My AN/DP/Helitrox course

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I don’t agree that 1 on 1 is bad.
My experience with my first deco course was 1 on 1. The instructor was actually more attentif to me and could provide me with even more training. Heck since he was my buddy he was able to turn on or off the silliness and when he had “issues”. It made. Even more realistic and challenging. I still remember when he was out of air, stuck in a wreck door, upside down.
What a great moment and learning. It couldn’t have been done with 2 students.
 
And I got up the pool ladder from deep end twice with doubles on. Needed pulls on manifold, but I don’t care. This alone is major improvement. I’m putting in 45-60 min 3-4 times a week on the recumbent bike at the gym.

Marie13: I remember when you first started talking about your plans for exercise and getting in shape for this course. I am impressed that you have done all that you have done to be ready. Good job.

Except 80% is a lame choice of deco gas. That one is certain.

Please elaborate and give us your insight. As I’ve been preparing for my AN/DP/Helitrox course, I’ve been doing a lot of side reading, and I am intrigued by the idea of decompression oxygen vacations. Especially on 100%. So I’d like your insight on why 80% is lame.
 
Please elaborate and give us your insight. As I’ve been preparing for my AN/DP/Helitrox course, I’ve been doing a lot of side reading, and I am intrigued by the idea of decompression oxygen vacations. Especially on 100%. So I’d like your insight on why 80% is lame.

Interested to hear the rationale as well - after all, some agencies still only certify up to 80% for accelerated deco...
 
For starters, O2 is the most effective deco gas. Zero inerts. You can deco at the same effectiveness anywhere between 20 and the surface, so you have the option of staying at 20 or ascending. For where you're going to spend the bulk of your time on shallow deco, between 20 and the surface, 80% has a lower PO2 and relies on changes in pressure gradient to offgas efficiently. You're also spiking your PO2 deeper when you switch at 30ft, so depending on what intermediate gas you used, you might be increasing your O2 exposure. It's also only 1.53 at 30ft, so by the time the gas gets to your blood, it's even lower. You're gonna make up that shortened 30ft stop on O2 later, so the time will work out even. But you'll have the flexibility and efficiency of O2 throughout your shallow stop instead of an inefficient gas.
 
For starters, O2 is the most effective deco gas. Zero inerts. You can deco at the same effectiveness anywhere between 20 and the surface, so you have the option of staying at 20 or ascending. For where you're going to spend the bulk of your time on shallow deco, between 20 and the surface, 80% has a lower PO2 and relies on changes in pressure gradient to offgas efficiently. You're also spiking your PO2 deeper when you switch at 30ft, so depending on what intermediate gas you used, you might be increasing your O2 exposure. It's also only 1.53 at 30ft, so by the time the gas gets to your blood, it's even lower. You're gonna make up that shortened 30ft stop on O2 later, so the time will work out even. But you'll have the flexibility and efficiency of O2 throughout your shallow stop instead of an inefficient gas.

In addition to the above, simpler to blend (none). Higher medical safety--ie can be used to treat medical issues on the surface.

Depending on dive profile,
50% provides benefits in reserve gas calculations and/or starting deco sooner

100%-the most efficient deco gas

80% is inbetween these two and doesn't do any of them particularly well. It's mostly a hold over from a time where shops couldn't fill more than 2300 psi of O2 and topped deco bottles with air to get to 3000 psi or that it was believed that people couldn't hold a stop so having an MOD of 30' was a margin of safety on deco.

You can do a dive profile where 80% mathematically clears deco a couple of minutes faster. That is a computer model and ignores real world practicality, execution, and safety margins.
 
Well, 80 % is particularly popular among North Carolina wreck divers because 100% brings you very close to a choppy surface with some serious wave action. Hanging at 20'ft for your 100% means you will be taking a beating by the waves. Even holding the line can feel like a rodeo :D at time. 80% gets you a little farther away from the surface so it is easier to hang there.
 
You can do a dive profile where 80% mathematically clears deco a couple of minutes faster. That is a computer model and ignores real world practicality, execution, and safety margins.

Other than mathmatical modelling that many of us rely on in the form of deco software, what other benchmark do you suggest to tell us when we have successfully eliminated inert gas to a safe level?
 
Other than mathmatical modelling that many of us rely on in the form of deco software, what other benchmark do you suggest to tell us when we have successfully eliminated inert gas to a safe level?

Apart from some stuff previously mentioned, It means that diving isn't a perfect computer simulation and no one is instantly jumping out of the water just as the clock hits triple zero.
 
80% is quite popular as a last bailout gas percentage on a RB too because it spreads the load across required cylinders by allowing a deeper switch, it's more likely that the deeper bailout and intermediate gasses will be hammered more than the last gas by which time you may be more composed, lower consumption rate etc.
 
https://www.shearwater.com/products/teric/
http://cavediveflorida.com/Rum_House.htm

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