The NAPI Safe Diving Principles:

Part III: The Application of Nitrogen Enriched Air

Introduction

After every dive, in every dive club, in every pub frequented by divers most of the stories are told by old divers, divers with years of experience, with amazing stories of how they faced danger and came out alive. The divers listening to these old divers are the newly qualified divers, who at night dream about doing what the old divers did. But while the new, fancy, expensive and brightly colour coordinated equipment may impress the old divers for a short while, the real stories only develop with time.

Yet which new diver cannot honestly admit that they would like to say things like: "I managed to get incredibly narc'ed today," or, "I breathed so little today that I seriously pushed the tables," or even "I spend some 25 minutes decompressing today?" The problem is, to get serious nitrogen narcosis one needs to go deep, and that means planning, lots of tanks, surface support, and many other things one would rather like to forget.

Similarly, to be able to push the tables by having enough air means that your breathing rate must actually be low, and, you must stay down long... Even worse, for decompression dives you not only have to go deep, but also stay long too, but which new diver can do that?

NAPI investigated this issue and came up with a simple and neat solution: nitrogen enriched air. Not only does nitrogen enriched air fulfil the wishes of new divers, but it also avoids some of the more serious problems with air, and especially nitrox, thus enhancing diver safety. It is because of this that NAPI named this new gas Safest-Air (c).

Safest-Air (c)

Safest-Air (c) comes in two varieties: Safest-Air (c) I, with a 15% Oxygen content, and the more useful Safest-Air (c) II, with a 10% Oxygen content. The question now is, how does Safest-Air (c) benefit the diver?

Equivalent Air Depth

With increased nitrogen the equivalent air depth is increased, that is, a certain depth on Safest-Air is equivalent to a much deeper depth on air, and even more so than on nitrox. This has the obvious advantages in that nitrogen narcosis sets in at shallower depths.

Conversely, for the same depths as on air the nitrogen narcosis is much more prominent.

But, not only does nitrogen narcosis set in at a shallower depth, but because of reduced ambient pressure and thus reduced breathing rate, the diver can also stay down there longer! Not only that, with the increased nitrogen the no decompression limits for a certain depth are shorter than those for the same depth on air, thus allowing the diver to enter decompression at a much earlier stage! And, to top it all, the time spent at decompression stops will be longer too! At the end of this article the decompression tables for Safest-Air (c) I and II are published. Compare these with the US Navy tables, and you will see the fantastic decompression schedules which are now possible!

Reduced Oxygen in Safest-Air (c)

You may wonder if the reduced oxygen found in Safest-Air (c) has any adverse effects on the diver, after all, with Safest-Air (c) II the oxygen content is half that of normal air, surely this cannot be healthy? Quite the opposite! The reduced oxygen is actually a benefit to the diver.

First of all, with Safest-Air (c) I, the normal 21% oxygen is reached at a depth of only 4msw (13fsw), with Safest-Air (c) II this is 10msw (33fsw). Once deeper than these limits the diver will be getting more than enough oxygen.

Secondly, there is oxygen poisoning and toxicity. One of the main pitfalls with nitrox is that because of the higher oxygen content it becomes lethal at shallow depths. Even if the diver stays shallower than those depths the oxygen tolerance (the "oxygen clock") is quickly used up. With Safest-Air (c) the sports diver will never reach depths where oxygen becomes toxic, and because there is less oxygen, the oxygen clock is slowed down. Even if the diver is exposed to high partial pressures of oxygen at depth, the shallow decompression stops ensure that the excess oxygen is safely vented!

Conclusion

Safest-Air (c) does not only allow the diver experience the joys of nitrogen narcosis at shallower depths, push the tables with more ease, and spend longer times at decompression stops, but the removal of oxygen as a potential hazard surely makes this the most useful gas mixture designed so far!

 


NAPI Safest-Air (c) Decompression Tables.
Copyright NAPI 1994

NAPI Safest-Air (c) I: 85%/15% Decompression Table
Decompression stops are at 3m, 6m, 9m (10ft, 20ft, 30ft.)

Depth Bottom Stops       Depth Bottom   Stops
       Time  6m 3m              Time  9m 6m 3m
-------------------      ----------------------
 15m   80       3         36m   15          2
 50ft  90       7        120ft  20          5
      100      11               25       2 10
      110      14               30       4 19
      120      18               40    2 15 25
-------------------      ----------------------
 18m   60       5         39m   10          1
 60ft  70      12        130ft  15          3
       80      17               20       1  6
       90      21               25       3 15
      100      30               30    1  7 22
-------------------      ----------------------
 21m   50       8         42m   10          1
 70ft  60      17        140ft  15       1  3
       70      24               20       3  8
       80      27               25    1  5 18
       90      37               30    2  9 25
-------------------      ----------------------
 24m   40       7         45m   10          2
 80ft  50      19        150ft  15       2  4
       60    3 25               20    1  3 11
       70   11 39               25    2  7 22
-------------------      ----------------------
 27m   30       3         48m   10       1  2
 90ft  40      16        160ft  15    1  2  5
       50    3 25               20    2  4 15
       60   13 28               25    3  8 24
-------------------      ----------------------
 30m   20       1         51m   10       1  2
100ft  25       3        170ft  15    1  3  6
       30       8               20    3  5 18
       40    3 22        ----------------------
       50   13 25
-------------------
 33m   15       1
110ft  20       3
       25       7
       30    1 15
       40    8 25
-------------------

NAPI Safest-Air (c) II 90%/10% Decompression Table
Decompression stops are at 3m, 6m, 9m (10ft, 20ft, 30ft.)

Depth Bottom Stops       Depth Bottom   Stops
       Time  6m 3m              Time 12m 9m 6m 3m
-------------------      -------------------------
 15m   70       6         36m   10             1
 50ft  80      11        120ft  15             3
       90      16               20          7 11
      100      20               25          3 16
      110      28               30          7 25
      120      38               40       4 20 35
-------------------      -------------------------
 18m   50       3         39m   10             1
 60ft  60      13        130ft  15          1  4
       70      20               20          2  8
       80      26               25       1  5 21
       90    2 35               30       2  8 28
      100    6 45        -------------------------
-------------------       42m   10             2
 21m   40       3        140ft  15          2  4
 70ft  50      16               20       1  4 12
       60      25               25       2  7 25
       70    5 29               30       4 14 29
       80   12 42        -------------------------
       90   17 53         45m   10          1  2
-------------------      150ft  15       1  2  6
 24m   30       2               20       1  4 18
 80ft  40      15               25       3  9 27
       50    1 27         ------------------------
       60    9 28          48m  10          1  2
       70   18 45         160ft 15       1  3  7
-------------------             20       3  6 20
 27m   20       1               25    1  4 12 28
 90ft  30       6        -------------------------
       40    2 23          51m  10          2  3
       50   10 29         170ft 15       2  3  8
       60   20 43               20    1  3  7 24
-------------------       -------------------------
 30m   20       2
100ft  30    1 15
       40    6 28
       50   20 36
-------------------
 33m   15       1
110ft  20       4
       25    1  9
       30    3 20
       40   14 29
-------------------

Notes:

These tables are actually not just figures I dreamed up, they were calculated using the US Navy 6 tissue model and m-values, but only with reduced oxygen content in the mixtures. The results are however easily comparable with the usual US Navy tables. Actually, using these tables with air should make your dives very safe!

Disclaimer:

If you actually believe anything in this article, please contact NAPI, we have a course just for you!

While all of the above is based on fact, I have taken liberties in the interpretation, so please please please do not use it seriously!

Guido Zsilavecz
Founder NAPI

This page was last updated on : 06 Sep 2011