dive to 300 ft
- Thread starter Crush
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I'm glad we can agree on something. One day, when I grow up, I wanna be like you and have access to the fountain of unlimited knowledge.
AJ and gsk3, your warnings fuzzing around inhaling hypoxic gas at surface are well received. Getting down to 1.6 ATA's on a breath hold may be safer than breathing 10% O2 at the surface. If for any unforeseen reason you find you need to take a breath before you get to 1.6 ATA's then you might want to start breathing out of the 35/25 bottle, and not out of the 10/70 bottle. After all, being kept there by an unforseen situation might mean you have to remain there longer than comfortable for 10/70. Once you start inhaling hypoxic you are on a short countdown to snoozing time or maybe even the afterlife.
So what is proper DIR procedure for a dive like this? Breath hold initial descent, one or two breaths of hypoxic 10/70, or using 35/25 as a travel mix?
Neither. You would use one of your deco gases for the initial descent.
Hth
John
What's the deepest deco gas you would use on a 300 foot dive?
PfcAJ
Contributor
Depends on the exposure. 120 or 190 deco gas (35/25 or 21/35).
that's what I was thinking.
On my last 250+ dive, I used 21/35 for my first deco gas. I also used it for the initial descent, and I was glad I did. We had to fight a ripping current to get to the descent line, and it took an unexpectedly long time just below the surface to get there.
I thought of the 21/35 as a travel gas when I used it for the descent, and that was the vocabulary that I was taught to use.
There is a difference in using a deco gas to travel and in actually carrying a travel gas that serves no other purpose. The idea of carrying a dedicated travel gas is where the objections are - not in using the terminology in the way you presented.
Completely understood. I am just getting the vocabulary usage clear.
Generally 21/35, I tend not to use 35/25 until the exposure is long enough that the 36-24m stops get longer than about 3-4 mins.
Or if I'm in a cave where the profile requires more gas in that region.
HTH
John
limeyx
Guest
Interesting to see you guys skipping the 120 bottle. Something we've been considering here as well, as the min gas just starts to get insane with only a 120 bottle, but if you bring the 120 as well, it just seems to get into bottle hell.
limeyx
Guest
Yeah, I have descended in reasonable conditions on 12/65 a few times with no ill effects (although it was annoying getting slammed in the face with surface chop on one dive as we tried to fix a reg leak)
for 10/70 I would almost certainly just breathe the 190 bottle on descent, not just to have something breathable but to save the bottom gas a little too (depending on how much of the 190 bottle you expect to use of course)
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