Nitrox Diving.

Nitrox Diving

Sources Joiner, J.T. (ed.) 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

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

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

Physiology Review

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

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

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

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

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

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

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

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

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

Nitrox

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

Oxygen Enriched Air: Terminology
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 All the mixes have more oxygen and less nitrogen than normal air

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

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 NAUI sanctions enriched air nitrox training

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

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 feet of sea water (fsw) depth range

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

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

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

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

No-stop deco times (minutes)
Advantages of Nitrox Longer no-stop dive times Depth No-stop deco times (minutes) (fsw) (msw) USN Air 21% NN32 32% NN36 36% 50 15 100 200 310 60 18 70 22 80 25 40 90 28 30 31 110 34 20 120 37 130 10 Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

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

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

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.

Physics Review

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)

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

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

Partial Pressure P = P1 + P2 + P3 +…+Pn
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

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

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)

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)

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

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

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

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

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

Oxygen Physiology, Toxicity, and Tolerance

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

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

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

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

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”)

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

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

Oxygen Toxicity – Whole Body Toxicity (also known as Pulmonary Toxicity)
Symptoms: Pulmonary - Chest pain or discomfort, coughing, chest tightness, fluid in the lungs, reduction in vital capacity Non-pulmonary – skin numbness and itching, headache, dizziness, nausea, effects on the eyes, reduction in aerobic capacity

Selecting Mixes

Partial pressure of oxygen (PO2) Exposure
The maximum oxygen partial pressure exposure for scientific diving is 1.6 ata, and you may want to further limit your exposure By contrast, 1.4 ata is the maximum PO2 exposure for most recreational diving

Concerns of the Mix A key facet to nitrox dive planning is to optimize the O2 level by displacing as much N2 as possible while remaining within the selected oxygen exposure limit Too much O2 increases the risk of oxygen toxicity Too much nitrogen shortens the no-stop time Using the wrong mix with the wrong table could lead to DCS

NOAA Oxygen Exposure Limits
Oxygen Exposure Time NOAA Oxygen Exposure Limits PO2 (atm) Maximum Single Exposure (minutes) Maximum per 24 hr 1.60 45 150 1.55 83 165 1.50 120 180 1.45 135 1.40 1.35 195 1.30 210 1.25 225 1.20 240 1.10 270 1.00 300 0.90 360 0.80 450 0.70 570 0.60 720 As your PO2 increases, your oxygen exposure limit decreases The NOAA O2 Exposure Limits table can be used to determine your dive time limits for a given PO2 Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

Oxygen Exposure Time NOAA Oxygen Exposure Limits PO2 (atm) Maximum Single Exposure (minutes) Maximum per 24 hr 1.60 45 150 1.55 83 165 1.50 120 180 1.45 135 1.40 1.35 195 1.30 210 1.25 225 1.20 240 1.10 270 1.00 300 0.90 360 0.80 450 0.70 570 0.60 720 The lower the PO2, the longer the dive can be conducted from an oxygen tolerance perspective Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

Oxygen Exposure Time However, reducing PO2 exposure limits also reduces the maximum depth at which mixtures can be used

Oxygen Exposure Time Using a 32% mix at 130 ft results in a PO2 of This limits the single dive exposure time to 45 minutes. NOAA Oxygen Exposure Limits PO2 (atm) Maximum Single Exposure (minutes) Maximum per 24 hr 1.60 45 150 1.55 83 165 Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

Oxygen Exposure Time Using the same 32% mix, but reducing your maximum PO2 exposure at depth to 1.4 increases your single dive exposure limit to 150 minutes. However, decreasing your PO2 exposure to 1.4 reduces the maximum depth you can use this mix from 132 fsw to 111 fsw. 1.45 135 180 1.40 150 1.35 165 195 Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

Maximum Operating Depth
Maximum Operating Depth (MOD) – the maximum depth that should be dived with a given nitrox mixture MOD is determined by calculating the depth limits of the selected oxygen exposure (PO2) for a given dive

Calculating: MOD To calculate the MOD for a 32% mix, which has an FO2 (fraction of oxygen) of 0.32, and a PO2 at depth of 1.4 ata:

Calculating: MOD The MOD for the same 32% mix using a PO2 of 1.6 ata:

Calculating Partial Pressure

Calculating Partial Pressures
Dalton’s law Pg = Fg x Ptotal Pg = partial pressure of the component gas Fg = fraction of the component gas Ptotal = total pressure of gas mixture

Calculating Partial Pressures
Calculate the partial pressure of oxygen (PO2) for air being breathed at 90 fsw: Pg = Fg x P PO2 = 0.21 x 3.7 PO2 = 0.78

PO2 Chart Depth atm abs 21% 28% 30% 31% 32% 33% 34% 35% 36% 37% 38%
39% 40% (fsw) (msw) 1.00 0.21 0.28 0.30 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.40 35 11 2.05 0.43 0.57 0.62 0.66 0.68 0.70 0.72 0.74 0.76 0.78 0.80 0.82 40 12 2.21 0.46 0.69 0.71 0.73 0.75 0.77 0.84 0.86 0.88 50 15 2.52 0.53 0.81 0.83 0.91 0.93 0.96 0.98 1.01 60 18 2.82 0.59 0.79 0.85 0.87 0.90 0.99 1.02 1.04 1.07 1.10 1.13 70 22 3.12 0.94 0.97 1.03 1.06 1.09 1.12 1.15 1.19 1.22 1.25 80 25 3.42 1.16 1.20 1.23 1.27 1.30 1.33 1.37 90 28 4.73 1.31 1.34 1.38 1.42 1.45 1.49 100 31 4.03 1.21 1.29 1.41 1.53 1.57 1.61 110 34 4.33 1.39 1.43 1.47 1.52 1.56 1.60 1.65 1.69 1.73 120 37 4.64 1.44 1.48 1.58 1.62 1.67 1.72 1.76 1.81 1.86 130 4.94 1.63 1.68 1.78 1.83 1.88 1.93 1.98 140 43 5.24 1.89 1.94 1.99 150 46 5.55 1.17 1.55 2.00 160 49 5.85 1.64 1.87 170 52 6.15 1.85 1.91 1.97 PO2 (atm) based on depth and percentage of oxygen. The body of the chart has PO2 values for various mixes at a range of depths. Standard 32% and 36% mixes are in light grey. PO2 levels higher than 1.6 ata, in red, are considered exceptional exposures and should be avoided Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

PO2 Chart Use the PO2 Chart to determine the PO2 of a 32% mix being breathed at 110 fsw

PO2 Chart Depth atm abs 21% 28% 30% 31% 32% 33% 34% 35% 36% 37% 38%
39% 40% (fsw) (msw) 1.00 0.21 0.28 0.30 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.40 35 11 2.05 0.43 0.57 0.62 0.66 0.68 0.70 0.72 0.74 0.76 0.78 0.80 0.82 40 12 2.21 0.46 0.69 0.71 0.73 0.75 0.77 0.84 0.86 0.88 50 15 2.52 0.53 0.81 0.83 0.91 0.93 0.96 0.98 1.01 60 18 2.82 0.59 0.79 0.85 0.87 0.90 0.99 1.02 1.04 1.07 1.10 1.13 70 22 3.12 0.94 0.97 1.03 1.06 1.09 1.12 1.15 1.19 1.22 1.25 80 25 3.42 1.16 1.20 1.23 1.27 1.30 1.33 1.37 90 28 4.73 1.31 1.34 1.38 1.42 1.45 1.49 100 31 4.03 1.21 1.29 1.41 1.53 1.57 1.61 110 34 4.33 1.39 1.43 1.47 1.52 1.56 1.60 1.65 1.69 1.73 120 37 4.64 1.44 1.48 1.58 1.62 1.67 1.72 1.76 1.81 1.86 130 4.94 1.63 1.68 1.78 1.83 1.88 1.93 1.98 140 43 5.24 1.89 1.94 1.99 150 46 5.55 1.17 1.55 2.00 160 49 5.85 1.64 1.87 170 52 6.15 1.85 1.91 1.97 PO2 (atm) based on depth and percentage of oxygen. The body of the chart has PO2 values for various mixes at a range of depths. Standard 32% and 36% mixes are in light grey. PO2 levels higher than 1.6 ata, in red, are considered exceptional exposures and should be avoided Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

PO2 Chart Use the PO2 Chart to determine the PO2 of a 32% mix being breathed at 110 fsw Answer – 1.39 ata

Calculating FO2

Calculating FO2 Standard Mixes like NN 32 or 36 are good for a variety of diving situations There are times, however, when a dive calls for maximizing no-stop time for a specific depth To maximize no-stop time, determine the “Best Mix” for a given depth by calculating the fraction of oxygen (FO2) at your desired PO2 exposure

Calculating FO2 To calculate the best mix for 120 fsw using a PO2 of 1.4: The best mix for 120 fsw using a PO2 of 1.4 is 30%

Calculating FO2 To calculate the best mix for 120 fsw using a PO2 of 1.6: The best mix for 120 fsw using a PO2 of 1.6 is 34%

Calculating FO2 fsw msw atm PO2 1.3 1.4 1.5 1.6 40 12 2.21 58% 63% 67% 72% 45 14 2.36 55% 59% 50 15 2.52 51% 55 17 2.67 48% 52% 56% 60 18 2.82 46% 49% 53% 65 20 2.97 43% 47% 50% 70 22 3.12 41% 44% 75 23 3.27 39% 42% 45% 80 25 3.42 38% 40% 85 26 3.58 36% 90 28 3.73 34% 37% 95 29 3.88 33% 100 31 4.03 32% 105 32 4.18 31% 35% 110 34 4.33 30% 115 35 4.48 29% 120 37 4.64 28% 125 38 4.79 27% 130 4.94 26% Table 15.4 of the NOAA Diving Manual may also be used to determine the best mix for a given PO2 This table provides PO2 levels from 1.3 to 1.6 ata and depths to 130 fsw Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

Calculating FO2 fsw msw atm PO2 1.3 1.4 1.5 1.6 40 12 2.21 58% 63% 67% 72% 45 14 2.36 55% 59% 50 15 2.52 51% 55 17 2.67 48% 52% 56% 60 18 2.82 46% 49% 53% 65 20 2.97 43% 47% 50% 70 22 3.12 41% 44% 75 23 3.27 39% 42% 45% 80 25 3.42 38% 40% 85 26 3.58 36% 90 28 3.73 34% 37% 95 29 3.88 33% 100 31 4.03 32% 105 32 4.18 31% 35% 110 34 4.33 30% 115 35 4.48 29% 120 37 4.64 28% 125 38 4.79 27% 130 4.94 26% Using the table to determine the best mix for a dive to 65 fsw using a with a maximum PO2 of 1.5 finds the best mix is 50% Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

Nitrox Dive Tables

Nitrox Dive Tables In 1979, NOAA introduced diving procedures and dive tables for a standard nitrox mixture of 32% O2, 68% N2 (NN32) NOAA later introduced tables for 36% oxygen (NN36)

Nitrox Dive Tables NOAA Nitrox dive tables are the basis for many recreational nitrox dive tables The display of the tables may even be in the same format as the NOAA tables, but have been made more conservative by lowering maximum dive times for certain depths Additionally, the recommended safety stop depth for recreational tables may be slightly different, and the surface interval for a dive not to be considered repetitive may be increased from the NOAA standard of 12 hours to 24 hours

Nitrox Dive Tables NOAA Nitrox tables were calculated on the “equivalent air depth” (EAD) concept, which is simply to decompress from a non-air dive using air decompression tables that have the same nitrogen partial pressure (PN2)

Nitrox Dive Tables NOAA offers abbreviated and full versions of Nitrox 32 and 36 dive tables in Appendix VII of the NOAA Diving Manual The abbreviated version of these tables provide for only one level of required decompression The full version of these tables are in the same format as US Navy Dive Tables and include multiple levels of required decompression

Equivalent Air Depth (EAD)
Equivalent Air Depth is the depth based on the partial pressure of nitrogen in the gas being breathed, rather than the actual depth of the dive For mixes with less N2 than air, the EAD is shallower than if air is being used A diver is physically at a specific depth, but is physiologically absorbing N2 equivalent to a shallower depth

EAD decompression is based on the equivalent inert gas exposure, not the actual depth of the dive Once the EAD has been determined, a diver can use the “equivalent air depth” with any air diving table to compute a diving profile

Table 15.6 of the NOAA Diving Manual may be used to calculate EAD, or the calculation may be made by formula

Equivalent Air Depth Conversion Table (Fraction of Oxygen and Actual Depths) EAD (fsw) 28% 29% 30% 31% 32% 33% 34% 35% 36% 37% 38% 39% 40% 30 36 37 38 39 40 41 42 43 44 46 47 49 50 48 51 53 54 55 57 58 60 62 63 59 61 64 66 67 69 71 72 74 76 70 73 75 78 80 81 83 85 87 89 84 86 88 90 92 94 96 98 100 102 95 104 106 108 110 113 101 103 107 109 112 114 116 118 121 117 119 123 126 128 130 133 135 120 134 137 139 142 145 148 150 140 156 159 167 Numbers in grey boxes = exceptional exposure depth for mix Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

To use the EAD Conversion Table: Enter the table under the oxygen percentage and move down that column to the actual depth, or the NEXT GREATER DEPTH, of your dive Move to the left end of that row to find the EAD

Equivalent Air Depth (EAD) – The table shows that diving at 90 fsw while breathing 34% nitrox is equivalent, physiologically, to diving at 70 fsw on air EAD (fsw) 28% 29% 30% 31% 32% 33% 34% 35% 36% 30 36 37 38 39 40 41 42 43 44 47 48 49 50 51 53 54 55 57 58 59 61 62 63 64 66 67 69 60 70 72 73 75 76 78 80 81 83 84 86 88 90 92 94 95 96 98 100 102 104 106 101 103 107 109 112 114 116 118 Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

EAD Formula (fsw) This is a dive to 81 fsw using 37% oxygen EAN
The EAD computes to 57.9 and rounds to 58 A 60 fsw air schedule would be used

Dive Computers & Nitrox
There are two options for using dive computers with Nitrox Use a computer designed for use with nitrox Breath nitrox while diving an air based computer

Nitrox Dive Computers Allow for a variety of nitrox mixes to be used
Compute the decompression profile based on the O2 percentage programmed into the unit by the diver Provide pre-programmed MOD limits based on the mix and PO2 Track Oxygen and Nitrogen exposure and provide feedback to the diver Allow bottom times to be extended by adjusting the decompression profile to take advantage of the mix

Nitrox Dive Computers Because computers calculate and adjust no-stop dive times throughout dives (thereby lengthening no-stop dive times), multilevel dives (when divers move to progressively shallower depths during a dive) are best planned and carried out using dive computers rather than dive tables Bottom time will be extended

Air Computers with Nitrox
Builds in a theoretical safety margin by reducing the amount of nitrogen absorbed at a given depth However, the computer “thinks” the diver is breathing air It will not alert the diver if he/she descends deeper than the MOD of a given mix Divers using air computers to dive nitrox must be aware of both the MOD of the nitrox being dived and the maximum exposure time of the deepest part of the dive in order to maintain oxygen limits

Using NOAA Nitrox Tables
NOAA Nitrox dive tables follow the same basic rules for use as US Navy Dive Tables Familiarize yourself with the abbreviated and full versions of the tables in Appendix VII of the NOAA Diving Manual

Remember, divers have certain single and cumulative time limits for oxygen exposure Use the NOAA Oxygen Exposure Limits table (Table 15.2) to determine time limits for particular PO2s

(atm) Maximum Single Exposure (minutes) Maximum per 24 hr 1.60 45 150 1.55 83 165 1.50 120 180 1.45 135 1.40 1.35 195 1.30 210 1.25 225 1.20 240 1.10 270 1.00 300 0.90 360 0.80 450 0.70 570 0.60 720 For example, A single dive reaching a maximum PO2 of 1.6 ata must not exceed 45 minutes Divers may not exceed 150 minutes at 1.6 ata during any 24 hour period Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

These limits are dependent on the PO2 at the maximum depth of the dive O2 exposure level and time need to be monitored carefully If a single planned dive exceeds the O2 exposure limit, reduce the PO2 level by choosing a mix with a lower oxygen content, or shorten the dive time

When analyzed, nitrox mixes must fall within tolerance limits of ±1% in order to be within the tolerance and NOAA nitrox tables When using the EAD principle, calculation should be based on the exact mix in the cylinder

Notice: Chart 1 of the NN32 and NN36 tables have a PO2 column, as well as the standard table information you are use to seeing Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

Calculate a dive using EAN 32 to 100 ft for 23 minutes followed by a 1 hour surface interval (SIT) and a second dive to 60 ft for 30 minutes with the same mix What is your max PO2 during dive 1? Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

The maximum PO2 experienced during dive 1 was 1.3

NOAA NN32 and NN36 decompression tables provide an expedient method for determining decompression information However, by using the EAD principle, any nitrox dive can be planned using the EAD formula and US Navy Air Dive Tables

EAD Calculation Calculate a dive to 100 ft for 30 minutes using a 30% nitrox mix Your first step is to determine the EAD by using the formula:

EAD Calculation You would use US Navy or other air dive tables to compute a dive to 85 fsw for 30 minutes

EAD Calculation Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

Repetitive Diving Repetitive diving with NOAA nitrox diving tables for the same mix is no different from the procedures used for repetitive air diving The expanded version of the NN32 and NN36 dive tables allow for better dive planning of dives conducted shallower than 40 fsw (12 msw)

Repetitive Diving Repetitive dives involving different mixes can be calculated with relative ease Remember: the RNT must be obtained from the RNT table for the gas mix to be used on the repetitive dive, not the table from the previous dive

Repetitive Diving With Different Nitrox Mixes
Example: A diver making a dive using NN32 to 120 fsw for 25 minutes surfaces with a letter group of H. A SIT of 1:48 results in a new group of E. To make a second dive using NN36, the diver needs to enter Chart 3 of the NN36 Table as an “E diver” and use the information provided there to calculate the dive plan.

Repetitive Diving With Different Nitrox Mixes
36 Credit: Permission granted by Best Publishing Company (NOAA Diving Manual 4th Ed.) Flagstaff, AZ

Diving Table Procedure Review
Descent rate 75 fpm (25 mpm) Ascent rate 30 fpm (9 mpm) Safety-Stop 3-5 minutes at fsw (3-6 msw) Cold or strenuous dive use the next greater bottom time Repetitive dives less than 12 hours Flying after diving use the table Altitude diving Tables good to 1,000 ft (328 m) elevation only Omitted decompression stay on surface breathe 100% oxygen monitor for DCS plan to evacuate to recompression chamber

Other Rules 10 minute minimum between dives
Bottom Time - time you enter the water until you leave the bottom for a direct assent (exception if delayed) Required Decompression stops are taken at specified depth and measured at diver’s mouth Make dives progressively shallower whenever possible

Out of Gas Emergencies

Out of Gas Emergencies Dives Within No-Decompression Limits:
A nitrox diver who has not exceeded the dive’s no-stop time can breath air or any nitrox mix for immediate ascent Likewise an out of gas air diver can breath an O2 rich mix

Out of Gas Emergencies Shifting to Air During a Decompression Dive:
A nitrox diver required to switch to air during a decompression stop can complete the deco schedule without adjustment This is because the deco stops in NOAA Nitrox Tables are based on US Navy Air Decompression Tables and assumes the diver is breathing air

Gas Preparation and Handling

Oxygen Handling Oxygen Fire is a rapid chemical reaction
Supports life Supports combustion Fire is a rapid chemical reaction Virtually everything will burn in oxygen Fire triangle: Fuel Ignition All 3 must be present to have fire Fuel Ignition Oxygen

Air to be Mixed with Oxygen
Some methods of preparing nitrox involve air being mixed with oxygen. It is extremely important that the air be clean and free of oil mist and particulate matter. Hydrocarbons and petroleum-based products ignite very easily in an oxygen-rich environment. The condensable hydrocarbon level of 0.1 mm/m3 is acceptable.

“NOAA & AAUS Standards for Oxygen Service”
Gas mixtures with oxygen content up to 40% can be handled as if the mix were air NOAA has used the “40% rule” on scuba equipment and gas distribution systems since the introduction of nitrox without any problems

“The 40% Rule” Any equipment used for 100% oxygen or an oxygen level above 40% at high pressure (above 200 psi) must be oxygen compatible, use oxygen compatible lubricants (NOT silicone lubricant), and be formally cleaned for oxygen service This includes cylinders and valves, first stage regulators, and high pressure hoses

Oxygen Cleaning There are two levels of oxygen cleaning:
Formal Oxygen Cleaning Informal Oxygen Cleaning

Formal Oxygen Cleaning
Formal oxygen cleaning requires strict procedures to be followed by trained technicians, and all steps must be documented in detail

Informal Oxygen Cleaning
Informal oxygen cleaning is intended to clean equipment as clean as formal oxygen cleaning, but without the certification and documentation It involves the cleaning of any visible debris and lubricants – then scrubbing and/or ultrasonic cleaning with a strong detergent in hot water, and rinsing thoroughly in clean hot water Oxygen-compatible lubricants are then used where necessary

Once Oxygen Cleaned Once cleaned, the equipment should be dedicated for use only with nitrox mixtures and not used with air from an oil-lubricated compressor without proper hyper-filtration

Equipment Cleaning List
Must be cleaned for enriched air service* Cylinder valves Scuba cylinders Recommended to be cleaned Regulator first stage Regulator second stage High pressure hoses Submersible pressure gauges Not necessary Buoyancy compensators Low pressure inflator Dry suit inflator *If used with >40%, or if mix is prepared using partial pressure blending technique

Identifying Nitrox Cylinders
4 inch green band on yellow tank NITROX or Enriched Air stenciled in 2 inch high letters Non-yellow cylinders have an additional 1 inch yellow band above and below the green

Other Identification Labels
Cylinder Oxygen Service Label designates cleanliness for O2 service new label required annually or if contaminated Visual Inspection annually or sooner

Other Identification Labels
Cylinder Contents identifies contents

Routine Care and Maintenance
Wash gear in fresh water Protect from dirt and grease Periodic service by trained technician annual for normal use more often if heavy use Maintain warranties Don’t contaminate with ordinary scuba air

Obtaining Nitrox Mixtures

Commercial Premix Purchasing premixed gas from a commercial supplier is the simplest method for obtaining gas Expensive – must both purchase gas and rent gas containers from supplier

Preparing Enriched Air Nitrox
Partial Pressure Mixing requires ultra clean air & O2 clean valves and cylinders A measured pressure of 100% O2 is trans-filled into a scuba cylinder then topped with air This requires training that is beyond the scope of this module

Continuous Flow Mixing Requires an “oil free” compressor Oxygen is metered into the air before being drawn into a compressor The 40% rule applies Gas is analyzed before entering the compressor and monitored during the filling operation

Pressure Swing Absorption Uses a “molecular sieve” to adsorb nitrogen This system does not require high pressure oxygen, but is somewhat complicated and moderately expensive to acquire and maintain

Membrane Separation Works by forcing clean low-pressure air through a membrane that allows oxygen to pass more readily than nitrogen The output gas, which is richer in oxygen than air, is then passed through a high pressure compressor to fill a cylinder or bank The O2 level of the mix can be controlled by varying the input flow rate

Performing Gas Analysis

Oxygen Analyzers Oxygen analyzers can use Digital or Analog display
Ideally they should have a resolution accuracy of 0.1% (one-tenth of one percent)

Oxygen Analyzers The heart of an oxygen analyzer is its detection method There are two primary types Paramagnetic and Electrochemical Paramagnetic analyzers are primarily used in research labs They are accurate, stable, relatively expensive, somewhat delicate, and intolerant of vibration

Oxygen Analyzers Electrochemical analyzers, the most common type, are relatively inexpensive, can be portable, are rugged, and show little interference from other gases They may need frequent calibration, especially as the O2 sensor cell begins to age The O2 sensor cell has a life span from 6 to 18 months, dependent on manufacturer and use

Analyzing Gas Each diver must analyze their own nitrox cylinders and insure the gas they will breath is acceptable for the planned dive

Analyzing Gas The process of analyzing a cylinder of gas involves calibrating the analyzer with a known gas such as air Both the calibrating gas and the unknown gas should be passed through the analyzer at the same flow rate

Analyzing Gas Ideally the flow rate should be around one liter per minute – but should be between one-half and two liters per minute When using air as the known gas, calibrate the analyzer to a reading of 20.9%

Analyzing Gas After calibration, analyze the unknown mix at the same flow rate (about 1 liter/minute) Analyze the mix until the readout on the analyzer becomes stable

Analyzing Gas Acceptable Analysis Range:
It is generally accepted that a mix within ±1% of the desired mix is acceptable for most nitrox tables

Analyzing Gas Once analyzed, the contents of cylinder must be recorded on a cylinder contents label and placed on the analyzed cylinder This label contains the percentage of O2 in the mix, the date, the MOD, and the initials of the diver analyzing the mix

Fill Station Log In addition to a contents label, the analysis of a cylinder is to be recorded on a Fill Station Log by the diver who analyzed the gas At a minimum, this log includes: The cylinder ID number, the analysis by the person mixing the gas (O2% & initials), the analysis by the diver diving the gas (O2%), the psi in the cylinder, the MOD, the date of analysis, and the signature of diver performing the analysis

Study Questions Use the following study questions to review some of the information presented in this self study module When you are finished you can print out your study questions results

Self Study Questions A diver wishes to plan two nitrox dives using EAN36 and NN36 tables. The first dive will be to a depth of 100ft for 20 minutes. Following a one hour surface interval, how long may the diver stay at 60ft on the second dive? 29 minutes 71 minutes 100 minutes 62 minutes

Self Study Questions A dive team plans a dive to a maximum depth of 70ft using EAN32 with NN32 tables and a PO2 of What is the maximum depth the divers should descend on the dive? 132' 65' 130' 70'

Self Study Questions What is the absolute pressure (ata) at 75 fsw?

Self Study Questions A dive team wants to make a dive using NN32 and a PO2 of 1.6, what is the MOD for the mix? 130' 132' 110' 190'

Self Study Questions The maximum oxygen partial pressure exposure for scientific diving is ___, and you may want to further limit your exposure. 1.3 1.4 1.5 1.6 1.8

Self Study Questions The maximum oxygen partial pressure exposure for recreational diving is ___. 1.3 1.4 1.5 1.6 1.8

Self Study Questions According to the NOAA Oxygen Exposure Limits Table 15.2 (page 15-5 of the NOAA Diving Manual), the maximum single dive exposure time for a PO2 exposure of 1.2 is ___ minutes. 45 150 210 240

Self Study Questions Calculate the maximum operating depth (MOD) for a 33% nitrox mix using a PO2 exposure at depth of 1.6. 127 fsw 31.4 fsw 60 fsw 99 fsw

Self Study Questions Calculate the MOD of a 50% nitrox mix using a PO2 exposure at depth of 1.5. 50 fsw 66 fsw 75 fsw 82 fsw

Self Study Questions Calculate the maximum operating depth (MOD) for a 21% nitrox mix using a PO2 exposure at depth of 1.6. 130 fsw 203 fsw 187 fsw 218 fsw

Self Study Questions Calculate the partial pressure of O2 (PO2) for air being breathed at 90 fsw. .78 .21 .57 1.6

Self Study Questions Calculate the partial pressure of Nitrogen (PN2) for air being breathed at 90 fsw. 2.9 1.6 .78 2.1

Self Study Questions Calculate the partial pressure of O2 (PO2) for a 36% nitrox mix being breathed at 130 fsw. As a scientific diver, would you want to make this dive? 1.6 / Yes 1.78 / Yes 1.6 / No 1.78 / No

Self Study Questions You need to maximize your no-stop dive time for a dive to 60 fsw. Calculate the best nitrox mix for this dive using a maximum PO2 exposure at depth of 1.6. 40% 57% 32% 36%

Self Study Questions You need to maximize your no-stop dive time for a dive to 140 fsw. Calculate the best nitrox mix for this dive using a maximum PO2 exposure at depth of 1.5. 21% 29% 32% 35%

Self Study Questions The _______ is the depth based on the partial pressure of nitrogen in the gas mixture to be breathed, rather than the actual depth of the dive. This was the concept used to develop NOAA nitrox dive tables. residual nitrogen time (RNT) equivalent nitrox depth (END) maximum operating depth (MOD) equivalent air depth (EAD)

Self Study Questions You are using an air based dive computer to compute your decompression profile. You are breathing a 36% nitrox mix and your maximum PO2 exposure limit at depth is 1.6. The bottom is 130 fsw. Your dive plan calls for a dive to 110 fsw for 30 minutes. Which of the following is a major concern? Your risk of decompression sickness is lower because you are using a nitrox based dive computer and breathing air. Your air based dive computer thinks you are breathing air, air based computers do not have any MOD alarms in place, and the maximum possible depth of the dive exceeds the MOD for the mix you will be breathing. Your planned dive time will exceed the single dive oxygen exposure limit for a PO2 of 1.6. Your risk of decompression sickness is higher because you are using an air based dive computer and breathing nitrox.

Self Study Questions Use NOAA NN32 dive tables to calculate a dive to 75 fsw for 35 minutes followed by a 1:30 SIT and a second dive to 75 fsw for 20 minutes. What is the ESDT of the second dive and the ending letter group? 20 minutes, E 24 minutes, F 50 minutes, H 46 minutes, J

Self Study Questions What is the EAD (Equivalent Air Depth) of a dive with an actual depth of 100 fsw where the diver is breathing 36% nitrox? 65 fsw 70 fsw 75 fsw 80 fsw

Self Study Questions The _______ method of blending nitrox requires ultra clean air, O2 clean valves and cylinders. 100% O2 is trans-filled into a scuba cylinder then topped with air. Membrane Separation Pressure Swing Adsorption Continue Flow Mixing Partial-Pressure Mixing

Self Study Questions In the ______ method of blending nitrox, oxygen is metered into the air being drawn into a compressor. This requires an "oil free" compressor and the 40% rule applies. Membrane Separation Pressure Swing Adsorption Continuous Flow Mixing Partial-Pressure Mixing

Self Study Questions The _______ method of blending nitrox works by forcing clean low-pressure air through a membrane that allows oxygen to pass more readily than nitrogen. Membrane Separation Pressure Swing Adsorption Continuous Flow Mixing Partial-Pressure Mixing

Self Study Questions Ideally, oxygen analyzers should have a resolution accuracy of ________. 0.01% (one-hundreth of one percent) 0.1% (one-tenth of one percent) 1% (one percent) 10% (ten percent)

Self Study Questions The heart of an oxygen analyzer is its detection method. There are two primary types Paramagnetic and Electrochemical. _________ analyzers are relatively inexpensive, can be portable, are rugged, and show little interference from other gases. They may need frequent calibration, especially as the O2 sensor cell begins to age. Paramagnetic Electrochemical

Self Study Questions Once analyzed, the contents of cylinder must be recorded on a cylinder contents label, and this label is to be placed on the analyzed cylinder. This label contains _________. (select all that apply) the percentage of O2 in the mix the date the MOD the initials of the diver analyzing the mix

Self Study Questions Nitrox is safer than air. True False

Self Study Questions Nitrox has very stringent depth limits because of the higher concentration of O2 in the mixture. (Nitrox has very stringent depth limits because of the higher concentration of O2 in the mixture.) True False

Self Study Questions Nitrox provides the greatest advantages for no-stop diving in the fsw depth range. True False

Self Study Questions Nitrox reduces narcosis. Yes No Not Really

Self Study Questions Nitrox makes treatment for DCS impossible. True
False

Nitrox Diving.

Similar presentations

Presentation on theme: "Nitrox Diving."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Nitrox Diving.

Similar presentations

Presentation on theme: "Nitrox Diving."— Presentation transcript:

Similar presentations

About project

Feedback