Technical Diving Gas Mix Question

[mathauck0814]

This question is also ask on other sites around the web. Very interesting to say the least.

The question itself isn't very interesting, it's just math and some obvious regurgitation from whichever text it was extracted. What's interested is the "why" behind it being asked.

 

[GrimSleeper]

Hi all,

Hopefully this will make sense to you tec divers. i have never done technical diving and would be interested in knowing the answer, if its not a hassle.

Here is the question a friend asked

What is the best mix for 457 feet - Trimix and the MOD + EAD of the mix. We will compare gas mixes. And your _________ can't have more nitrogen in it than your back gas or else you will experience _________ ___________________.

thanks

I often find that my friends ask me 'fill-in-the-blanks' advanced decompression diving questions when we're at the pub. Oh, hang on, no they don't.

And, as others have said, without having decided on an acceptable END and max ppO2, the first part of the question is unanswerable.

 

[Bombay High]

Hi all,

Hopefully this will make sense to you tec divers. i have never done technical diving and would be interested in knowing the answer, if its not a hassle.

Here is the question a friend asked

What is the best mix for 457 feet - Trimix and the MOD + EAD of the mix. We will compare gas mixes. And your _________ can't have more nitrogen in it than your back gas or else you will experience _________ ___________________.

thanks

I would use only Heliox for a dive deeper than 100 metres. I would also deco only on Heliox. I would also only do this dive Close Bell supplied. Attempting this open circuit or on a rebreather would involve really long inwater deco ... thats an expedition by itself. Also make sure you have a chamber topside. After you have all that in place, start worrying about your mix. Heliox is the best choice, because you eliminate the 2nd inert gas, which in any case would have to be very little for reasons of narcosis. If you go closed bell, you let the supervisor worry about mix and deco. You focus on the dive ...

However you may need more training than padi rescue

 

[wedivebc]

Heliox is the best choice, because you eliminate the 2nd inert gas, which in any case would have to be very little for reasons of narcosis. If you go closed bell, you let the supervisor worry about mix and deco. You focus on the dive ...

Actually the benefit of the small amount of nitrogen is to delay the onset of HPNS. Dives like these are being conducted all the time by non-commercial divers without the use of chambers or closed bell setups.

 

[Bombay High]

Actually the benefit of the small amount of nitrogen is to delay the onset of HPNS. Dives like these are being conducted all the time by non-commercial divers without the use of chambers or closed bell setups.

Accepted ...
HPNS can be avoided by a slow compression rate. I know these kind of dives are being done ( I have done open circuit dives to 150 metres many times) but there are huge logistics involved. At my age (24 yrs as a working diver) I only do those dives in a closed bell with a chamber to lock into at night

PS - One of my only deep dives (in excess of 100m) on Trimix landed me with Type 2, so I have a healthy fear of any hypoxic mix with high He and low N2 that involves deco on N2 mixes.

 

[EastEndDiver]

Guys,this may be a 17 year old kid asking the question.The same question was asked here:

West Australian Divers • View topic - Tec Gas Mix Question


And if you follow him on this board he is looking for a $300K boat and states he comes from money and is 17.

Technical Diving Gas Mix Question? - Yahoo!7 Answers

I have too much time on my hands.

 

[boulderjohn]

OK, so the guy has asked the same question on at least three different sites, maybe more. Each time he insists it is just out of curiosity. I will take him at his word for that, but on the off chance that he might be looking for enough information to get what he needs so that he can do a specific dive without first gong to the trouble of getting appropriate training, I am going to be even less forthcoming with details than before.

 

[Rhone Man]

OK, so the guy has asked the same question on at least three different sites, maybe more. Each time he insists it is just out of curiosity. I will take him at his word for that, but on the off chance that he might be looking for enough information to get what he needs so that he can do a specific dive without first gong to the trouble of getting appropriate training, I am going to be even less forthcoming with details than before.

Pretty unlikely. Can't see a 17 year old getting a 8/80 (or any other blend of trimix) fill from anyone.

 

[boulderjohn]

Pretty unlikely. Can't see a 17 year old getting a 8/80 (or any other blend of trimix) fill from anyone.

I agree, but what you can do and what you think you can do are not always the same thing.

 

[ianr33]

Pretty unlikely. Can't see a 17 year old getting a 8/80 (or any other blend of trimix) fill from anyone.

Even if he could afford it.