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BSAC Nitrox Tables and non standard mixes

3K views 3 replies 3 participants last post by  timmyg 
#1 ·
Please can anyone point me to the rules that govern which tables should be used for Nitrox mixes for which there are no actual tables?

For example, if (for whatever reason, this is just theoretical) I wanted to use a 35% mix, to plan a dive, I would have thought that it would be 'safer' to use the table for 32% whilst taking care not to exceed the MOD for a 35% mix.

It has been suggested to me that this may not be the case, can anyone point me to the right place which explains why/how?

I should mention that I was PADI trained initially and then moved over to BSAC and commenced training at Dive Leader level and I am concerned that I may have missed something that may have been taught at Sports or Ocean diver level regarding the use of BSAC 88 nitrox tables.
 
#2 · (Edited)
Do they not teach you how to work out a EAD,

32/35 nitron

using 35nx and running a 32nx profile is safer , from a NDL dive, ie (less nitrogen) but like you said you need to be able to work out mod , for the 35nx all so work out the cns numbers for the 35nx (as your computer or tables cant do that , for you


not sure how you guys are shown how to dive with nitrox , but if your only 1 point away from a stanard mix , ie 35%

i would use the 36% tables , as im sure your + or - 1% is still in the books you learn from , lol maybe not ,

can you work out the mod
can you work out the ead
can you work out the ppo2
can you work out the cns
if you can work out all the above your good to dive odd ball nitrox numbers , if not you will need to stick with a book, and dive your 35nx as a 36,

having said all the above , id be happy to dive 35nx and have 32 in my commputer , as long as i know the mod and cns for a 35nx dive , (NOT that id worrie about the cns difference between the two , but some missinformed wanker / trainer may , say something other , ) but for a 30min dive to 30m there is a cns count difference off around 3 points ,

hope thats of some help ,
 
#3 ·
Hello and thank you for your quick reply.

I followed a clue in your post and got hold of a Sports Diver Nitrox Workshop Student Workbook which contains the following:

"Supplied gas should not vary more than ±1% from the desired mix
In September 2006, a new British Standard BS7486:2006 was introduced defining what diver grade oxygen and nitrox is and what the measurement tolerances should be for a particular range of nitrox breathing mixes. This defines the standard for commercially supplied nitrox. For general measurements on site, it is acceptable that the tolerance of percentage of oxygen is within ±1%."

This suggests to me that if you end up with a 35% mix, it is considered satisfactory to use the 36% tables as the gas is within ±1% of the tables being used.

In reality, we would almost certainly be setting our computers to the actual mix as well as diving well within the limits, I just wanted to understand the reasoning behind the statement which I now do!

Thanks again.
 
#4 ·
I am surprised that this was not covered in your lecture.

In your example for 35% it's +/- 1% so the 36% tables are fine. If however it was 34% you should use the MOD of 36% (or work it out manually) & the deco from 32%.

To burgerbonzo. BSAC do not teach EAD unlike PADI or TDI.


TG

Sent from my iPad using Timmytalk
 
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