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Nitrox Diving

Nitrox Diving. Sources. Joiner, J.T. (ed.). 2001. NOAA Diving Manual - Diving for Science and Technology, Fourth Edition. Best Publishing Company, Flagstaff, AZ. Reference Materials: In conjunction with this presentation, refer to: NOAA Diving Manual Chapter 15

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Nitrox Diving

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  1. Nitrox Diving

  2. Sources • Joiner, J.T. (ed.). 2001. NOAA Diving Manual - Diving for Science and Technology, Fourth Edition. Best Publishing Company, Flagstaff, AZ. • Reference Materials: • In conjunction with this presentation, refer to: • NOAA Diving Manual Chapter 15 • NOAA Diving Manual Appendix VII

  3. Objectives • Upon completion of this module, the participant will be able to: • List and dispel six myths about nitrox; list three advantages of nitrox; and describe the difference between CNS & Pulmonary Oxygen Toxicity; • Select proper nitrox mixes; determine Oxygen Exposure; and calculate FO2, PO2, MOD, & EAD for a given dive; • Plan nitrox dives; • Explain the 40% Rule; the difference between formal and informal oxygen cleaning; and list four methods of nitrox preparation; • Describe proper marking and labeling requirements for nitrox cylinders; • Describe how to calibrate an O2 analyzer and analysis nitrox

  4. What’s Important • Using nitrox means having to manage nitrogen (N2) and oxygen (O2) while diving • The advantage of extended bottom times also means properly managing your available gas

  5. Physiology Review

  6. Composition of Air • 21% O2 - necessary for body metabolism, but may be toxic in excess • 78% N2 – inert gas (plays no role in body metabolism) – causes narcosis at high partial pressure • 1% other gasses (mostly argon, but also carbon dioxide (the waste product from the metabolism of oxygen), neon, helium, krypton, sulfur dioxide, methane, etc… ) • These are considered with the nitrogen component of air in nitrox calculations

  7. Nitrogen-Oxygen Breathing Mixtures • Air is readily available and inexpensive, but it is not the “ideal” breathing mixture because of the effects of nitrogen narcosis at deeper depths & the decompression liability it imposes

  8. Nitrogen and narcosis • Nitrogen narcosis – the pronounced anesthetic effect that occurs when nitrogen is breathed at higher pressures • Most people feel narcosis at roughly 100–130 feet (3–4 ata) • Martini’s Law – every 50 feet of depth is roughly equivalent to drinking one dry gin martini on an empty stomach • Symptoms include: • Feelings of euphoria • Shortened attention span • Tendency to giggle • Slurred speech • Numb lips • Inability to concentrate • Mechanisms of narcosis seem to be similar to that of anesthesia

  9. Nitrogen and narcosis • Feelings of well being may disguise threat – narcosis may leave diver unable to deal with problems • Sensitivity to narcosis varies among individuals – there seems to be some evidence that people learn to cope with narcosis as they gain experience diving • Divers may be unaware of impairment

  10. Nitrogen and narcosis • Other factors may contribute to nitrogen narcosis: • Psychological predisposition • Stress • Anxiety • Fatigue • Cold • Hard work • High carbon dioxide levels in the body • Alcohol

  11. Nitrogen-Oxygen Breathing Mixtures • Decompression obligation is dependent on exposure to inspired nitrogen • Decompression obligation can be reduced by replacing a portion of the nitrogen in a breathing mixture with oxygen • This is the fundamental benefit of nitrogen-oxygen diving

  12. Decompression sickness • Caused by the release of gas dissolved in tissues – may form bubbles in body while surfacing or after a dive • Symptoms and signs may occur anywhere from 5 minutes to 24 hours or more after a dive • Most commonly, however, they appear within one hour • Symptoms and signs do not generally manifest themselves in-water

  13. Joint pain Paralysis Muscle pain Skin rash Disorientation Slurred speech Dizziness Agitation Hearing disturbances Tingling Fatigue Vision problems Numbness Weakness Decompression sickness – signs and symptoms

  14. Treatment • Victims should breathe 100% oxygen • Evacuate victim to the nearest hyperbaric treatment facility • Note: signs and symptoms may dissipate during oxygen breathing – victim should still be evaluated at a hyperbaric treatment facility • Treatment protocols do not change for nitrox divers

  15. Nitrox

  16. Nitrox • Nitrox is a generic term that can be used for any mixture of nitrogen and oxygen other than air • For the purpose of this training module, all nitrox mixtures have an O2 percentage greater than air

  17. Oxygen Enriched Air (OEA) Enriched Air Nitrox (EAN or EANx (the “x” in EANx stands for the percentage of oxygen in the mix)) NN32 (a 32% mix) NN36 (a 36% mix) Most Common (standard) Mixes 32% oxygen 36 % oxygen EAN32 EAN36 Oxygen Enriched Air: Terminology All the mixes have more oxygen and less nitrogen than normal air

  18. Abbreviated History of Enriched Air in Diving • 19th century – Elihu Thompson proposed use of Hydrogen & O2 • USN explored nitrogen-oxygen mixtures in 1950s • International Underwater Contractors (IUC) and others began using enriched air in commercial diving in the 1960s • Dr. Morgan Wells introduced enriched air to NOAA, published in NOAA Diving Manual in 1979 – Dr. Wells is credited with developing and introducing nitrox diving techniques for standard scuba • NOAA Continuous Flow Blending techniques – 1984

  19. Abbreviated History of Enriched Air in Diving • 1984 NURC/UNCW established a strong Nitrox program • NOAA sponsored high-level workshop at Harbor Branch 1988 • Industry agreed to a standard for air to be mixed with oxygen • Dick Rutkowski (IANTD) introduced EANx to recreational diving in 1985 • Enriched air computers enter the market in 1992 • 1992 - NAUI sanctions enriched air nitrox training

  20. Myths About Nitrox • Nitrox is safer than air • False • Nitrox has a significant decompression advantage over air, but has other risks that must be managed • These additional areas of concern include O2 toxicity, required depth and time limits, mix conformation and analysis, special equipment requirements, and risks involved in gas mixing

  21. Myths About Nitrox • “Nitrox is for deep diving” • FALSE • Nitrox has very stringent depth limits because of the higher concentration of O2 in the mixture • The greatest advantages for no-stop diving are in the 50-110 feet of sea water (fsw) depth range

  22. Myths About Nitrox • “Nitrox eliminates the risk of decompression sickness (DCS)” • FALSE • Using nitrox provides significant decompression advantage over air, but the risk of DCS is likely unchanged if nitrox specific dive tables are used

  23. Myths About Nitrox • “Nitrox makes treatment for DCS impossible” • FALSE • Treatment for DCS in a nitrox diver is the same as treatment for an air diver, taking into account the possibility of extra oxygen exposure

  24. Myths About Nitrox • “Nitrox reduces narcosis” • Not Really • Although this has not been adequately studied, oxygen’s properties suggest that it can also be a narcotic gas under pressure. The result is that you should not expect a significant change in narcosis when diving nitrox as compared to air

  25. Myths About Nitrox • “Using nitrox is difficult” • FALSE • Once you understand the potential risks and simple requirements of using nitrox as a breathing gas, diving nitrox is as easy as inhale, exhale, repeat

  26. Advantages of Nitrox • Longer no-stop dive times Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

  27. Advantages of Nitrox • Less nitrogen absorbed = lower risk of DCS • Breathing a gas with less nitrogen coupled with air decompression tables effectively lowers the risk of DCS. This does not mean a diver will never get DCS; it means with proper management, the already small risk of DCS can be even smaller

  28. Advantages of Nitrox • Longer repetitive dives • Air Example • Dive # 1 - 90 fsw / 20 min no-stop • One hour surface interval Group F > E • Dive # 2 - 80 fsw / 17 min no-stop • Same Dive Using 36% O2 • Dive # 1 - 90 fsw / 20 min no-stop • One hour surface interval Group E > D • Dive # 2 - 80 fsw / 36 minutes no-stop time • Using EAN provided 24 minutes more no-stop dive time

  29. Advantages of Nitrox • Possibility of shorter required surface interval • Using Navy air tables and NOAA nitrox tables: • Two dive teams just completed a 30 minute dive to 80 fsw. Team 1 breathed air, while Team 2 breathed EAN36. Team 1 emerges with a letter group of G, while Team 2 emerges with a letter group of F. Using the appropriate dive tables to compute a 2nd dive to 55 fsw for 30 minutes finds Team 2 could enter the water in as few as ten minutes with a letter group of F, while Team 1 would have to wait at least 1 hour and 16 minutes for the air tables to allow sufficient adjusted maximum dive time for the planned dive.

  30. Physics Review

  31. Units of Measure • Pressure • One atmosphere (atm) equals the pressure of the air at sea level • 1 atm equals: • 760 millimeters of mercury • 29.92 inches of mercury • 101.3 kilopascals (kPa) • 1.013 bars • 14.7 lbs/in2 (psi) • 33 feet of seawater (fsw) • 34 feet of freshwater (ffw)

  32. Units of Measure • Atmospheres absolute (ata) equals water pressure (hydrostatic pressure) + atmospheric pressure

  33. Partial Pressure • The partial pressure of a specific gas in a mix is the portion of the total pressure exerted by that gas • It is the fraction of the component gas multiplied by the total pressure • When added, all of the partial pressures of the component gases become the total pressure Air at 1 atm Percentage Partial Pressure 79% N2=0.79 atm 21% O2=0.21 atm 100% =1.00 atm

  34. Partial Pressure • Dalton’s law - In a mixture of gases, the total pressure is made up of the sum of the partial pressures of the individual components • The partial pressure of a gas is the product of the fraction of that gas times the total pressure P = P1 + P2 + P3 +…+Pn Pg = Fg X P total Where Pg = partial pressure of the component gas Fg = fraction of the component gas in the mixture, and Ptotal = the total pressure of the gas mixture

  35. Pressure and Volume: Boyles Law • Pressure and volume (at constant temperature) are inversely proportional to each other. So, as pressure on a given mass of gas is increased, volume decreases – and as pressure on a given mass of gas decreases, volume increases. So: • P1V1=P2V2 where: • P1 = initial pressure • V1 = initial volume • P2 = final pressure • V2 = final volume

  36. Pressure and Temperature: Gay-Lussac’s Law • At constant volume, pressure is proportional to the absolute temperature - temperature increases when pressure increases. Temperature decreases when pressure decreases. • P1/T1=P2/T2 where: • P1 = initial pressure • T1 = initial temperature • P2 = final pressure • T2 = final temperature • Note: all temperatures must be expressed in either Rankine (temperature in Fahrenheit + 460) or Kelvin (temperature in Celsius + 273)

  37. Volume and Temperature:Charles’ Law • If pressure is held constant, then volume is proportional to temperature. So, volume increases when temperature increases, and volume decreases when temperature decreases. • V1T1/V2T2 where: • V1 = initial volume • T1 = initial temperature • V2 = final volume • T2 = final temperature • Note: all temperatures must be expressed in either Rankine (temperature in Fahrenheit + 460) or Kelvin (temperature in Celsius + 273)

  38. The Solubility of Gasses: Henry’s law “The amount of any given gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of the gas that is in contact with the liquid and the solubility coefficient of the gas in the particular liquid” • So, the solubility of a gas in a liquid is directly related to the pressure of the gas on the liquid – an increase in pressure causes an increase in solubility, while a decrease in pressure causes a decrease in solubility

  39. Converting fsw to atmospheres absolute (ata) D fsw + 33 fsw 33 fsw / atm = P ata For a depth of 75 fsw 75 fsw + 33 fsw 33 fsw / atm = 3.27 ata Depth plus 33 then divide by 33

  40. Converting fsw to ata Alternate Formula: ata = (fsw ) + 1 33 ata = (75) + 1 = 3.27 ata 33

  41. Converting ata to fsw (ata x 33 fsw/atm) - 33 fsw/atm = D fsw For a pressure of 3 ata (3 ata x 33 fsw/atm) – 33 fsw/atm = 66 fsw ata times 33 then minus 33 = fsw

  42. Converting fsw to ata • Alternate Formula: • D fsw = (ata – 1 atm) x 33 fsw/atm • For a pressure of 3 ata: (3 ata – 1 atm) x 33 fsw/atm = 66 fsw

  43. Oxygen Physiology, Toxicity, and Tolerance

  44. Hypoxia • Oxygen is necessary for metabolism • Hypoxia – an inadequate supply of oxygen • May occur when oxygen partial pressure falls at or below 0.16 ata • Symptoms include: euphoria, dimness of vision (“tunnel vision”), dizziness, breathlessness, itching and tingling. When severe enough, collapse and unconsciousness may occur • Possible signs – cyanosis (bluish skin coloration), blueness of the lips and nail beds

  45. Oxygen Toxicity • Exposure to oxygen at high partial pressures may damage tissue and disrupt function • This damage is dependent upon both the partial pressure of the oxygen, and upon the length of time the oxygen is breathed • The most common cause is exceeding the oxygen exposure limits, but using an incorrect mix for the depth being dived is also common

  46. Oxygen Toxicity – Central Nervous System Toxicity (CNS) • May occur after breathing oxygen at high partial pressures (above 1.6 ata) over a relatively short duration (a few breaths) • Signs & Symptoms – occur in an unpredictable sequence: • Mnemonic – “ConVENTID” Convulsion, Visual disturbances (including tunnel vision), Ear ringing, Nausea, Tingling, Twitching or muscle spasms (especially of the faced and lips) Irritability, Dizziness • Other symptoms – difficulty breathing, anxiety, confusion, poor coordination, fatigue, euphoria, dilated pupils, hiccups, hallucinations • ASCEND - If any symptoms are noted, diver should reduce the partial pressure of the breathing gas by ASCENDING; the dive should be terminated

  47. Oxygen Toxicity – Central Nervous System Toxicity (CNS) • Any of the symptoms above may warn of an oncoming convulsion • However, there may be NO WARNING proceeding a convulsion • Furthermore, divers have lost consciousness without warning, possibly from oxygen toxicity

  48. Oxygen Toxicity – Central Nervous System Toxicity (CNS) • Individual tolerance to oxygen toxicity varies over time • Tolerance also varies from individual to individual • Factors that may increase your susceptibility to CNS • Heavy exercise • Breathing dense gas • Breathing against resistance • Increased carbon dioxide buildup • Chilling or hypothermia • Water immersion (as opposed to “chamber diving”)

  49. If a convulsion occurs • May cause diver to spit out mouthpiece, usually impossible to reinsert - drowning is likely • Rapid or out-of-control ascent may lead to pulmonary barotrauma • Upon cessation of convulsion, diver should be taken to the surface at a slow ascent rate • Treat victim for near-drowning according to any signs or symptoms – all victims should be transported to a medical facility for evaluation by a physician

  50. Oxygen Toxicity – Whole Body Toxicity (also known as Pulmonary Toxicity) • Occurs from breathing oxygen at lower exposure levels for longer periods of time (multiple hours) • The lung is the organ primarily involved, but other parts of the body may also be affected • This generally is not an issue for scuba divers performing no-stop dives, but may become an issue for divers during intensive diving operations

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