, longer dive, you still load the
fast tissues first, but in this instance, you may also absorb a significant
amount into the slower tissues, tissues that will not release nitrogen as
quickly through normal safe resiration and which may, even after 12 hours of
more, retain enough nitrogen to cause a problem. This is also the reason
why it is recommended that the time to fly be extended for divers who have
done several days of repetitive dives.
Differing absorption and offgas rates ire the basis for all modern dive
computers. Note that the tissue compartments used by computers are
theoretical models designed to cover the full range of human tissues
somewhere within their modeling structure but not to represent specific
tissues individually. In other words, tissues are realy human parts that
can get bent. Compartments are models, not tissues.
Lee
George Cathcart
someone else straightened me out on this one by e-mail, so I am doubly
enlightened. I don't recall that much detail about tissue saturation in my
training. It was covered, but not in enough detail that I would have been able
to say what you did. I appreciate learning the difference.
Meanwhile, my intent was merely to try to simplify for the original poster, in
hopes of helping him realize that what the dive operator was suggesting was
probably not in his best interests. When in doubt, err on the side of safety,
right?
I'll go back to lurking and writing about nudes and sharks when moved to do so.
Thanks.
gc
Lee Bell wrote:
> Forgive me, but I really enjoy it when someone nitpicks and gets it wrong,
> as you just did. It is not the pressure group that matters, its the level
> of nitrogen remaining in the most saturated body tissue that matters.
> Charlie is correct. A longer shallower dive is more likely to be a problem
> than a correspondingly short one that results in the same pressure group.
> Here's why. Body tissues don't absorb and offgas nitrogen at the same rate.
> Some tissues do so much faster than others. A short, deep dive loads the
> faster tissue first but may not load slower tissues significantly. These
> same fast tissues offgas faster as well and may not require a long surface
> interval before flying. On a shallower, longer dive, you still load the
> fast tissues first, but in this instance, you may also absorb a significant
> amount into the slower tissues, tissues that will not release nitrogen as
> quickly through normal safe resiration and which may, even after 12 hours of
> more, retain enough nitrogen to cause a problem. This is also the reason
> why it is recommended that the time to fly be extended for divers who have
> done several days of repetitive dives.
>
> Differing absorption and offgas rates ire the basis for all modern dive
> computers. Note that the tissue compartments used by computers are
> theoretical models designed to cover the full range of human tissues
> somewhere within their modeling structure but not to represent specific
> tissues individually. In other words, tissues are realy human parts that
> can get bent. Compartments are models, not tissues.
>
> Lee
--
Lee Bell
> someone else straightened me out on this one by e-mail, so I am doubly
> enlightened. I don't recall that much detail about tissue saturation in my
> training. It was covered, but not in enough detail that I would have been
able
> to say what you did. I appreciate learning the difference.
Not to worry. Your contribution was made with the best of intentions and
simply a chance for the rest of us to show our stuff. We've all been on the
wrong end of one of these discussions.
>When in doubt, err on the side of safety, right?
Now there's a concept we won't disagree with.
Lee
MHK
"Treehorn" <DELETEabu...@home.com> wrote in message
news:i8ji7.24738$f01.6...@news3.rdc1.on.home.com...
of
> dives in the morning, when I am flying to Trinidad at 10 pm that night.
Treehorn,
DAN recommends 12 hours, down from their previous recommendation of 24
hours. On almost any given weekend I can be found getting out of the water
and rushing to an airport, often times with my hair and my gear still
dripping wet and that is often times after very deep and lengthy
decompression dives, so I wouldn't worry too much about doing a few
recreational dives and jumping on a puddle jumper...
Later
A boy called Sue
I'm going to have to disagree with you here - or admit to being under
somewhat of a misconception. Paging Bullshark! Deco question in thread!
:)
George (ghmorrisr...@telocity.com) wrote:
: If you are offgassing normally after a dive, your fast compartments and medium
: compartments are coming into equilibrium with the atmosphere reasonably soon,
: but your slowest compartments offgas so slowly some may take weeks to achieve
: equilibrium. However, even under the pressure differential of 8000', the slow
: compartments won't speed up much.
:
: The danger is the fast and medium compartments that are coming into equilibrium,
: when suddenly you subject them to 8000'. They then start to fizz again, just
: like a coke can. Voila, DCS. That's why you need 12 to 24 hours, to make sure
: the more "volatile" compartments are stable...
Well, as per my understanding, the fast tissues (up to 120 min) will have
all equalized (tissue loading within 1.5% of surface N2 loading) within 12
hours. So going up to 8000' feet isnt going in a particular tissue
M-value being violated.
OTOH, a 240 min compartment may not have off-gassed enough, and tN2 /
tN2-8000feet may exceed that compartment's M-value.
If the M-value is exceeded, then there is a likelihood of bubble formation
- I wasnt aware that slow tissues also bubbled more slowly (I thought the
fast/slow designation was only for dissolved gas exchange), but even so,
it could cause damage.
--
Vandit Kalia GO FLYERS!!!!!
Why didnt you just stab it with your dive knife?
Robert "Doc" Adelman
runs that dive op all the way down on the left at Pigeon Point?
> "Treehorn" <DELETEabu...@home.com> wrote in message
> > I was recently told by a dive shop in Tobago that I am ok to do a couple
> of
> > dives in the morning, when I am flying to Trinidad at 10 pm that night.
> >
> > He implied that it will only be a little island hopper that this made a
not jumping on a international when
or "if"
Remember that those island hoppers are less pressurized than "real
airplanes" . Not a good thing
> > I got to Trinidad that I would be ok.
Doc _(:)0
"I'm hiding in Honduras, I'm a desperate man,
Send Lawyers, Guns & Money...The sh*t has hit the fan"
-Warren Zevon
Lee Bell
> As I understand it, fast and medium tissues can still take quite a long
time to
> get into complete equalization, as equalization rates decrease the closer
you
> get to equilibrium. Example would be a glass of champagne. It starts to
off gas
> quickly, but slows down at the level of CO2 in it decreases. It still
takes a
> *very* long time to come to equilibrium. Go up in a plane, you've just
generated
> a big-ish differential again, and the champagne starts to fizz more
vigorously
> ruining your whole day.
I find nothing wrong with this analysis but remember, the issue was the
potentially greater risk from a long shallow dive, or series of long shallow
dives versus a single, quick deep one.
> Really slow tissues (cartilage, bone) take a long time to on gas, and a
> correspondingly long time to off gas. I would expect it be a given that
the rate
> of gas release has to be correspondingly slow, and probably wouldn't do
much
> harm for flying.
We are in agreement on the length of time it takes for nitrogen to reach
surface saturation/equalize, but that's where our respective understanding
seem to diverge. It is my understanding that bubble formation requires only
the presence of nitrogen in concentrations more than can be released through
respiration and a pressure differential between gas in the tissue and
ambient pressure such that the gas will not remain in solution.
> But hey, what do I know?? <g>
Me too. 8^)
Oh yes, If my nitpicking a nitpicker got me nitpicked, I'll take my picking
like a man. Let's see you say that half a dozen times quickly.
Lee
Brian Nadwidny
Brian
Edmonton, Alberta, Canada
Treehorn wrote:
>
> I was recently told by a dive shop in Tobago that I am ok to do a couple of
> dives in the morning, when I am flying to Trinidad at 10 pm that night.
snip
Steve
DELETEabu...@home.com wrote on 8/26/01 8:29 PM:
> Shold I play it safe and not dive the morning of my flight? Maybe I sould
> pass on the last morning of dives and see some of the other sights on the
> island.
>
> Thanks
> -Andrew
Play it safe, kick back smoke some pot, get laid and then fly. ;-)
Treehorn
> Treehorn, I just gotta know... was it "The Sweede"... the guy that
> runs that dive op all the way down on the left at Pigeon Point?
I don't think it would be fair to go telling tales and then put the
spotlight on someone's business. I will not confirm that it was "The Swede".
Also I will not deny it ;)
I guess everyone has there own personal risk point and as mentioned early
things get sticky when you are asked to help someone else decide what their
risk tolerance should be. The operator who will remain nameless was just
giving me his opinion based on his experiences.
Thanks everyone for all the info. I am not going to dive that morning
because more than anything I can't go through the stress of thinking that I
am about to die in response to every little dive ache and pain. With my
luck my foot would fall asleep from sitting in an uncomfortable position and
I would start screaming to be taken to the hospital and pushing my DAN tag
in everyone's face :)
Who needs the worry.
-Treehorn
chilly
Treehorn <DELETEabu...@home.com> wrote in message
news:VYFi7.29600$f01.8...@news3.rdc1.on.home.com...
Lee Bell
> because more than anything I can't go through the stress of thinking that
> I am about to die in response to every little dive ache and pain. With my
> luck my foot would fall asleep from sitting in an uncomfortable position
> and I would start screaming to be taken to the hospital and pushing my DAN
tag
> in everyone's face :) Who needs the worry.
A wise decision. You'll do well grasshopper (take off on Kung Fu, the
original)
Lee
jim frei
MHK, your post is incomplete and potentially dangerous. here is
what DAN says about flying after diving:
Realizing that just about all current recommendations for flying
after diving are based mostly on "best guess" and not hard data,
Dr. Richard Vann and Dr. Wayne Gerth launched DAN's Flying After
Diving study in 1993 at F.G. Hall Hypo/Hyperbaric Laboratory at
Duke University Medical Center. The data so far suggest that the
original recommendation of waiting 12 hours or more after making
single no-decompression dives is reasonable.
In addition, current research suggests that it may be wise to wait
17 hours or more after making repetitive dives. However, the
research is as yet incomplete and further work is continuing. More
specific data on DAN's FAD recommendations are scheduled for a
future issue of Alert Diver. The one unshakable truth is that the
longer the surface interval after diving, the less the risk of DCS
when flying afterward. Remember chamber trials are conducted
within a relaxed, dry environment unlike the open water, where the
multiple stresses of diving conditions may adversely affect the
rate of inert gas uptake and elimination.
Extended surface intervals allow for additional denitrogenation
and may reduce the likelihood of developing symptoms. For those
diving heavily during an extended vacation, it may not be a bad
idea to take a day off at midweek, or save the last day to buy
those last-minute souvenirs.
the above three paragraphs are quoted from DAN's website
http://diversalertnetowrk.org
Charlie Hammond
George <ghmorrisr...@telocity.com> writes:
>Pardon me for doing some thinking out loud, but I don't see the issue as being
>slow tissues (compartments).
>
>I suspect that background offgassing from slow tissues probably doesn't have
>much to do with getting you bent when flying shortly after diving.
>
>Slow tissues are too "slow" releasing N2 to do this.
You are correct that it is not the "background offgassing" that is the
problem. It has to do with the maximum levels of nitrogen that can
be contained in a given tissue without causing bends. This maximum
is usually called the M-value.
M-values are different for different tissues; slow compartments have
lower M-values.
M-values also varry with ambient pressure. 100 feet deep in the ocean
at an ambient pressure of 4 atmospheres, the M-values are high enough
so that there is minimal danger. M-values at the surface (1 atmosphere)
are much lower -- presenting serious dangers if we go too deep for too
long and don't decompress properly before returning to the surface.
At the 8000 ft cabing pressure maintained by airliners, the M-values
are still lower. Because slow compartments retain nitrogen longer and
have lower M-values to begin with, they are believed to be the source
of most flight/altitude related bends.
Fly to an high enough altitude quickly enough without a pressure suite
and you can get bend even if you NEVER scuba dive.
bullshark
>
> Heya George -
>
> I'm going to have to disagree with you here - or admit to being under
The no fly problem is no different from ordinary decompression.
Sea level is your stop depth, and altitude is your next stop. Safe ascent
calculations are exactly the same.
alt. fsw psi
Sea level: 33.0 14.7
3000 ft: 29.6 13.2
8000 ft: 24.5 10.9
10000 ft: 22.7 10.1
12000 ft: 21.0 9.4
30000 ft: 9.8 You don't wanna know
There are problems with this approach though.
One, not all carriers choose the same in flight pressurization.
I understand that European carriers in particular fly 'higher' than 8000.
I understand that to some extent, this is up to the pilots discretion.
Two, there are well known circulatory problems with long term sitting.
So longer flights may well be riskier than short ones. I have no data on
this. Circulatory problems in flight causing other problems, has been in
the news quite a lot. I can't help but think this complicates matters. YMMV.
Three, a decompressing diver waiting to surface from the last stop has
options that a flyer does not:
...he can extend the last stop
...he can continue on O2 at the surface
...he can recompress
...he can reach a chamber if problems develop (hopefully)
In 'TauchMedizin...'(Springer-Verlag) Buhlmann reported results of studies on
various decompression to altitude experiments. The data presentation is from
a point of view that is used to determine sufficiency of ZH-L16A coefficients.
It does *not* present results of exposure after calculated time-to-fly intervals.
Remarkably, the conclusion of the chapter leads to the introduction of the
modified ZH-L16B coefficients with the implication that the altitude experiments
had a good deal to do with the 'B' determinations. I can't help but also notice that
in all cases where symptoms appeared, they resolved on their own during the exposure,
and were never severe for the divers (skin rashes, transient muscle pains...)
I would not take this to mean that flight induced symptoms are always minor, but
it is interesting, nonetheless.
The question about short/deep vs long/shallow in the purest sense has an immediate
answer: neither is particularly advantageous without knowing the expected surface
interval or prior compartment status.
The reasonable argument about fast compartments really only applies to leading
the dive NDLs. If you are relying on compartmental indicators, an abrupt change
to about 15,000 ft altitude will bend a *non*-diver by ZH-L16B measures. So
*any* accumulations to the long compartments changes the outcomes.
You have a secondary problem that revolves around the divers RMV...What is long
and what is short may well be defined by that or by NDL, or a combination of
that and dive operator policy.
Time-To-Fly, Clean Diver on air to NDL, or arbitrary dive time limit:
[These calculations assume depress to 12,000 feet altitude. There are
undisclosed factors for ascent and descent rates and the figures are
not in any manner to be used for any guidance for any purpose. They
are examples for comparison only.]
Depth time TTF(H:mm)
130 fsw 12 min 7:55
60 60 9:15
40 60 7:50
30 60 6:50
On a dive for dive basis, you are not really getting much of an edge.
Meanwhile George can run a trimix dive to 260 fsw for 25 minutes and
be on a plane in 7:45 by the same calculation method. A pair of 30 minute
30 footers with a 1 hour SI, gives up 6:21.
The problem I have run into, using the deep-dive in actual practice is that I
(we) refused to surface with the air we had remaining...we wound up adding time
at 40-50 feet, because we had so much air remaining...if you add another half
hour (we did more than that) at 40 feet the no fly jacks right up to 9-10 hours again.
In the above examples, I limited the dive time to 60 minutes. In practice most
dive operators get edgy if you run much beyond that (we *are* presumably traveling).
In the end, I think that speculating over 'kind of dive' is not meaningful for
TTF purposes. YMMV.
Personally, we rely on computers that calculate our TTF, take that with a
grain of salt, and give due consideration to the conditions of the flight.
--
safe diving,
bullshark
Brian Nadwidny
You've got 3 paragraphs which state "Nobody knows and we have no valid
data. So we'll guess because people want a number" That's not even bad
science, it's pure bullshit. Of course the resorts love the extended
waits because it gets folks to stay an extra day and spend more money on
chi-chi's and trinkets.
The old "D" group rule is just as valid as any the experts are putting
out and that's what I use as a rule of thumb.
Brian
Edmonton, Alberta, Canada
Randy F. Milak
>
> Jim,
>
> You've got 3 paragraphs which state "Nobody knows and we have no valid
> data. So we'll guess because people want a number" That's not even bad
> science, it's pure bullshit.
*snicker*
I wonder? Do divers whom dive at altitude, wait 24 hours before
exiting the water? Small miracles I guess?
Randy F. Milak
~More Metric Equivalents: 1 kilogram of falling figs = 1 Fig Newton!~
A boy called Sue
It is at times like these that my lack of knowledge begins to scare me :)
Best,
Vandit
bullshark (bull...@my-dejanews.com) wrote:
:
: The no fly problem is no different from ordinary decompression.
:
Charlie Hammond
> I wonder? Do divers whom dive at altitude, wait 24 hours before
>exiting the water? Small miracles I guess?
Not usually -- but they must either make shorter and/or shallower dives,
or accept higher risks of DCS. Some dive computers automatically
compensate for this. Some dive table systems provide either different
tables for diving at altitude or methods for adapting sea level tables
for altitude diving.
It is generally accepted that diving at altitudes up to 1000 ft does not
introduce significant added risk. Diving at altitudes over 1000 ft
requires understanding and allowing for the differences..
Brian Nadwidny
> It is generally accepted that diving at altitudes up to 1000 ft does not
> introduce significant added risk. Diving at altitudes over 1000 ft
> requires understanding and allowing for the differences..
Generally accepted does not mean it has any factual basis.
Brian
Edmonton, Alberta, Canada
Charlie Hammond
Brian Nadwidny <BNad...@excite.com> writes:
I certainly agree, Brian.
It also does not mean that it does NOT have any factual basis.
A prudent person will regard going outside the range of what is
"generally accepted" as unknown and at least potentially dangerous.
So, when my a** is on the line, you can probably figure what I will do.
Others can choose their own course.
roger xalinx
"Charlie Hammond" <hammond@not@peek.ppb.cpqcorp.net> wrote in message
news:798j7.939$bB1....@news.cpqcorp.net...
> In article <3B8C1662...@yahoo.com>,
> "Randy F. Milak" <rfm...@yahoo.com> writes:
>
> > I wonder? Do divers whom dive at altitude, wait 24 hours before
> >exiting the water? Small miracles I guess?
I realize Randy is joking, but I suspect one could dive a 80' dive at an
altitude so high that coming up shallow or leaving the water would result in
DCS no matter how long your stop or how slow your ascent, at least without
suffering dehydration and hallucinatory dementia.
> Not usually -- but they must either make shorter and/or shallower dives,
> or accept higher risks of DCS. Some dive computers automatically
> compensate for this. Some dive table systems provide either different
> tables for diving at altitude or methods for adapting sea level tables
> for altitude diving.
If you have become acclimated, spent 48 hours at the altitude you will be
diving, the dives will be niether shorter nor shallower. If you have
recently (within 48 hours, some use 24 hours) arrived from a lower altitude
then your dives will be both shorter and shallower in order to accomodate
the assumed equivilent saturation.
But in either case, because you exit the water to less than 1 ATA, your
ascent should be much slower and your safety stop longer. If doing deco
dives you must also factor for the more numerable deco stops than would be
required at sea level. The shallow deco stops are almost always broken up
into 2 stops..one deeper and one even shallower. A 10 foot stop might become
a 14 foot stop AND a 6 foot stop.
All that would be for naught though, if the diver doesn't weight
sufficiently higher than they do at sea level to accomodate the greater
bubble expanse, if they were neoprene :^)
> It is generally accepted that diving at altitudes up to 1000 ft does not
> introduce significant added risk. Diving at altitudes over 1000 ft
> requires understanding and allowing for the differences..
I think disregarding a 1,000 foot change when diving within a day is not
prudent. The physical variable between divers is enough for one to at least
think about a 1 group change just for margin.
I live at 5,000 feet and during the summer make 20+/- dives at 10,000 feet.
I trust my computer at sea level......I do the calcs and use my tables at
altitude. I have seen 3 cases of DCS in diving 20 years of diving sea level.
I lost count (likely more than 40) the number of cases I have seen after a
concurrent 10 years of diving high altitude.
Either the divers at altitude aren't as careful as those at sea level or the
tables and computers aren't quite up to snuff yet.
Glawackus
>Of course the resorts love the extended
>waits because it gets folks to stay an extra day and spend more money on
>chi-chi's and trinkets.
Wrong. The dive ops hate it because people stop diving a day early.
Steve
The above can be construed as personal opinion in the absence of a reasonable
belief that it was intended as a statement of fact. Or it might just be to
generate discussion.
Glawackus
>if you're at 30,000 and there is a sudden
>pressure loss, you're going to be in DEEP trouble if you've violated
>no-fly. Most passengers in that situation DO fizz to a degree, but it
>is mostly subclinical and the O2 provided controls the situation.
If there's a sudden loss of cabin pressure regardless of altitude you can
expect to lose altitude in an extreme hurry, effectively recompressing you
within a minute or so. That probably means that the the sudden drop in pressure
doesn't put you in such deep trouble. If the loss of pressure isn't immediately
followed by a deliberate loss of altitude it probably means that everybody on
the plane is in deep trouble and being bent is not a long term concern.
At 30,000 feet the pressure is about 40% of sea level and would probably
result in more than subclinical DCS (and it should be noted that 40,000 feet
isn't an uncommon altitude). I'd hazard a guess that the O2 provided doesn't
do much to control any immediate DCS problem without a concurrent increase in
pressure.
Glawackus
>Forgive me, but I really enjoy it when someone nitpicks and gets it wrong,
>as you just did. It is not the pressure group that matters, its the level
>of nitrogen remaining in the most saturated body tissue that matters.
I guess this would be a nitpick to the 3rd. What does "most saturated tissue"
mean? I agree with everything after that, but think your phrasing is
misleading. Is a fast tissue at 93% (about 4 half-lives) more saturated than
a slow tissue at 87% (about 3 half-lives)? It seems to me that it's the less
saturated tissue that will take the longest of those two to offgas.
chilly
apples, oranges? ;^)
Somebody is making money.
Glawackus <glaw...@aol.compulsion> wrote in message
news:20010906005852...@mb-mv.aol.com...
Glawackus
>If you are offgassing normally after a dive, your fast compartments and
>medium
>compartments are coming into equilibrium with the atmosphere reasonably soon,
>but your slowest compartments offgas so slowly some may take weeks to achieve
>equilibrium. However, even under the pressure differential of 8000', the slow
>compartments won't speed up much.
>The danger is the fast and medium compartments that are coming into
>equilibrium,
>when suddenly you subject them to 8000'. They then start to fizz again, just
>like a coke can. Voila, DCS. That's why you need 12 to 24 hours, to make sure
>the more "volatile" compartments are stable..
Are you suggesting that N2 is more likely to remain in solution in slow tissues
than in fast tissues even under similar pressure differentials, even if the
slow tissues are at a higher level of saturation?
Eric
> Shold I play it safe and not dive the morning of my flight? Maybe I sould
> pass on the last morning of dives and see some of the other sights on the
> island.
>
If I have questions or issues about it I abort about 99% of the time.
I may miss a dive or two, but at least I know I'm being safe and not putting
myself at unnecessary risk.
eric
SSI AOW