© The Professional Scuba Association Nitrox Program PSAI Professional Scuba Association International

© The Professional Scuba Association

Nitrox Program

PSAIProfessional Scuba Association International

PSAIProfessional Scuba Association International

™3 © 2006 The Professional Scuba Association International

Introduction

• Welcome to the PSAI Nitrox Program

• Introduce Students

• Verify paperwork, liability release


Course Objectives

• Understand the definition of Nitrox• Limits of use for Nitrox• Benefits of Nitrox• Hazards of Nitrox• Analyzing Nitrox• Diving Nitrox


History of the Professional Scuba Association International

• Founded by Hal Watts in 1962, originally as the Florida Scuba Association.

• From the beginning, involved with Extended Range diving as the primary focus.

• Involved in recreational deep diving and mixed gas diving instruction.


History

• In the late 1980’s “technical diving” exploded all over the world.

• PSA was involved in extended range diving as well as rebreather applications.

• Small country offices until 2004.• 2004 PSAI expanding to service the

international market through PSAI Country Licensees.


Nitrox

• Air has two components– Nitrogen – Primary component– Oxygen – Life support component

• Nitrogen is the “diluent” – Cause of decompression sickness– Cause of nitrogen narcosis

• Oxygen – necessary for life, but not too much


Nitrox

• Air is: – 78% Nitrogen– 21% Oxygen– 0.9% Argon– 0.1% of lots of other gases!

• Nitrox is simply “air with more oxygen”.


Nitrox

• The common term used is “enriched air nitrox”– When first introduced, most was made by

adding oxygen to air.– Today there are a number of different

techniques, but it is still termed “enriched”.– Abbreviated as “EAN”.


Nitrox Identification

• When speaking or writing about nitrox, use “EAN” followed by the percentage of OXYGEN in the mix.

– Nitrox with 32 percent oxygen = EAN32– Nitrox with 40 percent oxygen = EAN40

No – air is NOT EAN21!


Nitrox Identification

• Some texts (incorrectly) use EANx32. • EANx is used only for an unknown oxygen

value, not as an identifier of nitrox “x”.• The argon and other trace gases are added

to the nitrogen component but not shown in the identifier.


Nitrox

• In “the old days” it was common to use just EAN32 and EAN36.

• Originated from NOAA – US National Oceanic and Atmospheric Administration.

• 32% nitrox was called NOAA Nitrox I.• 36% nitrox was called NOAA Nitrox II.• These terms are no longer used but may be

seen in old texts and charts.


Brief History of Nitrox

• Known in concept for many years.• Used by military divers in WWII for rebreathers.• Concept discussed but dismissed in 1950’s

popular dive book Science of Skin and Scuba.• Became widespread in 1980’s as Dick Rutkowski

(retired NOAA Deputy Diving Director) helped support recreational use.

• PSAI has had courses for Nitrox use from the beginning.


Advantages of Nitrox

• Primary advantage = More Bottom Time!– Reduces the nitrogen, hence less tissue loading

• Some divers report less “post dive fatigue”• Less narcosis • Again – Bottom Time!


Use of Nitrox

• Some divers who stay well within recreational depth limits (not exceeding 40 meters or 130 feet) simply use EAN32 and dive it as if it were Air.

• They use air tables and air computers, the decreased nitrogen improves the reliability of the tables.


Nitrox

• Why not just get rid of all the nitrogen?• High levels of oxygen can cause serious

harm to the body.• Oxygen is only used by highly trained

divers for decompression.• Nitrox divers MUST be aware of depth.


What Nitrox is NOT

• Nitrox is not a “deep diving gas”.• Nitrox is not a complicated technical gas.• Nitrox is not suitable for divers who are

careless in dive planning and monitoring.• Nitrox is not “safer” – it requires

understanding and use within specified parameters.


Effects of Pressure in Diving

• Water is significantly more dense than air!• Metric Pressure is measured in “bar”. • Imperial Pressure is measured in

“atmosphere” (atm).• 1 bar is approximately equal to 1 atm.• Pressures are in absolute terms, meaning at

the surface at sea level, the pressure is 1 bar (1 atm = 1.01325 bar).


Pressure

• Common terminology for Imperial use is that atmospheres referred back to sea level pressure are “atmospheres absolute” (ata).

• For each 10 m (33 fsw) pressure increases an additional bar, i.e. at 10 m (33 fsw) the pressure is 2 bar, 20 m (66 fsw) = 3 bar, etc.


Pressure - metric

• Surface 1 bar• 10 m 2 bar• 20 m 3 bar• 30 m 4 bar• 40 m 5 bar


Pressure - imperial

• Surface 1 ata• 33 feet 2 ata• 66 feet 3 ata• 99 feet 4 ata• 132 feet 5 ata


Depth and Pressure Conversion

Metric• To convert depth to pressure

– Divide depth by 10 and add 1

• P = (D/10) + 1

• Example: What is the pressure at 27m?P = (27m/10) + 1

P = 2.7 + 1

P = 3.7 bar


Depth and Pressure Conversion

Imperial• To convert depth to pressure

– Divide depth by 33 and add 1

• P = (D/33) + 1

• Example: What is the pressure at 89 fsw?P = (89/33) + 1

P = 2.7 + 1

P = 3.7 ata


Pressure and Depth Conversion

Metric• To convert a pressure to depth

– Subtract 1 from the pressure and multiply by 10• D = (P – 1) × 10

• Example: What is the depth at a pressure of 2.6 bar?

D = (2.6 – 1) × 10

D = 1.6 × 10

D = 16 m


Pressure and Depth Conversion

Imperial• To convert a pressure to depth

– Subtract 1 from the pressure and multiply by 33• D = (P – 1) × 33

• Example: What is the depth at a pressure of 2.6 ata?D = (2.6 – 1) × 33

D = 1.6 × 33

D = 53 fsw


Pressure and Volume

• As a diver descends, pressure increases.• Increased pressure on an airspace causes it to

“shrink” in volume.• Metric: Follows the “bar” numbers, i.e. at 10 m

(2 bar) a surface volume would be decreased by ½.

• Imperial: Follows the “ata” numbers, i.e. at 33' (2 ata) a surface volume would be decreased by ½.

• Squeeze, shrinking wet suits, increased gas density all caused by pressure.


Pressure and Depth (Descending)

• 0 m 1 bar 1 volume• 10 m 2 bar ½ volume• 20 m 3 bar ⅓ volume• 30 m 4 bar ¼ volume• 40 m 5 bar 1/5 volume

Metric


Pressure and Depth (Descending)

• 0' 1 ata 1 volume• 33' 2 ata ½ volume• 66' 3 ata ⅓ volume• 99' 4 ata ¼ volume• 132' 5 ata 1/5 volume

Imperial


Pressure and Volume

• Pressure effects studied by Boyle (1600’s)• Commonly termed “Boyle’s Law”• Some European countries term it “Marriot’s

Law”• Mathematically represented by

P X V = kMore commonly:

P1 X V1 = P2 X V2


Ascending Pressure

• If increasing pressure shrinks a volume, obviously a decreasing pressure causes a volume to expand.

• A full balloon at 40 m (5 bar) 132' (5 ata) would attempt to become 5 times larger as it went to the surface.


Pressure and Depth (Ascending)

• 0 m 1 bar 5 volumes• 10 m 2 bar 2.5 volumes• 20 m 3 bar 1.6 volumes• 30 m 4 bar 1.25 volumes• 40 m 5 bar 1 volume

Metric


Pressure and Depth (Ascending)

• 0' 1 ata 5 volumes• 33' 2 ata 2.5 volumes• 66' 3 ata 1.6 volumes• 99' 4 ata 1.25 volumes• 132' 5 ata 1 volume

Imperial


Pressure and Depth• All diving is affected by the “bar” (“ata”)

numbers.

• At 30 m (4 bar) 99' (4 ata) divers use 4 times the amount of gas than at the surface.

• Reaction time is slowed by the pressure, i.e. a BCD would require 3 times the gas (3 times the pushing of the inflator button) at 20 m (66') than at the surface.


Pressure and Gases

• Air is made up of 78% nitrogen, 21% oxygen and 1% other gases.

• For purposes of the course, air is 79% nitrogen and 21% oxygen.

• At sea level the pressure equals 1 bar• 79% of 1 bar = 0.79 bar nitrogen pressure• 21% of 1 bar = 0.21 bar oxygen pressure


Pressure and Gases• 0.79 bar + 0.21 bar = 1.0 bar

• The sum of all the “partial pressures” equals the total pressure.

• This is known as Dalton’s Law

• Mathematically: Ptotal = Pgas1 + Pgas2 + Pgas3 …. + Pgas(n)


Pressure of Air Gases at Depth

• Depth Pressure Nitrogen Oxygen

• 0 m 1 bar 0.79 bar 0.21 bar• 10 m 2 bar 1.58 bar 0.42 bar• 20 m 3 bar 2.37 bar 0.63 bar• 30 m 4 bar 3.16 bar 0.84 bar• 40 m 5 bar 3.95 bar 1.05 bar

Metric



• Depth Pressure Nitrogen Oxygen

• 0' 1 ata 0.79 ata 0.21 ata• 33' 2 ata 1.58 ata 0.42 ata• 66' 3 ata 2.37 ata 0.63 ata• 99' 4 ata 3.16 ata 0.84 ata• 132' 5 ata 3.95 ata 1.05 ata

Imperial



• Notice that at 40 m (132'), the pressure of oxygen (PO2) was 1.05 bar.

• This is physiologically identical to breathing “pure oxygen” at the surface.

• Notice that adding both nitrogen and oxygen gave the total pressure at depth.


Pressure of Nitrox Gases at Depth

• Depth Pressure EAN32 O2 EAN32 N2 EAN40 O2 EAN40 N2

• Surface 1 bar 0.32 0.68 0.40 0.60• 10 m 2 bar 0.64 1.36 0.80 1.20• 20 m 3 bar 0.96 2.04 1.20 1.80• 30 m 4 bar 1.28 2.72 1.60 2.40• 40 m 5 bar 1.60 3.40

• Notice that the maximum allowable oxygen pressure is 1.6 bar

Metric


Pressure of Nitrox Gases at Depth

• Depth Pressure EAN32 O2 EAN32 N2 EAN40 O2 EAN40 N2

• Surface 1 ata 0.32 0.68 0.40 0.60• 33' 2 ata 0.64 1.36 0.80 1.20• 66' 3 ata 0.96 2.04 1.20 1.80• 99' 4 ata 1.28 2.72 1.60 2.40• 132' 5 ata 1.60 3.40

• Notice that the maximum allowable oxygen pressure is 1.6 bar

Imperial


Comparing Nitrogen

• Notice the nitrogen gas pressure of EAN40 at 30 m (99') – 2.4 bar (ata)

• Recall the nitrogen gas pressure of Air at 20 m (66') – 2.37 bar (ata)

• Essentially – breathing EAN40 at 30 meters (99') is equivalent to breathing air at 20 meters (66') (for decompression purposes)

This means more bottom time!


Equivalent Air Depth

• What is the nitrogen component of the EAN mix?– Subtract the oxygen fraction from 1

• EAN40 1 – 0.40 = 0.60

• Compare (ratio) nitrogen to air nitrogen– Divide nitrox nitrogen by air nitrogen

• EAN40 0.60/0.79 = 0.76• Breathing EAN40 instead of air means the diver is

only taking in 76% of the nitrogen than with air


Equivalent Air Depth (cont’d)

• How deep is the dive?– To keep the math people happy, depth must be

“absolute depth”, i.e. “add 10 meters” (“add 33 feet”). We are using depth units as pressure units.

Example: Dive EAN40 at 21 meters (69 feet)

Absolute depth = 21 meters + 10 meters = 31 meters

Absolute depth = 69 feet + 33 feet = 102 feet



• Nitrox ratio at depth

– Multiply the nitrogen ratio and absolute depth

– 0.76 × 31 meters = 24 meters– 0.79 × 102 feet = 81 feet

– Wait! Where is the benefit?? Remember, this is absolute depth, we must subtract 10 meters (33 feet)



• Convert absolute depth to “gauge depth”

24 meters – 10 meters = 14 meters

69 feet – 33 feet = 36 feet

Breathing EAN40 at 21 meters (69') gives the same nitrogen loading as breathing air at 14 meters (36')!!


Oxygen Physiology

• Everything has its “catch”

• Too much nitrogen gives decompression problems

• Too much oxygen gives other body problems


Oxygen Physiology

• Oxygen is dangerous to handle and it must be done with care.

• From a physiology perspective, consider oxygen a “drug” – too much is a bad thing.

• Affects the body in two primary ways.


Oxtox or Oxygen Toxicity

• Two types of oxygen toxicity– Pulmonary (also known as whole body):

• Affects the lungs and breathing• Most like a “pneumonia” condition• Requires long exposure of low dose (0.5 bar to 1.0

bar oxygen)• Almost impossible for a recreational diver to

encounter


Oxtox or Oxygen Toxicity

• Two types of oxygen toxicity– Central Nervous System Oxygen Toxicity:

• Results from high pressure oxygen exposure (greater than 1.0 bar)

• Can occur in relatively short periods attainable by recreational nitrox divers (i.e. as short as 45 minutes at 1.6 bar oxygen pressure)

• Controlled by DIVE PLANNING


CNS Oxygen Toxicity

• Excessively high oxygen pressures may result in serious problems:– Affects vision, dizziness, muscle twitches,

nausea, euphoria, and irritability are some symptoms – “VENTID”

– The actual problem is that if left unchecked, it may result in a seizure (convulsions) that can cause drowning!


What do you need to know about CNS Oxygen toxicity?

• It is real.• It may, or may not give a warning

(symptom).• If it does give a warning, the diver may, or

may not recognize it.• It is controlled by planning.


More considerations for CNS Oxygen Toxicity

• The wildest and craziest “cowboy” diver does not mess around with CNS O2 toxicity.

• No one can “tough out” an oxygen convulsion.

“Plan your dive ~ Dive your plan!”


Planning Oxygen Exposure

• Pulmonary O2 toxicity is largely ignored as the CNS limits are far shorter.

• CNS planning centers around a chart developed by NOAA.

• Must know the expected PO2 of the planned dive.


NOAA Oxygen Limits

Oxygen Pressure Single 24 Hour

1.6 bar 45 min 150 min

1.5 bar 120 min 180 min

1.4 bar 150 min 180 min

1.3 bar 180 min 210 min

1.2 bar 210 min 240 min

1.1 bar 240 min 270 min

1.0 bar 300 min 300 min


CNS Oxygen Toxicity

• The effects of high pressure oxygen depend on two factors:– Oxygen pressure (PO2)– Time of exposure

• Caution: Diving at a PO2 of 1.4 bar is NOT necessarily safer than 1.6 bar – it also depends on TIME.


CNS Oxygen Toxicity

• A PO2 of 1.6 bar is considered the maximum oxygen exposure.

• If the dive conditions are cold, rough, high exertion, reduce accordingly.

• Most divers plan for 1.4 bar as a “normal operating depth” and keep 1.6 as the “absolute maximum operating depth”.


CNS Oxygen Toxicity

• You cannot tough out a convulsion.• Oxygen toxicity takes time to occur.• If anything seems wrong, it IS wrong!• There are no examples of people within

limits (and healthy) having an oxygen problem.

• Problems occur when the dive is not planned or the plan is not followed.


Planning a Nitrox Dive

• MUST know the planned depth!– Planned depth equals the pressure– Each nitrox mix has a “maximum operating

depth” typically at a PO2 of 1.6 bar, however many use a PO2 of 1.4 bar

• Example:– EAN32 has a MOD of 40 meters (132')– EAN40 has a MOD of 30 meters (99')


MOD, Best Mix and PO2 Chart

• In the manual, there is a chart that lists the maximum operating depth (MOD) for each mix from EAN22 to EAN40.

• The chart can also be used to determine the “best mix” for a particular depth and PO2.

• The chart lists PO2 for each depth and mix combination.


MOD Chart Practice

• Use the chart to determine the MOD for EAN36 at a PO2 of 1.6 bar.

• What is the depth where EAN36 has a PO2 of 1.4 bar?

• If a diver did not want to exceed a PO2 of 1.4 bar at 32 meters (105 feet), what is the best mix?


Dalton’s Law

• Dalton’s Law – Ptotal = Pgas1 + Pgas2 + Pgas3 … Pgas(n)

– Used to determine gas pressure at a depth

– PO2 = FO2 × Ptotal

– FO2 = PO2/Ptotal

– Ptotal = PO2/FO2


Dalton’s Law (cont’d)

• PO2 = Oxygen Exposure

• FO2 = Best Mix

• Ptotal = Pressure at Depth (convert to depth)

• Use the chart to avoid math mistakes!


Nitrox Dive Equipment

• For standard nitrox diving up to EAN40, use normal recreational equipment.

• For diving with O2 contents greater than 40%, equipment MUST be specially O2 serviced!

• NOTE:– Cylinders must be oxygen cleaned and serviced– Regulators must be maintained in accordance with

manufacturer’s recommendations– Gas cleanliness requirements must be maintained


Nitrox Production

• Nitrox is produced by several techniques:– Partial Pressure Blending

• Probably still the most common world wide– Differentially Permeable Membrane

• Uses special equipment to remove nitrogen from the air• Also known as “de-nitrogenated air”

– Continuous Blend• Special compressor with oxygen fed into air intake


Special Precautions

• Nitrox must be produced by an appropriately certified “gas blender”.

• Cylinders require special cleaning and care.• Aluminum cylinders may require extra care

when in the presence of pure oxygen.• Only certified clean air should be put in

oxygen cleaned cylinders.


Oxygen Analysis

• Prior to leaving the gas blender facility the gas must be analyzed.

• Use special test equipment:– Normal accuracy ± 1%– Requires test hose/fixture to ensure only the

cylinder gas is analyzed, not contaminated by outside air.


Oxygen Analysis

• Oxygen analyzer must be calibrated before each use.– Use air and calibrate to 20.9 or 21.0 for nitrox

mixes up to EAN40.– Recalibrate if the analyzer is bumped, dropped,

dial moved, or suspected error.• Recalibration should allow sufficient time to settle

the sensor.


Oxygen Analysis

• The oxygen analyzer measures PO2, NOT FO2.

• At 1 bar (ata), PO2 = FO2

• Avoid pressurizing oxygen sensor when analyzing to prevent serious errors.


Oxygen Analysis

• Sensor is sensitive and must be handled with care.– Avoid excessive heat or cold

• Sensor has very small voltage output, avoid using in high electric areas or where radio transmission is taking place.

• Analysis at high altitude requires calibration at that altitude, otherwise serious errors will occur.


Oxygen Analysis

• PSAI requires that students analyze at least two cylinders under guidance of the instructor.

• Cylinders require marking after analysis:– MOD in LARGE bold numbers

• Determined by the student, not the blender– Mix and date can be added in smaller numbers


Oxygen Analysis

• After analysis, the data is entered into the Fill Station Log.

• Each diver is responsible for the gas and must sign.

• Include the MOD and FO2 in the Log.


Practical Session

• Plan a dive based on instructor supplied gas.

• Analyze minimum of two cylinders.

• Ensure PO2 limits are understood.

• Check the increase in bottom time!


Final

• Review– What is nitrox?– What is Equivalent Air Depth?– What is Maximum Operating Depth?– What is PO2?– What are the PO2 limits?– How to plan a nitrox dive using Chart.– How to analyze and label gas cylinder.


PSAI Technical Diving Programs• Cave • Nitrox • Trimix • Cavern • Dry Suit • Rebreather • Nitrox Blender• Full Face Mask• Twin Set Diving• Advanced Nitrox • Advanced Wreck• Narcosis Management • Technical Dive Rescue• Advanced Gas Blender• Extended Range Nitrox • Oxygen Service Technician• Visual Inspection Technician• Overhead Sidemount Diving• Diver Propulsion Vehicle (DPV)


Welcome!

As you venture forth as a certified PSAI Nitrox Diver possessing the superior training of PSAI!

Documents

© The Professional Scuba Association Nitrox Program PSAI Professional Scuba Association International