Depth Blackout - Page 4

Ahmed Adly, Marlin Inn DC · September 19th, 2007, 10:05 AM

Quote: (Originally Posted by finbar.taylor)

My instructor at the time called it "passive panik" -but he was a complete idiot so might be nothing like it.
Fin

That is what you call the person who taught you to dive? Shucks, is it dir to say that about your dive instructor?

By the way, Passive Panic is real.

LauNar · September 19th, 2007, 10:32 AM

Quote: (Originally Posted by Ahmed Adly, Marlin Inn DC)

Funny

But seriously, what on earth are these "shit happens" explanations all about?

Poor excuse of a theory by people who know nothing!

It's kind of hard to pull a definitive explanation out of the hat with the information we have of the cases. What we have is people losing consciousness, with a mix of different depths, gases and environments. Given the info we have and the fact that it's mostly third-hand it would be the worst kind of pseudo-science to use a blanket explanation that happens to fit the amount of theory we happen to know. Yeah, we don't like nitrogen and CO2. We like helium. Most likely they have something to do with this. It's also likely that at least some or all of the cases mentioned have also some different contributing factors.

Basically this conversation is just an entertaining brain-wank, but that's what the Internet is best suited for.

Ahmed Adly, Marlin Inn DC · September 19th, 2007, 05:27 PM

Quote: (Originally Posted by LauNar)

Basically this conversation is just an entertaining brain-wank

Good one!

These assumption races need to be moderated!

Gene_Hobbs · September 24th, 2007, 05:10 PM

OK, so you guys managed to get my head moving again... Did find this one that is interesting:

Effects of nitrogen and helium on CNS oxygen toxicity in the rat.
Arieli et. al. J Appl Physiol. 2005 Jan;98(1):144-50.
PubMed ID: 15322063

Can I start using the term "brain-wank"? I like that one...

Marijn · September 24th, 2007, 05:41 PM

Quote: (Originally Posted by Gene_Hobbs)

OK, so you guys managed to get my head moving again... Did find this one that is interesting:

Effects of nitrogen and helium on CNS oxygen toxicity in the rat.
Arieli et. al. J Appl Physiol. 2005 Jan;98(1):144-50.
PubMed ID: 15322063

Can I start using the term "brain-wank"? I like that one...

Could you explain the article a bit to me?
I'm a bit hapered by the langage barrier, small talk isn't much of a problem, but scientific texts are at times a bit hard to understand correctly.

Dawn · September 25th, 2007, 03:24 PM

Hi Marijn,

From the last two paragraphs of the Discussion section of the paper:

"The bimodal response to PN2 was not found with PHe. The difference between the two inert gases may be related to the difference in their narcotic effect. Various narcotics such as ketamine and N2O have a protective effect against CNS oxygen toxicity (16, 21). It is possible that difference in individual sensitivity to nitrogen narcosis in the rat (similar to the observation in humans) may explain the difference in the protection afforded by PN2 against CNS oxygen toxicity. Because helium is nonnarcotic, the effect of helium is to shorten the latency to CNS oxygen toxicity. Further assessment of the relationship between individual sensitivity of CNS oxygen toxicity to PN2 in the rat and its specific sensitivity to nitrogen narcosis may pave the way for planning individual oxygen limits in mixed-gas diving based on the diver's personal sensitivity to nitrogen narcosis.

The introduction of trimix diving was aimed at avoiding nitrogen narcosis and obtaining the protective effect of narcosis against HPNS.

The present study suggests that trimix may also afford protection against CNS oxygen toxicity. However, both the beneficial and the harmful effect may be related to individual traits. Further evaluation of the effect of inert gas on CNS oxygen toxicity may improve safety in trimix and nitrox diving."

In summary (note that I am not supporting or arguing this paper, only giving a quick summary!), they found that there is a difference between individual rats when it comes to nitrogen narcosis and this might have an effect on how high pressure nitrogen affects CNS O2 toxicity between individuals. They saw this difference as a set trait in each individual rat, not random. However, there was no individual difference on the effect of high pressure helium on CNS 02 toxicity. At very high pressures, both nitrogen and helium resulted in a decrease in time until onset of CNS 02 toxicity.

If you still have questions, I have asked Gertjan Verhoef to translate the abstract for you and will send this along as soon as I receive it.

Take care,
Dawn

Marijn · September 25th, 2007, 07:12 PM

Quote: (Originally Posted by Dawn)

Hi Marijn,

From the last two paragraphs of the Discussion section of the paper:

"The bimodal response to PN2 was not found with PHe. The difference between the two inert gases may be related to the difference in their narcotic effect. Various narcotics such as ketamine and N2O have a protective effect against CNS oxygen toxicity (16, 21). It is possible that difference in individual sensitivity to nitrogen narcosis in the rat (similar to the observation in humans) may explain the difference in the protection afforded by PN2 against CNS oxygen toxicity. Because helium is nonnarcotic, the effect of helium is to shorten the latency to CNS oxygen toxicity. Further assessment of the relationship between individual sensitivity of CNS oxygen toxicity to PN2 in the rat and its specific sensitivity to nitrogen narcosis may pave the way for planning individual oxygen limits in mixed-gas diving based on the diver's personal sensitivity to nitrogen narcosis.

The introduction of trimix diving was aimed at avoiding nitrogen narcosis and obtaining the protective effect of narcosis against HPNS.

The present study suggests that trimix may also afford protection against CNS oxygen toxicity. However, both the beneficial and the harmful effect may be related to individual traits. Further evaluation of the effect of inert gas on CNS oxygen toxicity may improve safety in trimix and nitrox diving."

In summary (note that I am not supporting or arguing this paper, only giving a quick summary!), they found that there is a difference between individual rats when it comes to nitrogen narcosis and this might have an effect on how high pressure nitrogen affects CNS O2 toxicity between individuals. They saw this difference as a set trait in each individual rat, not random. However, there was no individual difference on the effect of high pressure helium on CNS 02 toxicity. At very high pressures, both nitrogen and helium resulted in a decrease in time until onset of CNS 02 toxicity.

If you still have questions, I have asked Gertjan Verhoef to translate the abstract for you and will send this along as soon as I receive it.

Take care,
Dawn

Hey Dawn,

Thank you very much!
I got lost a bit when reading it on my own.

I'll thank Gertjan for translating (i'll probably hop over to his shop on saturday)

Marijn

MattDuke · October 25th, 2007, 02:10 PM

Hello,

Just to add my 2p in terms of life experiences.

1.) Passive Panic - 10m, 3m viz, Novice Diver, 5th dive in the sea.

Total meltdown in their composure. Started with erratic movements and clawing at the surface. Lots of are you OK signals from instructor got replies, but she wasn't OK. Ended after 3-4 minutes with a vacant "Glazed" look and complete paralysis. I lifted the diver to the surface where she couldn't remember what had happend, but had an immediate recovery.

2.) Deep water Blackout. 36m, 4degrees C, Dive Leader, 250+ dives.

This is perhaps the interesting one for "Deep Air" fans. It was very early (06.00am) in a quarry in the UK, and me and my chum were doing "Depth warm up" for a trip to scapa and 50m air diving. At 36m my buddy just glazed over. It started with slightly delayed response to signals, and then I thumbed the dive. By the time we had positioned oursleves to go up the shot line he was gone. Gone completely too. Eyes open, peacful, reg in breathing.

At 30m only 6m off the bottom, he came round, and literally did a comical "Shake of the head" as is in: "Where the **** am I?" He then when straight for his depth guage and air guage and was confused how he had come to be back at 30m. I no longer needed to assist him, and we ended the dive without incident.

3.) Shallow water task overload. 4.5m, 10m viz, Diver with 75 dives, DIR-F course.

Interesting one this. On my DIR-F course I did it with my regular NACD trained buddy, 750 dives, and I had a similar number of dives. Our third member was a great lass who is a fantastic "natural" in the water, but none the less still only a few years into the course.

Gas switches. For what ever reason there was just too many things happening at once, and she kept getting the order wrong and consequently started getting REALLY pissed with her self. Me and my regualar buddy are very chilled in the water, and tried to assist and get her to try again, giving assistance and clear signals.

She failed to get the skill a few times, and then it happened again. Glazed. Totally unresponsive to signals and in her own little world. After some time she "Came Back" and we exited the dive. Had a long debrief and discussion and then did plenty of practice dives, where everything went well.

******************
I'm no expert, but my life experiences since 1992, have shown we these three scenarios where people go limp.

The deep air dive would have been a fatality without us being in a buddy team, or if both had been hit with the same. I think that extreme cold, tirdness and darkness have a serious role in that near miss.

Cold water and bad conditions even "Only" 36m on air can be a very hostile place to be.

Hope these experiences are of interest.

Matt.
Bergen, Norway.

Ahmed Adly, Marlin Inn DC · October 25th, 2007, 03:14 PM

Quote: (Originally Posted by Dawn)

Hi Marijn,

From the last two paragraphs of the Discussion section of the paper:

"The bimodal response to PN2 was not found with PHe. The difference between the two inert gases may be related to the difference in their narcotic effect. Various narcotics such as ketamine and N2O have a protective effect against CNS oxygen toxicity (16, 21). It is possible that difference in individual sensitivity to nitrogen narcosis in the rat (similar to the observation in humans) may explain the difference in the protection afforded by PN2 against CNS oxygen toxicity. Because helium is nonnarcotic, the effect of helium is to shorten the latency to CNS oxygen toxicity. Further assessment of the relationship between individual sensitivity of CNS oxygen toxicity to PN2 in the rat and its specific sensitivity to nitrogen narcosis may pave the way for planning individual oxygen limits in mixed-gas diving based on the diver's personal sensitivity to nitrogen narcosis.

The introduction of trimix diving was aimed at avoiding nitrogen narcosis and obtaining the protective effect of narcosis against HPNS.

The present study suggests that trimix may also afford protection against CNS oxygen toxicity. However, both the beneficial and the harmful effect may be related to individual traits. Further evaluation of the effect of inert gas on CNS oxygen toxicity may improve safety in trimix and nitrox diving."

In summary (note that I am not supporting or arguing this paper, only giving a quick summary!), they found that there is a difference between individual rats when it comes to nitrogen narcosis and this might have an effect on how high pressure nitrogen affects CNS O2 toxicity between individuals. They saw this difference as a set trait in each individual rat, not random. However, there was no individual difference on the effect of high pressure helium on CNS 02 toxicity. At very high pressures, both nitrogen and helium resulted in a decrease in time until onset of CNS 02 toxicity.

If you still have questions, I have asked Gertjan Verhoef to translate the abstract for you and will send this along as soon as I receive it.

Take care,
Dawn

Hi Dawn,

A little off topic, but the smile you have in that picture is the prettiest thing I have seen for a VERY long time.
If you ever want to make me do anything, just put those eyes on me!

Best,
Ahmed

MarkEm · October 25th, 2007, 09:45 PM

I think I experienced something like deep water blackout on a training dive back in 2002.

I was taking TDI Advanced Nitrox & Deco Procedures down in Portland. It was the first dive of the course, 28m on the Bennendijk using 32%. This was the deepest dive I had done in the UK at the time and was only something like my 10th UK dive ever. Previously I had done a few shallow dives around Portland and some dives in Stoney (& 50 dives in Thailand).

The shot line was practically horizontal due to being too long and due to a fair amount of tide still running during the descent we had to fin hard to get down. It seemed to take a very long time to reach the bottom. I reached the bottom then went into a little world of my own. I remember thinking 'please can someone take me back up' and having tunnel vision. I was not responding to signals. I had the fear, big time!

I can't remember much else about the bottom section of the dive, apart from the darkness.

I remember feeling totally fine soon after we began our ascent. I have always put it down to Co2 build up during the descent and lack of experience in the conditions.

I nearly pulled out of the course after that but I managed to continue the next day with a dive on the Aeolian Sky which was also dark and scary, but good

Cheers,

Mark.

September 19th, 2007, 10:05 AM	#31 (permalink)
Ahmed Adly, Marlin Inn DC(Offline) New Member Join Date: Feb 2006 Location: hurghada Posts: 849	Quote: (Originally Posted by finbar.taylor) My instructor at the time called it "passive panik" -but he was a complete idiot so might be nothing like it. Fin That is what you call the person who taught you to dive? Shucks, is it dir to say that about your dive instructor? By the way, Passive Panic is real. __________________ It has just dawned on me.... We are all just recycled stardust Ahmed Adly, www.deepvoyage.com

September 19th, 2007, 10:32 AM	#32 (permalink)
LauNar(Offline) ... Join Date: Nov 2005 Location: Finland Posts: 131	Quote: (Originally Posted by Ahmed Adly, Marlin Inn DC) Funny But seriously, what on earth are these "shit happens" explanations all about? Poor excuse of a theory by people who know nothing! It's kind of hard to pull a definitive explanation out of the hat with the information we have of the cases. What we have is people losing consciousness, with a mix of different depths, gases and environments. Given the info we have and the fact that it's mostly third-hand it would be the worst kind of pseudo-science to use a blanket explanation that happens to fit the amount of theory we happen to know. Yeah, we don't like nitrogen and CO2. We like helium. Most likely they have something to do with this. It's also likely that at least some or all of the cases mentioned have also some different contributing factors. Basically this conversation is just an entertaining brain-wank, but that's what the Internet is best suited for. __________________ //LN -- My UW photos

September 19th, 2007, 05:27 PM	#33 (permalink)
Ahmed Adly, Marlin Inn DC(Offline) New Member Join Date: Feb 2006 Location: hurghada Posts: 849	Quote: (Originally Posted by LauNar) Basically this conversation is just an entertaining brain-wank Good one! These assumption races need to be moderated! __________________ It has just dawned on me.... We are all just recycled stardust Ahmed Adly, www.deepvoyage.com

September 24th, 2007, 05:10 PM	#34 (permalink)
Gene_Hobbs(Offline) WKPP Join Date: Sep 2006 Location: Durham, NC, USA Posts: 60	Had to keep looking and could not give up... OK, so you guys managed to get my head moving again... Did find this one that is interesting: Effects of nitrogen and helium on CNS oxygen toxicity in the rat. Arieli et. al. J Appl Physiol. 2005 Jan;98(1):144-50. PubMed ID: 15322063 Can I start using the term "brain-wank"? I like that one... __________________ http://rubicon-foundation.org/ Home of the Rubicon Research Repository. For help getting started with the Repository, please visit our FAQ page. PLEASE support our work. "Oxygen is addictive and deadly. Everyone who uses it will eventually die" --RW Hamilton, PhD 1991

September 24th, 2007, 05:41 PM	#35 (permalink)
Marijn(Offline) Smurf #1 Join Date: Aug 2007 Location: Papendrecht, The Netherlands Posts: 385	Quote: (Originally Posted by Gene_Hobbs) OK, so you guys managed to get my head moving again... Did find this one that is interesting: Effects of nitrogen and helium on CNS oxygen toxicity in the rat. Arieli et. al. J Appl Physiol. 2005 Jan;98(1):144-50. PubMed ID: 15322063 Can I start using the term "brain-wank"? I like that one... Could you explain the article a bit to me? I'm a bit hapered by the langage barrier, small talk isn't much of a problem, but scientific texts are at times a bit hard to understand correctly. __________________ Its a fact that the humans can't go without water for more than 3 days

September 25th, 2007, 03:24 PM	#36 (permalink)
Dawn(Offline) New Member Join Date: Dec 2005 Location: North Carolina Posts: 153	Hi Marijn, From the last two paragraphs of the Discussion section of the paper: "The bimodal response to PN2 was not found with PHe. The difference between the two inert gases may be related to the difference in their narcotic effect. Various narcotics such as ketamine and N2O have a protective effect against CNS oxygen toxicity (16, 21). It is possible that difference in individual sensitivity to nitrogen narcosis in the rat (similar to the observation in humans) may explain the difference in the protection afforded by PN2 against CNS oxygen toxicity. Because helium is nonnarcotic, the effect of helium is to shorten the latency to CNS oxygen toxicity. Further assessment of the relationship between individual sensitivity of CNS oxygen toxicity to PN2 in the rat and its specific sensitivity to nitrogen narcosis may pave the way for planning individual oxygen limits in mixed-gas diving based on the diver's personal sensitivity to nitrogen narcosis. The introduction of trimix diving was aimed at avoiding nitrogen narcosis and obtaining the protective effect of narcosis against HPNS. The present study suggests that trimix may also afford protection against CNS oxygen toxicity. However, both the beneficial and the harmful effect may be related to individual traits. Further evaluation of the effect of inert gas on CNS oxygen toxicity may improve safety in trimix and nitrox diving." In summary (note that I am not supporting or arguing this paper, only giving a quick summary!), they found that there is a difference between individual rats when it comes to nitrogen narcosis and this might have an effect on how high pressure nitrogen affects CNS O2 toxicity between individuals. They saw this difference as a set trait in each individual rat, not random. However, there was no individual difference on the effect of high pressure helium on CNS 02 toxicity. At very high pressures, both nitrogen and helium resulted in a decrease in time until onset of CNS 02 toxicity. If you still have questions, I have asked Gertjan Verhoef to translate the abstract for you and will send this along as soon as I receive it. Take care, Dawn

September 25th, 2007, 07:12 PM	#37 (permalink)
Marijn(Offline) Smurf #1 Join Date: Aug 2007 Location: Papendrecht, The Netherlands Posts: 385	Quote: (Originally Posted by Dawn) Hi Marijn, From the last two paragraphs of the Discussion section of the paper: "The bimodal response to PN2 was not found with PHe. The difference between the two inert gases may be related to the difference in their narcotic effect. Various narcotics such as ketamine and N2O have a protective effect against CNS oxygen toxicity (16, 21). It is possible that difference in individual sensitivity to nitrogen narcosis in the rat (similar to the observation in humans) may explain the difference in the protection afforded by PN2 against CNS oxygen toxicity. Because helium is nonnarcotic, the effect of helium is to shorten the latency to CNS oxygen toxicity. Further assessment of the relationship between individual sensitivity of CNS oxygen toxicity to PN2 in the rat and its specific sensitivity to nitrogen narcosis may pave the way for planning individual oxygen limits in mixed-gas diving based on the diver's personal sensitivity to nitrogen narcosis. The introduction of trimix diving was aimed at avoiding nitrogen narcosis and obtaining the protective effect of narcosis against HPNS. The present study suggests that trimix may also afford protection against CNS oxygen toxicity. However, both the beneficial and the harmful effect may be related to individual traits. Further evaluation of the effect of inert gas on CNS oxygen toxicity may improve safety in trimix and nitrox diving." In summary (note that I am not supporting or arguing this paper, only giving a quick summary!), they found that there is a difference between individual rats when it comes to nitrogen narcosis and this might have an effect on how high pressure nitrogen affects CNS O2 toxicity between individuals. They saw this difference as a set trait in each individual rat, not random. However, there was no individual difference on the effect of high pressure helium on CNS 02 toxicity. At very high pressures, both nitrogen and helium resulted in a decrease in time until onset of CNS 02 toxicity. If you still have questions, I have asked Gertjan Verhoef to translate the abstract for you and will send this along as soon as I receive it. Take care, Dawn Hey Dawn, Thank you very much! I got lost a bit when reading it on my own. I'll thank Gertjan for translating (i'll probably hop over to his shop on saturday) Marijn __________________ Its a fact that the humans can't go without water for more than 3 days

October 25th, 2007, 02:10 PM	#38 (permalink)
MattDuke(Offline) New Member Join Date: Dec 2005 Location: Bergen, Norway Posts: 33	Hello, Just to add my 2p in terms of life experiences. 1.) Passive Panic - 10m, 3m viz, Novice Diver, 5th dive in the sea. Total meltdown in their composure. Started with erratic movements and clawing at the surface. Lots of are you OK signals from instructor got replies, but she wasn't OK. Ended after 3-4 minutes with a vacant "Glazed" look and complete paralysis. I lifted the diver to the surface where she couldn't remember what had happend, but had an immediate recovery. 2.) Deep water Blackout. 36m, 4degrees C, Dive Leader, 250+ dives. This is perhaps the interesting one for "Deep Air" fans. It was very early (06.00am) in a quarry in the UK, and me and my chum were doing "Depth warm up" for a trip to scapa and 50m air diving. At 36m my buddy just glazed over. It started with slightly delayed response to signals, and then I thumbed the dive. By the time we had positioned oursleves to go up the shot line he was gone. Gone completely too. Eyes open, peacful, reg in breathing. At 30m only 6m off the bottom, he came round, and literally did a comical "Shake of the head" as is in: "Where the ** am I?" He then when straight for his depth guage and air guage and was confused how he had come to be back at 30m. I no longer needed to assist him, and we ended the dive without incident. 3.) Shallow water task overload. 4.5m, 10m viz, Diver with 75 dives, DIR-F course. Interesting one this. On my DIR-F course I did it with my regular NACD trained buddy, 750 dives, and I had a similar number of dives. Our third member was a great lass who is a fantastic "natural" in the water, but none the less still only a few years into the course. Gas switches. For what ever reason there was just too many things happening at once, and she kept getting the order wrong and consequently started getting REALLY pissed with her self. Me and my regualar buddy are very chilled in the water, and tried to assist and get her to try again, giving assistance and clear signals. She failed to get the skill a few times, and then it happened again. Glazed. Totally unresponsive to signals and in her own little world. After some time she "Came Back" and we exited the dive. Had a long debrief and discussion and then did plenty of practice dives, where everything went well. **************** I'm no expert, but my life experiences since 1992, have shown we these three scenarios where people go limp. The deep air dive would have been a fatality without us being in a buddy team, or if both had been hit with the same. I think that extreme cold, tirdness and darkness have a serious role in that near miss. Cold water and bad conditions even "Only" 36m on air can be a very hostile place to be. Hope these experiences are of interest. Matt. Bergen, Norway.

October 25th, 2007, 03:14 PM	#39 (permalink)
Ahmed Adly, Marlin Inn DC(Offline) New Member Join Date: Feb 2006 Location: hurghada Posts: 849	Quote: (Originally Posted by Dawn) Hi Marijn, From the last two paragraphs of the Discussion section of the paper: "The bimodal response to PN2 was not found with PHe. The difference between the two inert gases may be related to the difference in their narcotic effect. Various narcotics such as ketamine and N2O have a protective effect against CNS oxygen toxicity (16, 21). It is possible that difference in individual sensitivity to nitrogen narcosis in the rat (similar to the observation in humans) may explain the difference in the protection afforded by PN2 against CNS oxygen toxicity. Because helium is nonnarcotic, the effect of helium is to shorten the latency to CNS oxygen toxicity. Further assessment of the relationship between individual sensitivity of CNS oxygen toxicity to PN2 in the rat and its specific sensitivity to nitrogen narcosis may pave the way for planning individual oxygen limits in mixed-gas diving based on the diver's personal sensitivity to nitrogen narcosis. The introduction of trimix diving was aimed at avoiding nitrogen narcosis and obtaining the protective effect of narcosis against HPNS. The present study suggests that trimix may also afford protection against CNS oxygen toxicity. However, both the beneficial and the harmful effect may be related to individual traits. Further evaluation of the effect of inert gas on CNS oxygen toxicity may improve safety in trimix and nitrox diving." In summary (note that I am not supporting or arguing this paper, only giving a quick summary!), they found that there is a difference between individual rats when it comes to nitrogen narcosis and this might have an effect on how high pressure nitrogen affects CNS O2 toxicity between individuals. They saw this difference as a set trait in each individual rat, not random. However, there was no individual difference on the effect of high pressure helium on CNS 02 toxicity. At very high pressures, both nitrogen and helium resulted in a decrease in time until onset of CNS 02 toxicity. If you still have questions, I have asked Gertjan Verhoef to translate the abstract for you and will send this along as soon as I receive it. Take care, Dawn Hi Dawn, A little off topic, but the smile you have in that picture is the prettiest thing I have seen for a VERY long time. If you ever want to make me do anything, just put those eyes on me! Best, Ahmed __________________ It has just dawned on me.... We are all just recycled stardust Ahmed Adly, www.deepvoyage.com

October 25th, 2007, 09:45 PM	#40 (permalink)
MarkEm(Offline) Site Sponsor Join Date: Nov 2005 Location: Essex, UK Posts: 220	I think I experienced something like deep water blackout on a training dive back in 2002. I was taking TDI Advanced Nitrox & Deco Procedures down in Portland. It was the first dive of the course, 28m on the Bennendijk using 32%. This was the deepest dive I had done in the UK at the time and was only something like my 10th UK dive ever. Previously I had done a few shallow dives around Portland and some dives in Stoney (& 50 dives in Thailand). The shot line was practically horizontal due to being too long and due to a fair amount of tide still running during the descent we had to fin hard to get down. It seemed to take a very long time to reach the bottom. I reached the bottom then went into a little world of my own. I remember thinking 'please can someone take me back up' and having tunnel vision. I was not responding to signals. I had the fear, big time! I can't remember much else about the bottom section of the dive, apart from the darkness. I remember feeling totally fine soon after we began our ascent. I have always put it down to Co2 build up during the descent and lack of experience in the conditions. I nearly pulled out of the course after that but I managed to continue the next day with a dive on the Aeolian Sky which was also dark and scary, but good Cheers, Mark. __________________ *WWW.DIVESIGNS.COM*