Nitrox mix question.

[MuddyRubberDuck]

Ok, story is, I am going to West Palm next week. I have a dive computer but I am trying to calculate the time. Usually our dives there are bt 90 and 110. so if I plan for 110. My mix in them right now is 28% which should be

@ 1.6 po2
Mod 155
EAD 97.33

Using naui dive tables for that ead I should have 22 min of bottom NDL time.
Just making sure my math is right so I defer to your wisdom.
I am just trying to figure out if I should have some more 02 put in them.

Thanks
Neil

 

[DiveNav]

....
@ 1.6 po2
Mod 155
EAD 97.33

I would suggest to use a po2 lower than 1.6ATA ..... like 1.4ATA

 

[MuddyRubberDuck]

Ok I was trained at 1.6, but for the sake of getting answers to my question I will say 1.4 as it changes the mod to 131 but the Ead remains the same either way. 131 is still a viable contengency depth for 110.

Trying to get my max NDL time.

Thanks
Neil

 

[Bubbletrubble]

The vast majority of divers would say that a standard 32% mix is very workable in the 90 - 110 fsw range.

If your goal is to maximize bottom time at max depth, then a 32% mix would be preferable.
If your goal is to add an extra level of conservatism to protect against ox-tox at the cost of bottom time, then stick with the 28% mix.
Sorry I don't have the NAUI tables handy...

 

[Puffer Fish]

Ok, story is, I am going to West Palm next week. I have a dive computer but I am trying to calculate the time. Usually our dives there are bt 90 and 110. so if I plan for 110. My mix in them right now is 28% which should be

@ 1.6 po2
Mod 155
EAD 97.33

Using naui dive tables for that ead I should have 22 min of bottom NDL time.
Just making sure my math is right so I defer to your wisdom.
I am just trying to figure out if I should have some more 02 put in them.

Thanks
Neil

I don't have any NAUI table with me right now, but decocheck and my Galileo show 16 minutes as the no deco time for 110 ft with ean 28. 22 would be a pretty good deco obligation.

I would also suggest not using a max of 1.6...

However, I would consider doing that dive with 32%.. if 110 is actually the maximum. Even then, you will not get 22 minutes.

 

[scubaswede]

1.4 Normal diving (Bottom mix)

1.5 Contingency plan if I f something up

1.6 for Deco only

 

[Puffer Fish]

If you are spear fishing at that depth, being a bit more conservative on the PO2 would also be suggested.

 

[MuddyRubberDuck]

I appreciate all the input guys thanks. I am just trying to get a grip on why there are so many different opinions. I have been sitting here going through different dive tables and my computer. While the aeris atmos 2 is no match for a galileo. At that mix my computer is giving me 21 min. Seriously I appreciate all your help.
thanks
neil

 

[scubaswede]

Different agencies, different levels of experience.

I do most of my planning with v-planner, or TDI tables. (Deco diving that is)

In this case somewhat shallow and short time, I go with;

I would use 32% for 110ft (1.4)

28% is good to 136ft (1.4)

 

[Guy Alcala]

Ok, story is, I am going to West Palm next week. I have a dive computer but I am trying to calculate the time. Usually our dives there are bt 90 and 110. so if I plan for 110. My mix in them right now is 28% which should be

@ 1.6 po2
Mod 155
EAD 97.33

Using naui dive tables for that ead I should have 22 min of bottom NDL time.
Just making sure my math is right so I defer to your wisdom.
I am just trying to figure out if I should have some more 02 put in them.

Thanks
Neil

I come up with an EAD of 96.4 ~97. My tables are SSI rather than NAUI, and IIRC NAUI tables include the next higher USN group in NDL compared to SSI, but figure bottom time as surface to surface (excluding stop time) instead of surface to start of ascent. So 22 minutes NAUI NDL for an EAD of 91-100 feet would be the same as my SSI 20 minutes at 91-100 EAD. As others have stated I'd personally choose 30%-32% for that dive, if I wanted to maximise my BT and/or minimise bubbles, but it's just a question what PO2 max. you're comfortable with, including contingency.

Using a richer mix you'll have an EAD of at/below 90 feet down to 105 feet (30%) or 109 feet (32%), which would buy you another 5 or so minutes of NDL.

Guy