Next step for longer bottom times on deep dives?

[Scuba Client]

If we asked Dr. Simon Mitchell if it is his professional recommendation that all recreational training agencies limit all recreational diving to 100' or below due to the gas density and/or narcosis safety concerns/risk in the current 101-130' recreational range until divers are trained on and using trimix to make the dive safe? I'd be very, very surprised to hear him say that should be done as a blanket "rule" for diving. I know he doesn't endorse "deep air diving", but I don't know that he 'opposes" diving on air/nitrox at 101' for instance. It seems to be that some people are saying that's his position however, so I'd love to get clarification on his professional thoughts for that scenario.

I could be wrong, and I'd love to hear his answer, so maybe @Dr Simon Mitchell will answer that question.

Assistant Professor Mitchell has stated using 32% as a decompression gas is fine.

 

[grantctobin]

Assistant Professor Mitchell has stated using 32% as a decompression gas is fine.

Sure. Do you know at what point in diving you begin to use 32% or 30/30 as a decompression gas? In your view, what is the difference between the two? At what depth do you switch to 32%?

 

[Scuba Client]

You can have a look at these reports, but they're a bit old:
http://media.dan.org/RF3_web.pdf
http://www.swiss-cave-diving.ch/PDF-dateien/2008TechDiverReport.pdf

Wikipedia has a lot of references here:
Rebreather - Wikipedia
Scuba diving fatalities - Wikipedia

There was a report about diving safety citing three categories of divers at high risk:
(1) newbies (<100 dives of experience)
(2) people who dive often (>300 dives per year)
(3) rebreather divers
Unfortunately, I do not manage to find this report anymore... so take my information with caution

All these reports are relatively old, so things may have changed now; the idea I got is that 10 to 20 years ago they were less safe because they were less known. Now I believe things are changing - but it's just an impression, nothing more.

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.

 

[Scuba Client]

Sure. Do you know at what point in diving you begin to use 32% or 30/30 as a decompression gas? In your view, what is the difference between the two? At what depth do you switch to 32%?

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.

 

[Scuba Client]

No, it's an opinion, and yours is well and truly in the minority.

Status is everything among peers.

 

[Scuba Client]

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!

 

[lostsheep]

@Scuba Client

you must be loads of fun at parties.

also, are you aware of the multi quote function?

 

[grantctobin]

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]

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]

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