Ean30?

[BDSC]

I was off the coast this weekend as well and 30% is the standard mix for the group I dive with.

 

[beaverdivers]

Is it common for shops to bank only 30%?

I wonder if it has more to do with the cost to profit ratio?

 

[HIGHwing]

Remember when it comes to staying within NDL's, you generally get more bottom time by doing your deeper dives first.

Give me an example and use the same gas for all repetitive dives as the initial dive.

 

[kotik]

Give me an example and use the same gas for all repetitive dives as the initial dive.

Okay...

Dive 1, 30 minutes, 80 feet, air.
1 hour surface interval.
Dive 2, 60 feet, air. 36 minutes of residual nitrogen time apply, total time allowed within NDL is 14 minutes

Contrast to:
Dive 1, 30 minutes, 60 feet, air.
1 hour surface interval.
Dive 2, 80 feet, air. 23 minutes of residual nitrogen time apply, total time allowed within NDL is 7 minutes

Now, for your half of the assignment... can you please give us the equivalent air depth of EAN36 at 80 feet, and tell us which sequence to use our gases for two dives to 80 feet, if our other tank is filled with air?

 

[Andy Lazar]

the shop I use banks 40% and dilutes it down from there to whatever the customer wants. Kinda the best of both I think. I can get the super rich stuff but don't have to have my tanks O2 cleaned.

 

[Colliam7]

Is it common for shops to bank only 30%? Particularly, is it common enough that I should be asking about this when planning a dive trip? The shops around the area where I live either do partial pressure blending or bank 36% from a membrane system.

I cannot say if it is 'common', but it is certainly not unheard of on the East Coast, particularly as you move north into colder water areas. In fact, I think the trend is growing. I started a thread related to the topic at the beginning of the year (http://www.scubaboard.com/forums/ad...ox-mixes-you-use-best-mix-what-available.html) because I was curious about the issue - how many shops bank something other than 32% (or 36%) and what mixes do they bank. Based on the comments, it appears that quite a few bank mixes lower than 32%.

It sounds like you are set for your local diving. But, if you travel to dive, you should certainly ask in advance. While some shops do membrane blending, many (? most) do not - at least the higher volume fill stations often do not, and choose instead to bank a standard mix, such as 30% or 32%. I encounter very few shops in the mid-Atlantic that bank 36%.

We bank 30% because the mix works for the majority of wrecks dive-able within recreational limits off the NC coast. The MOD (121 ft) works, even if the diver loses buoyancy and ends up in the sand at a slightly greater depth (130-135 feet) on a couple of the deeper NC recreational wrecks (e.g. the Naeco). Given that most recreational charters off the coast are 2-tank dives (with the 3-tank trip being an uncommon exception), some additional nitrogen loading from diving 30% vs 32% really isn't an issue. With enriched air, I am more concerned about oxygen toxicity than I am about nitrogen loading (even if I go out 2-3 days in a row, for 2-tank charters).

Also, I'm curious - why would a shop choose to bank a mix like that instead of blending or banking a higher mix they could thin out if necessary?

From our perspective (we bank 30%), convenience / cost and the possibility of error. If we have to re-blend every time we fill a cylinder with nitrox, that is an extra step that takes time (which adds to cost) and opens the door to error. We would rather charge a modest amount for a nitrox fill, and would have trouble doing that if we had to partial pressure blend each time we filled a nitrox request.

 

[oly5050user]

At first glance your dive profiles did not look correct. So I had to dig up a PADI RDP and an old USN table here at home;

Okay...

Dive 1, 30 minutes, 80 feet, air.
1 hour surface interval.
Dive 2, 60 feet, air. 36 minutes of residual nitrogen time apply, total time allowed within NDL is 14 minutes

....80' @ 30minutes makes you a "R" diver on a RDP..stay out for 1 hour now you are a "F" pressure group.now want to make 2nd dive to 60' your ANDL time is 36 minutes .. not 14..

Contrast to:
Dive 1, 30 minutes, 60 feet, air.
1 hour surface interval.
Dive 2, 80 feet, air. 23 minutes of residual nitrogen time apply, total time allowed within NDL is 7 minutes

60' for 30 minutes makes you a pressure group "L"..take a 1 hour SI now you are pressure group "C"..dive 2 for 80' as a pressure group "C" diver gives you 20 minutes of ANDL time..
My answers came from a PADI RDP..if you used a different table,what was it? If it was US Navy table your answers are wrong there too.
US Navy table; 1st dive 80' 30 minutes makes you a "G" diver,,1 hr SI now you are at "F".dive #2 at 60'does give you RNT of 36 minutes with a ANDL of 24 minutes, not 14 minutes.

 

[beanojones]

I will buy anyone who actually dives recreationally with tables free 36% nitrox for life (Not really)

I just have never seen, in last twenty years, since dive computers became reasonably available, anyone actually plan and execute repetitive dives using a table. (Outside of being forced to do so during a class before they allowed computers for PADI classes.)

I have seen lots of people say they were planning dives on a table after their computer died so that they would not be held out of the water, and I have seen people say they were diving tables before they hit the water and just followed their buddy who was using a dive computer, or just waved the table around so they could say they were using a table. But I have not seen anyone ever use a dive to plan and execute repetitive dives (and this is seeing 4-20 divers a day every work day, so the numbers are well into tens of thousands).

Especially on a 121 foot dive, where they table allows for a dive time of "just about long enough to equalize one's way to the bottom" for most divers.

The reason I mention this, is because worrying about tables makes people give bad advice like "dive the leanest mix first" because "tables", which no one is actually using.

Always minimize the nitrogen loading for every dive. Always. The boat can break down, weather can cancel the second dive, etc. etc.

We have one body for life, and people can get bent on any dive. Reduce the risk, use the best mix on the dive ahead of you and worry about later dives later.

 

[kotik]

Well shoot-- many ways to be wrong, but only one way to be right. If only you'd checked the SSI table!

If you prefer using the navy table, then take a look at a first dive of 25 minutes, with a 1 hour surface interval before a second dive. Use 100 feet and 80 feet for the dive depths. I believe you'll find that you get a longer bottom time allowed within the NDL's if you do the deeper dive first.

The point I intended to make wasn't so much the exact quantity of NDL time stated by any given algorithm or table. It seems to be the case that most of the time, given two dive depths, a specified time for the first dive, and a specified surface interval, you're allowed more total NDL time if the deeper dive comes first. Since a richer nitrox mix equates to a shallower equivalent depth, it's usually going to make sense to save the richer mix for the last dive, all else being equal.

At first glance your dive profiles did not look correct. So I had to dig up a PADI RDP and an old USN table here at home;

....80' @ 30minutes makes you a "R" diver on a RDP..stay out for 1 hour now you are a "F" pressure group.now want to make 2nd dive to 60' your ANDL time is 36 minutes .. not 14..

60' for 30 minutes makes you a pressure group "L"..take a 1 hour SI now you are pressure group "C"..dive 2 for 80' as a pressure group "C" diver gives you 20 minutes of ANDL time..
My answers came from a PADI RDP..if you used a different table,what was it? If it was US Navy table your answers are wrong there too.
US Navy table; 1st dive 80' 30 minutes makes you a "G" diver,,1 hr SI now you are at "F".dive #2 at 60'does give you RNT of 36 minutes with a ANDL of 24 minutes, not 14 minutes.

The reason I mention this, is because worrying about tables makes people give bad advice like "dive the leanest mix first" because "tables", which no one is actually using.

Whether people plan on tables or a computer, the theory comes from the same place. Generally, I plan my dives using a computer, and if I have one mix leaner than the other, I very definitely look at which one to dive first. I don't see why it's bad advice, you have to pick one or the other, what's the problem with using some sort of reasoning to arrive at the answer?

 

[AfterDark]

I always use the tables to plan and the PDC to execute. If the PDC differs sigfinicantly from the tables and the tables are more conservative, I go with the tables, if the PDC is more conservative I'll go with it. Haven't been bent yet, even did a lot of deep air deco pre PDC days.