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Warning!

This page is intended only to provide individuals who are interested in Nitrox diving with general information! It is not to be used for dive planning, as a replacement for training received from certified Nitrox instructors or as a substitute for information found in Nitrox instruction manuals and official dive tables. Accuracy cannot be guaranteed. Use this information at your own risk.




Some of the values listed below were calculated from US Navy Dive Tables and NOAA Nitrox Tables. Others were obtained from an on-line Nitrox calculator. No copyrighted material was used.

If you find an error on this page, please use the email link below to report it:

rainmaker@trailquest.net
About Nitrox ATM Table Nitrox Tables Nitrox Links








About Nitrox

The air used for scuba diving is a mixture of primarily two gases, oxygen and nitrogen. It is the same as the air we breathe and the percentage of each gas in the mixture is about 79% nitrogen and 21% oxygen. Nitrox is a special blend of air than contains more oxygen (and less nitrogen) than the air we normally breathe, and it has become increasingly popular among scuba divers in recent years. By increasing the amount of oxygen and reducing the amount of nitrogen in the breathing gas, the maximum allowable bottom time is increased. In addition, since less nitrogen is being absorbed on any given dive, the surface interval between dives can usually be shortened.

"Partial Pressure" is the pressure exerted by a gas in a mixture of gases. As the partial pressure of oxygen reaches certain levels in the body, central nervous system (CNS) toxicity can occur. This is also referred to as oxygen toxicity ("oxtox") or oxygen poisoning. Therefore, every Nitrox mixture has a maximum operating depth (MOD). The MOD of a given mixture varies depending on the maximum partial pressure of oxygen to which a diver wishes to be exposed. As the percentage of oxygen in the mix increases, the maximum operating depth decreases (becomes shallower).

The maximum pressure of 1.6 atmospheres (ATM) is often quoted for Nitrox diving, since it is referenced in the U.S. Navy Diving Manual, as well as the NOAA Manual. This value is also expressed as "P02". "P" is an abbreviation for "partial pressure", and "O2" is the chemical symbol for oxygen.

"EAN" is an abbreviation for Enriched Air Nitrox. The number following "EAN" is the percentage of oxygen in the mix. For example, EAN32 is a mix that contains 68% nitrogen and 32% oxygen. When Nitrox is mentioned but the mix is not known, it is usually expressed as EANx.

Many divers strongly suggest a maximum P02 of 1.4 (or less). Using the figure of 1.4, the MOD for EAN 32 is 110 feet and 90 feet for EAN 36. By using EAN 36 a person diving to 90 feet can nearly double the length of the dive, when compared to breathing regular air (see the "Comparison Of Dive Times" table below).

Decompression sickness (DCS) occurs when there is excess nitrogen in the body. Some divers also use Nitrox to try to lessen the chances of getting DCS. They accomplish this by diving with Nitrox, but using air tables instead of Nitrox tables. In other words, on any given dive they reduce the amount of nitrogen that is being absorbed by using Nitrox, but they do not extend the bottom times of their dives or shorten their surface intervals. Historically, some of these divers have been overweight, out of shape, elderly or have suffered DCS previously. This is how Nitrox got the nickname "geezer gas".

Most divers report that they feel less tired after diving with Nitrox than they do after diving with air. Some divers also feel that using Nitrox will lessen the chances of getting nitrogen narcosis at depth.

A diver must be certified in order to use Nitrox. He or she must present a Nitrox certification card when having tanks filled. The cost of Nitrox fills is generally about 1.5 the amount of air fills.

There is a difference of opinion concerning whether actual dives should be made with Nitrox before a diver becomes certified to use Nitrox. Some certifying agencies require book and classroom work only, and others also require that Nitrox dives be made. The cost of the courses varies from about $100 - $250. Generally, the cost of the course is higher if actual dives are required.



ATM Table

At sea level, the atmosphere exerts a pressure of 1 atmosphere (ATM). Every 33 feet of water exerts another ATM, so that the pressure increases dramatically with depth:

Depth
Pressure
surface
1 ATM
33 feet
2 ATM
66 feet
3 ATM
99 feet
4 ATM
132 feet
5 ATM




Nitrox Tables

*Equivalent Air Depths
(In Feet)

Actual Depth
EAN 32
EAN 36
40
30
26
50
38
34
60
47
42
70
56
50
80
64
59
90
73
67
100
81
75
110
90
83
120
99
91
130
107
n/a


*Equivalent Air Depth (or EAD) is a calculation that shows that the pressure of nitrogen and oxygen in a Nitrox mixture at a given depth is the same as breathing air at a shallower depth.



The following table shows a comparison of the maximum possible �no-decompression� dive times:

*Comparison of Dive Times for Various Gas Mixtures
(dive times in minutes)

Depth in Feet
Air
EAN 32
EAN 36
50
100
200
200
60
60
100
100
70
50
60
60
80
40
50
60
90
30
40
50
100
25
30
40
110
20
25
40
120
15
25
n/a

*Times are for single dives, based on US Navy Dive Tables and NOAA Nitrox Tables




Depth, Mix & PO2 Chart

PO2
O2 Time
.21
.28
.32
.36
1.0
300
124
84
70
58
1.1
240
139
96
80
67
1.2
210
155
108
90
77
1.3
180
171
120
101
86
1.4
150
187
132
111
95
1.5
120
202
143
121
104
1.6
45
218
155
132
113


This table shows the maximum allowable oxygen exposures for different oxygen mixtures at PO2's up to 1.6. The left column shows PO2 values. The next column shows oxygen exposures in minutes. The columns for PO2 values list the depths at which the mixture (in that column) reaches a range of PO2 values from 1.0 to 1.6.

For example, with a PO2 of 1.4, how long can a diver spend at 111 ft. breathing EAN 32? Answer: 150 minutes



Nitrox Links

NOAA Nitrox 36 No-Decompression Table

NOAA Nitrox 32 No-Decompression Table

Extensive Nitrox Discussion Thread At ScubaBoard.com

Oxygen Toxicity Discussion Thread at ScubaBoard.com

International Association of Nitrox & Technical Divers (IANTD)