Quiz - Skills & Environment - Diving at Altitude

[NAM001]

here is a link to a discussion of some of hte issue in this thread
Altitude Diving - Scuba Diving With An Attitude - DeeperBlue.com

the theory depth makes sense to me, As I understand it as you go to higher atmospheres you have to deco until you adapt to the new altitude. do these theory depths still apply once you spend the time to adapt to the higher altitude. As I read it you have to add 2 pressure groups for every 1000 ft until you deco to the higher atmosphere. At that,,,, again as I am understanding the contents,,, you dont have to add groups any more. Likewise would not the early onset of narcosis be present unless you took the time to adapt to a new altitude. I say this because the aspect of MOD and notrox says ,,,,,,per the arrticle,,, that if you had a mod of 100 at sea level at higher altitudes it would change to IE 105 feet or more depending on the altitude. It says the reason is that MOD is driven by absolute presssure if mod is 4 atm apx 60 psi ambient pressure,,, then at sea level it takes 100 ft to get there and at higher altitudes it would take 105 feet or more to get to the same 60 psi ambient presure. It has always been my understanding that narcosis is a pressure driven effect just as MOD or CNS issues. Your body,, I would think,,, would already physically be the same as splashing at 20 feet instead of 0 feet until your body adapts to the new altitude.

This brings up all sorts of questions ,,,,,,,,,,, 2 groups???? is that on a 24 group padi table or a 12 group nauii table??? how do you comp for the table you use. Next will the dive computer handle the corrections for this,,, and if so do you have to power the computer on prior to leaving sea level until arrival of the high altitude to make the computer process the deco or at least power on upon departure of sea level and then again at altitude. It seams that if you dont do that you have to do the wait at altitude of 6> recommended 24 hours prior to starting your dive. I would guess that the computer would assume you are not in the process of any deco at all when you start the first dive of the day, and just take the current atmosphere pressure and go form there without any knowledge that 20 minutes before you were at sea level.. the puter knowing the time and pressure of the last dive which may have been days before would only be able to process the change as you started the altitude change at the time of the last dive end. Making any altitude change and immediately starting the dive would make that computer assumption a bad one. All the puter would know was what the condition the last time it was powered on. I can also envision that turning on your puter at sea level shutting down and turning on again at altitude may cause problems from the puter having a pressure time info form sea level in the last 24 hour window, making it a bad ides to power on the computer untill the dive.

Next with the puter , at least with the shearwater I can watch second by second changes in the barometric pressure. once a dive is started that pressure is locked in so it can do its thing like calculating surf GF and other things under water. I dont know when i can see atmosphere changes again. Ill guess it is because it monitors the atmosphere with the sensor until it hits water and then the pressure sensor is assumed to be water pressure and not atmosphere pressure. Another I dont know is. When does the computer release the sensor to read pressure as atmosphere pressure again ,,,,, 24 hours after last surface????? If so then using a puter at altitude prior to that perhaps 24 hour period would assume the dive was at sea level or the pressure last noted in perhaps the last 24 hour period. Even to the point of going into surface mode before hitting the surface.



This is a great topic.

 

[BRT]

Yes, you are. Say you are at 66 ft at sea level. Your pressure at depth is two atmospheres of water, plus one of atmosphere, or 3 atm total pressure on you. At altitude, you still have two atm of water, but LESS than one atmosphere of air above you, so you are at (say) 2.8 atm at maybe 4000 ft altitude (just making up numbers).

Added: I interpreted your comment as being about reduced pressure at depth. Did you mean reduced even lower than at the surface? No, certainly not. All that water above you is heavy....

Total pressure at any depth is reduced as is the PP of nitrogen at any depth and you are diving fresh water so total pressure at any depth is further reduced. Seem highly unlikely that narcosis hits shallower. However...often those freshwater lakes get really dark down there so there may be a perception of narcosis????

 

[boulderjohn]

Is this a current version of the test?

I seem to remember being told that there was once an incorrect question on a quiz that related nitrogen narcosis and altitude. I seem to remember the question being corrected in later versions.

I have never heard anywhere that narcosis happens at shallower depths at altitude, and I have written articles on diving at altitude. The US Navy manual has no mention of it in its altitude diving section. I don't believe it appears in any PADI publication of which I am familiar. As some have pointed out already, logic tells you it should be the oppposite.

In this question, the correct answer is B. A is simply incorrect. C does not answer the question--it tells what some special procedures are, but it does not say why they must be used.

 

[tursiops]

I don't believe it appears in any PADI publication of which I am familiar.

There is no mention of altitude and narcosis in the PADI Altitude Manual or the PADI Encyclopedia of Recreational Diving.

Is this a current version of the test?

I seem to remember being told that there was once an incorrect question on a quiz that related nitrogen narcosis and altitude. I seem to remember the question being corrected in later versions.

As far as I can tell (I do not have all the old IDC Dive Theory Exams) the question's answer was definitely wrong on Exam Version 2 in 2007, and probably unchanged through 2019, but appears to have been changed for 2020. Someone with newer copies will need to check that.

 

[Pedro Burrito]

The exam was given to me in 2013. I'm not sure what the actual date of the exam was, however, but definitely earlier.

Spoiler: Probably Not the Correct Answer

d. all of the above are correct.

 

[BRT]

Is this a current version of the test?

I seem to remember being told that there was once an incorrect question on a quiz that related nitrogen narcosis and altitude. I seem to remember the question being corrected in later versions.

I have never heard anywhere that narcosis happens at shallower depths at altitude, and I have written articles on diving at altitude. The US Navy manual has no mention of it in its altitude diving section. I don't believe it appears in any PADI publication of which I am familiar. As some have pointed out already, logic tells you it should be the oppposite.

In this question, the correct answer is B. A is simply incorrect. C does not answer the question--it tells what some special procedures are, but it does not say why they must be used.

My answer too.

 

[boulderjohn]

B y the way, I used to teach students how to make good guesses on multiple choice exams.

In this question, choice c is incorrect because it does not answer the question. In fact, it almost repeats the question. That makes Choice D wrong, leaving only A and B.

Choice B is correct, as you should know from your reading.

Therefore, without knowing anything about altitude and narcosis, you should know that A is wrong.

 

[Divedoggie]

With many hundreds of dives at altitude over the last 20 years, and having taught thousands of students at altitude, as well as teaching the Altitude Specialty for many many years, the correct answer to the quiz is B.

As to the discussion about Narcosis at Altitude:
100' FW exerts less pressure on a diver compared with 100' SW. (6250 lbs in the direct water column vs 6400 lbs )
The atmospheric pressure is measurably less as well. (12 psi in Denver, 14.7 psi at sea level.)
The absolute pressure of a 100' FW dive in Denver is 55.2 psia
The absolute pressure of a 100' SW dive in the ocean is 59.2 psia

All other factors being equal, since we generally begin experiencing the effects of nitrogen narcosis at around 100' sw, the narcosis experienced diving at altitude is slightly, but measurably less than at sea level.

The extreme pressure change experienced upon surfacing at altitude is our chief concern. Disciplined and responsible diving with Altitude protocol is important. Adjusted altitude tables are only a small part of the process.

 

[EFX]

Why would nitrogen narcosis happen at shallower depths at altitude?

I believe the survey question assumes the diver is saturated at the surface higher altitude. Increasing water pressure with increasing depth does not change regardless of how high (or low) the body of water is relative to sea level, assuming the density of water doesn't change relative to the same type of water at lower altitudes. The amount of uptake of inert gas in a tissue partly depends on the pressure difference between the existing pressure (which is lower than sea level at the surface) and the new pressure at depth. This pressure difference is greater at altitude than it would be at sea level so more inert gas is absorbed hence more nitrogen narcosis at shallower depths.

 

[boulderjohn]

here is a link to a discussion of some of hte issue in this thread
Altitude Diving - Scuba Diving With An Attitude - DeeperBlue.com

the theory depth makes sense to me, As I understand it as you go to higher atmospheres you have to deco until you adapt to the new altitude. do these theory depths still apply once you spend the time to adapt to the higher altitude. As I read it you have to add 2 pressure groups for every 1000 ft until you deco to the higher atmosphere. At that,,,, again as I am understanding the contents,,, you dont have to add groups any more. Likewise would not the early onset of narcosis be present unless you took the time to adapt to a new altitude. I say this because the aspect of MOD and notrox says ,,,,,,per the arrticle,,, that if you had a mod of 100 at sea level at higher altitudes it would change to IE 105 feet or more depending on the altitude. It says the reason is that MOD is driven by absolute presssure if mod is 4 atm apx 60 psi ambient pressure,,, then at sea level it takes 100 ft to get there and at higher altitudes it would take 105 feet or more to get to the same 60 psi ambient presure. It has always been my understanding that narcosis is a pressure driven effect just as MOD or CNS issues. Your body,, I would think,,, would already physically be the same as splashing at 20 feet instead of 0 feet until your body adapts to the new altitude.

This brings up all sorts of questions ,,,,,,,,,,, 2 groups???? is that on a 24 group padi table or a 12 group nauii table??? how do you comp for the table you use. Next will the dive computer handle the corrections for this,,, and if so do you have to power the computer on prior to leaving sea level until arrival of the high altitude to make the computer process the deco or at least power on upon departure of sea level and then again at altitude. It seams that if you dont do that you have to do the wait at altitude of 6> recommended 24 hours prior to starting your dive. I would guess that the computer would assume you are not in the process of any deco at all when you start the first dive of the day, and just take the current atmosphere pressure and go form there without any knowledge that 20 minutes before you were at sea level.. the puter knowing the time and pressure of the last dive which may have been days before would only be able to process the change as you started the altitude change at the time of the last dive end. Making any altitude change and immediately starting the dive would make that computer assumption a bad one. All the puter would know was what the condition the last time it was powered on. I can also envision that turning on your puter at sea level shutting down and turning on again at altitude may cause problems from the puter having a pressure time info form sea level in the last 24 hour window, making it a bad ides to power on the computer untill the dive.

Next with the puter , at least with the shearwater I can watch second by second changes in the barometric pressure. once a dive is started that pressure is locked in so it can do its thing like calculating surf GF and other things under water. I dont know when i can see atmosphere changes again. Ill guess it is because it monitors the atmosphere with the sensor until it hits water and then the pressure sensor is assumed to be water pressure and not atmosphere pressure. Another I dont know is. When does the computer release the sensor to read pressure as atmosphere pressure again ,,,,, 24 hours after last surface????? If so then using a puter at altitude prior to that perhaps 24 hour period would assume the dive was at sea level or the pressure last noted in perhaps the last 24 hour period. Even to the point of going into surface mode before hitting the surface.



This is a great topic.

Deep Adventure Scuba Colorado Technical Diving - For Those Looking to Take Diving to a New Level
The article on my resource page should answer a lot of the questions, but I will answer some of them quickly here:
1. The 2 pressure groups per 1,000 feet of altitude only works with PADI tables.
2. It starts when you reach that altitude. If you arrive at 6,000 feet from sea level, you are an L diver, and a 2:10 surface interval later you are an A diver.
3. Since you spent some time ascending while getting there, you were off-gassing on the way, but there is no way to calculate that.
4. Putting 2 and 3 together, the odds are you won't have to worry about it.
5. If you got there from a higher altitude, you are already off the table, much to the surprise of the local dive shop here that tells the students coming from our mile-high altitude that they will be J divers when they descend to 4,600 feet to dive in New Mexico.
6. I don't know of any computer that calculates your change in altitude before you have done your first dive. Some software programs do that (like multi-deco).
7. The first Shearwater computers did not calculate altitude at all. A friend of mine bought one and contacted the company because the depths seemed wrong. As they talked to him, they realized he was diving at altitude and made that adjustment in their computers. Years later, during a weekend of diving at altitude, our group noticed that different divers were getting different depth readings on our Shearwaters. I contacted them, and they figured out that the difference was in how the computers turned on. If we turned the computer on before diving, it knew we were at altitude. If the computer turned on by itself after the dive started, it thought we were at sea level. They then corrected that so that now Shearwater computers that turn on after being submerged will go back to their last altitude reading.
8. Suunto RGBM computers used to (maybe still do) require manual settings for altitude. They gave you the choice of 3 ranges.
9. When you start getting over 10,000 feet, things get serious, and you should do some real investigation before doing anything but shallow dives.