Next step for longer bottom times on deep dives?

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Scuba Client

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I was referring to comments like these:



As @Bob DBF has commented: "I was told by one of my mentors, the real problem with narcosis is not knowing you are narked, then finding out during an emergency that you are. That surprise may last long enough to kill you."
That's why you dive with reliable buddies who are seasoned and are trained to standards which I believe are out of your league. Here's the contradiction. Below 30 metres, you're narcosis is tangible. How much is tolerable is at the diver's discretion, period!
 

grantctobin

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Thank you for your question. I've had the privilege to meet some very experienced divers. Their opinions vary and I accept both for the very reason, if you wish to dive with them, they propose the gases. Example: 32% switch at 40 metres PO2 1.6. The other example: 30/30 at either PO2 1.1 or whatever the software generated dive plan allows. Plus whatever the last/next decompression gas was or is. Isobaric Counter Diffusion theories are extrapolated and debatable. Sometimes, you just can't demand the gas you want. So if my software generated dive plan has no spike in the Equivalent Air Depth, and looks reliable, I propose it to my buddy.
I’m not asking what your acquaintances do, I’m asking what you do when you’re doing these dives. Thanks for the extended response.
 

100days-a-year

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:deadhorse:Kapow! Kapow! Kapow! Just a visual of my brain during the quarterly " deep air " discussions.
Sharing theory without experience ( particularly in a condescending or patronizing manner) about diving is no different than men sharing about childbirth or virgin about sex.
 

lermontov

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Put it this way; if planning a dive to 60m/200' and you turn up a the boat to be told that dive's off but we'll do a sheltered one at 30m/100'....

On OC you'd probably throw some toys around and take your kit home rather than face throwing away £100/€120/$140 of gas.

On CCR you'd say "lets go diving!"
or youd go get your spare dil bottle
 

ginti

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The real discussion lies in respiratory issues with old people who partake in technical/recreational dives. Young energetic, vigorous individuals shouldn't concern themselves when breathing dry air.

Your ability to give answers that have nothing to do with the posts you are answering is surprisingly good :popcorn:
 

Scuba Client

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It amazes me how maximum gas density is ignored. I guess folks know more about decompression than Dr. Simon Mitchell.
Anaesthetic gases allow the rapid introduction of an agent into arterial blood via the pulmonary circulation as compared to the more circuitous route of venous circulation. I have been made aware that certain individuals with a high VO2 Max may be difficult to sedate. This also applies to individuals under the influence of Methamphetamine. The narcotic effect at depth can be negated provided you have a developed breathing technique.
2006 Manic Person of the Year.
 

Gareth J

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It's not an opinion that narcosis impedes your ability to function. That is fact.
Those of us who where doing a lot of deep air diving prior to the availability of Trimix can attest to this.

As with everything, the level is the issue. The alcohol analogy is a reasonable base line comparison.

Not only is the depth (PON) an issue, but environment, and the individual on the day.
To state this is not a fact is idiotic in he extreme.

Yes we used to attempt to mitigate the issue. Having very good skills that where automatic. Diving the same kit setup. Ensuring you where mentally and physically fit and not tired. Avoiding heavy workloads. Work up dives to increasing narcosis tolerance [1].
But you where always fully aware that you apparent control of the situation was not as good as you believed.

Many of us have done Chamber exercises at 0m, 40m, 50m and 60m on air.
Interestingly, often the score was better at depth. When we looked at this more closely it became e very apparent this was a case of task narrowing. Task narrowing does allow you to complete tasks, but your perception of other issues is significantly hampered, even ignored, as the task becomes the total focus of the individual. Task narrowing was normally the reason for out of air emergencies and dive depth and time overruns.

One of the guys I occasionally dived with where doing a lot of survey dives for new marks. They adopted the policy of taking video cameras on all of these dives. This was well before GoPro's etc. They where constantly sending lights and housing back to the manufacturer for repair after they failed - so it was not an inexpensive policy.
They found on reviewing footage that there where huge sections of the dive they where totally in ignorance off. Including items of specific interest. When Trimix training became available, (although shunned by many of the dive training organisations at the time,) they leaped at the opportunity.
They revisited many of the previous dives, these where all experienced as new un-dived sites.

For myself, deep air diving did result in a number of incidents that I was involved in, both as the rescuer and potential casualty. I well remember having to lift my buddy off a wreck in 50m when he was totally overcome by narcosis. As we went through 30m, he recovered. On discussing it afterwards he remembered being totally overcome by dread, and was certain we where getting deeper as I took him shallower. He also remembers recovering, - it was like switching a light on. Thankfully, having recovered, he (and I ) where able to complete our decompression stops, although he was mighty relieved to get back on the boat.
He was lucky, when narcosis levels are high, expecting your buddy to be fully functional is a bit Darwinian! This is probably one of the reasons that deep air diving often resulted in double fatalities.

Apart from the issues of Narcosis. There is also the issue of Work Of Breathing (WOB). At depth the gas is denser, the ability to ventilate is impeded, and the risk of CO2 build up is increased.
In case you are unaware high levels of CO2 induce narcosis and paranoia - not good at depth.
It has become apparent, that a large number of 'deep air' incidents where probably induced by CO2 due to high WOB.

One of the reasons that there has been a push towards 'Sports Trimix', in the mid depth range, is to reduce WOB, rather than to address narcosis. In the case of Sports Trimix, it's a win / win.

I am not saying I don't occasionally dive deep on air. In some places, O2 and Helium are unavailable, or equipment is not available. This is now an extremely rare activity for me.
Modern dive computers, rebreathers etc all make Trimix diving much less complex than it was when I started. In addition, it is much more available. In addition, diving CCR means Trimix costs are more than reasonable. (Granted, all the expense and inconvenience of buying and maintaining the bailout kit still exists).


[1] -Narcosis tolerance, if it exists, is a very short term tolerance.
In much the same way as consuming large amounts of alcohol regularly, allows an alcoholic to appear to function normally. It was believed/hoped, that regular deep diving allowed you to function when suffering from narcosis.
I do wonder if this was more a mental stress thing. Doing deep diving regularly, meant you where relaxed and calm at depth. Unlike those who where unused too deep complex dives.
 

Scuba Client

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I’m not asking what your acquaintances do, I’m asking what you do when you’re doing these dives. Thanks for the extended response.
I dive air to 65 metres. Would like to go to 70 metres wearing a full-face mask. If I'm successful in poaching abalone, then I probably have the extra cash to pay for Nitrox and use Best Mix. Decompression gas can be whatever the operator has on hand. Either 32/40/50/80/100%. Ask a more specific question and I'll give you a better answer.
 
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