the white tunnel and the black frame all around

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Posted by RaiderKarl on March 19, 2001 at 14:58:17:

In Reply to: Re: thats classified posted by Jeff B on March 19, 2001 at 12:30:21:

My visual field at depths "in excess of 130 feet" SEEMED TO ME to be affected either by the extreme water pressure that I was at and its effect on my circulatory system in getting oxygen to my brain, or else by the effect of the elevated partial pressure of the N2 in my blood and lungs causing extended N2 narcosis for me. I could be wrong, it could have been some kind of manifestation of O2 toxicity, but I doubt it because I wasnt deep enough for that to happen.

I was familiar with N2 narcosis from previous deep dives "in excess of 100 feet." On this particular dive last Saturday, I first noticed the narcosis beginning at 110 feet, which is consistent for me. I often wonder why some people say they cant tell if they have been narked or not, because I can always tell easily. It was not bad at that depth, but I noticed it, and it did not interfere at that depth with my monitoring my computer & instruments.

Compensating for my increased negative buoyancy seemed to require more attention on my part than normal, and since I hate dragging along the bottom of the Ocean and destroying undersea life in my wake, I do take buoyancy control personally.

At 130 feet I noticed that the narcosis had become more pronounced, although still not enough to interfere with my monitoring my computer and my backup analog gauges, and I still had good buoyancy control, although it was requiring me a couple of tries at this depth to get my buoyancy back to neutral from the negative that it was becoming due to the increased depth and pressure on my BodyGlove wetsuit.

At 141 feet I noticed a very pronounced major increase in the effect of the N2 narcosis, in that monitoring all my gauges and time and keeping my buoyancy neutral seemed overwhelming. By this point in the dive I had been descending down the sandy channel beside the wall of the reef for 10 minutes, and I totally forgot that my timelimit on this dive was 7 minutes max according to my dive plan.

The computer indicated that I was now had a decompression ceiling to deal with. That didnt bother me because I was not yet even close to my air turn around pressure, and I had already planned for enough air for 2 decomp stops, if I needed them. I was wearing a huge 120 cu ft tank, the biggest tank I owned, and I knew it gave me enough air at shallow depth to decompress.

The N2 narcosis however was now definitely bad enough for me that I could only handle doing two or three things, so I continued to monitor my depth off my computer and the approach of my air turn-around pressure on my SPG, and I gave up on all the other items, including buoyancy control, time at depth, backup depth reading on my analog gauge, or looking around at the surrounding scenery.

I was content from this point on to just push myself up off the sandy bottom, like a novice beginner diver with no buoyancy control at all, something I would NEVER do if my faculties had been in total control.

At 150 feet I remember noticing that the N2 narcosis was really bad now, and i was having a hard time seeing clearly ahead of me in the water. I could see my computer and my SPG fine, but everything else seemed to wiggle somehow underwater, even the reef to my right (north) and the canyon to my left (south) were wiggling in the water, which shouldnt have been happening, so I attributed that to N2 narcosis also.

I had lost track of my time at depth, and I didnt give a rats ass about my negative buoyancy anymore. But I had plenty of air to ascend slowly if needed and decomp stop if needed, and I still wasnt near my turn-around air pressure, so I continued.

The last thing I remember next was looking at my computer for another digital depth indication, seeing "the number," thinking 'wow this is really deep for me,' then looking up and seeing a basketball sized tunnel enclosed by blackness, so that over half of my visual field was black in front of me, even though the water was fairly bright from the late morning sunshine directly overhead, together with my being on a fairly bright sandy channel that reflected blue light well.

I then watched for a moment as this dark frame actually enlarged right in front of me, and the white tunnel shrank, and I realized quickly then that it was time to go home, that i was too deep, and that if i didnt turn around now and head up for my decomp stops, I might pass out into unconsciousness down here.

I turned to my right, using the reef wall as my guide, began kicking slowly, noticed I wasnt gaining height very much, so I put more air into my B/C, til I began to ascend slowly with my relaxed fin kicks. I remember that the round tunnel that used to be the size of a basketball was now shrunken to the size of a grapefruit, and I began to worry a little that I was in trouble.

Nevertheless, all I could do was control my ascent, keeping it really slow, to where the computer decreased in depth by only a foot every couple of seconds, my usual procedure for ascending safely.

I could see my computer and a piece of the reef in front of me fine, but everything else was blacked out by the large black frame. At one point my buoyancy caught up to me, like it always does on every ascent, so I stopped kicking and began to dump air out of the B/C to regain neutral buoyancy, which made me glad, because it meant my ascent was now normal and under control.

I had to vent air a lot after that, like I always do, before I got back to 89 feet depth, where my dive leader came face to face with me, and he gave me the OK signal with a quizzical look. I nodded and gave him the OK signal back.

By now, the black frame was all gone, and I could see everything and everybody and the whole world fine again. I spent 3 minutes around 75 feet, while the other divers in our group frolicked around like all rec divers do, poking their noses into all the nooks and crannies, a sport that has never interested me at all.

After 3 minutes I resumed my ascent, slowly, proceeding to 35 feet, where I established neutral buoyancy again. The other divers were way below me now, in the crystal clear water. I stayed at 30 feet for 5 minutes, then noticed I had only 1000 psi left in my 120 cubic foot tank, so i signaled to the dive leader 500 + 500 and he signalled back OK and GO BACK HOME. I signaled back to him OK and I waved goodbye to him, and I headed to 20 feet.

I stayed at 20 feet for 10 minutes, after which I had 700 psi left in my tank, which was plenty of air to go to 10 feet for awhile. At 10 feet after about a minute my computer said the decomp was over, and the ceiling sign disappeared. There was 600 psi left in my tank still, and normally I would have bled this down to about 200 or 300 psi, but since this was a rough beach, I decided to egress to the surface, in case I needed the air later for an underwater egression, fins-on crawling out of the surf.

I exited the water fins off walking, no problem, surf was light to moderate, although the surf did roll one of my buddies on his egression a few minutes later.

What caused the bright tunnel surrounded by the black frame? I believe personally that it was caused by imminent unconsciousness. What was the underlying reason for it? It could have been due to prolonged exposure (11 minutes at depth) to N2 narcosis, or decreased blood pressure and decreased oxygen to my brain as my heart tried to speed up to compensate for the stimulae it was receiving from the high pressure environment, sort of like when you are jogging, although I was swimming very slow and relaxed down a sandy channel next to a rocky reef.

I only know about O2 toxicity from what I have read, which is that it results at various PPs of O2 for different people, and it often causes convulsions at great depth. I am not a diving physician, so I cant give you a definitive authoritative answer. If anybody here, who knows what they are talking about, has any ideas, I would appreciate hearing that much.

But spare me the B/S about not diving deep. I will always dive deep. I love exploring this particular reef, and the purpose of this dive was to monitor my depth and my instruments and my own body's reaction, so that in the future I could preplan a deep dive here where I could concentrate on the reef not on diving deep itself.

I have already enrolled in a TDI course that starts in June and runs to September, where I can learn all about trimix. I will become a trimix diver then. In the meantime, I will explore this reef with what I have available to me, which is air, scuba, and my own knowledge and training.

OK, your turn, go for it, Big Jeff!

/s/ RaiderKarl
[i raid things of value from the Ocean floor]

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