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Student Performance: By the end of the lesson you will be able to:. Describe what nitrox is. List other names for nitrox. State the early history of diving with gases other than air. State when NAUI sanctioned nitrox diving. Describe what nitrox is not. Unit 1: Introduction. What is Nitrox

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Student performance by the end of the lesson you will be able to l.jpg

Student Performance:By the end of the lesson you will be able to:

  • Describe what nitrox is.

  • List other names for nitrox.

  • State the early history of diving with gases other than air.

  • State when NAUI sanctioned nitrox diving.

  • Describe what nitrox is not.


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Unit 1: Introduction

  • What is Nitrox

  • A Bit of History

  • Why Dive with Enriched Air Nitrox

  • Common Misconceptions About Nitrox

  • Terminology


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What is Nitrox?

  • Nitrox is air in which fraction of nitrogen is reduced

  • Nitrox is also called:

    • Oxygen-enriched air

    • Enriched air nitrox

    • EANx

  • Reducing Nitrogen

  • Increasing Oxygen


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A Bit of History

  • Development of nitrox use

    • Early research and use

    • Controversy

    • NAUI endorsement of EANX

    • NAUI Standards for EANX training


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Common Misconceptions About Nitrox

  • Myth 1: “It is hard to dive with nitrox.”

  • Myth 2: “Nitrox is for technical diving.”

  • Myth 3: “Nitrox is for deep diving.”

  • Myth 4: “If you dive with nitrox you won’t get bent.”

  • Myth 5: “Nitrox is safer than air.”

  • Myth 6: “If you dive with nitrox you won’t get narcosis.”


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Why Dive With Enriched Air Nitrox

  • Extended Dive Time


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Unit 2: Gases & Gas Mixtures

  • Gas Basics

  • What’s in Air

  • Some Facts About Individual Gases

  • How Gases Behave

  • Converting Between Depth and Pressure

  • Calculating Partial Pressures


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Student Performance:By the end of the lesson you will be able to:

  • State the composition of air.

  • Describe how gases behave.

  • Explain the relationship between pressure and gas volume.

  • Describe the solubility of gases.

  • Explain what partial pressure is and determine various partial pressures.

  • Determine absolute pressure at depth.

  • Determine the partial pressure of a gas in a mixture at depth.


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Gas Basics

  • Matter

  • Composition of a gas

  • Gas mixtures

  • Gas pressure

  • Dissolved gases


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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


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How Gases Behave

Dalton’s Law:Partial Pressure in Gas Mixtures

Henry’s Law:

Solubility

Boyle’s Lay:

Pressure and volume


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Converting Between Depth and Pressure

Gauge

  • Absolute vs. gauge pressure


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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


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Calculating Partial Pressures

  • If you know the absolute pressure:

    • The basic formula:

      Pg = Fg x Ptotal

    • Using agraphical figure


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What is the PO2 of EAN38 at 34 msw (112 fsw)?

Pg = Fg x Ptotal

0.38 * 4.4 atm = 1.67 ata


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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.


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Calculating Partial Pressurescontinued

Using a table


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Unit 3: The Physiology of Diving and Nitrox

  • Narcosis

  • Decompression Sickness

  • Physiological Effects of High Oxygen Levels

  • Physiological Effects of High Oxygen Levels


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Student Performance:By the end of the lesson you will be able to:

  • List the physiological effects of nitrogen in diving.

  • State physiological effects of low oxygen levels.

  • List the physiological effects of high oxygen levels.

  • Recite signs and symptoms of oxygen toxicity.

  • State limits of hyperbaric oxygen exposure.


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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.


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Decompression Sickness

  • What causes it

  • DCS signs and symptoms


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Decompression Sickness continued

  • How to avoid DCS

  • Treatment for DCS

NITROX REDUCES THE RISK OF DCS . IT DOES NOT ELIMINATE IT!!!!!!!!


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Oxygen: The Good and the Bad

  • Is necessary to sustain life

  • Too high an oxygen level can be just as harmful as too low

  • Oxygen is our life-support gas

  • Theprimary waste product is carbon dioxide

Oxygen and Metabolism


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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


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To avoid Oxygen Toxicity we have 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 and is the standard at MLML


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Physical Effects of High Oxygen Levels

  • Central Nervous System Toxicity

    • has a wide range of signs and symptoms, the most dramatic being epilepsy-like convulsions

    • CNS toxicity can result from relatively short exposures to high partial pressures of oxygen

  • Pulmonary Toxicity or Whole Body Toxicity

    • results from prolonged exposure to elevated partial pressures of oxygen (above about 0.5 atmosphere)

    • not a concern for recreational nitrox diver


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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


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Central Nervous SystemToxicitycontinued

  • 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


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Central Nervous SystemToxicitycontinued

  • 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).


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Managing Oxygen Exposure

  • The best way to avoid oxygen toxicity problems is to stay within correct oxygen exposure limits.


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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

    • PO2=1.4 ata 111’ on EAN32


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Avoiding CNS Toxicity

  • CNS toxicity is avoided by abiding by easily managed limits.

    • Remember that the recommended maximum PO2 for recreational nitrox diving is 1.4 atmospheres, with a PO2 of 1.6 atmospheres as a contingency amount.

    • Plan your dives and choose a nitrox mix that is appropriate to the dive.


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Unit 4:Choosing the Best Nitrox Mix

  • Enriched Air Nitrox Mixtures

  • Calculating MOD

  • Choosing your “Best Mix”


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Student Performance:By the end of the lesson you will be able to:

  • Define Maximum Operating Depth and determine it for any nitrox mixture.

  • Describe what “Best Mix” means and how to calculate it.


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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


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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


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Find the MOD for EAN36 (use 1.4 ata as O2 partial pressure limit)?

Maximum Operating Depthcontinued

  • 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


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Maximum Operating Depthcontinued

  • MOD by Table (imperial)


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Best Mix

  • “Best mix” is the nitrox mixture with highest fraction or percentage of oxygen that can be used at the target depth.


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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


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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


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Choosing Best Mix continued

For my thesis work dive surveys my maximum depth will be 120’ as a contingency I am planning my maximum depth as 125’. I want to find the EAN mix with the highest percentage of O2 that I can use for my survey dives. What is the EAN mix I should take with me??????????? My oxygen partial pressure limit is the MLML/AAUS standard.

Pg = Fg x Ptotal


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Choosing Best Mixcontinued

  • The Best Mix Table


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Unit 5:Dive Tables and Dive Computers

  • Dive Tables

  • Equivalent Air Depth and Standard Air Tables

  • Using NAUI’s RGBM Tables

  • The Rule of Halves

  • Dive Computers


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Student Performance:By the end of the lesson you will be able to:

  • Demonstrate the use of NAUI EANX Dive Tables.

  • Define Equivalent Air Depth and how it is used with Air Dive Tables.

  • Demonstrate how to determine and calculate Equivalent Air Depth.

  • Demonstrate the use of the NAUI RGBM Nitrox Dive Tables.

  • State the “Rule of Halves” and how to use it in all of your diving.

  • Describe the procedures for using dive computers for EANX diving.


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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


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Air Dive Tables

  • So-called “standard dive tables” are designed for diving while breathing air.


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No-required Stop Times

  • EANx Dive Tables give increased maximum dive times for standard mixes.


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Enriched Air Nitrox Dive Tables

  • Enriched Air Nitrox Tables


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Enriched Air Nitrox Dive Tablescontinued

  • 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.


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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.


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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.


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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


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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: Determine the absolute pressure at the depth to which you will be diving.

Pg = Fg x Ptotal


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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


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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.


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Equivalent Air Depth and Standard Air Tables continued

  • Equivalent Air Depth by Table (imperial)


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Using NAUI’s RGBM Tables

  • NAUI RGBM Dive Tables are “No-Calculation” tables and do not require use of letter groups, a surface interval credit table, or residual nitrogen times, thus making repetitive dive planning extremely easy and straightforward.

  • NAUI RGBM Dive Tables have been prepared for EAN32 and EAN36 as well as for air diving. The sea-level tables provide dive-planning information for altitudes up to 2000 feet/610 meters.

  • Additional sets of tables are available for diving at altitudes between 2000 and 6000 feet/610 to 1829 meters and for 6000 and 10,000 feet/1829 to 3048 meters.


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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 one-minute safety stop. Then continue your ascent to the 5 meter/15 foot safety stop and complete the last two minutes of your three-minute safety stop at 5 meters/15 feet.


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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.


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Dive Computers and Nitroxcontinued

  • 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.


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Unit 6:O2 Precautions and Preparing EANx

  • O2 Precautions

  • The Fire Triangle

  • 40% Rule

  • Methods of Making Nitrox


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Student Performance:By the end of the lesson you will be able to:

  • State the precautions that must be taken when around oxygen.

  • Describe what the fire triangle is and how it applies to nitrox use.

  • Describe oxygen cleaning is and what scuba equipment must be oxygen cleaned for nitrox use.

  • Define the “40% Rule.”

  • Describe how cylinders and valves are prepared for nitrox use and how they are marked as nitrox cylinders.

  • List five methods that are used to make nitrox and which are most common.


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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.


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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.

  • GENRAL RULE IS ANYTHING OVER 40% NEEDS SPECIAL PREPARATION


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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.


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Oxygen Handling continued

  • Equipment Considerations

    • Hydrocarbons and petroleum-based products must be avoided FOR ALL MIXES. 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.


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Oxygen Handling continued

  • Oxygen Cleaning (>40% mixes)

    • 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.


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Oxygen Handlingcontinued

  • Equipment Preparation

    • Normal maintenance service is sufficient for your regulator.

    • Your cylinder is a different matter.


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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.


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How Nitrox is Made

  • Partial-Pressure Mixing(MLML)

    • 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.


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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


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How Nitrox is Made continued

  • Pressure Swing Absorption

    • This method removes nitrogen from air rather than adding oxygen to it.

    • PSA passes air alternately over a molecular seive that adsorbs nitrogen.


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How Nitrox is Made continued

  • Membrane Separation

    • Membrane separation uses a semi-permeable “membrane” that allows oxygen to flow through it more readily than nitrogen.


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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 whatyou 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.


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Unit 7:Knowing What You Breathe

  • Oxygen Analyzers

  • Analyzing Your Gas

  • Cylinder Labeling

  • Filling Out The Logbook


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Student PerformanceBy the end of this lesson, you will be able to:

  • Describe oxygen analyzers and why analysis is necessary.

  • State how to analyze your nitrox list.

  • Describe how your cylinder should be labeled after it is filled.

  • Explain why a fill station logbook is kept and how to enter your fill information in the log.


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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%)


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How Oxygen Analyzers Workcontinued

  • 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


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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.


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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.


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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.


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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.


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