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Nitrox Overview

Nitrox Overview. Introduction. Review of Nitrox course We will cover The Pressure ‘T’ Oxygen partial pressure Oxygen toxicity Use of Nitrox Carbon dioxide Equivalent Air Depth Oxygen tracking – in detail. pPg. Fg. P. The Pressure ‘T’. P = Pressure

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Nitrox Overview

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  1. Nitrox Overview

  2. Introduction • Review of Nitrox course • We will cover • The Pressure ‘T’ • Oxygen partial pressure • Oxygen toxicity • Use of Nitrox • Carbon dioxide • Equivalent Air Depth • Oxygen tracking – in detail

  3. pPg Fg P The Pressure ‘T’ • P = Pressure • Fg = Decimal fraction gas in mix • pPg = Partial Pressure gas pPg = Fg x P Fg = pPg/P P = pPg / Fg

  4. Oxygen Partial Pressure • 0.16 – hypoxia symptoms appear • 0.21 – normoxic • >0.50 – considered for oxygen loading • CFT Recommendations • 1.4 maximum for recreational diving • 1.6 maximum for decompression schedule • 1.4 is used to determine the MOD of bottom gas

  5. Oxygen Partial Pressure Dive to 30m on EAN 34 pPO2 = 0.34 x 4 pPO2 = 1.36 (Appendix 1) MOD of EAN 34 = 1.4 / 0.3 = 4.1 Bar or 31m

  6. Oxygen Toxicity • Two types • Central Nervous System • Sudden onset • Exposure to high pPO2 • Symptoms as per ConVENTID

  7. Oxygen Toxicity CNS symptoms: Con = Convulsions V = Visual disturbances E = Ears -e.g. tinnitus (ringing in ears). N = Nausea T = Twitching of muscles, especially facial I = Irritability D = Dizziness, lack of coordination

  8. Oxygen Toxicity • Pulmonary toxicity • Breathing elevated pPO2 over period of time • Symptoms • Breathing difficulties • Sore chest and throat

  9. Oxygen Toxicity Oxygen Tolerance Dependant on pPO2 and time • Central Nervous System toxicity expressed as CNS% • Pulmonary toxicity expressed as Oxygen Tolerance Unit - OTU

  10. Use of Nitrox • Allows for recompression treatment • Oxygen loading tracked correctly • Keep within all daily limits

  11. Carbon Dioxide • By-product of metabolism • Predispose diver to: • Decompression Illness • Nitrogen narcosis • Oxygen toxicity

  12. Equivalent Air Depth To calculate: EAD formula EAD (in bar) = FN2in mix xP FN2 in air FN2 = the decimal fraction of nitrogen P = pressure of dive in bar Convert bar to metres

  13. Equivalent Air Depth Dive to 30m on EAN 34 EAD = 0.66 x 4 0.79 = 3.34 bar or 23.4m - Use Air Table for 24m Use EAD Table – Appendix 2

  14. Table 1 NOAA

  15. Oxygen Tracking CNS Tracking Use equation CNS% = ( Bottom time at depth ) x 100 (Single exposure time pPO2) (Time from NOAA Table 2)

  16. Oxygen Tracking • Use CNS% per minute & multiply by time at depth (Appendix 3) • Add exposure at each depth = Total CNS% exposure • 0.5 pPO2 or less no need to track

  17. CNS% Tracking CFT Recommendations • Using single exposure time: • If CNS% > 80% the minimum SI = 2 hours. • Maximum total duration in 24 hours: • If CNS% > 80% the minimum SI = 12 hours. • A maximum CNS% of 80% should not be exceeded for a single or multiple dives • Allows for complete recompression treatment

  18. CNS% Tracking Surface Intervals • Reduce CNS% by 50% for each 90 minutes • Carry remainder to next dive • CNS% is accumulative

  19. CNS% Tracking, Example Dive EAN34 to 30m for 50 min Stop EAN50 at 4.5m for 13 min CNS% at 30m (EAN34) pPO2 = 1.36 CNS% per min @ pPO2 1.36 = 0.62 Total CNS% for bottom = 0.62 x 50 = 31% (Use Appendix 1 & 3)

  20. CNS% Tracking, Example CNS% at 4.5m for 13 min (EAN50) pPO2 = 1.45 x 0.5 = 0.725 CNS% per min @ pPO2 0.725 = 0.19 Total CNS% for deco = 0.19 x 13 = 2.47% Total CNS% for dive = 31 + 2.47 = 33.47%

  21. CNS% Tracking, Example • Total CNS% for dive = 33.47% • After a 2 hour (120 minutes) surface interval Reduce the CNS% by one half = 16.74% • CNS% for next dive = 16.74%

  22. Oxygen Tracking Pulmonary Toxicity Calculate Oxygen Tolerance Unit (OTU) • Use Equation OTU = t [ (pPO2 – 0.5) / 0.5 ] 0.83 (t = time of exposure & pPO2 in bar) • Use OTU per minute (Appendix 4)

  23. Pulmonary Tracking Oxygen Tolerance Units based on: • Breathing 100% oxygen at 1 Bar accumulates 1 OTU per minute • Accepted limit per day = 1425 OTU • OTU accumulative • No surface reduction • Maximum daily exposure (Appendix 5)

  24. OTU Example Dive EAN34 to 30m for 50 min Stop EAN50 at 4.5m for 13 min OTU at 30m pPO2 = 1.36 OTU per min @ pPO2 1.36 = 1.63 Total OTU for bottom = 1.63 x 50 = 81.5 (Use Appendix 1 & 4)

  25. OTU Example OTU at 4.5m on EAN 50 pPO2 = 1.45 x 0.5 = 0.725 OTU per min @ pPO2 0.725 = 0.56 Total OTU for deco = 0.56 x 13 = 7.3 Total OTU for dive = 81.5 + 7.3 = 88.8 OTU after 2 hour surface interval = 88.8

  26. Summary Review of Nitrox course • The Pressure ‘T’ • Oxygen partial pressure • Oxygen toxicity • Use of Nitrox • Carbon dioxide • Equivalent Air Depth • Oxygen tracking – CNS% & OTU

  27. Questions?

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