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ozorowsky
April 24th, 2011, 01:53 PM
Hi everyone,

I am curious here. I went diving yesterday and think I got super lucky I followed my dive computer.

First dive I was down 47 ft for 59 minutes. Simple right leaves me in pressure group C.

Then, my fiance and I got out of the water, went to lunch for a bit, had a surface interval of 3 hours 20 minutes.

Then we went out to a different dive site. This time visibility was absolutely terrible and I went a little deeper than expected. We went down 78 ft (at that depth for about 12 mins) and when I noticed how deep we were we went up to 35 ft for a bit hung out there, did a 10 minute deco stop at 15 ft then ended our dive. According to my dive computer total bottom time on this dive was 68 minutes.

I am doing my Dive log and am very confused. According to this we should be dead. Here is what I am factoring please tell me where my calculations are wrong.

1) 47 ft Down for 59 minutes puts us at pressure group S
2) Surface interval of 3 hours 20 minutes puts me at pressure group A.
3) Assuming our residual nitrogen time at 80 ft in pressure group A is 4 minutes, and we then went down to 80 ft for tbt of (68 + 4) 72 minutes, I don't understand.

The RDP says 80 feet for 30 mins is pressure group R with mandatory 5 minute decompression stop. I more than doubled that according to above.

Can someone explain to me why we are fine and what is wrong with my calculation? I watched my computer nitrogen calculator cautiosly when we were hanging out at 15/20 feet.

flots am
April 24th, 2011, 02:01 PM
A comparison between tables and a computer is invalid for multilevel diving. Table data is based on a square profile, which you didn't dive.

Computers measure actual depth and time and will allocate an appropriate amount of nitrogen for time spent at various depths.

A dive that's perfectly fine on a computer could easily be way off the end on the dive tables.

flots.

willembad
April 24th, 2011, 02:02 PM
You wrote that your computer said total bottom time for dive 2 was 68 min. What it really told you was TRT (total run time) of the dive was 68 min. You yourself said you left 78 ft after 12 minutes. No computer will ever match up with tables since tables assume square profiles and computers use real time info to calculate NDL. That's one of the reasons divers choose to use computers.

You mention a deco stop. Was that a called for obligation by your computer or you chose to stop yourself?

Willem

wedivebc
April 24th, 2011, 02:09 PM
Your mistake was adding the bottom time from the first dive. The TBT = the Actual bottom time of the second dive + the residual nitrogen time (RNT) you obtained from the table after the surface interval.
Calculating dives from tables is almost becoming a lost art. I encourage you to continue thinking along these lines, even if you eventually become a computer diver as it will make you a more aware diver.

Bubble_Boy
April 24th, 2011, 02:21 PM
Hi everyone,
According to my dive computer total bottom time on this dive was 68 minutes.


The OP says the computer gave him that bottom time for the second dive only....
Did you hang out for 30 min at the surface before going down? Next time just keep an eye on your computer.... it shouldn't start counting before 5 feet or so but maybe something is wrong with the depth meter.... unlikely, but maybe....

TSandM
April 24th, 2011, 02:25 PM
You have just been introduced to the basic issue with dive tables. They are designed for square profile dives, where you go down to a wreck or reef and stay at the same depth for the entire bottom time. When you don't do that, the tables don't really model the nitrogen absorption you had, and the more you multi-level a dive, the worse that discrepancy gets.

When I started diving, I was doing a lot of shore dives with max depths in the 60 to 70 foot range, and the dives were often an hour long. I couldn't figure out how to log them at all, because they all came out serious mandatory deco dives . . . but the profiles were big "U" or "V" shapes, where we swam downhill for a while, and then uphill for a while, and those dives are just about the worst to try to plug into tables.

You can use a multi-level table, like the PADI Wheel or e-RDPML, to try to get a better sense for what you are actually doing, or you can use your computer, which is doing what it is designed to do.

boulderjohn
April 24th, 2011, 02:34 PM
Your second dive was a multilevel dive. It is as if you did a 78 foot dive followed by a 35 foot dive followed by a 15 foot dive, each with no surface interval. Think of it that way and you will see why you are OK.

As mentioned earlier, tables assume a square profile. In contrast, a computer constantly recalculates your dive based on actual depth. The next time you are diving a similar profile to your second dive, look at what your computer is telling you in terms of how much no decompression time you have left when you are at your deepest depth. As you ascend, watch what happens to those minutes. Look especially at what happens when you get in the 35 foot range.

Hoomi
April 24th, 2011, 06:05 PM
Additionally, both tables and computers default to a conservative calculation. Basically, they work on the assumption of what is safe for most people, and then factor in a bit extra for safety.

I.E., if most people's nitrogen absorption is fine at Y depth for X minutes, then the computer or table will reflect that data minus a percentage to accommodate those who aren't quite so tolerant. At the other end of the scale, though, are those who are more tolerant, who would be just as fine at Y+10 depth at X+10 minutes, for example. The safety margin also accommodates variations that will occur in the same person under different conditions.

Both tables and computers are conservative guidelines that, if followed, should keep a diver safe. However, neither is so definitive and cut-close that, if you accidentally go beyond the limits stated, you're definitely going to die. It's much like the stopping distance ratings for automobiles, and the guidelines for distance between your car and the car in front of you. Your car might be able to stop in much less distance than the average, but for a general guideline, the average is good to keep in mind. Even if you're following too close, you may still be able to stop in time, but the advice of safety experts, just as with the tables/computers, is, "why chance it?"

ozorowsky
April 25th, 2011, 10:23 AM
Thank you all for your prompt replies. I think BoulderJohn explained it perfectly.

So as long as I follow my dive computer I should be safe right?

and to willembad: Yes the computer recommended a 5 minute deco stop. I did 10 to be safe.

Thank you all again for your reassurance.

TSandM
April 25th, 2011, 10:40 AM
Your dive computer will most likely keep you safe, although no decompression program works flawlessly for all people. It is best not to push no-deco limits, and "riding the computer" (ascending just fast enough to keep the gauge from clicking down to zero) is a good way to see if it doesn't work for YOU. It is also a very good thing to have some idea of what the computer OUGHT to be telling you, because no electronic gadget is without the possibility of malfunction -- if your computer is feeding you nonsense, you ought to be able to recognize that.

ianr33
April 25th, 2011, 10:55 AM
Thank you all for your prompt replies. I think BoulderJohn explained it perfectly.

So as long as I follow my dive computer I should be safe right?

and to willembad: Yes the computer recommended a 5 minute deco stop. I did 10 to be safe.

Thank you all again for your reassurance.

What was your plan in the event you ran out of air during your deco stop?

(And yes, I'm just playing Devils Advocate to point out there is more to diving than just blindly following a computer)

NetDoc
April 25th, 2011, 10:56 AM
Your second dive was a multilevel dive. Your first dive was probably a multilevel one as well. PDCs (Personal Dive Computers) do a wonderful job of accurately tracking our depth and time in a way a human can not hope to keep up. As was previously pointed out, using a table for a multilevel dive is like using a hammer to set a wood screw. You can do it, but its the wrong tool for the job!

That being said, with the longer dive times, please consider increasing your safety stop from 3 to five minutes as well as doing a two minute "half stop" when your depth is greater than 60 fsw.

fnfalman
April 25th, 2011, 11:10 AM
Thank you all for your prompt replies. I think BoulderJohn explained it perfectly.

So as long as I follow my dive computer I should be safe right?

and to willembad: Yes the computer recommended a 5 minute deco stop. I did 10 to be safe.

Thank you all again for your reassurance.

Others have already addressed the dive computer versus table issue.

Let's talk about something else. YOU DID NOT do a "Deco" stop. Yuo did a "Safety" stop. Big difference.

NetDoc
April 25th, 2011, 11:26 AM
Let's talk about something else. YOU DID NOT do a "Deco" stop. Yuo did a "Safety" stop. Big difference. If it was suggesting five minutes, then it probably WAS a obligatory deco stop. As for a safety stop NOT being a deco stop, there are a number of us who would disagree with you. All stops involve decompression of some sort. Some are optional and some are not, but they are still deco stops.

ozorowsky
April 25th, 2011, 11:27 AM
Others have already addressed the dive computer versus table issue.

Let's talk about something else. YOU DID NOT do a "Deco" stop. Yuo did a "Safety" stop. Big difference.

Point taken thank you for clarifying.

and to ianr33: during my "safety stop" I still had 1800psi. Also there were 2 dive buddies with me, and 3 classes going on with about 5 students each.

That was part of the reason I picked this dive spot "controlled environment" without an instructor to get my feet wet and get more and more comfortable with diving.

Thank you all for sharing your experience, and not slamming me for potentially making a mistake.

One thing I am trying to gain a better grasp on is the safety stop. I know per the dive computer when to make one and per the table approximately when to make one, but what if you mess up? Will you go to the surface feeling sick? Go into convulsions, die instantly, is there any physical forewarning?

Thank you.

NetDoc
April 25th, 2011, 11:39 AM
One thing I am trying to gain a better grasp on is the safety stop. I know per the dive computer when to make one and per the table approximately when to make one, but what if you mess up? Will you go to the surface feeling sick? Go into convulsions, die instantly, is there any physical forewarning?

Thank you. Probably none of those things.

There are two types of stops: obligated and optional (Safety).

Violating either of those will not necessarily give you DCS. However, doing them does not completely keep you safe from them either. There are many factors that affect DCS including ascent rate, breathing rate, temperature, hydration, sickness, elevation and so on. Its up to you to dive in a reasonable manner and mitigate those risk factors by decreasing your dive time (conservancy) or not diving until things are normal.

If you miss an optional stop, there is nothing to be done. You can continue to dive normally.

If you miss an obligatory stop, then you should stay out of the water for 24-48 hours and monitor yourself for symptoms of DCS. Call DAN (http://www.diversalertnetwork.org/)and get to a hospital/hyperbaric chamber if you are suspicious.

Signs and Symptoms of DCS (http://en.wikipedia.org/wiki/Decompression_sickness#Signs_and_symptoms)

rhwestfall
April 25th, 2011, 12:35 PM
I applaud you for asking why, but am disturbed as to the apparent lack of education by a person with a c-card. What is in dive training/certification these days?:confused:

boulderjohn
April 25th, 2011, 12:40 PM
I applaud you for asking why, but am disturbed as to the apparent lack of education by a person with a c-card. What is in dive training/certification these days?:confused:

I would say that in most cases the problem is where it always was: teaching tables with square profiles only to the OW student. Multi-level and computer diving is not usually part of OW training. This is changing.

DevonDiver
April 25th, 2011, 12:49 PM
YOU DID NOT do a "Deco" stop. Yuo did a "Safety" stop. Big difference.

5 minutes on a PADI table is an emergency deco stop. It is mandatory, in the event of exceeding an NDL. Full rules for emergency deco is written in the special rules on the table.

Likewise, a 5 minute STOP on a computer is also highly likely to be deco. I don't know of any computer that gives more than 3 minutes as a safety stop. If it was deco on the computer, then it would also indicate a ceiling, that you could not ascend beyond for the given stop time.

fnfalman
April 25th, 2011, 12:50 PM
Safety Stops are optional. Deco Stops are not.

You may or may not get a DCS hit by skipping a Safety Stop. I'd like to see somebody does a 45-minutes dive at 150-ft and skip a Deco Stop while not getting the bend.

The OP's second dive profile was nowhere close to having to do a deco. Maybe the computer was generous in the 5-minutes safety stop.

I suppose we need to clarify a bit about deco stops. If a rec diver were to push the No Decompression Limit for a little bit, then the computer will recommend a "deco" stop that either longer than the typical safety stop, or maybe a "deco" stop somewhere deeper and then a longer safety stop. This is a lot different than technical/commercial divers doing some serious deep bottom time and have to use the hyperbaric chamber or have to hang for an extended period of time while sucking on high-O2 mix while doing a true obligatory deco stop. Skip this stop and you'll be in a world of hurt for sure and not just maybe.

Decompression diving (even if it were just a little bit over the NDL) should not be executed until the diver knows what he or she doing. Trust the computer to do a "deco" stop for you is a recipe looking for trouble.

fnfalman
April 25th, 2011, 12:54 PM
5 minutes on a PADI table is an emergency deco stop. It is mandatory, in the event of exceeding an NDL. Full rules for emergency deco is written in the special rules on the table.

Likewise, a 5 minute STOP on a computer is also highly likely to be deco. I don't know of any computer that gives more than 3 minutes as a safety stop. If it was deco on the computer, then it would also indicate a ceiling, that you could not ascend beyond for the given stop time.


and to ianr33: during my "safety stop" I still had 1800psi.


Hi everyone,

Then, my fiance and I got out of the water, went to lunch for a bit, had a surface interval of 3 hours 20 minutes.

Then we went out to a different dive site. This time visibility was absolutely terrible and I went a little deeper than expected. We went down 78 ft (at that depth for about 12 mins) and when I noticed how deep we were we went up to 35 ft for a bit hung out there, did a 10 minute deco stop at 15 ft then ended our dive. According to my dive computer total bottom time on this dive was 68 minutes.

Please enlighten me as how the OP would have been under long enough to do a "deco" stop, be it a 5-minutes emergency deco stop or otherwise?

RTee
April 25th, 2011, 02:38 PM
Please enlighten me as how the OP would have been under long enough to do a "deco" stop, be it a 5-minutes emergency deco stop or otherwise?

Some computers will add up time to your safety stop if you fail to come up at the recommended ascent rate...ie coming up faster than the 30 ft/min which might have been the case here especially when he noticed they were much deeper than anticipated and the vis was fairly poor (based on his initial remark)

NetDoc
April 25th, 2011, 03:02 PM
I applaud you for asking why, but am disturbed as to the apparent lack of education by a person with a c-card. What is in dive training/certification these days?:confused: Unfortunately, many classes (past and present) never train diving with a PDC. They might say, "Read your manual" and that's about it.

Today's divers are increasingly using this capable and versatile tool to plan and execute their dives. Their use and how to avoid their abuse should be an integral part of every class. Many see this as "dumbing" down the class, I see it as showing due diligence in teaching them how to use a great tool.

NetDoc
April 25th, 2011, 03:05 PM
Please enlighten me as how the OP would have been under long enough to do a "deco" stop, be it a 5-minutes emergency deco stop or otherwise? The table didn't give him a deco stop: his PDC did. Depending on the personal conservancy set by the user, it's certainly not unthinkable for him to be in deco.

Why not take him at his word?

Hoomi
April 25th, 2011, 03:06 PM
If we start really dumbing down the classes, will they serve Brawndo for the refreshment.

Brawndo. It's what Divers crave!

:D

ozorowsky
April 25th, 2011, 03:27 PM
Unfortunately, many classes (past and present) never train diving with a PDC. They might say, "Read your manual" and that's about it.

Today's divers are increasingly using this capable and versatile tool to plan and execute their dives. Their use and how to avoid their abuse should be an integral part of every class. Many see this as "dumbing" down the class, I see it as showing due diligence in teaching them how to use a great tool.

I agree with you NetDoc; I bought all my gear from my training shop, and they STILL wanted me to use the "training gear." Don't get me wrong I enjoyed my training but I had to persuade them to let me use my training gear. My reasoning was if I'm paying for training I would like to learn on gear I will actually be using (My own).

And yes, NetDoc; my PDC said to do stop at 15 feet for 5 minutes. My dive (last dive) went like this:

1) Dive down to 15 feet sit for a minute and equalize
2) Dive down to 35 feet (low visibility but wanting to explore. They had a rope to guide you down so I just pulled along the rope and followed for a bit. I wanted to go to 60/70 feet and see how I felt because I am going to do advanced open water soon and I wanted to see how I took to 60 or so feet.)
3) My mask was fogged so I had a hard time seeing my dive computer. So I cleared etc and looked at computer again shining my flashlight on it, and saw I was at 78 feet. Felt fine.
4) ascended along the line to about 30 ft. I saw my computer said to do a deco stop, slowly ascended to 20 ft, deco counter started, said to be at 15 ft, so I went up to 15 ft hung out there for 10 minutes.
5) I dove around between 15 and 30 ft after deco stop for a bit then hung out at 15 ft for 10 mins then ended my dive when I was down to about 400psi

fnfalman
April 25th, 2011, 03:43 PM
IAnd yes, NetDoc; my PDC said to do stop at 15 feet for 5 minutes.


I'm curious but what brand and model is that dive computer?

Your second dive profile was most conservative. I can't understand why the computer would prescribe a 5-minutes stop unless that's what the computer was automatically programmed to do - 5-minutes stop versus 3-minutes stop.

DBailey
April 25th, 2011, 03:44 PM
So as long as I follow my dive computer I should be safe right?

I would change this a bit:

Use your computer to help plan the dive.
Conduct your dive following the plan you developed.
Use the computer to help you follow that plan.

merxlin
April 25th, 2011, 03:56 PM
I'm curious but what brand and model is that dive computer?

Your second dive profile was most conservative. I can't understand why the computer would prescribe a 5-minutes stop unless that's what the computer was automatically programmed to do - 5-minutes stop versus 3-minutes stop.

My guess, since he really did not have a 68 minute second dive, was that his computer did not reset during the surface interval, or somehow was activated before he hit the water.

fnfalman
April 25th, 2011, 04:02 PM
The table didn't give him a deco stop: his PDC did. Depending on the personal conservancy set by the user, it's certainly not unthinkable for him to be in deco.

Exactly my point. Why did the PDC do this? Nothing in his said second dive profile warrants a true deco stop.


Why not take him at his word?

No offense, but maybe he was a newbie and still trying to feel his way around? Maybe he doesn't know the difference between a deco stop and a safety stop? Maybe he need to figure out why his computer gave him a 5-minutes deco stop? Maybe RTee was right about the OP ascended too quickly and got penalized.

Wouldn't this be the best time for him to find out why the computer gave him a 5-minutes stop? Computers just don't go into deco for nothing.

And as DBaily had eloquently stated, use your computer to aid in your dive planning and dive monitoring. Don't trust the damn thing to do the thinking for you. It's only a machine.

Bubbletrubble
April 25th, 2011, 04:02 PM
I'm curious but what brand and model is that dive computer?

Your second dive profile was most conservative. I can't understand why the computer would prescribe a 5-minutes stop unless that's what the computer was automatically programmed to do - 5-minutes stop versus 3-minutes stop.
RTee initially brought this up. I'll expand on it a little...

Suunto dive computers may convert the "recommended" shallow safety stop from 3 minutes to a "mandatory" safety stop of 3 minutes or longer (5 min.?) if the ascent rate exceeded the Suunto-specified "maximum" rate (39 ft/min) instantaneously or 33 ft/min "continuously." The duration of the shallow safety stop is determined by the severity of the ascent rate violation.

It's certainly possible that the OP is confusing "stop" terminology: "recommended" safety stop vs. "mandatory" safety stop vs. "deco" stop. The most likely explanation of what happened is that the OP accidentally caused an ascent rate violation which resulted in a 5 min. "mandatory" safety stop. This was caused by suboptimal buoyancy control or raising the computer through the water column too quickly to read it. With some computers, it's also possible to cause an ascent rate violation simply by moving a wrist-mounted computer too quickly, particularly if it's attached to an arm/wrist that's being used to lift and exhaust gas from the BCD corrugated hose.

When it comes to operating a dive computer, it's always advisable to read the manual before using it.

Hope this helps...

ben_wilson3301
April 25th, 2011, 04:03 PM
Safety stops are just that, for safety. Deco stops are mandatory, but both the tables and your computer are giving us NO Decompression limits. Any stop would then be just a safety stop unless you go over your limit and are no longer within your NO Decompression limits. In which case your computer would freak out, put you into deco and not let you dive for 24hrs in most cases.

ianr33
April 25th, 2011, 04:05 PM
And yes, NetDoc; my PDC said to do stop at 15 feet for 5 minutes. My dive (last dive) went like this:



I very much doubt that is a DECO stop.

Every computer I have ever used has deco stops at 10 foot levels. i.e 10,20.30 etc.
Also,if it was a deco stop then when it first appears it will be for one minute.Not 5.

To the OP, what type of computer do you use?

ozorowsky
April 25th, 2011, 04:25 PM
I use the aeris elite T3 computer.

I pulled the log software last night and yes there was one point when it said my ascent was 39ft/min vs 30ft/min

Bubbletrubble
April 25th, 2011, 04:27 PM
I use the aeris elite T3 computer.

I pulled the log software last night and yes there was one point when it said my ascent was 39ft/min vs 30ft/min
Please let us know what your computer instruction manual says with regard to "recommended" safety stop vs. "mandatory" safety stop vs. "deco" stop. The manual should talk about how it deals with ascent rate violations, too.

Also, it might be helpful to let us know what personal adjustment setting you used to designate the level of conservatism for your dives in question.

ozorowsky
April 25th, 2011, 04:33 PM
Please let us know what your computer instruction manual says with regard to "recommended" safety stop vs. "mandatory" safety stop vs. "deco" stop.

Also, it might be helpful to let us know what personal adjustment setting you used to designate the level of conservatism for your dives in question.

The aeris manual is very confusing. You can set the stop depths; but by default it is 15 ft.

As far as personal adj setting; I don't really have one I have concervative on or off; conservative is on

fnfalman
April 25th, 2011, 04:36 PM
I use the aeris elite T3 computer.

I pulled the log software last night and yes there was one point when it said my ascent was 39ft/min vs 30ft/min

I have the same computer. It had never given me anything more than 3-minutes safety stops and I KNOW that I've gone faster than 39-ft/min a couple of times (CESA practice).

The safety stop is set at 15-ft but usually kicks in at around 20-ft. The only "conservative" setting is if one were to manually set the altitude level higher than the actual altitude.

Thalassamania
April 25th, 2011, 04:41 PM
Probably none of those things.

There are two types of stops: obligated and optional (Safety).

Violating either of those will not necessarily give you DCS. However, doing them does not completely keep you safe from them either. There are many factors that affect DCS including ascent rate, breathing rate, temperature, hydration, sickness, elevation and so on. Its up to you to dive in a reasonable manner and mitigate those risk factors by decreasing your dive time (conservancy) or not diving until things are normal.

If you miss an optional stop, there is nothing to be done. You can continue to dive normally.

If you miss an obligatory stop, then you should stay out of the water for 24-48 hours and monitor yourself for symptoms of DCS. Call DAN (http://www.diversalertnetwork.org/)and get to a hospital/hyperbaric chamber if you are suspicious.

Signs and Symptoms of DCS (http://en.wikipedia.org/wiki/Decompression_sickness#Signs_and_symptoms)
Let's face it, walking up a hill requires "decompression." The accepted usage of "decompression stop" and "safety stop" has to do with the prediction of a model that you will bend as a result of a direct ascent to the surface at the approved rate of ascent in the former situation and that you will not in the latter case.

Unfortunately, many classes (past and present) never train diving with a PDC. They might say, "Read your manual" and that's about it.

Today's divers are increasingly using this capable and versatile tool to plan and execute their dives. Their use and how to avoid their abuse should be an integral part of every class. Many see this as "dumbing" down the class, I see it as showing due diligence in teaching them how to use a great tool.
I agree with you completely. Unfortunately many instructors are using dive computers as a way to minimize (and even eliminate) a subject that takes them too long to get across.

I have no problem with computer only courses (that when well done equip the new diver with a way to use a valuable tool, but leave them unprepared for when something goes wrong with their computer), but such courses don't really save any teaching time.

fnfalman
April 25th, 2011, 04:45 PM
I just re-read the Elite T3's manual. There are only two stops: safety and deco. Safety stops are optional and you won't be penalized for it by the computer. Deco stops are mandatory and if you were to violate the deco stop (i.e. skip it or not following the depth/timer or both), the computer will lock out for 24-hrs before it will work again. There are no mandatory safety stop versus optional safety stops.

NetDoc
April 25th, 2011, 04:47 PM
If we start really dumbing down the classes, will they serve Brawndo for the refreshment.

Brawndo. It's what Divers crave!

:DIts got electrolytes! :rofl3: The movie is a study of subtlety.

boulderjohn
April 25th, 2011, 04:55 PM
I have no problem with computer only courses (that when well done equip the new diver with a way to use a valuable tool, but leave them unprepared for when something goes wrong with their computer), but such courses don't really save any teaching time.

I have never heard of anyone advocating such teaching for the purpose of saving time.

No matter what, one is required to teach at least the basics of decompression theory. That is the same no matter what. In addition, one must teach tables (or the electronic version), computers, or both.

I don't know anything about the SDI program, and I have never taught the computer version of the PADI course, which is an option for the student. I have, however, reviewed the outline of the PADI computer OW course, and it is extremely thorough. The student will come out knowing a lot more than what to do when the computer fails.

ianr33
April 25th, 2011, 04:55 PM
Today's divers are increasingly using this capable and versatile tool to plan and execute their dives. Their use and how to avoid their abuse should be an integral part of every class. Many see this as "dumbing" down the class, I see it as showing due diligence in teaching them how to use a great tool.

I think the training agencies are missing an opportunity when it comes to computers.

How long will it be until I am not allowed to dive without proof of
"computer certification" ?

Oh you may laugh, but its already happening with drysuits and solo diving and sidemount.

Bubbletrubble
April 25th, 2011, 05:05 PM
I just re-read the Elite T3's manual. There are only two stops: safety and deco. Safety stops are optional and you won't be penalized for it by the computer. Deco stops are mandatory and if you were to violate the deco stop (i.e. skip it or not following the depth/timer or both), the computer will lock out for 24-hrs before it will work again. There are no mandatory safety stop versus optional safety stops.
Does the manual set forth ascent rate guidelines and discuss the consequences of exceeding recommended ascent rates?

NetDoc
April 25th, 2011, 05:06 PM
The T-3 is one of my favorite PDCs and here's the rub...

The shallow stop (it calls it this) can be set for 3 or 5 minutes.

There are also settings for adding a deep stop and at what depth you want to spend your shallow stop. Indeed, it can show a deco stop at 15 ft and not 10.
Let's face it, walking up a hill requires "decompression." The accepted usage of "decompression stop" and "safety stop" has to do with the prediction of a model that you will bend as a result of a direct ascent to the surface at the approved rate of ascent in the former situation and that you will not in the latter case. That's "old school" thought. As I said, many of us view all dives as decompression dives and all stops as decompression stops. Some are optional (safety) and some are obligatory (mandatory). Telling him that he is wrong about this is to show a complete misunderstanding or ignorance of how some teach this concept.
I agree with you completely. Unfortunately many instructors are using dive computers as a way to minimize (and even eliminate) a subject that takes them too long to get across. I haven't met them. You must be exposed to more shops than I am here in Key Largo.
I have no problem with computer only courses (that when well done equip the new diver with a way to use a valuable tool, but leave them unprepared for when something goes wrong with their computer), but such courses don't really save any teaching time. Unfortunately, the clarion cry that using PDCs dumbs down a course has severed communications on several levels. What was possible if the PDC hadn't been the butt of agency's blind phobias is now almost past. There are a number of us who feel no need to teach tables and spend the time discussing the ins and outs of diving with a PDC.

Blackwood
April 25th, 2011, 05:14 PM
You may or may not get a DCS hit by skipping a Safety Stop. I'd like to see somebody does a 45-minutes dive at 150-ft and skip a Deco Stop while not getting the bend.
.

Which one?

I'd be willing to bet I could blow off my 40' stop on such a dive without substantially increasing the statistical likelihood of developing DCS.

Care to join me?


A bit hyperbolic, yes, but really goes to the meat of a poorly understood concept.

Decompression methodology is all theory-based. The only guarantee you won't get bent diving is by not diving.

So called safety stops were originally used because it was observed that divers were vastly exceeding modeled ascent rates. They can be used to hedge your bets. So can conservatism in models. So can holding margin against ascent rates. How does it all work? By doing more in-water-deco.

A safety stop is a stop during which you decompress. Changing the name based on whether or not they are mandatory seems silly to me, especially considering that "mandatory" is a moving target.

Thalassamania
April 25th, 2011, 05:39 PM
As I have often said, what needs to be taught is decompression theory and at least one model. Tables are just snapshots of a model and computers are just cartoons, both are potentially effective ways of interfacing with the model and each has its place. I've been saying that since well before the Dive Computer Workshop in 1989 that moved dive computers from vodoo that all the agencies opposed to acceptable devices in the course of three days.

Your say that the idea of differentiation of "stops" into decompression and safety is somehow "old school" yet all you do is change the name to "optional (safety)" and "obligatory (mandatory)." That clarifies nothing, it just introduces new terminology that creates further confusion.

The real point is, as I mentioned, that all reductions in pressure (remember walking up a hill?) result in decompression and the accepted usage of "decompression stop" is: "the prediction of a model that you will bend as a result of a direct ascent to the surface at the approved rate," while "safety stop" are made to off-gas when that is not the case.

How that shows "a complete misunderstanding or ignorance of how some teach this concept." is a topic that I'd like you to explore further.


Which one?

I'd be willing to bet I could blow off my 40' stop on such a dive without substantially increasing the statistical likelihood of developing DCS.

Care to join me?


A bit hyperbolic, yes, but really goes to the meat of a poorly understood concept.

Decompression methodology is all theory-based. The only guarantee you won't get bent diving is by not diving.

So called safety stops were originally used because it was observed that divers were vastly exceeding modeled ascent rates. They can be used to hedge your bets. So can conservatism in models. So can holding margin against ascent rates. How does it all work? By doing more in-water-deco.

A safety stop is a stop during which you decompress. Changing the name based on whether or not they are mandatory seems silly to me, especially considering that "mandatory" is a moving target.Exactly.

NetDoc
April 25th, 2011, 05:48 PM
Your say that the idea of differentiation of "stops" into decompression and safety is somehow "old school" yet all you do is change the name to "optional (safety)" and "obligatory (mandatory)." That clarifies nothing, it just introduces new terminology that creates further confusion.


:gans:

"Safety" is what muddies the picture. "Its called a safety stop, but you are still safe if you omit it" is the height of waffle speak. You might find "Waffle Speak" to be acceptable, but I don't. They are all stops and decompression will occur, ergo they are all deco stops. Some are optional, while some are mandatory. I shouldn't have to define "optional" or "mandatory" for the student as you would have to define "safety" that you don't need to do to be safe. THAT'S what's confusing to a new student.

Calling one "safe" and the other not kind of implies that I should skip the other so I will be safe! Shenanigans. It was a poor choice of words by the old school. The new way is much simpler and intuitive. I'm surprised that you can't see that.

Bubbletrubble
April 25th, 2011, 05:53 PM
Guys, must we have a semantic/ideologic argument in the Basic Scuba Discussions forum?

Scott L
April 25th, 2011, 05:53 PM
Oh, boy!

:popcorn:

Thalassamania
April 25th, 2011, 05:55 PM
I dislike the use of the "safety" stop term also ... but from the opposite perspective.

Safety means "without risk" and by making a "safety stop" you do not eliminate all risk, you just lesson it. I argued hard against that term, and I lost. But that was years ago and that has become the accepted terminology so, for clarity's sake I begrudging adopted it.

I agree, it is a semantic argument, but unfortunately it is one that confuses many new divers. I hope a short exploration of the issues will help with some of that confusion.

DwayneJ
April 25th, 2011, 05:58 PM
I would suggest spending some time with an instructor and going over dive planning and execution.

1. As a new diver, you need to understand how your computer is programmed (15ft vs 20ft) safety stops.

2. Your first dive of a multi dive day should be the deepest dive, not start shallow and dive deeper later.

3. Ascent should be 30ft/min or less... and most importantly this also includes the last 15ft to the surface... which should take 30 secs or more.

4. Be very aware of depth and the maximum you have planned for the dive. At 70'+ you really should have more gas for redundancy for you and your buddy.

5. Makes no sense (and bad for you) to head to the surface to complete a safety stop and/or deco stop then go back down again.

6. Dont do deco diving by accident or by design until you have had appropriate training in gas management and dive planning.

A well executed NDL dive may see you with 500lbs of gas at the surface or 1500lbs of gas at the surface - Do not bounce dive just to use up gas... because its bad for you.



Dwayne

Thalassamania
April 25th, 2011, 06:15 PM
A few thoughts:

I would suggest spending some time with an instructor and going over dive planning and execution.

1. As a new diver, you need to understand how your computer is programmed (15ft vs 20ft) safety stops.

2. Your first dive of a multi dive day should be the deepest dive, not start shallow and dive deeper later.
As I understand it your computer may penalize you for doing so but it does not appear (despite our conventional wisdom) that mother nature is perfectly happy for you to make dives in whatever order you wish. It is not physiology that has problems with that, it is the models.


3. Ascent should be 30ft/min or less... and most importantly this also includes the last 15ft to the surface... which should take 30 secs or more.

4. Be very aware of depth and the maximum you have planned for the dive. At 70'+ you really should have more gas for redundancy for you and your buddy.

5. Makes no sense (and bad for you) to head to the surface to complete a safety stop and/or deco stop then go back down again.
In the case of a blown optional stop (OK, I'll try Pete's approach for a while) it makes not sense to return to the water since what the optional stop is there to do is lessen the risk of surfacing, something that you have already done. However, in the case of a blow mandatory stop, if you are not symptomatic, it is advisable to follow omitted decompression procedures, such as:

Should a diver not realize that they have exceeded the nodecompression limits prior to reaching the surface, or they have insufficient gas to perform in-water decompression, they should:
– Proceed to the surface at a normal rate of ascent

– Once on the surface they should notify the divemaster of their omitted decompression

– If asymptomatic, and the diver can be returned safely to the water within 5 minutes after surfacing, they should dive to the depth of the missed decompression stops and remain for 1 times the required decompression stop time

– If the diver cannot be returned to the water within 5 minutes, they should be placed on oxygen for a minimum of 60 minutes

- If asymptomatic after breathing oxygen for 60 minutes, they should be observed for a minimum of 12 hours for signs and
symptoms of DCS and restricted from diving during this observational period

– If symptoms occur during or after breathing oxygen for 60 minutes, they should be transported (on oxygen) to the
nearest medical facility for treatment.

Note: If a diver is asymptomatic and unable to return to the water to complete omitted decompression, and a recompression chamber is available within 1 hour travel, the diver should be transported to the chamber for possible treatment using USN TT5 or 6.


6. Dont do deco diving by accident or by design until you have had appropriate training in gas management and dive planning.

A well executed NDL dive may see you with 500lbs of gas at the surface or 1500lbs of gas at the surface - Do not bounce dive just to use up gas.

Dwayne
A good warning, if just because repeated bounce diving can cause bubble pumping.

rhwestfall
April 25th, 2011, 06:15 PM
Their use and how to avoid their abuse should be an integral part of every class.

Despite my own convictions about PDC's and new divers, I have no reason to object to that fabulous statement. I just wish that there would be a little more to the theory. Look at what has been typed in regard to the OP's question.... "Flots" nailed the explanation in a few paragraphs. How much more time would that take in a class?

Classes are "dumbed down" enough, lets see them brought back to what is needed.

I applaud the agencies/instructors that care about training the student. Many, IMHO, are just there for the $$.....

DwayneJ
April 25th, 2011, 06:37 PM
A few thoughts:
As I understand it your computer may penalize you for doing so but it does not appear (despite our conventional wisdom) that mother nature is perfectly happy for you to make dives in whatever order you wish. It is not physiology that has problems with that, it is the models.

Thank you for the clarification - I had not seen that referenced elsewhere.

Dwayne

fnfalman
April 25th, 2011, 06:42 PM
Does the manual set forth ascent rate guidelines and discuss the consequences of exceeding recommended ascent rates?

The manual stated that the ascent rate is set at 30-ft/s but no warnings or consequences about exceeding recommended ascent rate.

Various doctrines still call for 60-ft/min ascension rate.

NetDoc
April 25th, 2011, 06:47 PM
Safety means "without risk" and by making a "safety stop" you do not eliminate all risk, you just lesson it. Precisely why I don't like it. Its waffle speak.

fnfalman
April 25th, 2011, 06:51 PM
Yes, in theory all stops are "deco" stops. However, some decos are necessary and some aren't. That's why the industry coined "safety stop".

Hell, the industry experts can't even agree on the benefits of deep stops.

NetDoc
April 25th, 2011, 06:55 PM
If the diver cannot be returned to the water within 5 minutes, they should be placed on oxygen for a minimum of 60 minutes Oxygen is always a great option in this case. Too many boats and professionals freak out at the use of Oxygen, and it's not such a big deal. I had one charter suggest that if they use their O2 that they HAVE to initiate EMS. Such rubbish.

Asymptomatic is asymptomatic: without symptom.

Thalassamania
April 25th, 2011, 07:08 PM
You got that one right. As Billy-Bob says, "green gas is good gas." Well ... he's right, up to a point.

ben_wilson3301
April 25th, 2011, 09:08 PM
More like DOWN to a point.

Get it, a Nitrox joke, there aren't too many of those

willembad
April 25th, 2011, 09:42 PM
Lots of info but I think most of it beyond where the OP is at this point. I'll add these:

- Situational awareness and the practice/training to be more aware will serve you well and now is a good time for you to work on this. No good to clear your mask and find yourself deeper than target depth for any dive just to name one example.
- Spend some time learning the ins and outs of your computer if you are going to use it. You should know what it is telling you at all times. You should know what to expect next from it and if you don't you either don't know the computer well yet or you failed on the first point (SA).
- Even when you understand the computer it is not a good idea to fly it so close to the edge at your level. Once you better understand how it functions and "where exactly you are" in a dive, you can push it a little and have the knowledge to make good decisions when the info doesn't jive or you step over the line.

Have fun and keep learning.

Willem

ianr33
April 25th, 2011, 10:16 PM
Oxygen is always a great option in this case. Too many boats and professionals freak out at the use of Oxygen, and it's not such a big deal. I had one charter suggest that if they use their O2 that they HAVE to initiate EMS. Such rubbish.


I've come across this as well:

Girl surfaced from a dive at our local lake with a splitting headache. Her group did not want to give her O2 as ("She would have to go to hospital if we did" ?? !!! )

Lent her my O2 deco tank which she sucked on for 20 minutes and started feeling better. Very much doubt she was having DCS issues but O2 is very cheap insurance.

If I had the hint of a suspicion of a problem after a dive I would be straight on O2.

NetDoc
April 26th, 2011, 07:50 AM
- Spend some time learning the ins and outs of your computer if you are going to use it. You should know what it is telling you at all times. You should know what to expect next from it and if you don't you either don't know the computer well yet or you failed on the first point (SA). I agree and disagree with this. Most Dive Shops', and quite a few divers' situational awareness on PDCs is that they are somewhat evil. I've even seen it suggested that real divers use tables and that's implied often even here on ScubaBoard. I would suggest that you learn about your PDC at DiveNav (http://www.divecomputertraining.com/classes.php). Alberto is creating a new class that is all about using a PDC to dive and I can't wait to see how it turns out. You can bet that this will become a part of my curriculum for my OW students.

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