Decompression Tables for Nitrox

[Aquabot]

I was trying to ferret out which is correct... For Deco - it is intuitive that when you have a stop time it is a hard stop/ceiling...
I do not plan on using the Deco tables but I wanted to make sure I understood them.

Yes that becomes a virtual ceiling.

 

[victorzamora]

Is anybody else uncomfortable covering deco topics with someone without even a rudimentary understanding of Nitrox and with less than 24 dives (per the account info)?

Please seek training. What sine guys on the Internet tell you is NOT enough. Seek good recreational Nitrox training. Seek a good dive mentor. Read remedial material your instructor and mentor suggest. Then, after MUCH more dive experience, progress into tech.

 

[rivers]

You view is not supported by the incidents reports.

How many people are actually using the 88s? Because I don't know a single diver who will touch them. Even the ODs in my club were lent computers for their training from other divers so they wouldn't have to rely on the 88s. In fact, in my ADP course we were told by my club DO that we were only learning the ox-stop tables because he had to teach them. We wouldn't actually be using them to plan our dives because of how aggressive they were. I believe we used VPM +3 conservatism (it was while ago and i tend to use 30/85. I was outvoted on the course and went with the rest of the team). The Ox-Stop tables gave us something like 3 minutes of deco at 6 for a 30 minute, 35m dive on air with 80% as a deco gas (not that any of us were actually doing the dive on air, but that's not the point). VPM gave us somewhere in the region of 15 minutes of total stops spread between 15 and 6m. Now tell me how the BSAC tables are not aggressive? Even a GF of 100/100 gives me 7 minutes of stops at 6 for that profile (including the BSAC polaris ascent rate of 15m/m until the stop).

 

[Edward3c]

How many people are actually using the 88s?

As easy to answer as how many people use computers? Your guess is as good as mine.

Because I don't know a single diver who will touch them. Even the ODs in my club were lent computers for their training from other divers so they wouldn't have to rely on the 88s.

Was that really the case or was it the instructors have become reliant on their computers?

In fact, in my ADP course we were told by my club DO that we were only learning the ox-stop tables because he had to teach them. We wouldn't actually be using them to plan our dives because of how aggressive they were. I believe we used VPM +3 conservatism (it was while ago and i tend to use 30/85.

Again riding a computer rather than calculating depth/time.

I was outvoted on the course and went with the rest of the team). The Ox-Stop tables gave us something like 3 minutes of deco at 6 for a 30 minute, 35m dive on air with 80% as a deco gas (not that any of us were actually doing the dive on air, but that's not the point). VPM gave us somewhere in the region of 15 minutes of total stops spread between 15 and 6m. Now tell me how the BSAC tables are not aggressive? Even a GF of 100/100 gives me 7 minutes of stops at 6 for that profile (including the BSAC polaris ascent rate of 15m/m until the stop).

Your comparing algorithms based on different criteria. At 15m you're still on-gassing some tissues so your algorithm must compensate. Doesn't mean one is better or worse than the other they're just different. In addition your citing different dive profiles. The BSAC ascent rate is a red-herring as the 30 minute point you should be at 6m.

Its unfortunate that most of the divers I see, and dive with, jump in and rely on their computer to control the dive. I'm enjoying going in at the moment with newly qualified CCR divers whom haven't become blasé, so I can plan my 30-35m, 60+ minute OC dives and know how much gas I'm going to surface with.

 

[Aquabot]

Careful Edward3c, next you'll be explaining gradient factors lol

 

[rivers]

Again riding a computer rather than calculating depth/time.

Actually they were planned and executed with tables cut using mutli-deco. Ran exactly to time thanks. i don't use a computer. i either cut my own tables on multi-deco or use GUE min deco tables

 

[KenGordon]

Read Deco For Divers by Mark Powell.

There are two distinct types of "nitrox" tables.

The first type is for simple dives with one gas. Some (but not all) air tables can be used to derive these for a given depth by using an equivalent air depth (EAD) as mentioned by others. Alternatively there are tables which give times by actual depth and mix. The BSAC Nitrox tables do that. By way of an illustration the no stop time for 32% at 30m is 40% longer than the same dive on air.

The other type is for multiple gas dives where a rich mix is used for shallow stops. This is technical territory. Using these might cut stops by 75% compared to deco on air. The BSAC Ox-Stop tables do this.

I guess you are interested in the first. You can get them from BSAC but you'd need the training to go with them really. It isn't hard but it is not the same as for other systems.

Your PADI course isn't going to cover decompression diving but ought to explain why a no stop dive can be longer and why diving 36% to 40m is a bad plan.

If you are interested in the tables just to get an idea of the advantages of nitrox then have a play with some of the free dive planning software. The absolute values do not matter, just see how long a dive you can do before you get into deco with air, then again with some other mix. Tables are better at this though, see www.bsac.com if you want to buy a set.

I am a fan of nitrox. There is more to it than avoiding deco, it is insurance too.

 

[tursiops]

I was trying to ferret out which is correct... For Deco - it is intuitive that when you have a stop time it is a hard stop/ceiling...
I do not plan on using the Deco tables but I wanted to make sure I understood them.

OP, in your post #50, Aquabot and I are saying two different things, we are not disagreeing with each other. He uses "deco" to mean a mandatory stop; I was using it to mean all the off-gassing that occurs as you come to the surface...much of which occurs as the stops, but some of which also occurs during the ascent. In fact, if you could ascend at exactly the right (which would be very slow!) rate, you would not need to stop at all. But you can't control your ascent that well, so we use stops instead.

 

[Basking Ridge Diver]

I was using it to mean all the off-gassing that occurs as you come to the surface...much of which occurs as the stops, but some of which also occurs during the ascent. In fact, if you could ascend at exactly the right (which would be very slow!) rate, you would not need to stop at all. But you can't control your ascent that well, so we use stops instead.

Can I ask a question - I think I understand your point about ascending slowly enough to the surface to avoid any "stop or stops"... It makes sense if you had enough gas and could control the ascent with precision - which is currently beyond my buoyancy control.
But does it "really" matter the ascent rate to the first stop? Taking the shaken Tonic Bottle approach (yes I am originally from Boston and can't say Pop or Soda) - will I cause bubbles to form if I ascend faster than 30 feet per minute to my first stop? Or is that overblown theory and as long as you hit your stop and stay there you are relatively safe?
Thanks.

 

[tursiops]

Can I ask a question - I think I understand your point about ascending slowly enough to the surface to avoid any "stop or stops"... It makes sense if you had enough gas and could control the ascent with precision - which is currently beyond my buoyancy control.
But does it "really" matter the ascent rate to the first stop? Taking the shaken Tonic Bottle approach (yes I am originally from Boston and can't say Pop or Soda) - will I cause bubbles to form if I ascend faster than 30 feet per minute to my first stop? Or is that overblown theory and as long as you hit your stop and stay there you are relatively safe?
Thanks.

No, the 60 would be fine (if you are not too close to the surface), but you'd only spend half as much time getting to that next stop, so you'd only get half as much off-gassing during that ascent. When you set up the software, it asks what ascent rates you will use. That is so it knows how long you will be getting some off-gassing between stops. The point is the fractional releaase of pressure...so a 10 ft ascent when you at 100 ft is a small fractional release (10/133), but from 30 ft to 20 ft that change is a much larger fraction (10/63) of the ambient pressure. So going faster deep is ok, but you want to go slower when shallow. Also, there is the problem of trying to offgas when you are very deep.....you may be releasing pressure, by ascending, but some of your "compartments" may still be on-gassing. This is sometimes approximated by some cross-over depth (probably around 80 feet in the OP's 120ft-max example), below which you are still on-gassing, and above which you are usefully off-gassing.