Scuba/Nitrox

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Nitrox

Primary benefit: gives you longer no stop times compared to air

Nitrox or Enriched Air is any mixture above 21% Oxygen

40% is limit for normal dive equipment

2 most common: EANx32 (32%) and EANx36 (36%)

Oxygen Partial Pressure

Oxygen Partial Pressure - refers to pressure exerted only by the oxygen part of the blend

  • Expressed as ata (Atmospheres Absolute) or bar
  • Abbreviated as POv2 or Ov2 p.p. (eg. POv2 0.21 ata or POv2 0.21 bar) (often listed as POv2 0.21)
  • POv2 = O% x pressure
  • ex. 10 m / 33 feet using EANx40 -> 2ata/bar x .40 = .80 ata/bar
  • ex. 12m / 40 feet using EANx36 -> 2.2ata/bar x .36 = .80 ata/bar

Max Depths:

  • EANx40 max depth = 1.4 / .40 = 3.5 ata/bar or 25 meters ~ 75 feet
  • EANx36 max depth = 1.4 / .36 = 3.88 ata/bar or 29 meters ~ 87 feet
  • EANx32 max depth = 1.4 / .32 = 4.38 ata/bar or 33 meters ~ 99 feet
  • EANx21 max depth = 1.4 / .32 = 5.66 ata/bar or 46 meters ~ 138 feet


Maximum POv2 is 1.4 ata/bar - if your planned dive would exceed 1.4, select an enriched air with less oxygen, plan a shallower dive, or both

  • Contingency oxygen partial pressure limit is 1.6 - is critical limit and will likely result in oxygen toxicity
  • Treat range between 1.4 and 1.6 as a margin for error only

Issues with Nitrox

Narcosis should be no different from diving with air. Different issues though.

Primary hazard of improper enriched air filling: fire or explosion hazard due to high oxygen content coming in contact with combustible substances, and inaccuracies in the blend leading to uncertainty of what the final blend is.

Primary hazard of exceeding oxygen limits is having a convulsion which is likely to lead to drowning underwater.

High oxygen is flammable and dangerous if not properly cared for.

Two Types of Oxygen Toxicity:

  • CNS (Central Nervous System) Toxicity - convulsions can cause drowning
  • Pulmonary Toxcity - Highly unlikely within computer limits making no stop EANx dives

Signs and symptoms do not always precede a CNS convulsion

Signs and Symptoms of CNS Toxicity: (VENTID)

  • V-vision
  • E-ears
  • N-nausea
  • T-twitching
  • I-irritability
  • D-dizziness
  • (and anxiety)

Penetration Dives (cavern, wreck) - better to use air, or keep PO2 very low

CNS Toxicity while Scuba diving is often fatal

Oxygen partial pressure:

  • is used to measure the concentration of oxygen a diver is exposed to.
  • expresses the part of a gas pressure exerted by the oxygen in the gas.
  • is usually expressed in “atmospheres,” abbreviated “ata” or in bar.
  • will vary at a given depth depending upon the oxygen percent.

You use your EANx dive computer and take other steps to manage oxygen exposure by:

  • setting its maximum PO2 at 1.4.
  • staying well within its oxygen limits and above the maximum depth for the blend you’re using.
  • avoiding heavy exercise and carbon dioxide buildup.
  • maintaining good buoyancy and depth control.

Blend Analysis

You must personally verify the oxygen analysis of the cylinder

Analyzer should be set to 20.8% to 21% - calibrated for air, then flow the air slowly from the tank across sensor

Minor variations (+/- less than 1%) are okay. Round to nearest whole percent.

Never blow into sensor

Sticker:

  • Fill Date
  • Oxygen %
  • Bar/PSI
  • Max Depth
  • Analyzed by
  • Diver

Some divers write "empty" on a used tank so it isn't mistaken.

Dive Computers

Know the EANx blend's maximum depth

Stay within your computer's limits: no stop and oxygen exposure limits

Set your computer for the O2%

After each dive, set the computer again.

Having a backup dive computer isn't bad when doing Nitrox, as computer failure could end the day, and you have to wait 12 hours to dive again!

Air-Only Computer:

  • Option #1 - use DSAT Equivalent Air Depth and Oxygen Exposure Tables
  • Option #2 - Use these limits:
    • Use EANx blend with 32% or less oxygen
    • Limit your depth to 30 meters / 100 feet
    • Stay within your computer's no decompression limits
    • Limit your total dive time for the day to 160 minutes

Recommended 1 hour surface interval when making repetitive dives with enriched air.

Emergency Situations

Handle the situation as you would any unresponsive diver underwater

  • Hold mouthpiece in place
  • Surface the diver immediatly, establish buoyancy, check for breathing
  • Call for assistance
  • Get victim out of water
  • Get diver to care of EMS
  • Contact Divers Alert Network

Practical Application

  • Use analyzer
  • Determine maximum depth
  • Request blend, analyze it, confirm it
  • See how they blend air
  • Quick Review (10 questions)
  • Training Dives
  • Predive Simulation (possibly)
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