Some Basic Nitrox Questions

[Vibenz]

I'm considering nitrox as the next step, and will greatly appreciate some input on the following:

1. Is there rule of thumb for how much longer BT EAN32 and EAN36 offer, as compared to regular air, all else being equal?
2. Considering oxygen toxicitiy, what would be the depth limits for EAN32 and EAN36, as compared to the general depth limit of 120ft for recreational dives with regular air, all else being equal?

Thanks!

 

[Raphus]

Depends on what ppO2 you want to dive. Most people will set 1.4 as a maximum.

So ean32 is 0.32 ppo2 at the surface.

1.4 /0.32 = 4.4 atm

So max depth(MOD) would be about 34m. ( = about 111ft?). So cou can see it is close to being the rec limit.
The time you can spend longer compared to air depends on the mix and on the depth. Its quit a lot. Most computer can plan a dive with different o2 mixes. So you can try it yourself.

Nitrox expands the divetime and/or makes it safer. A must have in my opinion.

 

[Gareth J]

Using BSAC 88's

Nx 36 @ 30m gives 32 minutes no-stop
Nx 32 @ 30m gives 28 minutes no-stop
Nx 27 @ 30m gives 23 minutes no-stop
Nx 21 @ 30m gives 20 minutes no-stop

Whilst you can argue about which table / algorithm you wish to use, this gives a comparative differential between air (Nx21) and the other standard gases.

 

[tbone1004]

@Vibenz
1. not really. NDL's are set by exposure to partial pressures of nitrogen, since nitrox has less nitrogen than air does, you are able to plan the dive at a shallower depth than you are diving. For EAN32 that is 86%, for EAN36 that is 81%, but you have to think about depth in terms of absolute pressure instead of depth. I.e. 86% of 100ft is 80ft not 86ft. 81% of 100ft is 73ft not 81ft. What does that equate to in terms of time? Depends on which tables/computer you are using, so unfortunately you can't really quantify that.

2. EAN32 is considered to have a Max Operating Depth of 130ft/ppO2=1.6, and a planned max of 110ft/ppO2=1.4. EAN36 is 110ft and 90ft respectively. This is due SOLELY to the partial pressure of oxygen, and is independent of maximum gas density recommendations where many agencies recommend no deeper than 100ft without helium in the mix.

 

[Vibenz]

Raphus, thanks for the lead. Didn't get the calculation the add up so I did some more research.

The correct formula seem to be:

((1.4 / 0.36) -1) = 3.9 atm

Using 0.33 meter in a foot, that would equal roughly 111 feet

 

[Vibenz]

@Vibenz

2. EAN32 is considered to have a Max Operating Depth of 130ft/ppO2=1.6, and a planned max of 110ft/ppO2=1.4. EAN36 is 110ft and 90ft respectively.

Could you please help understand the difference between MOD and 'planned max'?

 

[tbone1004]

Could you please help understand the difference between MOD and 'planned max'?

I teach a "maximum operating depth" which is the max that you can safely breathe that gas and uses a ppO2 of 1.6. I teach "planned maximum operating depths" based on a ppO2 of 1.4.

Example. Say there is a wreck where the sand is 110ft and the deck is at 90ft. If you plan on diving at the deck level, then EAN36 would have a maximum operating depth of 110ft, i.e. if you have to go down to the sand, the gas won't be toxic, but you are planning on hanging out at 90ft where it is considered "best mix". If however you are planning on diving on the sand, say to hunt for shark teeth, then you would want to use EAN32 because you are planning to dive at 110ft and you don't want to exceed a ppO2 of 1.4.

This is rather complicated to explain without full nitrox lectures being involved, but choosing a ppO2 for your "best mix" is very complicated with a lot of variables and depending on the type of diving you are doing can be anywhere from 1.0 to 1.6.

 

[Centrals]

I'm considering nitrox as the next step, and will greatly appreciate some input on the following:

1. Is there rule of thumb for how much longer BT EAN32 and EAN36 offer, as compared to regular air, all else being equal?
2. Considering oxygen toxicitiy, what would be the depth limits for EAN32 and EAN36, as compared to the general depth limit of 120ft for recreational dives with regular air, all else being equal?

Thanks!

You will learn them in the course.
It is one of the course that you really do not need anyone to help out!
You can learn a lot more if you bother to use your own search engine. More than enough for you to digest. And the mathematical calculation is dead simple.
But the diving agency will charge you for that and call it a speciality.

Nitrox

 

[DogDiver]

I haven’t breathed air in over 20 years. Nitrox percentage determined by planned depth.

 

[BoltSnap]

I'm considering nitrox as the next step, and will greatly appreciate some input on the following:

1. Is there rule of thumb for how much longer BT EAN32 and EAN36 offer, as compared to regular air, all else being equal?
2. Considering oxygen toxicitiy, what would be the depth limits for EAN32 and EAN36, as compared to the general depth limit of 120ft for recreational dives with regular air, all else being equal?

Thanks!

You are "considering nitrox as the next step" as in taking a nitrox course or as in getting the answers to your questions here and then just using nitrox without going through a proper Nitrox certification course?

The questions you pose are/should be answered in an entry level nitrox course in detail. I don't understand what you are trying to achieve asking these questions here.