Nitrox Diving
Sources
• Joiner, J.T. (ed.). 2001. NOAA Diving
Manual - Diving for Science and
Technology, Fourth Edition. Best
Publishing Company, Flagstaff, AZ.
• Reference Materials:
– In conjunction with this presentation, refer to:
• NOAA Diving Manual Chapter 15
• NOAA Diving Manual Appendix VII
Objectives
• Upon completion of this module, the participant will be
able to:
– List and dispel six myths about nitrox; list three advantages of
nitrox; and describe the difference between CNS & Pulmonary
Oxygen Toxicity;
– Select proper nitrox mixes; determine Oxygen Exposure; and
calculate FO2, PO2, MOD, & EAD for a given dive;
– Plan nitrox dives;
– Explain the 40% Rule; the difference between formal and
informal oxygen cleaning; and list four methods of nitrox
preparation;
– Describe proper marking and labeling requirements for nitrox
cylinders;
– Describe how to calibrate an O2 analyzer and analysis nitrox
What’s Important
• Using nitrox means having to manage
nitrogen (N2) and oxygen (O2) while
diving
• The advantage of extended bottom times
also means properly managing your
available gas
Physiology Review
Composition of Air
• 21% O2 - necessary for body metabolism, but
may be toxic in excess
• 78% N2 – inert gas (plays no role in body
metabolism) – causes narcosis at high partial
pressure
• 1% other gasses (mostly argon, but also carbon
dioxide (the waste product from the metabolism
of oxygen), neon, helium, krypton, sulfur
dioxide, methane, etc… )
– These are considered with the nitrogen component of
air in nitrox calculations
Nitrogen-Oxygen Breathing
Mixtures
• Air is readily available and inexpensive,
but it is not the “ideal” breathing mixture
because of the effects of nitrogen narcosis
at deeper depths & the decompression
liability it imposes
Nitrogen and narcosis
• Nitrogen narcosis – the pronounced anesthetic effect that
occurs when nitrogen is breathed at higher pressures
• Most people feel narcosis at roughly 100–130 feet (3–4 ata)
– Martini’s Law – every 50 feet of depth is roughly equivalent to
drinking one dry gin martini on an empty stomach
• Symptoms include:
–
–
–
–
–
–
Feelings of euphoria
Shortened attention span
Tendency to giggle
Slurred speech
Numb lips
Inability to concentrate
• Mechanisms of narcosis seem to be similar to that of
anesthesia
Nitrogen and narcosis
• Feelings of well being may disguise threat
– narcosis may leave diver unable to deal
with problems
• Sensitivity to narcosis varies among
individuals – there seems to be some
evidence that people learn to cope with
narcosis as they gain experience diving
• Divers may be unaware of impairment
Nitrogen and narcosis
• Other factors may contribute to nitrogen
narcosis:
–
–
–
–
–
–
–
–
Psychological predisposition
Stress
Anxiety
Fatigue
Cold
Hard work
High carbon dioxide levels in the body
Alcohol
Nitrogen-Oxygen Breathing
Mixtures
• Decompression obligation is dependent
on exposure to inspired nitrogen
• Decompression obligation can be reduced
by replacing a portion of the nitrogen in a
breathing mixture with oxygen
• This is the fundamental benefit of
nitrogen-oxygen diving
Decompression sickness
• Caused by the release of gas dissolved in tissues
– may form bubbles in body while surfacing or
after a dive
• Symptoms and signs may occur anywhere from
5 minutes to 24 hours or more after a dive
– Most commonly, however, they appear within one
hour
• Symptoms and signs do not generally manifest
themselves in-water
Decompression sickness – signs
and symptoms
•
•
•
•
•
•
•
•
Joint pain
Paralysis
Muscle pain
Skin rash
Disorientation
Slurred speech
Dizziness
Agitation
•
•
•
•
•
•
Hearing disturbances
Tingling
Fatigue
Vision problems
Numbness
Weakness
Treatment
• Victims should breathe 100% oxygen
• Evacuate victim to the nearest hyperbaric
treatment facility
– Note: signs and symptoms may dissipate
during oxygen breathing – victim should still
be evaluated at a hyperbaric treatment facility
– Treatment protocols do not change for nitrox
divers
Nitrox
Nitrox
• Nitrox is a generic term that can be used
for any mixture of nitrogen and oxygen
other than air
• For the purpose of this training module,
all nitrox mixtures have an O2 percentage
greater than air
Oxygen Enriched Air:
Terminology
• Oxygen Enriched Air
(OEA)
• Enriched Air Nitrox
(EAN or EANx (the “x” in
EANx stands for the percentage
of oxygen in the mix))
• NN32 (a 32% mix)
• NN36 (a 36% mix)
• Most Common
(standard) Mixes
– 32% oxygen
– 36 % oxygen
• EAN32
• EAN36
All the mixes have more oxygen and
less nitrogen than normal air
Abbreviated History of Enriched
Air in Diving
• 19th century – Elihu Thompson proposed use of
Hydrogen & O2
• USN explored nitrogen-oxygen mixtures in 1950s
• International Underwater Contractors (IUC) and
others began using enriched air in commercial diving
in the 1960s
• Dr. Morgan Wells introduced enriched air to NOAA,
published in NOAA Diving Manual in 1979 – Dr.
Wells is credited with developing and introducing
nitrox diving techniques for standard scuba
• NOAA Continuous Flow Blending techniques – 1984
Abbreviated History of Enriched
Air in Diving
• 1984 NURC/UNCW established a strong Nitrox
program
• NOAA sponsored high-level workshop at Harbor
Branch 1988
• Industry agreed to a standard for air to be mixed
with oxygen
• Dick Rutkowski (IANTD) introduced EANx to
recreational diving in 1985
• Enriched air computers enter the market in 1992
• 1992 - NAUI sanctions enriched air nitrox training
Myths About Nitrox
• Nitrox is safer than air
– False
– Nitrox has a significant decompression
advantage over air, but has other risks that
must be managed
– These additional areas of concern include O2
toxicity, required depth and time limits, mix
conformation and analysis, special equipment
requirements, and risks involved in gas
mixing
Myths About Nitrox
• “Nitrox is for deep diving”
– FALSE
– Nitrox has very stringent depth limits because
of the higher concentration of O2 in the
mixture
– The greatest advantages for no-stop diving
are in the 50-110 feet of sea water (fsw) depth
range
Myths About Nitrox
• “Nitrox eliminates the risk of
decompression sickness (DCS)”
– FALSE
– Using nitrox provides significant
decompression advantage over air, but the
risk of DCS is likely unchanged if nitrox
specific dive tables are used
Myths About Nitrox
• “Nitrox makes treatment for DCS
impossible”
– FALSE
– Treatment for DCS in a nitrox diver is the
same as treatment for an air diver, taking into
account the possibility of extra oxygen
exposure
Myths About Nitrox
• “Nitrox reduces narcosis”
– Not Really
– Although this has not been adequately
studied, oxygen’s properties suggest that it
can also be a narcotic gas under pressure. The
result is that you should not expect a
significant change in narcosis when diving
nitrox as compared to air
Myths About Nitrox
• “Using nitrox is difficult”
– FALSE
– Once you understand the potential risks and
simple requirements of using nitrox as a
breathing gas, diving nitrox is as easy as
inhale, exhale, repeat
Advantages of Nitrox
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual
4th Ed.) Flagstaff, AZ
• Longer no-stop dive times
Depth
No-stop deco times (minutes)
(fsw)
(msw)
USN Air
21%
NN32
32%
NN36
36%
50
15
100
200
310
60
18
60
100
100
70
22
50
60
60
80
25
40
50
60
90
28
30
40
50
100
31
25
30
40
110
34
20
25
30
120
37
15
25
130
40
10
20
Advantages of Nitrox
• Less nitrogen absorbed = lower risk of
DCS
– Breathing a gas with less nitrogen coupled
with air decompression tables effectively
lowers the risk of DCS. This does not mean a
diver will never get DCS; it means with
proper management, the already small risk of
DCS can be even smaller
Advantages of Nitrox
• Longer repetitive dives
• Air Example
• Dive # 1 - 90 fsw / 20 min no-stop
• One hour surface interval Group F > E
• Dive # 2 - 80 fsw / 17 min no-stop
• Same Dive Using 36% O2
• Dive # 1 - 90 fsw / 20 min no-stop
• One hour surface interval Group E > D
• Dive # 2 - 80 fsw / 36 minutes no-stop time
Using EAN provided 24 minutes more no-stop dive time
Advantages of Nitrox
• Possibility of shorter required surface interval
– Using Navy air tables and NOAA nitrox tables:
• Two dive teams just completed a 30 minute dive to 80 fsw.
Team 1 breathed air, while Team 2 breathed EAN36. Team 1
emerges with a letter group of G, while Team 2 emerges with
a letter group of F. Using the appropriate dive tables to
compute a 2nd dive to 55 fsw for 30 minutes finds Team 2
could enter the water in as few as ten minutes with a letter
group of F, while Team 1 would have to wait at least 1 hour
and 16 minutes for the air tables to allow sufficient adjusted
maximum dive time for the planned dive.
Physics Review
Units of Measure
• Pressure
– One atmosphere (atm) equals the pressure of the air
at sea level
– 1 atm equals:
• 760 millimeters of mercury
• 29.92 inches of mercury
• 101.3 kilopascals (kPa)
• 1.013 bars
• 14.7 lbs/in2 (psi)
• 33 feet of seawater (fsw)
• 34 feet of freshwater (ffw)
Units of Measure
• Atmospheres absolute (ata) equals water
pressure (hydrostatic pressure) +
atmospheric pressure
Partial Pressure
• The partial pressure of a specific gas in a mix is the
portion of the total pressure exerted by that gas
• It is 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
Partial Pressure
79% N2
21% O2
100%
=
=
=
0.79 atm
0.21 atm
1.00 atm
Partial Pressure
• Dalton’s law - In a mixture of gases, the total
pressure is made up of the sum of the partial
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
Where Pg = partial pressure of the component gas
Fg = fraction of the component gas in the mixture, and Ptotal
= the total pressure of the gas mixture
Pressure and Volume:
Boyles Law
• Pressure and volume (at constant temperature)
are inversely proportional to each other. So, as
pressure on a given mass of gas is increased,
volume decreases – and as pressure on a given
mass of gas decreases, volume increases. So:
– P1V1= P2V2 where:
• P1 = initial pressure
• V1 = initial volume
• P2 = final pressure
• V2 = final volume
Pressure and Temperature:
Gay-Lussac’s Law
• At constant volume, pressure is proportional to
the absolute temperature - temperature increases
when pressure increases. Temperature decreases
when pressure decreases.
– P1/T1=P2/T2 where:
• P1 = initial pressure
• T1 = initial temperature
• P2 = final pressure
• T2 = final temperature
– Note: all temperatures must be expressed in either Rankine
(temperature in Fahrenheit + 460) or Kelvin (temperature in
Celsius + 273)
Volume and Temperature:
Charles’ Law
• If pressure is held constant, then volume is
proportional to temperature. So, volume
increases when temperature increases, and
volume decreases when temperature decreases.
–
–
–
–
–
V1T1/V2T2 where:
V1 = initial volume
T1 = initial temperature
V2 = final volume
T2 = final temperature
– Note: all temperatures must be expressed in either Rankine
(temperature in Fahrenheit + 460) or Kelvin (temperature in
Celsius + 273)
The Solubility of Gasses:
Henry’s law
“The amount of any given gas that will dissolve in a liquid at a given
temperature is a function of the partial pressure of the gas that is in
contact with the liquid and the solubility coefficient of the gas in the
particular liquid”
• So, the solubility of a gas in a liquid is
directly related to the pressure of the gas
on the liquid – an increase in pressure
causes an increase in solubility, while a
decrease in pressure causes a decrease in
solubility
Converting fsw to atmospheres
absolute (ata)
D fsw + 33 fsw
= P ata
33 fsw / atm
For a depth of 75 fsw
75 fsw + 33 fsw = 3.27 ata
33 fsw / atm
Depth plus 33 then divide by 33
Converting fsw to ata
Alternate Formula:
ata
ata
=
=
(fsw ) + 1
33
(75) + 1 = 3.27 ata
33
Converting ata to fsw
(ata x 33 fsw/atm) - 33 fsw/atm = D fsw
For a pressure of 3 ata
(3 ata x 33 fsw/atm) – 33 fsw/atm = 66 fsw
ata times 33 then minus 33 = fsw
Converting fsw to ata
•Alternate Formula:
– D fsw = (ata – 1 atm) x 33 fsw/atm
– For a pressure of 3 ata:
(3 ata – 1 atm) x 33 fsw/atm = 66 fsw
Oxygen Physiology, Toxicity,
and Tolerance
Hypoxia
• Oxygen is necessary for metabolism
– Hypoxia – an inadequate supply of oxygen
– May occur when oxygen partial pressure falls
at or below 0.16 ata
• Symptoms include: euphoria, dimness of vision
(“tunnel vision”), dizziness, breathlessness, itching
and tingling. When severe enough, collapse and
unconsciousness may occur
• Possible signs – cyanosis (bluish skin coloration),
blueness of the lips and nail beds
Oxygen Toxicity
• Exposure to oxygen at high partial pressures
may damage tissue and disrupt function
• This damage is dependent upon both the partial
pressure of the oxygen, and upon the length of
time the oxygen is breathed
• The most common cause is exceeding the
oxygen exposure limits, but using an incorrect
mix for the depth being dived is also common
Oxygen Toxicity – Central
Nervous System Toxicity (CNS)
• May occur after breathing oxygen at high partial
pressures (above 1.6 ata) over a relatively short
duration (a few breaths)
• Signs & Symptoms – occur in an unpredictable
sequence:
– Mnemonic – “ConVENTID” Convulsion, Visual disturbances
(including tunnel vision), Ear ringing, Nausea, Tingling,
Twitching or muscle spasms (especially of the faced and lips)
Irritability, Dizziness
– Other symptoms – difficulty breathing, anxiety, confusion,
poor coordination, fatigue, euphoria, dilated pupils, hiccups,
hallucinations
• ASCEND - If any symptoms are noted, diver should
reduce the partial pressure of the breathing gas by
ASCENDING; the dive should be terminated
Oxygen Toxicity – Central
Nervous System Toxicity (CNS)
• Any of the symptoms above may warn of an
oncoming convulsion
• However, there may be NO WARNING
proceeding a convulsion
• Furthermore, divers have lost consciousness
without warning, possibly from oxygen toxicity
Oxygen Toxicity – Central
Nervous System Toxicity (CNS)
• Individual tolerance to oxygen toxicity varies
over time
• Tolerance also varies from individual to
individual
• Factors that may increase your susceptibility to
CNS
–
–
–
–
–
–
Heavy exercise
Breathing dense gas
Breathing against resistance
Increased carbon dioxide buildup
Chilling or hypothermia
Water immersion (as opposed to “chamber diving”)
If a convulsion occurs
• May cause diver to spit out mouthpiece, usually
impossible to reinsert - drowning is likely
• Rapid or out-of-control ascent may lead to
pulmonary barotrauma
• Upon cessation of convulsion, diver should be
taken to the surface at a slow ascent rate
• Treat victim for near-drowning according to any
signs or symptoms – all victims should be
transported to a medical facility for evaluation
by a physician
Oxygen Toxicity – Whole Body Toxicity
(also known as Pulmonary Toxicity)
• Occurs from breathing oxygen at lower exposure
levels for longer periods of time (multiple hours)
• The lung is the organ primarily involved, but
other parts of the body may also be affected
• This generally is not an issue for scuba divers
performing no-stop dives, but may become an
issue for divers during intensive diving
operations
Oxygen Toxicity – Whole Body Toxicity
(also known as Pulmonary Toxicity)
• Symptoms:
– Pulmonary - Chest pain or discomfort,
coughing, chest tightness, fluid in the lungs,
reduction in vital capacity
– Non-pulmonary – skin numbness and itching,
headache, dizziness, nausea, effects on the
eyes, reduction in aerobic capacity
Selecting Mixes
Partial pressure of oxygen (PO2)
Exposure
• The maximum oxygen partial pressure
exposure for scientific diving is 1.6 ata,
and you may want to further limit your
exposure
• By contrast, 1.4 ata is the maximum PO2
exposure for most recreational diving
Concerns of the Mix
• A key facet to nitrox dive planning is to optimize
the O2 level by displacing as much N2 as
possible while remaining within the selected
oxygen exposure limit
• Too much O2 increases the risk of oxygen
toxicity
• Too much nitrogen shortens the no-stop time
• Using the wrong mix with the wrong table could
lead to DCS
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Oxygen Exposure Time
NOAA Oxygen Exposure Limits
PO2
(atm)
Maximum Single
Exposure
(minutes)
Maximum
per 24 hr
(minutes)
1.60
45
150
1.55
83
165
1.50
120
180
1.45
135
180
1.40
150
180
1.35
165
195
1.30
180
210
1.25
195
225
1.20
210
240
1.10
240
270
1.00
300
300
0.90
360
360
0.80
450
450
0.70
570
570
0.60
720
720
• As your PO2
increases, your
oxygen exposure limit
decreases
• The NOAA O2
Exposure Limits table
can be used to
determine your dive
time limits for a given
PO2
NOAA Oxygen Exposure Limits
• The lower the
PO2, the longer
the dive can be
conducted from
an oxygen
tolerance
perspective
PO2
(atm)
Maximum Single
Exposure
(minutes)
Maximum
per 24 hr
(minutes)
1.60
45
150
1.55
83
165
1.50
120
180
1.45
135
180
1.40
150
180
1.35
165
195
1.30
180
210
1.25
195
225
1.20
210
240
1.10
240
270
1.00
300
300
0.90
360
360
0.80
450
450
0.70
570
570
0.60
720
720
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Oxygen Exposure Time
Oxygen Exposure Time
• However, reducing PO2 exposure limits
also reduces the maximum depth at which
mixtures can be used
Oxygen Exposure Time
• Using a 32% mix at 130 ft results in a PO2 of
1.58. This limits the single dive exposure time to
45 minutes.
NOAA Oxygen Exposure Limits
PO2
(atm)
Maximum Single
Exposure
(minutes)
Maximum
per 24 hr
(minutes)
1.60
45
150
1.55
83
165
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Oxygen Exposure Time
• Using the same 32% mix, but reducing your
maximum PO2 exposure at depth to 1.4
increases your single dive exposure limit to 150
minutes.
• However, decreasing your PO2 exposure to 1.4
reduces the maximum depth you can use this
mix from 132 fsw to 111 fsw.
1.45
135
180
1.40
150
180
1.35
165
195
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Maximum Operating Depth
• Maximum Operating Depth (MOD) – the
maximum depth that should be dived with a
given nitrox mixture
• MOD is determined by calculating the depth
limits of the selected oxygen exposure (PO2) for
a given dive
Calculating: MOD
 PO2 limit,ata

MOD  
 1 atm  33 fsw/atm
 FO2 mix 

To calculate the MOD for a 32% mix, which has an FO2
(fraction of oxygen) of 0.32, and a PO2 at depth of 1.4 ata:
 1.4

MOD  
 1 atm  33  111fsw
 0.32

Calculating: MOD
The MOD for the same 32% mix using a PO2
of 1.6 ata:
 1.6

MOD  
 1 atm  33  132fsw
 0.32

Calculating Partial Pressure
Calculating Partial Pressures
• Dalton’s law
Pg = Fg x Ptotal
Pg = partial pressure of the component gas
Fg = fraction of the component gas
Ptotal = total pressure of gas mixture
Calculating Partial Pressures
• Calculate the partial pressure of oxygen
(PO2) for air being breathed at 90 fsw:
Pg = Fg x P
PO2 = 0.21 x 3.7
PO2 = 0.78
Depth
(fsw)
(msw)
0
0
35
atm
abs
21%
28%
30%
31%
32%
33%
34%
35%
36%
37%
38%
39%
40%
1.00
0.21
0.28
0.30
0.31
0.32
0.33
0.34
0.35
0.36
0.37
0.38
0.39
0.40
11
2.05
0.43
0.57
0.62
0.66
0.66
0.68
0.70
0.72
0.74
0.76
0.78
0.80
0.82
40
12
2.21
0.46
0.62
0.66
0.69
0.71
0.73
0.75
0.77
0.80
0.82
0.84
0.86
0.88
50
15
2.52
0.53
0.71
0.76
0.78
0.81
0.83
0.86
0.88
0.91
0.93
0.96
0.98
1.01
60
18
2.82
0.59
0.79
0.85
0.87
0.90
0.93
0.96
0.99
1.02
1.04
1.07
1.10
1.13
70
22
3.12
0.66
0.87
0.94
0.97
1.00
1.03
1.06
1.09
1.12
1.15
1.19
1.22
1.25
80
25
3.42
0.72
0.96
1.03
1.06
1.09
1.13
1.16
1.20
1.23
1.27
1.30
1.33
1.37
90
28
4.73
0.78
1.04
1.12
1.16
1.19
1.23
1.27
1.31
1.34
1.38
1.42
1.45
1.49
100
31
4.03
0.85
1.13
1.21
1.25
1.29
1.33
1.37
1.41
1.45
1.49
1.53
1.57
1.61
110
34
4.33
0.91
1.21
1.30
1.34
1.39
1.43
1.47
1.52
1.56
1.60
1.65
1.69
1.73
120
37
4.64
0.97
1.30
1.39
1.44
1.48
1.43
1.58
1.62
1.67
1.72
1.76
1.81
1.86
130
40
4.94
1.04
1.38
1.48
1.53
1.58
1.63
1.68
1.73
1.78
1.83
1.88
1.93
1.98
140
43
5.24
1.10
1.47
1.57
1.62
1.68
1.73
1.78
1.83
1.89
1.94
1.99
150
46
5.55
1.17
1.55
1.67
1.72
1.78
1.83
1.89
1.94
2.00
160
49
5.85
1.23
1.64
1.76
1.81
1.87
1.93
1.99
170
52
6.15
1.29
1.72
1.85
1.91
1.97
PO2 (atm) based on depth and percentage of oxygen. The body of the chart has PO 2 values for various mixes at a range of depths. Standard 32% and 36% mixes
are in light grey. PO2 levels higher than 1.6 ata, in red, are considered exceptional exposures and should be avoided
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
PO2 Chart
PO2 Chart
• Use the PO2 Chart to determine the PO2 of
a 32% mix being breathed at 110 fsw
Depth
(fsw)
(msw)
0
0
35
atm
abs
21%
28%
30%
31%
32%
33%
34%
35%
36%
37%
38%
39%
40%
1.00
0.21
0.28
0.30
0.31
0.32
0.33
0.34
0.35
0.36
0.37
0.38
0.39
0.40
11
2.05
0.43
0.57
0.62
0.66
0.66
0.68
0.70
0.72
0.74
0.76
0.78
0.80
0.82
40
12
2.21
0.46
0.62
0.66
0.69
0.71
0.73
0.75
0.77
0.80
0.82
0.84
0.86
0.88
50
15
2.52
0.53
0.71
0.76
0.78
0.81
0.83
0.86
0.88
0.91
0.93
0.96
0.98
1.01
60
18
2.82
0.59
0.79
0.85
0.87
0.90
0.93
0.96
0.99
1.02
1.04
1.07
1.10
1.13
70
22
3.12
0.66
0.87
0.94
0.97
1.00
1.03
1.06
1.09
1.12
1.15
1.19
1.22
1.25
80
25
3.42
0.72
0.96
1.03
1.06
1.09
1.13
1.16
1.20
1.23
1.27
1.30
1.33
1.37
90
28
4.73
0.78
1.04
1.12
1.16
1.19
1.23
1.27
1.31
1.34
1.38
1.42
1.45
1.49
100
31
4.03
0.85
1.13
1.21
1.25
1.29
1.33
1.37
1.41
1.45
1.49
1.53
1.57
1.61
110
34
4.33
0.91
1.21
1.30
1.34
1.39
1.43
1.47
1.52
1.56
1.60
1.65
1.69
1.73
120
37
4.64
0.97
1.30
1.39
1.44
1.48
1.43
1.58
1.62
1.67
1.72
1.76
1.81
1.86
130
40
4.94
1.04
1.38
1.48
1.53
1.58
1.63
1.68
1.73
1.78
1.83
1.88
1.93
1.98
140
43
5.24
1.10
1.47
1.57
1.62
1.68
1.73
1.78
1.83
1.89
1.94
1.99
150
46
5.55
1.17
1.55
1.67
1.72
1.78
1.83
1.89
1.94
2.00
160
49
5.85
1.23
1.64
1.76
1.81
1.87
1.93
1.99
170
52
6.15
1.29
1.72
1.85
1.91
1.97
PO2 (atm) based on depth and percentage of oxygen. The body of the chart has PO 2 values for various mixes at a range of depths. Standard 32% and 36%
mixes are in light grey. PO2 levels higher than 1.6 ata, in red, are considered exceptional exposures and should be avoided
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
PO2 Chart
PO2 Chart
• Use the PO2 Chart to determine the PO2 of
a 32% mix being breathed at 110 fsw
• Answer – 1.39 ata
Calculating FO2
Calculating FO2
• Standard Mixes like NN 32 or 36 are good
for a variety of diving situations
• There are times, however, when a dive
calls for maximizing no-stop time for a
specific depth
• To maximize no-stop time, determine the
“Best Mix” for a given depth by
calculating the fraction of oxygen (FO2) at
your desired PO2 exposure
Calculating FO2
To calculate the best mix for 120 fsw using a
PO2 of 1.4:
 PO2 atm 

FO2  
 Depth atm 

 1.4

1.4
 
FO2  
 .30
 (120 / 33  1)  4.64
The best mix for 120 fsw using a PO2 of 1.4 is 30%
Calculating FO2
To calculate the best mix for 120 fsw using a
PO2 of 1.6:
 PO2 atm 

FO2  
 Depth atm 

 1.6

1.6
 
FO2  
 .34
 (120 / 33  1)  4.64
The best mix for 120 fsw using a PO2 of 1.6 is 34%
• Table 15.4 of the
NOAA Diving
Manual may also be
used to determine the
best mix for a given
PO2
• This table provides
PO2 levels from 1.3 to
1.6 ata and depths to
130 fsw
PO2
fsw
ms
w
atm
1.3
1.4
1.5
1.6
40
12
2.21
58%
63%
67%
72%
45
14
2.36
55%
59%
63%
67%
50
15
2.52
51%
55%
59%
63%
55
17
2.67
48%
52%
56%
59%
60
18
2.82
46%
49%
53%
56%
65
20
2.97
43%
47%
50%
53%
70
22
3.12
41%
44%
48%
51%
75
23
3.27
39%
42%
45%
48%
80
25
3.42
38%
40%
43%
46%
85
26
3.58
36%
39%
41%
44%
90
28
3.73
34%
37%
40%
42%
95
29
3.88
33%
36%
38%
41%
100
31
4.03
32%
34%
37%
39%
105
32
4.18
31%
33%
35%
38%
110
34
4.33
30%
32%
34%
36%
115
35
4.48
29%
31%
33%
35%
120
37
4.64
28%
30%
32%
34%
125
38
4.79
27%
29%
31%
33%
130
40
4.94
26%
28%
30%
32%
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Calculating FO2
• Using the table to
determine the best
mix for a dive to 65
fsw using a with a
maximum PO2 of 1.5
finds the best mix is
50%
PO2
fsw
ms
w
atm
1.3
1.4
1.5
1.6
40
12
2.21
58%
63%
67%
72%
45
14
2.36
55%
59%
63%
67%
50
15
2.52
51%
55%
59%
63%
55
17
2.67
48%
52%
56%
59%
60
18
2.82
46%
49%
53%
56%
65
20
2.97
43%
47%
50%
53%
70
22
3.12
41%
44%
48%
51%
75
23
3.27
39%
42%
45%
48%
80
25
3.42
38%
40%
43%
46%
85
26
3.58
36%
39%
41%
44%
90
28
3.73
34%
37%
40%
42%
95
29
3.88
33%
36%
38%
41%
100
31
4.03
32%
34%
37%
39%
105
32
4.18
31%
33%
35%
38%
110
34
4.33
30%
32%
34%
36%
115
35
4.48
29%
31%
33%
35%
120
37
4.64
28%
30%
32%
34%
125
38
4.79
27%
29%
31%
33%
130
40
4.94
26%
28%
30%
32%
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Calculating FO2
Nitrox Dive Tables
Nitrox Dive Tables
• In 1979, NOAA introduced diving
procedures and dive tables for a
standard nitrox mixture of 32% O2, 68%
N2 (NN32)
• NOAA later introduced tables for 36%
oxygen (NN36)
Nitrox Dive Tables
• NOAA Nitrox dive tables are the basis for many
recreational nitrox dive tables
• The display of the tables may even be in the
same format as the NOAA tables, but have been
made more conservative by lowering maximum
dive times for certain depths
• Additionally, the recommended safety stop
depth for recreational tables may be slightly
different, and the surface interval for a dive not
to be considered repetitive may be increased
from the NOAA standard of 12 hours to 24
hours
Nitrox Dive Tables
• NOAA Nitrox tables were calculated on
the “equivalent air depth” (EAD) concept,
which is simply to decompress from a
non-air dive using air decompression
tables that have the same nitrogen partial
pressure (PN2)
Nitrox Dive Tables
• NOAA offers abbreviated and full versions of
Nitrox 32 and 36 dive tables in Appendix VII of
the NOAA Diving Manual
• The abbreviated version of these tables provide
for only one level of required decompression
• The full version of these tables are in the same
format as US Navy Dive Tables and include
multiple levels of required decompression
Equivalent Air Depth (EAD)
• Equivalent Air Depth is the depth based on the
partial pressure of nitrogen in the gas being
breathed, rather than the actual depth of the
dive
• For mixes with less N2 than air, the EAD is
shallower than if air is being used
• A diver is physically at a specific depth, but is
physiologically absorbing N2 equivalent to a
shallower depth
Equivalent Air Depth (EAD)
• EAD decompression is based on the
equivalent inert gas exposure, not the
actual depth of the dive
• Once the EAD has been determined, a
diver can use the “equivalent air depth”
with any air diving table to compute a
diving profile
Equivalent Air Depth (EAD)
• Table 15.6 of the NOAA Diving Manual
may be used to calculate EAD, or the
calculation may be made by formula
 D fsw  33 fsw1  FO2  
EAD fsw  
  33 fsw
0.79


Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Equivalent Air Depth (EAD)
Equivalent Air Depth Conversion Table (Fraction of Oxygen and Actual Depths)
EAD
(fsw)
28%
29%
30%
31%
32%
33%
34%
35%
36%
37%
38%
39%
40%
30
36
37
38
39
40
41
42
43
44
46
47
49
50
40
47
48
49
50
51
53
54
55
57
58
60
62
63
50
58
59
61
62
63
64
66
67
69
71
72
74
76
60
69
70
72
73
75
76
78
80
81
83
85
87
89
70
80
81
83
84
86
88
90
92
94
96
98
100
102
80
90
92
95
96
98
100
102
104
106
108
110
113
90
101
103
106
107
109
112
114
116
118
121
100
112
114
117
119
121
123
126
128
110
123
126
128
130
133
135
120
134
137
139
142
130
145
148
150
140
156
159
150
167
Numbers in grey boxes = exceptional exposure depth for mix
Equivalent Air Depth (EAD)
• To use the EAD Conversion Table:
– Enter the table under the oxygen percentage
and move down that column to the actual
depth, or the NEXT GREATER DEPTH, of
your dive
– Move to the left end of that row to find the
EAD
Equivalent Air Depth (EAD) – The table shows
that diving at 90 fsw while breathing 34% nitrox
is equivalent, physiologically, to diving at 70 fsw
on air
EAD
(fsw)
28%
29%
30%
31%
32%
33%
34%
35%
36%
30
36
37
38
39
40
41
42
43
44
40
47
48
49
50
51
53
54
55
57
50
58
59
61
62
63
64
66
67
69
60
69
70
72
73
75
76
78
80
81
70
80
81
83
84
86
88
90
92
94
80
90
92
95
96
98
100
102
104
106
90
101
103
106
107
109
112
114
116
118
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
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 and rounds to 58
•A 60 fsw air schedule would be used
Dive Computers & Nitrox
• There are two options for using dive
computers with Nitrox
– Use a computer designed for use with nitrox
– Breath nitrox while diving an air based
computer
Nitrox Dive Computers
• Allow for a variety of nitrox mixes to be used
• Compute the decompression profile based on
the O2 percentage programmed into the unit
by the diver
• Provide pre-programmed MOD limits based
on the mix and PO2
• Track Oxygen and Nitrogen exposure and
provide feedback to the diver
• Allow bottom times to be extended by
adjusting the decompression profile to take
advantage of the mix
Nitrox Dive Computers
• Because computers calculate and adjust
no-stop dive times throughout dives
(thereby lengthening no-stop dive times),
multilevel dives (when divers move to
progressively shallower depths during a
dive) are best planned and carried out
using dive computers rather than dive
tables
• Bottom time will be extended
Air Computers with Nitrox
• Builds in a theoretical safety margin by reducing
the amount of nitrogen absorbed at a given
depth
• However, the computer “thinks” the diver is
breathing air
– It will not alert the diver if he/she descends deeper
than the MOD of a given mix
• Divers using air computers to dive nitrox must
be aware of both the MOD of the nitrox being
dived and the maximum exposure time of the
deepest part of the dive in order to maintain
oxygen limits
Using NOAA Nitrox Tables
• NOAA Nitrox dive tables follow the same
basic rules for use as US Navy Dive Tables
• Familiarize yourself with the abbreviated
and full versions of the tables in Appendix
VII of the NOAA Diving Manual
Using NOAA Nitrox Tables
• Remember, divers have certain single
and cumulative time limits for oxygen
exposure
• Use the NOAA Oxygen Exposure
Limits table (Table 15.2) to determine
time limits for particular PO2s
NOAA Oxygen Exposure
Limits
• For example, A single
dive reaching a
maximum PO2 of 1.6
ata must not exceed
45 minutes
• Divers may not
exceed 150 minutes at
1.6 ata during any 24
hour period
NOAA Oxygen Exposure Limits
PO2
(atm)
Maximum Single
Exposure
(minutes)
Maximum
per 24 hr
(minutes)
1.60
45
150
1.55
83
165
1.50
120
180
1.45
135
180
1.40
150
180
1.35
165
195
1.30
180
210
1.25
195
225
1.20
210
240
1.10
240
270
1.00
300
300
0.90
360
360
0.80
450
450
0.70
570
570
0.60
720
720
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Using NOAA Nitrox Tables
• These limits are dependent on the PO2 at
the maximum depth of the dive
• O2 exposure level and time need to be
monitored carefully
• If a single planned dive exceeds the O2
exposure limit, reduce the PO2 level by
choosing a mix with a lower oxygen
content, or shorten the dive time
Using NOAA Nitrox Tables
• When analyzed, nitrox mixes must fall
within tolerance limits of ±1% in order to
be within the tolerance and NOAA nitrox
tables
• When using the EAD principle, calculation
should be based on the exact mix in the
cylinder
Using NOAA Nitrox Tables
• Notice: Chart 1 of the NN32 and NN36 tables
have a PO2 column, as well as the standard table
information you are use to seeing
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Using NOAA Nitrox Tables
• Calculate a dive using
EAN 32 to 100 ft for
23 minutes followed
by a 1 hour surface
interval (SIT) and a
second dive to 60 ft
for 30 minutes with
the same mix
• What is your max PO2
during dive 1?
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Using NOAA Nitrox Tables
• The maximum PO2 experienced during dive 1
was 1.3
Using NOAA Nitrox Tables
• NOAA NN32 and NN36 decompression
tables provide an expedient method for
determining decompression information
• However, by using the EAD principle, any
nitrox dive can be planned using the EAD
formula and US Navy Air Dive Tables
EAD Calculation
• Calculate a dive to 100 ft for 30 minutes
using a 30% nitrox mix
– Your first step is to determine the EAD by
using the formula:
 D fsw  33 fsw1  FO2  
EAD fsw  
  33 fsw
0.79


EAD Calculation
 100  33 fsw1  .30 
EAD fsw  
  33 fsw
0.79


 93.1 
EAD  
  33  118 33
 0.79
EAD  85 fsw
• You would use US Navy or other air dive tables
to compute a dive to 85 fsw for 30 minutes
EAD Calculation
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Repetitive Diving
• Repetitive diving with NOAA nitrox
diving tables for the same mix is no
different from the procedures used for
repetitive air diving
• The expanded version of the NN32 and
NN36 dive tables allow for better dive
planning of dives conducted shallower
than 40 fsw (12 msw)
Repetitive Diving
• Repetitive dives involving different mixes
can be calculated with relative ease
• Remember: the RNT must be obtained
from the RNT table for the gas mix to be
used on the repetitive dive, not the table
from the previous dive
Repetitive Diving With Different
Nitrox Mixes
• Example:
– A diver making a dive using NN32 to 120 fsw
for 25 minutes surfaces with a letter group of
H. A SIT of 1:48 results in a new group of E.
To make a second dive using NN36, the diver
needs to enter Chart 3 of the NN36 Table as
an “E diver” and use the information
provided there to calculate the dive plan.
Repetitive Diving With Different
Nitrox Mixes
36
Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ
Diving Table Procedure
Review
• Descent rate 75 fpm
(25 mpm)
• Flying after diving
• Ascent rate 30 fpm
(9 mpm)
• Altitude diving
• Safety-Stop
– 3-5 minutes at 10-20 fsw
(3-6 msw)
• Cold or strenuous dive
– use the next greater
bottom time
• Repetitive dives
– less than 12 hours
– use the table
– Tables good to 1,000 ft
(328 m) elevation only
• Omitted decompression
–
–
–
–
stay on surface
breathe 100% oxygen
monitor for DCS
plan to evacuate to
recompression chamber
Other Rules
• 10 minute minimum
between dives
• Bottom Time - time
you enter the water
until you leave the
bottom for a direct
assent (exception if
delayed)
• Required
Decompression
stops are taken at
specified depth and
measured at diver’s
mouth
• Make dives
progressively
shallower
whenever possible
Out of Gas Emergencies
Out of Gas Emergencies
• Dives Within No-Decompression Limits:
– A nitrox diver who has not exceeded the
dive’s no-stop time can breath air or any
nitrox mix for immediate ascent
– Likewise an out of gas air diver can breath an
O2 rich mix
Out of Gas Emergencies
• Shifting to Air During a Decompression
Dive:
– A nitrox diver required to switch to air during
a decompression stop can complete the deco
schedule without adjustment
– This is because the deco stops in NOAA
Nitrox Tables are based on US Navy Air
Decompression Tables and assumes the diver
is breathing air
Gas Preparation and
Handling
Oxygen Handling
• Oxygen
– Supports life
– Supports combustion
• Fire is a rapid chemical reaction
– Virtually everything will burn in oxygen
• Fire triangle:
– Oxygen
– Fuel
– Ignition
All 3 must be present
to have fire
Oxygen
Air to be Mixed with Oxygen
• Some methods of preparing nitrox involve air
being mixed with oxygen. It is extremely
important that the air be clean and free of oil
mist and particulate matter. Hydrocarbons and
petroleum-based products ignite very easily in
an oxygen-rich environment.
• The condensable hydrocarbon level of 0.1
mm/m3 is acceptable.
“NOAA & AAUS Standards for
Oxygen Service”
• Gas mixtures with oxygen content up to
40% can be handled as if the mix were air
• NOAA has used the “40% rule” on scuba
equipment and gas distribution systems
since the introduction of nitrox without
any problems
“The 40% Rule”
• Any equipment used for 100% oxygen or an
oxygen level above 40% at high pressure (above
200 psi) must be oxygen compatible, use oxygen
compatible lubricants (NOT silicone lubricant),
and be formally cleaned for oxygen service
• This includes cylinders and valves, first stage
regulators, and high pressure hoses
Oxygen Cleaning
• There are two levels of oxygen cleaning:
– Formal Oxygen Cleaning
– Informal Oxygen Cleaning
Formal Oxygen Cleaning
• Formal oxygen cleaning requires strict
procedures to be followed by trained
technicians, and all steps must be
documented in detail
Informal Oxygen Cleaning
• Informal oxygen cleaning is intended to clean
equipment as clean as formal oxygen cleaning,
but without the certification and documentation
• It involves the cleaning of any visible debris and
lubricants – then scrubbing and/or ultrasonic
cleaning with a strong detergent in hot water,
and rinsing thoroughly in clean hot water
• Oxygen-compatible lubricants are then used
where necessary
Once Oxygen Cleaned
• Once cleaned, the equipment should be
dedicated for use only with nitrox
mixtures and not used with air from an
oil-lubricated compressor without proper
hyper-filtration
Equipment Cleaning List
• Must be cleaned for
enriched air service*
– Cylinder valves
– Scuba cylinders
Not necessary
Buoyancy compensators
Low pressure inflator
Dry suit inflator
• Recommended to be
cleaned
– Regulator first stage
– Regulator second
stage
– High pressure hoses
– Submersible pressure
gauges
*If used with >40%, or if mix is prepared using partial pressure blending
technique
Identifying Nitrox Cylinders
• 4 inch green band on
yellow tank
• NITROX or Enriched Air
stenciled in 2 inch high
letters
• Non-yellow cylinders have
an additional 1 inch
yellow band above and
below the green
Other Identification Labels
• Cylinder Oxygen Service Label
– designates cleanliness for O2 service
– new label required annually or if
contaminated
• Visual Inspection
– annually or sooner
Other Identification Labels
• Cylinder Contents
– identifies contents
Routine Care and Maintenance
• Wash gear in fresh water
• Protect from dirt and grease
• Periodic service by trained technician
– annual for normal use
– more often if heavy use
• Maintain warranties
• Don’t contaminate with ordinary scuba air
Obtaining Nitrox Mixtures
Commercial Premix
• Purchasing premixed gas from a
commercial supplier is the simplest
method for obtaining gas
• Expensive – must both purchase gas and
rent gas containers from supplier
Preparing Enriched Air
Nitrox
• Partial Pressure Mixing
– requires ultra clean air & O2 clean valves
and cylinders
– A measured pressure of 100% O2 is transfilled into a scuba cylinder then topped
with air
– This requires training that is beyond the
scope of this module
Preparing Enriched Air Nitrox
• Continuous Flow Mixing
– Requires an “oil free” compressor
– Oxygen is metered into the air before being
drawn into a compressor
– The 40% rule applies
– Gas is analyzed before entering the
compressor and monitored during the filling
operation
Preparing Enriched Air Nitrox
• Pressure Swing Absorption
– Uses a “molecular sieve” to adsorb nitrogen
– This system does not require high pressure
oxygen, but is somewhat complicated and
moderately expensive to acquire and maintain
Preparing Enriched Air Nitrox
• Membrane Separation
– Works by forcing clean low-pressure air
through a membrane that allows oxygen to
pass more readily than nitrogen
– The output gas, which is richer in oxygen
than air, is then passed through a high
pressure compressor to fill a cylinder or bank
– The O2 level of the mix can be controlled by
varying the input flow rate
Performing Gas Analysis
Oxygen Analyzers
• Oxygen analyzers can use Digital or
Analog display
• Ideally they should have a resolution
accuracy of 0.1% (one-tenth of one percent)
Oxygen Analyzers
• The heart of an oxygen analyzer is its
detection method
• There are two primary types
Paramagnetic and Electrochemical
• Paramagnetic analyzers are primarily
used in research labs
– They are accurate, stable, relatively
expensive, somewhat delicate, and
intolerant of vibration
Oxygen Analyzers
• Electrochemical analyzers, the most common
type, are relatively inexpensive, can be portable,
are rugged, and show little interference from
other gases
• They may need frequent calibration, especially as
the O2 sensor cell begins to age
The O2 sensor cell has a life span
from 6 to 18 months, dependent
on manufacturer and use
Analyzing Gas
• Each diver must analyze their own nitrox
cylinders and insure the gas they will
breath is acceptable for the planned dive
Analyzing Gas
• The process of analyzing a cylinder of gas
involves calibrating the analyzer with a
known gas such as air
• Both the calibrating gas and the unknown
gas should be passed through the analyzer
at the same flow rate
Analyzing Gas
• Ideally the flow rate should be around one
liter per minute – but should be between
one-half and two liters per minute
• When using air as the known gas,
calibrate the analyzer to a reading of
20.9%
Analyzing Gas
• After calibration, analyze the unknown mix at the
same flow rate (about 1 liter/minute)
• Analyze the mix until the readout on the analyzer
becomes stable
Analyzing Gas
• Acceptable Analysis Range:
– It is generally accepted that a mix within ±1%
of the desired mix is acceptable for most
nitrox tables
Analyzing Gas
• Once analyzed, the contents of cylinder
must be recorded on a cylinder contents
label and placed on the analyzed cylinder
• This label contains the percentage of O2 in
the mix, the date, the MOD,
and the initials of the diver
analyzing the mix
Fill Station Log
• In addition to a contents label, the analysis of a
cylinder is to be recorded on a Fill Station Log
by the diver who analyzed the gas
• At a minimum, this log includes: The cylinder
ID number, the analysis by the person mixing
the gas (O2% & initials), the analysis by the diver
diving the gas (O2%), the psi in the cylinder, the
MOD, the date of analysis, and the signature of
diver performing the analysis
Study Questions
• Use the following study questions to
review some of the information presented
in this self study module
• When you are finished you can print out
your study questions results
Self Study Questions
A diver wishes to plan two nitrox dives using
EAN36 and NN36 tables. The first dive will
be to a depth of 100ft for 20 minutes.
Following a one hour surface interval, how
long may the diver stay at 60ft on the second
dive?
• 29 minutes
• 71 minutes
• 100 minutes
• 62 minutes
Self Study Questions
A diver wishes to plan two nitrox dives using
EAN36 and NN36 tables. The first dive will
be to a depth of 100ft for 20 minutes.
Following a one hour surface interval, how
long may the diver stay at 60ft on the second
dive?
• 29 minutes
• 71 minutes
• 100 minutes
• 62 minutes
Self Study Questions
A dive team plans a dive to a maximum
depth of 70ft using EAN32 with NN32
tables and a PO2 of 1.6. What is the
maximum depth the divers should
descend on the dive?
• 132'
• 65'
• 130'
• 70'
Self Study Questions
A dive team plans a dive to a maximum
depth of 70ft using EAN32 with NN32
tables and a PO2 of 1.6. What is the
maximum depth the divers should
descend on the dive?
• 132'
• 65'
• 130'
• 70'
Self Study Questions
What is the absolute pressure (ata) at 75
fsw?
• 3.27 ata
• 2.37 ata
• 3.72 ata
• 7.32 ata
Self Study Questions
What is the absolute pressure (ata) at 75
fsw?
• 3.27 ata
• 2.37 ata
• 3.72 ata
• 7.32 ata
Self Study Questions
A dive team wants to make a dive using
NN32 and a PO2 of 1.6, what is the MOD
for the mix?
• 130'
• 132'
• 110'
• 190'
Self Study Questions
A dive team wants to make a dive using
NN32 and a PO2 of 1.6, what is the MOD
for the mix?
• 130'
• 132'
• 110'
• 190'
Self Study Questions
The maximum oxygen partial pressure
exposure for scientific diving is ___, and
you may want to further limit your
exposure.
• 1.3
• 1.4
• 1.5
• 1.6
• 1.8
Self Study Questions
The maximum oxygen partial pressure
exposure for scientific diving is ___, and you
may want to further limit your exposure.
• 1.3
• 1.4
• 1.5
• 1.6
• 1.8
Self Study Questions
The maximum oxygen partial pressure
exposure for recreational diving is ___.
• 1.3
• 1.4
• 1.5
• 1.6
• 1.8
Self Study Questions
The maximum oxygen partial pressure
exposure for recreational diving is ___.
• 1.3
• 1.4
• 1.5
• 1.6
• 1.8
Self Study Questions
According to the NOAA Oxygen Exposure
Limits Table 15.2 (page 15-5 of the NOAA
Diving Manual), the maximum single dive
exposure time for a PO2 exposure of 1.2 is
___ minutes.
• 45
• 150
• 210
• 240
Self Study Questions
According to the NOAA Oxygen Exposure
Limits Table 15.2 (page 15-5 of the NOAA
Diving Manual), the maximum single dive
exposure time for a PO2 exposure of 1.2 is
___ minutes.
• 45
• 150
• 210
• 240
Self Study Questions
Calculate the maximum operating depth
(MOD) for a 33% nitrox mix using a PO2
exposure at depth of 1.6.
• 127 fsw
• 31.4 fsw
• 60 fsw
• 99 fsw
Self Study Questions
Calculate the maximum operating depth
(MOD) for a 33% nitrox mix using a PO2
exposure at depth of 1.6.
• 127 fsw
• 31.4 fsw
• 60 fsw
• 99 fsw
Self Study Questions
Calculate the MOD of a 50% nitrox mix
using a PO2 exposure at depth of 1.5.
• 50 fsw
• 66 fsw
• 75 fsw
• 82 fsw
Self Study Questions
Calculate the MOD of a 50% nitrox mix
using a PO2 exposure at depth of 1.5.
•
•
•
•
50 fsw
66 fsw
75 fsw
82 fsw
Self Study Questions
Calculate the maximum operating depth
(MOD) for a 21% nitrox mix using a PO2
exposure at depth of 1.6.
• 130 fsw
• 203 fsw
• 187 fsw
• 218 fsw
Self Study Questions
Calculate the maximum operating depth
(MOD) for a 21% nitrox mix using a PO2
exposure at depth of 1.6.
•
•
•
•
130 fsw
203 fsw
187 fsw
218 fsw
Self Study Questions
Calculate the partial pressure of O2 (PO2)
for air being breathed at 90 fsw.
• .78
• .21
• .57
• 1.6
Self Study Questions
Calculate the partial pressure of O2 (PO2)
for air being breathed at 90 fsw.
•
•
•
•
.78
.21
.57
1.6
Self Study Questions
Calculate the partial pressure of Nitrogen
(PN2) for air being breathed at 90 fsw.
• 2.9
• 1.6
• .78
• 2.1
Self Study Questions
Calculate the partial pressure of Nitrogen
(PN2) for air being breathed at 90 fsw.
•
•
•
•
2.9
1.6
.78
2.1
Self Study Questions
Calculate the partial pressure of O2 (PO2)
for a 36% nitrox mix being breathed at 130
fsw. As a scientific diver, would you want
to make this dive?
• 1.6 / Yes
• 1.78 / Yes
• 1.6 / No
• 1.78 / No
Self Study Questions
Calculate the partial pressure of O2 (PO2)
for a 36% nitrox mix being breathed at 130
fsw. As a scientific diver, would you want
to make this dive?
• 1.6 / Yes
• 1.78 / Yes
• 1.6 / No
• 1.78 / No
Self Study Questions
You need to maximize your no-stop dive
time for a dive to 60 fsw. Calculate the
best nitrox mix for this dive using a
maximum PO2 exposure at depth of 1.6.
• 40%
• 57%
• 32%
• 36%
Self Study Questions
You need to maximize your no-stop dive
time for a dive to 60 fsw. Calculate the
best nitrox mix for this dive using a
maximum PO2 exposure at depth of 1.6.
• 40%
• 57%
• 32%
• 36%
Self Study Questions
You need to maximize your no-stop dive
time for a dive to 140 fsw. Calculate the
best nitrox mix for this dive using a
maximum PO2 exposure at depth of 1.5.
• 21%
• 29%
• 32%
• 35%
Self Study Questions
You need to maximize your no-stop dive
time for a dive to 140 fsw. Calculate the
best nitrox mix for this dive using a
maximum PO2 exposure at depth of 1.5.
• 21%
• 29%
• 32%
• 35%
Self Study Questions
The _______ is the depth based on the partial
pressure of nitrogen in the gas mixture to be
breathed, rather than the actual depth of the
dive. This was the concept used to develop
NOAA nitrox dive tables.
•
•
•
•
residual nitrogen time (RNT)
equivalent nitrox depth (END)
maximum operating depth (MOD)
equivalent air depth (EAD)
Self Study Questions
The _______ is the depth based on the partial
pressure of nitrogen in the gas mixture to be
breathed, rather than the actual depth of the
dive. This was the concept used to develop
NOAA nitrox dive tables.
•
•
•
•
residual nitrogen time (RNT)
equivalent nitrox depth (END)
maximum operating depth (MOD)
equivalent air depth (EAD)
Self Study Questions
You are using an air based dive computer to compute your
decompression profile. You are breathing a 36% nitrox
mix and your maximum PO2 exposure limit at depth is
1.6. The bottom is 130 fsw. Your dive plan calls for a dive
to 110 fsw for 30 minutes. Which of the following is a
major concern?
• Your risk of decompression sickness is lower because you are using
a nitrox based dive computer and breathing air.
• Your air based dive computer thinks you are breathing air, air based
computers do not have any MOD alarms in place, and the
maximum possible depth of the dive exceeds the MOD for the mix
you will be breathing.
• Your planned dive time will exceed the single dive oxygen exposure
limit for a PO2 of 1.6.
• Your risk of decompression sickness is higher because you are using
an air based dive computer and breathing nitrox.
Self Study Questions
You are using an air based dive computer to compute your
decompression profile. You are breathing a 36% nitrox
mix and your maximum PO2 exposure limit at depth is
1.6. The bottom is 130 fsw. Your dive plan calls for a dive
to 110 fsw for 30 minutes. Which of the following is a
major concern?
• Your risk of decompression sickness is lower because you are using
a nitrox based dive computer and breathing air.
• Your air based dive computer thinks you are breathing air, air based
computers do not have any MOD alarms in place, and the
maximum possible depth of the dive exceeds the MOD for the mix
you will be breathing.
• Your planned dive time will exceed the single dive oxygen exposure
limit for a PO2 of 1.6.
• Your risk of decompression sickness is higher because you are using
an air based dive computer and breathing nitrox.
Self Study Questions
Use NOAA NN32 dive tables to calculate a
dive to 75 fsw for 35 minutes followed by
a 1:30 SIT and a second dive to 75 fsw for
20 minutes. What is the ESDT of the
second dive and the ending letter group?
• 20 minutes, E
• 24 minutes, F
• 50 minutes, H
• 46 minutes, J
Self Study Questions
Use NOAA NN32 dive tables to calculate a
dive to 75 fsw for 35 minutes followed by
a 1:30 SIT and a second dive to 75 fsw for
20 minutes. What is the ESDT of the
second dive and the ending letter group?
• 20 minutes, E
• 24 minutes, F
• 50 minutes, H
• 46 minutes, J
Self Study Questions
What is the EAD (Equivalent Air Depth) of a
dive with an actual depth of 100 fsw
where the diver is breathing 36% nitrox?
• 65 fsw
• 70 fsw
• 75 fsw
• 80 fsw
Self Study Questions
What is the EAD (Equivalent Air Depth) of a
dive with an actual depth of 100 fsw
where the diver is breathing 36% nitrox?
•
•
•
•
65 fsw
70 fsw
75 fsw
80 fsw
Self Study Questions
The _______ method of blending nitrox
requires ultra clean air, O2 clean valves
and cylinders. 100% O2 is trans-filled into
a scuba cylinder then topped with air.
• Membrane Separation
• Pressure Swing Adsorption
• Continue Flow Mixing
• Partial-Pressure Mixing
Self Study Questions
The _______ method of blending nitrox
requires ultra clean air, O2 clean valves
and cylinders. 100% O2 is trans-filled into
a scuba cylinder then topped with air.
• Membrane Separation
• Pressure Swing Adsorption
• Continue Flow Mixing
• Partial-Pressure Mixing
Self Study Questions
In the ______ method of blending nitrox,
oxygen is metered into the air being
drawn into a compressor. This requires an
"oil free" compressor and the 40% rule
applies.
• Membrane Separation
• Pressure Swing Adsorption
• Continuous Flow Mixing
• Partial-Pressure Mixing
Self Study Questions
In the ______ method of blending nitrox,
oxygen is metered into the air being
drawn into a compressor. This requires an
"oil free" compressor and the 40% rule
applies.
• Membrane Separation
• Pressure Swing Adsorption
• Continuous Flow Mixing
• Partial-Pressure Mixing
Self Study Questions
The _______ method of blending nitrox
works by forcing clean low-pressure air
through a membrane that allows oxygen
to pass more readily than nitrogen.
• Membrane Separation
• Pressure Swing Adsorption
• Continuous Flow Mixing
• Partial-Pressure Mixing
Self Study Questions
The _______ method of blending nitrox
works by forcing clean low-pressure air
through a membrane that allows oxygen
to pass more readily than nitrogen.
• Membrane Separation
• Pressure Swing Adsorption
• Continuous Flow Mixing
• Partial-Pressure Mixing
Self Study Questions
Ideally, oxygen analyzers should have a
resolution accuracy of ________.
• 0.01% (one-hundreth of one percent)
• 0.1% (one-tenth of one percent)
• 1% (one percent)
• 10% (ten percent)
Self Study Questions
Ideally, oxygen analyzers should have a
resolution accuracy of ________.
•
•
•
•
0.01% (one-hundreth of one percent)
0.1% (one-tenth of one percent)
1% (one percent)
10% (ten percent)
Self Study Questions
The heart of an oxygen analyzer is its detection
method. There are two primary types
Paramagnetic and Electrochemical. _________
analyzers are relatively inexpensive, can be
portable, are rugged, and show little interference
from other gases. They may need frequent
calibration, especially as the O2 sensor cell
begins to age.
• Paramagnetic
• Electrochemical
Self Study Questions
The heart of an oxygen analyzer is its detection
method. There are two primary types
Paramagnetic and Electrochemical. _________
analyzers are relatively inexpensive, can be
portable, are rugged, and show little interference
from other gases. They may need frequent
calibration, especially as the O2 sensor cell
begins to age.
• Paramagnetic
• Electrochemical
Self Study Questions
Once analyzed, the contents of cylinder
must be recorded on a cylinder contents
label, and this label is to be placed on the
analyzed cylinder. This label contains
_________. (select all that apply)
• the percentage of O2 in the mix
• the date
• the MOD
• the initials of the diver analyzing the mix
Self Study Questions
Once analyzed, the contents of cylinder
must be recorded on a cylinder contents
label, and this label is to be placed on the
analyzed cylinder. This label contains
_________. (select all that apply)
• the percentage of O2 in the mix
• the date
• the MOD
• the initials of the diver analyzing the mix
Self Study Questions
Nitrox is safer than air.
a.True
b.False
Self Study Questions
Nitrox is safer than air.
a.True
b.False
Self Study Questions
Nitrox has very stringent depth limits
because of the higher concentration of O2
in the mixture. (Nitrox has very stringent
depth limits because of the higher
concentration of O2 in the mixture.)
a.True
b.False
Self Study Questions
Nitrox has very stringent depth limits
because of the higher concentration of O2
in the mixture. (Nitrox has very stringent
depth limits because of the higher
concentration of O2 in the mixture.)
a.True
b.False
Self Study Questions
Nitrox provides the greatest advantages for
no-stop diving in the 50-110 fsw depth
range.
a.True
b.False
Self Study Questions
Nitrox provides the greatest advantages for
no-stop diving in the 50-110 fsw depth
range.
a.True
b.False
Self Study Questions
Nitrox reduces narcosis.
• Yes
• No
• Not Really
Self Study Questions
Nitrox reduces narcosis.
• Yes
• No
• Not Really
Self Study Questions
Nitrox makes treatment for DCS impossible.
a.True
b.False
Self Study Questions
Nitrox makes treatment for DCS impossible.
a.True
b.False