Nitrox

 

There is a misconception that Nitrox is some kind of "Voodoo Gas".
It's not

There is a misconception you can go deeper with Nitrox.
You can't.

 

Normal air is about 79% Nitrogen (N2) and 21% Oxygen (O2). If you are a diver, you know that our bodies adsorb N2 during diving. This is because the pressure of air in our lungs becomes greater that the normal (1 atmosphere's worth) of N2 in our body tissues. It's the way that Coke or Pepsi make their drinks fizzy. Of course we also absorb O2 from the air, but our body metabolizes that, leaving only residual nitrogen.

During the most basic scuba class, students are taught about the need to ascend slowly (30 feet / minute) and to do safety stops (stop at 15 feet deep for 3 minutes) and surface intervals (an hour between dives). All these are to slowly release N2 from the body and not be saturated or cause bubbles to form inside the diver.

So........ if we can reduce the amount of N2 in the scuba tank, we can reduce the amount of dangerous N2 build-up inside our bodies. Nitrox replaces some of the air inside the tank with more O2. Nitrox is also know as EAN - Enriched Air Nitrox.

Common blends are 32% Oxygen or 36% Oxygen

Also known as EAN 32 or EAN 36

 

Nitrox - Advantages

 

Because we absorb less N2 over time, it means we can spend more time at a shallow depth that when diving air. For example, if we use the PADI dive tables for air, we can spend 55 minutes at 60 feet before we hit non-decompression limits.

If we dive 36% Nitrox, we could spend 110 minutes at 60 ft before NDL.

So, the biggest advantage of Nitrox diving is we can spend more time underwater before we hit decompression limits. If you have paid a lot of money to go on a dive trip, it may be worth spending a little extra to spend more time underwater or have a higher safety margin at shallow depths. Some divers reckon their air consumption is better when using Nitrox. Others say they are "fresher" or "less-tired" after a dive.

 

Nitrox - Disadvantages

 

Apart from the higher cost (about $5 per tank) is there any other disadvantage of using Nitrox?

OXYGEN is TOXIC

Sorry, that was not a typo - O2 is toxic to the Central Nervous System (CNS). If the absolute pressure of O2 in your lungs becomes too high you will immediately go into convulsions - then you will drown. Without warning. Wow - a big disadvantage.

However, This is only when the pressure of O2 exceeds 1.6 atmospheres absolute  (ATA).
PADI say 1.4 ATA is the maximum, with 1.6 ATA as the contingency depth in case you go  deeper than you plan.

On the most basic scuba class, students are taught that the absolute pressure in water increases by 1 atmosphere every 33 feet. So lets look at the air pressure, Air O2 pressure, and 36% nitrox O2 pressure at different depths.

Absolute Pressure in Atmospheres (ATA)
Depth Total Pressure 21% O2 36% O2
Surface 1 0.21 0.36
33 feet 2 0.42 0.72
66 feet 3 0.63 1.38
99 feet 4 0.84 1.44
132 feet 5 1.50 1.80
167 feet 6 1.71 2.16

 

There are two ways of determining your Maximum Operating Depth (MOD). Dive tables can show you your MOD or it can be calculated using the following formula.

 

 

So, I calculated the MOD's for Air, EAN32 and EAN36.

Maximum Operating Depth

Pressure (ATA) Air EAN32 EAN36
1.4 Imperial 187 111.375 95.33
1.6 Imperial 218.42 132 113.6
1.4 Metric 56.66 33.75 28.89
1.6 Metric 66.19 40 34.44

See, you have to stay shallower when diving Nitrox compared to air.

 

Nitrox - Disadvantages - Continued

 

If you dive Nitrox all the time, then Residual O2 can build up in your body - just like residual N2. So, you have to monitor your O2 exposure as well as how much N2.

There are dive tables produced to calulated your N2 loading and your O2 exposure - which must not exceed in any 24 hour period. 

An easier way of tracking everything is to use a nitrox dive computer.

 

Nitrox - Disadvantages - Continued

 

If normal greases come into contact with high levels of O2, it can explode or catch fire. All equipment used for nitrox diving has to be cleaned and used with compatible materials, such as O rings and lubricants.  Tanks have to be specially cleaned. Extra handling precautions have to be taken in handling nitrox equipment.

 

Conclusion

If you plan on doing multiple, repetitive dives, it is worth the extra trouble and expense. Unless, of course, you are planning to go deep.

What I often do, is use air for the first, deep, dive of the day. Then I use nitrox for the rest of the day, to keep away from no decompression limits.

 

 

  See? It's not so bad: