NAUI Nitrox:
Diving With Oxygen Enriched Air
EAN 1 - 1
Open Water Requirements
• Two dives with oxygen enriched air
– one of which is to be a repetitive dive
• Students analyze their own gases
• Plan and safely execute each dive
Academic Requirements
• NAUI: 75 % on multiple choice test
• MLML: 100% on Final exam ?’s
EAN 1 - 2
1. Introduction
8. Using NAUI diving tables
2. Gases and gas
properties
9. Overview of gas mixing
3. Pressure and partial
pressure
10. Obtaining and analyzing
enriched air nitrox
4. Oxygen physiology,
toxicity, and tolerance
with enriched air nitrox
11. Diving equipment
considerations
12. Having enough to breathe
5. How to pick a nitrox mix
and staying warm
6. Decompression
principles
13. Contingencies: if things
don’t go as planned
7. Diving tables
14. Technical diving overview
EAN 1 - 3
Benefits of Enriched Air
•
•
•
•
•
Longer no-stop dive times
Shorter surface intervals
Longer repetitive dives
Less nitrogen absorbed
Lower risk of
decompression illness
EAN 1 - 4
Myths of Enriched Air Nitrox
•
•
•
•
•
Nitrox is safer than air
Nitrox is for deep diving
You can’t get decompression sickness
Narcosis is eliminated
Using enriched air nitrox is difficult
EAN 1 - 5
Oxygen Enriched Air: Terminology
•
•
•
•
Oxygen Enriched Air
Enriched Air Nitrox
NOAA Nitrox I
NOAA Nitrox II
• Common Mixes
– 32% oxygen
– 36 % oxygen
• EAN32
• EAN36
All the mixes have more oxygen and
less nitrogen than in normal air.
EAN 1 - 6
Justification for Enriched Air
• The lower nitrogen
content in oxygen
enriched air allows
for longer no-stop
dive times.
• Some are almost
100% longer.
EAN 1 - 7
Repetitive Dive (fsw)
• Air Example
– Dive # 1
90 fsw / 20 min no-stop
– One hour surface interval Group F > G
– Dive # 2
80 fsw / 12 min no-stop
• 36% O2 Example
– Dive # 1
90 fsw / 20 min no-stop
– One hour surface interval Group E > D
– Dive # 2
80 fsw / 36 minutes no-stop time
Enriched air provided 24 minutes more no-stop dive time.
EAN 1 - 8
History of enriched air in
recreational diving
• USN had explored nitrogen-oxygen mixtures in
1950's
• International Underwater Contractors (IUC) and
others had used it in commercial diving since
the 1960’s
• Dr. Morgan Wells introduced enriched air to
NOAA, published in 1979
• University of NC Wilmington had a strong NOAA
program
• Dick Rutkowski introduced “nitrox” to
recreational divers in 1988 in Key Largo
EAN 1 - 9
• NOAA sponsored high-level workshop at
Harbor Branch 1989
• 1992 Nitrox Workshop in Houston
– Scuba Diving Resource Group
– aquaCorps Journal
• Industry agreed to a standard for air to be
mixed with oxygen
• NAUI approved enriched air training 1992
• Enriched air computers enter the market
1992
• Enriched air diving centers expand all over
the world 1992 through the present.
EAN 1 - 10
Gases:
Basic Principles
• Matter takes 3 forms: solid, liquid, and gas
• Gases are compressible and fill the container
• Gases are affected by temperature
• Gas mixtures are made up of individual gases
• Once mixed, gases stay mixed and are hard to
separate
• Gases dissolve in liquids in proportion to
pressure
EAN 1 - 11
Boyle’s Law
• As pressure on a given mass of gas is
increased, the volume decreases, or as
volume is reduced the pressure
increases.
Air Balloon
P V = kt
Or
P1 V1 = P2 V2
surface
1
33 fsw (10 msw)
1/2
66 fsw (20 msw)
1/3
99 fsw (30 msw)
1/4
EAN 1 - 12
Composition of air
•
•
•
•
Oxygen 0.2095
Nitrogen 0.7808
Argon
0.00934
Others
• Total
Oxygen
Nitrogen
Argon
Others
1.0000
EAN 1 - 13
Composition of air
• Oxygen, O2 20.95%
– essential component of all breathing mixes
• Nitrogen, N2 78.08%
– inert gas in air and nitrox mixtures
– narcotic properties are main disadvantage
• Argon, Ar 0.934 %
– makes up about 1% of air and is considered with the
nitrogen component.
• Trace gases include
– CO2, neon, helium, methane, nitrogen oxides
EAN 1 - 14
Nitrogen and Narcosis
• What is narcosis?
–
–
–
–
Numbing or state of stupor
Is sneaky because of its euphoric feeling.
Slows down information processing
Affects most people at 100-130 fsw (30-40 msw)
• Dangers of narcosis at depth
– Unable to deal with problems
– Difficulty in managing multiple tasks
EAN 1 - 15
Gas Laws
• Pressure and temperature
– On compression gases get hot
– Heating increases pressure
– Heating increases volume at constant P
• Solubility
–
–
–
–
–
Gases dissolve in liquids
Amount dissolved proportional to pressure
Solubility is a function of gas and liquid
Most gases have higher solubility in fat
N2 is more soluble than He or Ne
EAN 1 - 16
Partial Pressure
• The effect of a single gas component in a gas
mixture.
• The fraction of the component gas multiplied
by the total pressure.
• When added, all of the partial pressures of
the component gases become the total
pressure.
Air at 1 atm
Percentage
79% N2
21% O2
100%
Partial Pressure
=
=
=
0.79 atm
0.21 atm
1.00 atm
EAN 1 - 17
Partial Pressure of Gases in a Mix
• In a mixture of gases, the total pressure is
made up of the sum of the pressures of the
individual components.
P = P1 + P2 + P3 +…+Pn
• The partial pressure of a gas, is the product
of the fraction of that gas times the total
pressure.
Pg = Fg X P total
Dalton’s Law
EAN 1 - 18
Calculating Partial Pressures
Pg = P x Fg
Pg = partial pressure
P = absolute pressure
Fg = fraction of the gas
EAN 1 - 19
Calculating Partial Pressures
Pg
Partial pressure
Total
pressure
Gas
fraction
P
Fg
EAN 1 - 20
Maximum depth for EAN32
?
1.4 atm
0.32
P
P = 1.4 atm / 0.32
P = 4.375 atm
Dfsw = (4.375 atm - 1atm) x 33 fsw
or
Dmsw = (4.375atm - 1atm) x 10 msw
D fsw = 111
D msw = 34
110 fsw is maximum operating depth
33 msw is maximum operating depth
EAN 1 - 21
Maximum depth for EAN40
?
P = 1.4 atm / 0.40
1.4 atm
P = 3.5 atm
Dfsw = (3.5 atm - 1atm) x 33 fsw
Dmsw = (3.5atm - 1atm) x 10 msw
0.40
P
D fsw = 82.5
D msw = 25
80 fsw is maximum operating depth
25 msw is maximum operating depth
EAN 1 - 22
Oxygen
• Metabolism:
– Oxygen is essential for life and energy
• The need for oxygen:
– Hypoxia
• Oxygen’s role in decompression
• Oxygen as an inert gas:
– Narcosis and decompression
• Toxic effects of oxygen:
– The need for management
• Oxygen is a powerful oxidizing agent
EAN 1 - 23
Effects of different levels of
oxygen partial pressure (atm)
• 3.0 50/50 enriched air nitrox recompression treatment
gas for use in the chamber at 6 atm abs.
• 2.8 100% O2 recompression treatment gas at
60 fsw (18 msw)
• 2.4 40% O2-60% N2 enriched air nitrox recompression
treatment gas at 6 atm abs.
• 2.2 Commercial/military “Sur-D” chamber surface
decompression, 100% O2 at 40 fsw (12 msw) pressure.
• 1.6 Maximum exposure for working diver, NOAA limits.
• 1.4 Recommended maximum exposure for recreational
diver.
EAN 1 - 24
Effects of different levels of
oxygen partial pressure (atm)
• 0.50 Threshold for whole-body effects; maximum
saturation dive exposure.
• 0.35-0.40 Normal saturation dive PO2 level.
• 0.21 Normal environment oxygen (sea level air).
• 0.14-0.16 Initial signs/symptoms of hypoxia.
• 0.09-0.10 Serious signs/symptoms of hypoxia.
• <0.08-0.10 Unconsciousness in most people.
• <0.08 Coma leading to death.
EAN 1 - 25
Oxygen Toxicity
• CNS: Effects on the central nervous
system
• Variations in tolerance
• Benefits of intermittent exposure
EAN 1 - 26
CNS Oxygen Toxicity
Signs and Symptoms
•
•
•
•
•
•
•
Convulsion
Visual disturbances, tunnel vision
Ear ringing
Nausea
Tingling, twitching (facial or muscle spasms)
Irritability, restlessness, euphoria, anxiety
Dizziness, dyspnea
EAN 1 - 27
Managing oxygen exposure:
CNS limits
•
•
•
•
A convulsion can be fatal
Methods exist for management
Single Dive Oxygen
Uses limits; NOAA
Exposure Limits
Monitor percentage of limit
PO2 atm Minutes
– Limit fraction
– Oxygen clock
1.60
1.55
1.50
1.45
1.40
1.35
1.30
1.25
1.20
45
83
120
135
150
165
180
195
210
EAN 1 - 28
Oxygen Exposure Chart
EAN 1 - 29
Toxicity Prevention
• Keep PO2 levels at 1.4 atm or less
• 1.5 and 1.6 for contingency purposes only
• If signs of toxicity appear
– Ascend to a shallower depth
– Diver should be taken to surface
– Do not delay ascent
EAN 1 - 30
The Nitrox Mixes
Nitrogen-Oxygen Mixtures
100
80
60
40
20
0
Air
EAN 32
Oxygen
EAN 36
EAN 40
Nitrogen
EAN 1 - 31
How to pick the right mix?
Concerns of the Mix
• Maximum Operating
Depth
• Contingency Operating
Depth
• These are
recommended and
contingency limits
Maximum and Contingency
Operating Depths
EAN32
EAN 36
PO2
Maximum
1.39
110 fsw
33 msw
1.34
90 fsw
27 msw
PO2
Contingency
1.58
130 fsw
40 msw
1.56
110 fsw
33 msw
EAN 1 - 32
Concerns of the mix
• Consider upper
limits of mix at
depth
• Pick a mix for
planned dive time
NOAA Oxygen Exposure Limits
PO2 atm
1.60
1.55
1.50
1.45
1.40
1.35
1.30
1.25
1.20
Maximum
Maximum
Single Limit
24-Hour Limit
45
83
120
135
150
165
180
195
210
150
165
180
180
180
195
210
225
240
EAN 1 - 33
Calculating:
Maximum Operation Depth
(fsw)
 PO2 limit , atm 

MOD , fsw  
 1 atm   33 fsw/atm
 PO2 mix, atm 

To calculate the MOD for 32% oxygen, which
has an FO2 of 0.32, at a limit of 1.4 atm:
 1.4 atm 

MOD , fsw  
 1 atm   33 fsw/atm  111 fsw
 0.32 atm 

EAN 1 - 34
Use the chart
EAN 1 - 35
Percentage of Oxygen at Various PO2 Levels
Choosing a
“Best Mix”
•Fraction of Oxygen
for the Mix
PO 2
Fraction 
Depth in atm
1.4
0.38 =
3.73 atm
38% mix is best for 90 fsw (27 msw)
Percentage of Oxygen
at Various PO2 Levels
fsw msw atm
40 12 2.21
45 14 2.36
50 15 2.52
1.3
59%
55%
52%
1.4
63%
59%
56%
1.5
68%
63%
60%
1.6
72%
68%
64%
55
60
65
70
75
80
85
90
95
100
105
110
115
17
18
20
21
23
24
26
27
29
30
32
33
35
2.67
2.82
2.97
3.12
3.27
3.42
3.58
3.73
3.88
4.03
4.18
4.33
4.48
49%
46%
44%
42%
40%
38%
36%
35%
34%
32%
31%
30%
29%
53%
50%
47%
45%
43%
41%
39%
38%
36%
35%
33%
32%
31%
56%
53%
51%
48%
46%
44%
42%
40%
39%
37%
36%
35%
33%
60%
57%
54%
51%
49%
47%
45%
43%
41%
40%
38%
37%
36%
120
125
130
36 4.64
38 4.79
39 4.94
28%
27%
26%
30%
29%
28%
32%
31%
30%
35%
33%
32%
EAN 1 - 36
Table 1 “Best Mix” choose desired PO2 then intersect with the
Selecting the Appropriate Table
• Prepared table
– EAN 32% and EAN 36 % tables
• EAD principle
– convert and use air table
• Oxygen Exposure
– NOAA oxygen exposure limits
• Breathing gas
• Repetitive diving procedures
• Mix in the tank
EAN 1 - 37
EAD and NAUI Air Tables
•
•
•
•
Air table at theoretical shallower depth
Use EAD chart or OCEANx calculator
Use EAD formula
Write down dive plan on a slate
EAN 1 - 38
EAD Formula (fsw)
 D fsw  33 fsw1  FO2  
EAD fsw  
  33 fsw
0.79


 81  331  0.37  
57.9 fsw  58 fsw  
  33
0.79


•This is a dive to 81 fsw using 37% oxygen EAN.
•The EAD computes to 57.9 rounds to 58.
•A 60 fsw air schedule would be used.
EAN 1 - 39
EAD Conversion Chart
Use the air schedule for no-stop times
EAN 1 - 40
Diving Table Procedure Review
• Descent rate 75 fpm
(25 mpm)
• Ascent rate 30 fpm
(9 mpm)
• Safety-Stop
– 3-5 minutes at 15 fsw
(5 msw)
• Cold or strenuous dive
– use the next greater
bottom time
• Repetitive dives
– less than 24 hours
• Flying after diving
– 12 hours for single dive
– 24 hours for all others
• Altitude diving
– tables good to 1,000 foot
(328 meters) elevation only
• Omitted decompression
–
–
–
–
stay on surface
breathe 100% oxygen
monitor for DCS
plan to evacuate to
recompression chamber
EAN 1 - 41
36% oxygen
32% oxygen
EAN 1 - 42
Table #1
Start
No-stop time limits
EAN 1 - 43
Table #2
Surface interval time table
EAN 1 - 44
Table #3
Repetitive dive time table
EAN 1 - 45
Repetitive Diving
• With same gas
– use same table
– dives should be progressively shallower
– shallower than 50 fsw (16 msw) use 50 fsw (16
msw) schedule
• With different gas
– must use EAD conversion and air table
• Monitor oxygen exposure
EAN 1 - 46
Dive Computers overview
• Air
• Enriched Air
• Multi-level diving
• Repetitive diving with computers
• Return to dive from computer failures
EAN 1 - 47
Using an air computer
•
•
•
•
•
•
OK to use
Show “air” limits
Monitor depth
Observe O2 limit
Watch MOD
Make a safety stop
Write MOD on computer
EAN 1 - 48
Using an enriched air computer
• Mix specific
– program oxygen %
• Calculates
– no-stop time
– deco time
• Monitors
– oxygen exposure
• Make a safety stop
EAN 1 - 49
Other dive computer
applications
• Multi-level diving
– makes it easy to do
– calculates no-stop dive time in real time
– monitors oxygen exposure
• Repetitive diving
– calculates surface intervals
– updates no-stop dive time
– monitors oxygen exposure
EAN 1 - 50
Return to dive from
computer failure
• Failure and no backup ?
– ascend to 15 fsw
(5 msw)and make 3-5
minute safety stop.
• Delay further diving
– check manufacturer
requirements for specified
time.
• Mix specific table
• Air table with EAD
EAN 1 - 51
Obtaining Nitrox Fills
• Certification required
• Rental cylinders
– usually pre-mixed
– 32% and 36% most
popular
– restrictions on refilling
• Filling a cylinder
– qualified technician only
EAN 1 - 52
Oxygen Analyzers
• Digital
• Analog
• 0.1% accuracy
is desirable
• Electrochemical
oxygen sensor
– has limited life span
EAN 1 - 53
The Need for Calibration
• Sets analyzer at a
known value
• Allows for adjustment of
sensor deterioration
• Affected by flow rate
• Better to calibrate one
well than to use two
• Air calibrates at 20.9%
EAN 1 - 54
Analyzing the Gas
• Flow Rate
– affects reading
– 1-2 lpm for one minute
– calibrated at same flow
• Acceptable range
–
–
–
–
desired mix +/- 1%
NAUI EAN tables account for this
36% tables ok for 35-37%
32% tables ok for 31-33%
EAN 1 - 55
The EAN Cylinder
•
•
•
•
Calibrate analyzer
Analyze cylinder
Check for accuracy
If not right
– check again
– have gas re-mixed
• Write information
– contents label or tag
EAN 1 - 56
Cylinder Contents Label
• Only way to know contents
• Write on label
–
–
–
–
–
–
–
–
Use permanent marker
Fill date
Oxygen %
PSI (pressure)
MOD
Filled by
Analyzed by
User’s name
08 January 1998
31.8 %
3,000
130 fsw
Amer Diving
Bram
Bram
EAN 1 - 57
Fill Station Log
•
•
•
•
•
•
•
•
Name
Certification number
Date
Fill pressure
Oxygen percentage
Maximum depth limit
Cylinder serial number
Signature
EAN 1 - 58