Karlīs Nitrox Seite

Gas Logistic for Nitrox- Diver


 

Diving Nitroxetc. means filling the Bottles with a Gas different than Air.

This Website can not serve you with information about regulations for all four corners of the earth , so it only speaks about technical aspects.
I strictly recommend to qualify as gas-blender before blending gases.

 Take care that tanks only get filled with gases they are rated, cleaned and labelled for.

For most Divers getting a fill with Nitrox or any other gas is just walking into the diveshop and ordering the fill they want. But it is always good to understand how something works.

 

Nitrox Fills

 

Oxygen Fills

 

Argon Fills

 

Van der Waals-Gas Equation

a description for the behaviour of real Gases in the 10-6 bar to 103 bar Range. In the most cases it has a good performance (as long as the Isotherms are above the critical temperatures in the pV- Diagram; which is normally fulfilled for Helium, Nitrogen and Oxygen at diving applications, not for CO2, most of it is liquid at the pressure in a CO2-cartridge).

p:= Pressure, n:= Number of Mol's (a mol expanded gas means 22.4liter at 1bar), V:= Volume, a:= Van der Waals-Coeffizient for attraction-effects, b:= Van der Waals-Coeffizient for repulsion effects (~volume of the atoms/molecules of the gas), R:= Gas-constant = 8.314 J K-1 mol-1, T:= Temperatur [Kelvin]

For Gasmixes, that can be looked upon as a homogenous Gas (same Aggregate state, only Van der Waals-interrelations), the Van der Waals-Coeffizients can be estimated like this:

         
with xj, xi:= Molar-fraction of gas i and j, aij=(ai aj)1/2 and bij=(bi bj)1/2

Gas

a [dm6 bar mol-2]

b [10-2 dm3 mol-1]

Mass [Gramm/22.4bar*l]

O2   = Oxygen

1.38

3.18

32

N2   = Nitrogen

1.408

3.913

28.02

He   = Helium

0.034

2.37

  4.0026

Ar   = Argon

1.363

3.22

39.95

CO2= Carbon-Dioxide

3.640

4.267

44.01

 

Gas Analysis

has to be done (at minimum) twice when diving with mixed gases: 1) as part of the filling process, 2) prior to diving.
The predive analysis should be done by the diver, using instruments that are independent from those used during the filling.
When you are sure about the rest, a measurement of the oxygen-percentage is all what is needed. Being sure about the rest is the other important thing. You surely do not want to get a chronically oil-poisoning, a carbon-monoxide poisoning, water or oil in your tanks, so always check that you get your fills at a responsible and competent Filling station.

 

  Nitrox-Index

 

http://Rebreather.de/nitrox/gas_logistic.htm © Karl Kramer, 16.11.1998