Nitrox

Course Overview

• This is not a basic scuba class and it will not be taught as such.

• You should already have the skills and knowledge to dive safely and with common sense.

• However because we have divers at different levels of skill, experience, and knowledge we will review some basic academic areas such as gas laws, dive tables and decompression theory.

• This is a BASIC NITROX COURSE and we will limit our discussions to BASIC NITROX USE.

Qualifications of Graduates

• Competent to utilize EANx in open water diving activities without direct supervision.

• Obtain EANx cylinder refills with a maximum percentage of Oxygen of 40%.

Objectives• Identify the agency through which your certification will be issued.• Identify the maximum percentage of oxygen you will be certified to use.• Identify the maximum depth to which you will be certified to dive.• Describe the concept of Partial Pressure (Dalton’s Law) as it applies to

Nitrox.• Describe the benefits and risks of using Nitrox on scuba.• Describe the benefits and risks of using air on scuba.• Identify the recommendations for P02 exposures for

– Maximum scuba limit for recreational/low exertion dives.– Bottom times over 45 minutes.– Particularly hard dives. (This limit applies to all dives in Monterey.)

• Discuss concerns for applying P02 limits to any individual.• Describe two factors associated with causing CNS Oxygen toxicity.• Identify signs and symptoms of CNS Oxygen toxicity, and discuss

procedures to minimize the risk of CNS 02 toxicity.

Objectives cont.• Convert pressure in atmospheres absolute (ata) to depth.• Convert depth to pressure in atmospheres absolute (ata). • Calculate Maximum 02 dose when given F02 and Pressure (depth).• Calculate Maximum depth when given P02 and F02.• Calculate the best mix to use when given P02 and Pressure (depth).• Describe Equivalent Air Depth (EAD) Theory.• Determine appropriate EAD using either the EAD formulas or the EAD

Table.• Calculate P02 and single limit exposures using the TDI chart.• Using the appropriate P02 and EAD charts as well as the NAUI dive tables,

correctly plan and calculate end of dive letter groups for dives using various Nitrox mixes.

• Discuss equipment issues and concerns and describe appropriate markings for scuba cylinders used for Nitrox.

• Discuss the 40% rule as it applies to Nitrox.• Discuss and compare various methods of making Nitrox.

Terminology

• NOAA NITROX I 32% 02 68% N2• NOAA NITROX II 36% 02 64% N2• GOD’S NITROX 21% 02 79% N2

• Other terms you will hear include:• Enriched Air• Enriched Air Nitrox (EANx) (x = %02 in mix)• Safe Air• Normoxic

History of Nitrox• First documented use 1879• U.S. Military published NITROX tables 1950s• NOAA published NOAA NITROX tables

– NOAA Nitrox 1 1979– NOAA Nitrox II 1991

• NOAA PUBLISHED equivalent air depth (EAD) tables– Technique for diving NITROX while using air tables

• First recreational Nitrox agency established1988• NAUI Sanctions teaching Nitrox 1992• Credit for developing and introducing Nitrox

diving techniques goes to Dr. Morgan Wells

NOAA/NATIONAL UNDERSEA RESEARCH PROGRAM• 1988Workshop on Enriched Air Nitrox Diving

– Concluded the approaches to use of Nitrox were sound– Basically endorsed the use of Oxygen enriched air– Settled on the term Enriched Air Nitrox EANx

DAN/Dr Peter Bennett: • Technical diving with Nitrox is not in the category of recreational diving for

the diver whose training is limited and whose goal is fun.• “...should be left to the organizations with appropriate specialized

equipment, training, and control.”

EVALUATING ENRICHED AIR (“NITROX”) DIVING TECHNOLOGY• 1992 symposium sponsored by Scuba Diving Resource Group

– Conclusions: • Basic NITROX is not technical diving.• Basic NITROX does not require a great deal of special training.

– For most recreational divers, the understanding of basic physics and physiology is generally weak.

NITROX Misconceptions

• Deep Diving

• Extensive Course

• Expensive Course

• Expensive Gear

• Cave or Technical Diver

• Recreational Divers not smart enough

• Recreational Divers not safe enough

NITROX Realities

• Most dives shallower than 130” therefore not technical diving

• 4 hour course – some formulas – use of tables

• Doesn’t require new gear• Perform same underwater activities• Safety proven since 1985• Sport divers are smart enough

Air vs. EANxAir• A mixed gas consisting of 21% 02 79% N2

Advantages of Air compared to EANX• Cheap (maybe)• Easily available• You can dive it right now• Depth

Disadvantages of Air compared to Enriched Air Nitrox• Narcosis (maybe!)• DCS• Fatigue (Maybe!)

Air vs. EANx cont.

• NITROX– A mixed gas consisting of any combination of 02 &N2.

• Advantages of EANX compared to Air– More bottom time or shorter Surface Interval

• N2 is still the limiting factor– Safety factor using air tables/computers– Decreased risk of narcosis (not documented)

• O2 may contribute to narcosis

• Decreased post dive fatigue (not documented)• Improved gas consumption (not documented)• Warmth (not documented)

Advantages of EANX compared to Air cont.

• Less risk of DCS– Risk factors of DCS

• older age• obesity• dehydration• poor circulation• illness• scar tissue• alcohol • fatigue• strenuous exercise• cold• repetitive dives• multi day diving• history of DCS

Disadvantages of EANx compared to air

• Shallower 02 toxicity concern– Using 1.4 atm

• air 187 fsw• NNI 111 fsw • NNII 95 fsw

• CNS 02 Toxicity can be confused with N2 Narcosis but 02 Toxicity more serious

Physiology

• Body is concerned with– P02 and – Exposure time

• Recommended max exposure limit– 1.6 ata maximum exposure– 1.4 ata recreational,cold or working dive

• O2 tolerance limits vary from individual to individual and from day to day– No good test available

Depth and Pressure Review

• Depth = Actual depth underwater• Pressure atmospheres in Seawater

– (Depth +33)/33or

– (Depth/33) + 1

• Pressure atmospheres in fresh water – (Depth +34)/34

or– (Depth/34) +1

Review Dalton’s Law

• P=Pg1+Pg2+Pg3 etc.– P=absolute pressure– Pg=partial pressure of gas

• Dalton’s Law for Air at sea level– P = P02 + PN2– 1.0 ata = .21 ata + .79 ata

• Dalton’s Law for Nitrox: – P = P02 + PN2

• Dalton’s Law for NNI at sea level– 1.0 ata = .32 ata + .68 ata

• Dalton’s Law for NNII at sea level– 1.0 ata = .36 ata + .62 ata

Determining the Partial Pressure of a Gas

2 Step Process

• Step 1

P total = (Dfsw/33 fsw/atm) + 1 atm

• Step 2

P02 = F02 x P total

Determining the Partial Pressure of a Gas

What is the P02 of EAN 38 at 112 fsw?

• Step 1P total = (Dfsw/33 fsw/atm) + 1 atm

P total = (112 fsw/33 fsw/atm) + 1atm = 4.4 atm

• Step 2P02 = F02 x P total

P02 = .38 x 4.4 atm = 1.67 atm

Dalton’s Law cont.

• Partial pressure can also be used to determine the percentage or fraction of a component gas.– Pg/P = Fg

• P02 / P = F02– .21 ata / 1.0 ata = .21

• PN2 / P = FN2– .79 ata / 1.0 ata = .79

Determining the Percentage or Fraction of a Gas

2 Step Process

• Step 1

P total = (D fsw/33 fsw/atm) + 1 atm

• Step 2

F02 = P02/P total

Determining the Percentage or Fraction of a Gas

• If the P02 of your Nitrox mix is 1.2 atm at 122 fsw, what is the F02 of the mix?

• Step 1

P total = (D fsw/33 fsw/atm) + 1 atm

P total = (122 fsw/33fsw/atm) + 1 atm• Step 2

F02 = P02/P total

F02 = 1.2 atm/4.7 atm =0.255 = 25.5%02

Dalton’s Law cont.

• Remember that the fraction of a gas delivered during a dive is constant. However the partial pressure changes with depth.

EQUIVALENT AIR DEPTH THEORY

• During a NITROX dive less N2 will be absorbed than on an air dive of same depth and duration. Don’t forget you will be exposed to a higher partial pressure of oxygen.

• EAD is a technique whereby you calculate the N2 partial pressure for your mix and use the air table depth that has the same partial pressure.

Equivalent Air Depth

• Formula

EAD fsw =[ (FN2ean x Dfsw+33fsw/atm) – 1atm] x 33fsw/atm

FN2 air 33fsw/atm

Or

Use a table

Oxygen Physiology Concerns

• O2 used can be aviation or medical

• Individual tolerance to 02 varies from person to person.

• Individual tolerance to 02 varies from day to day.

Oxygen Physiology Concerns

• O2 tolerance is decreased by CO2– C02 is the primary waste product from the

metabolism of 02.– C02 retention which can be caused by

• Poorly functioning regulator• Inefficient breathing• Labored breathing (hard work)• Heavy exercise

Oxygen Physiology Concerns

• 02 Exposure limits assume:– Low/moderate exercise– No breathing restriction– No excess C02 (snorkel)– No unusual 02 exposure prior to the dive

Oxygen Toxicity

CNS 02 Toxicity

• Caused by short term exposure to high P02

• P02 levels below 1.5 ata are unlikely to cause CNS toxicity no matter what the duration of exposure.

• Maximum recommended P02 for recreational diving of EANx = 1.4 ata

CNS 02 Toxicity• CONvulsions

• Visual symptoms

• Eurphoria/Ears

• Nausea

• Twitching (lips, cheeks, nose, diaphragm)

• Irritability

• Dizziness

Warning signs vary greatly and sometimes

do not occur at all.

CNS 02 Toxicity

Emergency Techniques

• Ascend immediately

• Switch to air immediately– Have a hang tank or bailout bottle of Air.

• On deep dives be aware of the danger of N2 Narcosis

Pulmonary/Whole Body 02 Toxicity

• Caused by long term exposure to P02 over .5 ata.

• Not very likely in recreational diving

Pulmonary/Whole Body 02 Toxicity

Signs• Soreness in chest and airway• Dry cough• Head ache• Fatigue• Loss of aerobic capacity• Numb fingertips• Parestheses• Aches and pains• Vital capacity decreased

– If not caught soon enough = may be chronic

Pulmonary/Whole Body 02 Toxicity

The effects of Pulmonary/Whole Body 02 Toxicity typically are relieved when the P02 drops below .5 ata.

To avoid problems with 02 Toxicity

• Always analyze the gas– Too much 02 = less depth– Too little 02 = less time

• Do not exceed the time and depth limits for your gas mix.

• Biggest risk is not knowing what you are diving

Other Concerns

• DCS– You can get bent while using Nitrox– If diving within the recreational limits the treatment will

be as if you were on air

• Narcosis– You can get narcosis while diving Nitrox– Nitrogen is inert gas so our bodies do no use the N2

in the gas we breathe acts similar to anesthia– 02 may contribute to narcosis– Treatment is to ascend

Hypoxia (Low 02 levels)

• Onset of symptoms– PO2 .14-.16 ata

• More severe symptoms– P02 .09-.10 ata

• Unconscious for most people– P02 .08-.10 ata

• Coma-death– P02 <.08 ata

Hypoxia Signs/Symptoms

• Euphoria• Itching/tingling• Tunnel vision• Impaired mental performance• Defective memory• Cyanosis• Fatigue• Visual disturbances• Dizziness

Dive Planning

• Maximum Operating Depth (MOD)– The maximum depth a particular gas can be

used without exceeding an oxygen toxicity limit, based on the partial pressure of the oxygen at depth.

– NAUI P02 =1.4 ata

• Factors– Percentage of 02– Depth

Calculating MOD

2 step process

• Step 1– Pata = P02 limit/F02

• Step 2– Dfsw = (Pata – 1 atm) x 33 fsw/atm

Calculating MOD

• What is the maximum operating depth (MOD) for air using 1.4 ata?

• Step 1P ata = 1.4 atm/.21 = 6.67 atm

• Step 2 Dfsw = (Pata – 1 atm) x 33 fsw/atmDfsw = (6.67 atm -1 atm) x 33 fsw/atmDfsw = 187 fsw

Dive Planning cont.

• Best Mix– A gas mix chosen to optimize oxygen for

efficient decompression yet minimal toxicity risk.

– Maximize P02 without exceeding 1.4 ata.

Calculating Best Mix

Two step Process

• Step 1

P ata = (D fsw / 33 fsw/atm) + 1 atm

• Step 2

F02 = P02 limit/P ata

Calculating Best Mix

• What is the bes tmix for a dive to 89 fsw using a maximum P02 of 1.4 ata?

• Step 1P ata = (D fsw / 33 fsw/atm) + 1 atm(89 fsw /33 fsw/atm) + 1 atm = 3.7 atm• Step 2F02 = P02 limit/P ataF02 = 1.4 atm/3.7 atm = 0.378 = 37%

02 Use and Handling

• Regulators– No special requirements

• Cylinders– Must be 02 clean

• No oil, grease or other hydrocarbons present• Materials must be 02 compatible

– Viton “O” rings– 02 compatible lubricants

02 Use and Handling

• Fire triangle– Fuel, oxygen, heat

• 40% rule– General rule of thumb for scuba industry – Any equipment used with F02 above 40% and

at a pressure above 200 psi must be cleaned for 100% 02 service and have only oxygen compatible parts.

– Cylinder may see 100% 02

02 Use and Handling

• Label all Nitrox cylinders so as to avoid confusion with air tanks

• EANx cylinder ID– 4” wide green band completely around the top

of a yellow cylinder– 6” wide band with

• 1” yellow top and bottom border and• the words “Enriched Air Nitrox” is acceptable for

non-yellow cylinders.

02 Use and Handling

• Each cylinder should have a contents tag– F02– Max 02 Depth– Cylinder pressure– Date– Serial number– Diver’s initials

Fill Station Log

The fill station should maintain a log of all

fills

• Verify cylinder was analyzed

• Verify user is aware of mix and MOD

• Verify cylinder has not been filled with and contaminated

Gas Analysis

• Always analyze your own gas – Calibrate analyzer to known gas (100% 02)– 02 analyzer should be accurate to within 2%

• Flow rate– Should be the same as when unit was calibrated with

air or other gas.– Sample for at least 30 seconds with appropriate flow

• Ensure good seal for sample and do not block exit of gas from collection system.

Gas Analysis

• Response can also be effected by

• pressure– changes in barometric pressure effect reading

• Humidity– if humidity increases 02 concentration

decreases

• Temperature

Fill Techniques• Partial pressure mixing

– Technician first puts in a measured amount of 02– Fills to service pressure with air

• 02 compatible air vs.• Breathing air

– Technician will typically empty a partially full cylinder• Continuous Flow

– Injects a measured flow of 02 into the air before it reaches the compressor

• Pressure swing– Removes N2 from the air itself– Air is passed over a molecular sieve that absorbs N2

• Membrane– passes air through a membrane that allows 02 to flow through more

readily than N2

• Pre-Mix or Banked EANx– The fill station will keep a supply of pre-mixed

gas on hand and ready to pump.

ABCs to Minimize the Risks Associated with Nitrox Diving

• Always analyze

• Before you breath

• Check for correct

• Depth Limit

• EAD

• F02