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· A short fat well off crap cave diver. Likes wrecks
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Twins = extended bottom time
Nitrox = extended bottom time with less / no deco

It makes sense to use Nitrox in twins up to the 50m mark and especialy in the 30-40 zone. TDI entry level Nitrox is a test only with a bit on analizing a tank and costs about £79.00. Well worth it IMHO


Mark Chase

· A short fat well off crap cave diver. Likes wrecks
15,284 Posts
Imported post

[b said:
Quote[/b] (MATTBIN @ May 04 2004,10:20)]Mark
50m on Nitrox?
30/40m ?

I though the max benefits were in the 15/25m range.

50m would give 23% 02, below 40 wouldnt tri-mix be much better after all the N PP would still be likely to cause narcosis.
If you think in terms of run time as aposed to no decompresion time you can see the advantage:

All these are on a 20/85GF

40m for 40min on air 130min run 88min deco
40m for 40min on 28% 93 min run 50min deco
38min les deco

50m for 35min on air 163min 125min deco
50m for 35mn on 24% 137min 99min deco
26mn less deco

I realise the PPo2 fr 24 is 1.44 but the CNS for the whole dive is only 28% so its not exactly cutting edge stuff.
Lets face it you wont do the whole dive with your belly in the gravel.

Trimix is just Nitrox + Helium the 02 percentage is unafected by the He percentage it is what it is. The Helium will alter the shape of the deco but it doesent affect the CNS and it dosent have a great impact on the total deco time unless you are using a lot of it.

50m for 35m 24/20 Trimix 136min with 98min deco

1 mins less deco for the He.  

50m for 35m 24/30 Trimix 154min with 116min deco

18mins more deco due to the 30% He

However using a rich deco mix can sort this out:

50m for 35min 24/30 Trimix 32% and 80% for deco 73min 34min deco

50m for 35min 24% Nitrox 78min 39min deco

Te High o2 pushes out the He quickley so it actualy reduces the deco

All good fun

Mark Chase
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