Looking to use 100% O2 on an upcoming Scapa trip for some of the deco dives. Not a concentration I'm too familiar with for 6m stops. I know that gas breaks off it are adviseable every 20 minutes or so for 5 minutes but is that to the travel gas (which will be 50) or back gas (probably weak trimix)? How does the pause affect planned runs times for deco that haven't included a break, do you just do an extra 5 minutes on 100% to make up for the break? Information recommending to take the break is widely available but not the implementation.
How long are you expecting to be @6m for? Realistically unless the 6m O2 stop is getting up to 25-30mins then there is no benefit to gas breaks. Since most of Scapa is max 40-45m ish I'm not sure that I see the point, unless you're planning really long run times. Personally I do 12min on, 6min off, and count all of it towards my 6m time, but this is for dives with 30-90minute 6m stops after the same amount of time getting from 21-9m. HTH John
Thanks, I don't plan to use 100% for long deco stops at Scapa, but to eek out resources ie air top on remainder for next deco dive. Qu was really just to try and expand my knowledge on the application of 100% as a deco gas. Since asking, have found the gas break tool in v-planner.
Thanks. If I do ever use it for longer breaks, apart from a bit of a difference to run times, is there any benefit breaking to the travel gas such as 50% or bottom gas such as air or weak nitrox; is the lower o2 concentration preferable or does it not matter?
I always switch to a trimix for my gas breaks. Ideally the lowest O2/highest He but it needs to be breathable at 6m. I've stopped using 10/70 for break gas now and tend to use 21/35. HTH John
Sometimes Gary I have to question what you were taught on AN/DP and trimix courses, Iv noticed youve asked some questions in the past that should have a fresh answer at the front of your mind. Hope I dont sound Negative in anyway but the use of O2 was discussed in some depth on both courses as I remember when I took them. sorry couldnt find a nicer way of saying it
Like what specifically know all? Neither the TDI AN/DP nor the Trimix Advanced goes in to any depth whatsoever about the use of oxygen for accelerate deco and certainly nothing about the use of gas breaks, ratio deco, isobaric counter diffusion nor, believe it or not, trimix diving by gekko and guess work (sound familiar). There is a chapter on gas choices for accelerated deco but nothing at all about specifically using 100% O2. So what else are you on about that I've asked questions that you think I should have known the answer to? Don't forget, my technical training and theory was perfectly adequate and I dive safely to advanced levels. However, some of us aren't locked in to one way of thinking and want to widen their knowledge to include other concepts and ideas. That may lead to questions asked that someone else reads too much in to or draws the wrong conclusion to, which you've done. So come on then Si, back up your statement with some facts. What else have I asked that you think I should already know...Or maybe you misread what I was questioning. You do sound negative actually, the post was unecessary, I thought you knew me better. The statement was a bit rich considering many of the dumb ass comments you've made on forums but I left alone.
Sorry I didnt mean it to come across like that I dont know whats in the TDI course criteria on gas selection for deco and wether the use of 100% O2 and gas breaks are to be covered. I do know in my training covered it in quite some depth. Maybe its down to instructor descretion on wether the subject is to be covered and some cover it and some dont or some chose to add it as its valueble information that should be knownand understood. I cant remember what else it was that you asked about at the moment but I do remember saying something like 'youve just done your trimix ticket'. It will come to me. Also Im not questioning your abilities as I dive quite often with you and you are very skilled and safe. More than you say, as being perfectly adequate. So I apolagise if my post came across as negative and dumb ass and can say that my mis understanding comes down to choice of instructor and what information they wish to convey during the course.
Also, how much info is taken on board during these intensive courses? Some will inevitably be forgotten.
Two trimix dives today. First to 60m, second to 50m, deco gas 50 and 100. Not quite sure how, but I survived
The second dive was quite conservative. At risk of revealing more of my lack of knowledge, though I understand the risks of over exposure, I've never quite understood why 2 deco dives in a day would be a problem if absorbed nitrogen and helium levels have lowered to acceptable surface levels, there's a good surface interval and total CNS for 24 hours stays within parameters etc. Is there good reason to indicate to the contary or subjective factored-in conservatism? If it's not a good idea, why? Is an undeserved bend more likely.
Surely you were taught that if you went in to decompression you had to stay out of the water for 24hrs
That time of the month already? For me it's conservatism due to lack of fitness and increased podge. Gawd knows what those nitrogen bubble will latch on to.
For last dive chugged 50 til deco time cleared and then about another 15 minutes swimming around, so didn't need the 100 but did some on it anyway to finish. Very clear head and no tiredness for 3 hour drive home.
