Unit 1:
What is NITROX?
Is it better than air?
Do you need it?
What is Nitrox?
Nitrox is air in which fraction of nitrogen is
reduced (PO2 table)
• Nitrox is also called:
– Oxygen-enriched air
– Enriched air nitrox
• EANX
A Bit of History
• Development of nitrox
use
– Early research
and use
– Controversy
– NAUI
endorsement of
EANX
– NAUI Standards for
EANX training
Why Dive With
Enriched Air Nitrox
• Extended Dive Time
Why Dive With
Enriched Air Nitrox continued
• Repetitive dive times and surface
intervals
• Safety margins and post dive
fatigue
Common Misconceptions
About Nitrox
• Myth: “Nitrox is for technical diving”
• Myth: “Nitrox is for deep diving”
• Myth: “If you dive with nitrox you won’t
get bent”
• Myth: “Nitrox is safer than air”
• Myth: “If you dive with nitrox you won’t
get narcosis”
Q: What causes narcosis? (PO2 table)
• Myth: “It is hard to dive with nitrox”
Unit 2:
Gases & Gas Mixtures
Do you have the “v-planner” app?
What’s in Air?
• Composition of air
– Oxygen (O2) 0.2095
– Nitrogen (N2) 0.7808
– Argon (Ar) 0.00934
– Carbon dioxide (CO2)
~0.00035 (average)
– Others 0.00004
• Simplifying the numbers:
– 21% oxygen / 79% nitrogen
Some Facts About
Individual Gases
•
•
•
•
•
•
Oxygen (O2)
Nitrogen (N2)
Argon (Ar)
Carbon Dioxide (CO2)
Helium (He)
Neon (Ne)
How Gases Behave
Boyle’s Law:
Pressure,
Volume, and
Density
How Gases Behave continued
Henry’s Law:
The Solubility of
Gases
How Gases Behave continued
Dalton’s Law:
Partial Pressure
in Gas Mixtures
Converting Between Depth
and Pressure
• Absolute vs.
gauge pressure
Converting Between Depth and
Pressure continued
• Converting by formula
• To find absolute pressure:
P ata = (D fsw / 33 fsw/atm) + 1 atm
= (D fsw + 33 fsw) / 33 fsw/atm
• To find depth:
D fsw = (P ata – 1 atm) x 33 fsw/atm
Converting Between Depth and
Pressure continued
• Converting
by table
Calculating Partial
Pressures
• If you know the
absolute
pressure:
– The basic
formula:
Pg = Fg x Ptotal
– Using a
graphical
figure
Calculating Partial
Pressures continued
• Moving between partial pressure and depth using
formulas:
• Depth to partial pressure
– First find the absolute pressure at depth.
– Then find the partial pressure of the
component gas at that absolute pressure.
• Partial pressure to depth
– First find the absolute pressure of the gas
mixture from the partial pressure and fraction
of the component gas.
– Then find the depth for that absolute pressure.
Calculating Partial
Pressures continued
Using a table
Unit 3:
The Physiology of
Diving and
Nitrox
Nitrogen Narcosis
• The mechanisms of nitrogen narcosis are
similar to that of gases used in general
anesthesia.
• Divers may not be aware that they are
impaired.
• There is no appreciable benefit to
breathing nitrox.
• Ascent to a shallower depth is all that is
required.
Decompression Sickness
• What causes it
• DCS signs and symptoms
Decompression Sickness continued
• How to avoid DCS
• Treatment for DCS
Oxygen: The Good and the Bad
• Is necessary to sustain life
• Too high an oxygen level can be
just as harmful as too low
“Love, is like oxygen... You get too much you
get too high. Not enough and you're gonna die.”
Oxygen and Metabolism
• Oxygen is our life-support gas
• The primary waste product is
carbon dioxide
Physiological Effects of Low
Oxygen Levels (Hypoxia)
• Hypoxia means “low oxygen” symptoms
begin to appear if the partial pressure of
inspired oxygen falls below about 0.16
atmosphere
• Onset of symptoms at a PO2 of about
0.16 ata
• Signs and symptoms include impaired
mental performance and defective
memory, blueness of the lips (cyanosis),
fatigue, visual disturbances, and dizziness
Physiological Effects of Low
Oxygen Levels (Hypoxia) continued
– If the PO2 falls below about 0.10 ata
more severe symptoms leading to
unconsciousness will occur.
– Hypoxia must be monitored in
some rebreather situations or deep
diving applications.
Oxygen Partial Pressure Limits
• The generally accepted limit for
nitrox diving is:
– 1.4 ata PO2
– 1.6 ata PO2 as a contingency
• 1.4 ata PO2 is more than adequate for
99.9% of the dives you may want to
accomplish
Central Nervous System
Toxicity
• Factors that can increase your
susceptibility to CNS oxygen toxicity
– heavy exercise, increased carbon
dioxide build-up, chilling or
hypothermia, and water immersion
– One cannot predict oxygen toxicity
“the bell curve...”
Central Nervous System
Toxicity continued
• Central Nervous System Toxicity
– The mnemonic acronym “ConVENTID” is
useful for remembering the most obvious of
them:
• Convulsions
• Visual disturbances
• Ears
• Nausea
• Twitching or Tingling
• Irritability
• Dizziness or Dyspnea
Central Nervous System
Toxicity continued
• Central Nervous System Toxicity
– Convulsions are the most obvious and most serious signs.
– Possible precursors to convulsions are:
• Visual disturbances, tunnel vision, dazzle or seeing
“fireflies.”
• Ear ringing, tinnitus, or sounds like an approaching train in
a tunnel.
• Nausea, including vomiting.
• Twitching, especially of the lips and small facial muscles or
the hands, or tingling (paresthesia) especially in the
fingers.
• Irritability, restlessness, euphoria, dysphoria (uneasiness
or feelings of impending doom), anxiety, or general
confusion.
• Dizziness and vertigo or dyspnea (difficult or labored
breathing).
Managing Oxygen Exposure
• The best way to avoid oxygen
toxicity problems is to stay within
correct oxygen exposure limits.
OR...
What would you do?
Managing Oxygen
Exposure continued
• NOAA Oxygen
Exposure Limits
– In addition to a general
PO2 limit, NOAA has
oxygen exposure time
limits for a range of
oxygen partial pressures
from 0.6 ata to 1.6 ata
Unit 4:
Choosing the Best
Nitrox Mix
Enriched Air Nitrox Mixtures
• Two Standard Nitrox Mixes
– EANx 32 or NOAA Nitrox I
– EANx 36 or NOAA Nitrox II
• Partial Pressure of Oxygen is the
Limiting Factor
– Limit P02 to 1.4 ATA
• 1.6 ATA as a contingency
Maximum Operating Depth
• The maximum operating depth (MOD)
is the maximum depth that should be
dived with a given nitrox mixture.
– MOD should be derived from the
recommended maximum oxygen partial
pressure of 1.4 atmospheres
– MOD should be written prominently on
the cylinder’s contents label
Maximum Operating Depth
continued
• MOD by Table (imperial)
Maximum Operating Depth
continued
• Calculating MOD
– Begin by finding the total
pressure that it takes to
produce the maximum
acceptable oxygen
partial pressure
Pg = Fg x Ptotal
– Then convert to a depth
D fsw = (P ata – 1 atm) x 33 fsw/atm
Maximum Operating Depth
continued
• Combining the two steps
P
O
2
l
i
m
i
t


D
f
s
w
=
1
a
t
m
x
3
3
f
s
w
/
a
t
m


F
O
2


P
O
2
l
i
m
i
t


D
f
s
w
=
x
3
3
f
s
w
/
a
t
m
3
3
f
s
w


F
O
2


Maximum Operating Depth
continued
• Using the OCEANx to
Establish MOD
Best Mix
• “Best mix” is the nitrox mixture
with highest fraction or
percentage of oxygen that can
be used at the target depth.
Choosing Best Mix
• Using the Best Mix Table
• Calculating the Best Mix
• Using the OCEANx to establish
best mix
Choosing Best Mix continued
• The Best Mix
Table
Choosing Best Mix continued
• Calculating best mix is similar to the
calculation for maximum operating depth
in reverse.
• Step 1: Determine the absolute pressure
at the target depth
or
D
f
s
w
P
a
t
a
=
+
1
a
t
m
3
3
f
s
w
/
a
t
m
D
f
s
w
+
3
3
f
s
w
P
a
t
a
=
3
3
f
s
w
/a
t
a
Choosing Best Mix continued
• Step 2: Determine what fraction will
produce the target partial pressure at that
absolute pressure
Fg = Pg / P total
or
FO2= PO2 / P total
What do these abbreviations stand for?
Choosing Best Mix continued
• The two steps can be combined into
a single formula.
D
f
s
w
P
O
2
l
i
m
i
t
x
3
3
f
s
w
/
a
t
m


F
O
2
=
P
O
2
l
i
m
i
t
/
+
1
=


3
3
f
s
w
/
a
t
mD
s
w
+
3
3
f
s
w

 f
Choosing Best Mix continued
• Using the OCEANx
Calculator for
Best Mix
Unit 5:
Dive Tables and
Dive Computers
Dive Tables
• There are many different dive
tables in use today
– NAUI Dive Tables
– NAUI RGBM Tables
– U.S. Navy Tables
– DCIEM Tables
– Buhlmann based tables
– Other Tables
Air Dive Tables
• So-called “standard dive tables” are
designed for diving while breathing air.
No-required Stop Times
• EANx Dive Tables give increased
maximum dive times for standard mixes.
Enriched Air Nitrox Dive
Tables
• Enriched Air Nitrox Tables
Enriched Air Nitrox Dive
Tables continued
• NAUI EAN Dive Table Rules
– Treat each dive as a square profile dive, with the deepest point
reached on the dive being used as the depth for the whole
dive.
– If the exact depth or time does not appear on the table, round
up to the next greater number.
– The tables assume an ascent rate of 30 feet/9 meters per
minute.
– Planning repetitive dives progressively shallower will yield
shorter required surface interval times.
– The required surface interval between two separate dives is 10
minutes; the minimum recommended surface interval is one
hour.
– The tables are designed to be used at sea-level atmospheric
pressure, and adjustments must be made for altitudes above
about 1000 feet/300 meters.
– If flying or ascending to altitude after diving, wait 12 hours
after a single dive and 18 hours after a repetitive dive series.
Equivalent Air Depth and
Standard Air Tables
• Equivalent Air Depth is
determined by the partial
pressure of nitrogen that the diver
is actually breathing
– Because nitrox has a lower fraction
of nitrogen than air, the nitrogen
partial pressure will also be less than
with air for any given depth, and the
diver’s equivalent depth for nitrogen
absorption will also be less than with
air.
– It is not the actual depth, but the
partial pressure of nitrogen in the
breathing gas that matters.
Equivalent Air Depth and
Standard Air Tables continued
• EAD Example:
– If you were breathing a mixture that is 36%
oxygen, then the nitrogen percentage would be
64%, and the nitrogen fraction would be 0.64.
– When you dive with this mixture, you expose
yourself to 64/79ths the nitrogen partial
pressure that you would encounter if breathing
air.
– Therefore, you can consider your depth to be
64/79ths (roughly 80%) of the absolute
pressure that you would encounter at your
actual depth if you were breathing air.
Equivalent Air Depth and
Standard Air Tables continued
• Equivalent Air Depth by Table (imperial)
Equivalent Air Depth and
Standard Air Tables continued
• Calculating Equivalent Air Depth
• Equivalent air depth can be calculated in
discrete steps, or the procedure can be
combined into a single formula.
• Step 1: Determine the absolute pressure at
the depth to which you will be diving.
• Step 2: Apply the nitrogen “credit” that your
nitrox blend gives you.
• Step 3: Convert this air-equivalent absolute
pressure to an equivalent air depth
Equivalent Air Depth and
Standard Air Tables continued
• Step 1:
P ata = (D fsw / 33 fsw/atm) + 1 atm
• Step 2:
P ataEAD = (Fin mix / Fin air) x P ata
• Step 3:
EAD fsw = (P ataEAD – 1 atm) x 33 fsw/atm
Equivalent Air Depth and
Standard Air Tables continued
• Calculating EAD
– Example: What is the equivalent air
depth for a diver diving with EAN32 to a
depth of 80 feet/24 meters?
Step 1: Find the absolute pressure at 80 fsw
using the formula from Chapter 2: or = 3.42 ata
Equivalent Air Depth and
Standard Air Tables continued
• Calculating EAD
– Step 2: Apply your nitrogen “credit.” Since
you are diving with EAN32, the nitrogen
fraction of your mix is 0.68
(= 1.0 - 0.32). Your air-equivalent absolute
pressure is set by the ratio between the
fraction of nitrogen in your mix and the
fraction of nitrogen in air, or:
P ata (air equiv) = (0.68/0.79) x 3.42 ata = 2.94 ata
Equivalent Air Depth and
Standard Air Tables continued
• Calculating EAD
– Step 3: Convert 2.94 ata to an equivalent
air depth:
– D fsw = (P ata – 1 atm) x 33 fsw / atm
– D fsw = (2.94 ata – 1 atm) x 33 fsw / atm
= 64 fsw
– You would use for 70 feet / 21 meters on
your dive tables.
Equivalent Air Depth and
Standard Air Tables continued
• Calculating EAD using a single formula
D
f
s
w
+
3
3
f
s
w
x
F
N
2




E
A
D
f
s
w
=
3
3
f
s
w


0
.
7
9


D
f
s
w
+
3
3
f
s
w
+
1
F
O
2






E
A
D
f
s
w
=
3
3
f
s
w


0
.
7
9


Equivalent Air Depth and
Standard Air Tables continued
• Calculating EAD with the
OCEANx
– To find equivalent air
depth with the OCEANx
calculator, dial-in the
oxygen percentage into the
upper window. The long
window immediately below
shows the maximum actual
depth to be used with each
equivalent air depth, which
is printed immediately to
the right.
Rule of Halves
• When ending any no-decompression dive
in excess of 12 meters / 40 feet, halve the
distance from the dive’s deepest depth to
the surface. Ascend to that depth and
make a two to three minute stop (with two
and one-half minutes being optimum).
Then continue your ascent to the 3-6
meter/10-20 foot safety stop for one
minute before surfacing.
Dive Computers and Nitrox
• Dive computers perform real time dive calculations.
• Generally, their algorithms are quite conservative.
• Because they sample the diver’s depth and dive time
every few seconds and recalculate nitrogen
absorption over a range of theoretical tissue
compartments, divers enjoy extended dive times
when using a dive computer.
• In effect, the diver receives “credit” for the shallow
portions of the dive, which is not possible with the
“square-profile” assumptions of dive tables.
Dive Computers and Nitrox
continued
• Two basic options
– Use a Nitrox capable computer
– Use an Air capable computer to
increase your safety margins.
Note: Currently, many manufacturers have
incorporated the NAUI RGBM algorithms as well
as the NAUI Rule of Halves into their dive
computers.
Diving on air tables while using nitrox...
Diving your computer on air mode while using nitrox...
Unit 6:
O2 Precautions and
Preparing EANx
Q: Is oxygen flamable?
Oxygen Handling
• Firefighters use the concept
of the “fire triangle.” In order
for a fire to occur or continue,
three things must be present:
fuel, oxygen, and heat.
• As the fraction and partial
pressure of oxygen increase,
many materials that do not
burn under normal conditions
will burn if ignited.
Oxygen Handling continued
• Equipment that will be used with pure or
very high concentrations of oxygen must
be specially prepared to withstand the
oxygen and to prevent fires and oxidation.
Oxygen Handling continued
• Equipment Considerations
– Hydrocarbons and petroleum-based products
must be avoided. This includes not only
petroleum-based compressor lubricants but
also the silicone lubricants normally used in
scuba air systems. Neoprene, silicone
“rubber,” plastic and metal shavings, even
finely divided particulate matter all become
potential fuels for a fire in an oxygen-rich
environment, especially one at high pressure.
Oxygen Handling continued
• Oxygen Cleaning
– The equipment must be “oxygen clean,”
and “oxygen compatible” parts must be
used in order to minimize the risk of fire
or destruction by the oxygen.
– After cleaning, future contamination
must be avoided.
Oxygen Handling continued
• The 40% Rule
– Any equipment that is to be used with
pure oxygen or an oxygen level that is
above 40% (and at a pressure above 200
psi) must be cleaned for oxygen service
and have only oxygen-compatible parts.
– This is a “rule of thumb,” but it is
generally accepted for oxygen handling.
Oxygen Handling continued
• Equipment Preparation
– Normal maintenance service is
sufficient for your regulator.
– Your cylinder is
a different matter.
Oxygen Handling continued
• Equipment Preparation
continued
– Cylinders must be prepared for
designated nitrox service because most
of the time pure oxygen will be used in
preparing a nitrox fill.
– After being cleaned for use with
oxygen-enriched air, the cylinder will be
labeled to clearly identify it as a nitrox
cylinder.
Tell me what you see...
How Nitrox is Made
• Partial-Pressure
Mixing
– In partial-pressure
mixing, the blending
technician first puts a
measured amount
(pressure) of oxygen
into the cylinder and
then fills the cylinder
to its service pressure
with air.
How Nitrox is Made continued
• Continuous-Flow Mixing
– The continuous-flow method
injects a measured flow of
pure oxygen into the air
before it reaches the intake
of the compressor
Your Responsibility
• As a nitrox diver, you are responsible not
only for your dive planning and execution
but also for your equipment.
• You are also responsible for the
correctness of what you will breathe.
• You are responsible for your cylinder’s
contents being what you asked for.
• A final step before you take the cylinder
away with you is verifying the contents.
Unit 7:
Knowing What You
Breathe
When should you analyze your gas?
What do you do if “they” do it for you...?
How Oxygen Analyzers Work
• Oxygen analyzers come in
all sizes
• Most have digital readouts,
but analog readouts are
also available
• Analyzers should have an
accuracy of one-tenth of
one percent (e.g., 31.7%
vs. 32%)
How Oxygen Analyzers
Work continued
• The sensor commonly used in nitrox
analysis is electrochemical
– They are rugged, portable and
relatively less expensive than other
types
• An essential operation in using any
analyzer is calibrating it
– Must be calibrated before each use
– Nitrox analyzers are normally
calibrated using standard air
(20.9% or 21%)
• Generally accepted that mix be within
±1% of target value
Analyzing Your Gas
• Accurate analysis depends
on the reliability of the
analyzer and the flow rate
through the oxygen sensor.
• Acceptable flow rate is about
1 liter per minute and should
be between ½ and 2 liters per
minute.
Analyzing Your Gas continued
• Accurate oxygen analysis depends on
accurate calibration of the analyzer.
– Use a known source such as an air
cylinder to ensure proper calibration.
• Once calibrated, attach the analyzer to
your nitrox cylinder, confirm that flow rate
is the same as during calibration and
allow analyzer to stabilize.
• Record this information on your cylinder
contents label.
Tracking Your Nitrox Cylinder
• Cylinder Labeling
– Every nitrox cylinder must be
properly labeled with
contents and other pertinent
information.
– Prepare cylinder label
immediately after analyzing
to avoid forgetful errors.
– Data should include fill date,
oxygen percentage,
maximum operating depth,
cylinder pressure, and name
of analyzer/end-user.
Tracking Your Nitrox Cylinder
continued
• Filling Out The Logbook
– Once you have analyzed your cylinder and
labeled it, you will be asked to complete the
permanent Fill Station Logbook and sign that
you have received the cylinder.
– Enter your name, date, your certification,
cylinder’s serial number, pressure, oxygen
mix, maximum operating depth, signature.
– Logbook tracks all nitrox cylinders leaving
facility.
– Logbook verifies that you either analyzed the
contents or knew the particulars of the fill
when you received your cylinder.
What's next...
“Advanced Nitrox”...
“Decompression Procedures”...
...longer and deeper dives!
Thank You