There is a misconception that Nitrox is some kind of
There is a misconception you can go deeper with
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
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
See, you have to stay shallower when diving Nitrox
compared to air.
Nitrox - Disadvantages -
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
An easier way of tracking everything is to use a nitrox
Nitrox - Disadvantages -
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.
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