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View Full Version : Trimix Help. PLEASE



vegas911diver
02-11-2011, 18:14
OK. I hope the Trimix gurus on here can help, and please provied me a fairly simple answer.

I will be doing my first trimix dive this weekend. Dive is to 175 feet hard bottom. I will have a 21/40 for my back gas, a 21/30 for a travel gas, 50% ean, and 100% O2.

Running in Vplanner, to accomplish my "mission" my total run time is 92 minutes.

My O2 stop at 20 feet will be 18 minutes. We are putting in a 5 minute airbreak, so total 20 foot stop will be 23 minutes, including the airbreak.

I have been told, that while doing an airbreak, it is a good idea to switch to my 50% mix, instead of my back gas.

Can someone here give me readers digest version as to why?

Thanks in advance for any help.

UCFKnightDiver
02-11-2011, 21:48
I believe oxygen is a vasoconstrictor and thus it make sense to open up the lungs with a lower o2 mix (ie. backgas) once in awhile to facilitate efficient gas exchange when on the high oxygen content , makes no sense to me to switch to 50% over backgas but I'm not an expert on it. Seems though if you're asking these questions that you may not be ready to do the dive...

jbres1
02-11-2011, 23:04
This question would be better to ask over on THE DECO STOP.
But , be ready to be jumped on with both feet by the posters over there.
Your question is one that most normal divers can't answer, but THE DECO STOP
has those guys .
Jim Breslin

jj1987
02-11-2011, 23:23
OK. I hope the Trimix gurus on here can help, and please provied me a fairly simple answer.

I will be doing my first trimix dive this weekend. Dive is to 175 feet hard bottom. I will have a 21/40 for my back gas, a 21/30 for a travel gas, 50% ean, and 100% O2.

Running in Vplanner, to accomplish my "mission" my total run time is 92 minutes.

My O2 stop at 20 feet will be 18 minutes. We are putting in a 5 minute airbreak, so total 20 foot stop will be 23 minutes, including the airbreak.

I have been told, that while doing an airbreak, it is a good idea to switch to my 50% mix, instead of my back gas.

Can someone here give me readers digest version as to why?

Thanks in advance for any help.
First, you're running a semi high ppo2 for a mix dive. People have toxed below 1.4 even, so typically you want to keep your working portion of the dive around 1.2 by most modern ways of thought. I would consider 18/45 rather than 21/xx.

Why bother with an air break at 18min of o2? I would do the 30ft stop on back gas while you clean up your 70ft bottle.

Why are you using a travel gas on a normoxic mix? Extra regulators floating around aren't a good idea IMO.

Anyways, to answer your question about back gas breaks, the idea behind them is that you lower your ppo2 temporarily because oxygen is a vasoconstrictor and will limit blood flow and therefore limit the amount of blood that crosses the various tissues (and hence you're losing the gradient advantage).