Preparing for Devil's Throat

[boulderjohn]

Just some information for readers who might not be totally on top of common thinking on nitrox:

1. Agencies identify a maximum operating depth (MOD) for the safe use of nitrox, depending upon what is considered to be a safe amount of oxygen at the diver's depth. This is measured by the partial pressure (ppO2) of oxygen in the mix, which is determined by multiplying the percentage of oxygen by the depth as measured by atmospheres of pressure.

2. Using the 1.4 standard for ppO2 advocated by almost all agencies, the MOD for EANx 32 is 111 feet of sea water, or 115 feet of fresh water.

3. Those same agencies usually identify a ppO2 of 1.6 as the "contingency standard." For contingency purposes, the MOD for EANx 32 is 132 feet of sea water or 136 feet of fresh water. As one handbook says, the range between 1.4 and 1.6 is for a "margin of error." Technical divers, however, use 1.6 as the standard MOD for the decompression part of their diving, because they are usually barely moving during that portion of their dives. Physical activity is considered to be a factor in oxygen toxicity.

4. Oxygen toxicity has a time component. Dipping briefly below the MOD for a "brief" period of time will not bring on oxygen toxicity. What do we mean by "brief"? It is hard to say because it is unpredictable. However, the current standards are considered to be quite safe, so divers do not have to fear that unexpected dip when they are not watching their gauges closely.

 

[cvchief]

Personally, I would rather avoid both.

Certainly good advice. Not so helpful in "Preparing for the Devil's Throat," but still worthy of consideration.

 

[fishi]

Personally, I would rather avoid both.

When we dove Coz, we dove 32% and set a hard deck at 100 feet. We saw beautiful reef, lots of canyons and short swim-throughs . . . At no time in the trip did I say to myself, "This would have been a great trip if we had just been able to go a little deeper."

On our last trip we cut a hole in the bottom of the boat and installed a sheet of glass. We saw beautiful fish and coral with 0 risk of oxygen toxicity or the bends. We had a great trip and at no time in the trip did I say to myself "I wish we had got in the water."



I apologize for the sarcasm, but why stop at 100'. 80 would be safer.

 

[cvchief]

On our last trip we cut a hole in the bottom of the boat and installed a sheet of glass. We saw beautiful fish and coral with 0 risk of oxygen toxicity or the bends. We had a great trip and at no time in the trip did I say to myself "I wish we had got in the water."



I apologize for the sarcasm, but why stop at 100'. 80 would be safer.

So you think Fishi. I could tell you a story I heard about about the dangers of a glass bottom boat. WAY more danger, I'm just saying....

 

[boulderjohn]

So you think Fishi. I could tell you a story I heard about about the dangers of a glass bottom boat. WAY more danger, I'm just saying....

Only if you cover it over, rename it, and take a long ocean voyage. Otherwise, it should be fine.

 

[fishi]

So you think Fishi. I could tell you a story I heard about about the dangers of a glass bottom boat. WAY more danger, I'm just saying....

In 07 Blue Angel took me across the channel. When they said "we are going to the other side to see the turtles" I thought they were joking. Not getting off that small boat was probably the stupidest thing I've done. I don't consider diving DT on nitrox stupid. Crossing that channel was stupid.

 

[TSandM]

Yes, fishi, you are pointing out that risk is not cut and dried, and we all make risk assessment decisions when diving.

I just don't understand the fixation on this particular dive, which is quite deep for a single tank diver, is an honest overhead environment (from the videos I've watched), and is conducted as a group with people who have neither deep diving nor overhead diving training.

If you want to dive in an overhacead environment, why not go over to the mainland and do some cenote tours? Surely you are safer in a tunnel in 20 feet of water than you are in 120?

It's like the Blue Hole in Belize. What is there about these dives that makes people accept a short dive with higher risk, just to do it?

 

[Ron Lee]

What is there about these dives that makes people accept a short dive with higher risk, just to do it?

You are making a qualitative determination that there is a higher risk than what......Paradise reef?

Maybe we can quantify the risk increase. Perhaps a typical dive in that area but not in DT has a fatality risk of 0.0000058%.
Doing DT raises the risk to 0.000006%. If these numbers are remotely close, it is a non-issue.

However, we can look at recent fatalities and with actual understanding of where things went bad, you could come up with ways to make a real difference. Frankly, most of these deaths are perhaps due to violating basic safety fundamentals already taught to every diver.

 

[ggunn]

In 07 Blue Angel took me across the channel. When they said "we are going to the other side to see the turtles" I thought they were joking. Not getting off that small boat was probably the stupidest thing I've done. I don't consider diving DT on nitrox stupid. Crossing that channel was stupid.

I have done that dive with BA a couple of times. I enjoyed it very much. DSFDF.

 

[fishi]

Yes, fishi, you are pointing out that risk is not cut and dried, and we all make risk assessment decisions when diving.

I just don't understand the fixation on this particular dive, which is quite deep for a single tank diver, is an honest overhead environment (from the videos I've watched), and is conducted as a group with people who have neither deep diving nor overhead diving training.

If you want to dive in an overhacead environment, why not go over to the mainland and do some cenote tours? Surely you are safer in a tunnel in 20 feet of water than you are in 120?

It's like the Blue Hole in Belize. What is there about these dives that makes people accept a short dive with higher risk, just to do it?

I was watching 60 minutes a while ago. They had a women freediving to over 500 feet. After her dive a newspaper reporter asked her what she saw down there? She said I don't dive deep to look at "stuff". I dive deep to "look within".
I think a lot of people like the challenge a dive like the Blue Hole presents even though they know they might not be ready for it.


I did go over and dive the cenotes once. My ista buddy had 20 dives. She didn't understand that you have to use the rear dump valve when you're pinned to the ceiling. The front one doesn't work in that situation. I went up and got her off the ceiling. Two minutes later she was back on the ceiling. Before the dive she told me her last dive was DT so she was sure she could handle the cenote. I'm sure if she pinned herself to the ceiling of DT somebody would have got her down and out.