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Maximum operating depth
 
 
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In technical diving
Technical diving

Technical diving is a form of scuba diving that exceeds the scope of recreational diving . Technical divers require advanced training, extensive experience, specialized equipment and often breathe breathing gases other than air or standard nitrox....
, the maximum operating depth (MOD) of a breathing gas
Breathing gas

Air is the most common and only natural breathing gas. Other artificial gases, either pure gases or mixtures of gases, are used in breathing equipment and enclosed habitats such as Scuba set, surface supplied diving equipment, recompression chambers, submarines, space suits, spacecraft and anaesthetic machines....
 is the depth at which the partial pressure
Partial pressure

In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
 of oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
 (ppO2) of the gas mix exceeds a safe limit. This safe limit varies depending on the diver training
Diver training

Diver training is the process of developing skills and building experience in the use of diving equipment and techniques so that the diver is able to diving activities safely and have fun....
 agency, the level of underwater exertion planned and the planned duration of the dive, but is normally in the range of 1.2 to 1.6 bar
Bar (unit)

The bar , decibar and the millibar are units of pressure. They are not SI units, nor are they cgs units, but they are accepted for use with the SI....
.

The MOD is significant when planning dives using gases such as nitrox and trimix
Trimix

Trimix is a breathing gas, consisting of oxygen, helium and nitrogen, and is often used in deep commercial diving and during the deep phase of dives carried out using technical diving techniques....
 because the proportion of oxygen in the mix determines the maximum safe depth for breathing that gas.






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In technical diving
Technical diving

Technical diving is a form of scuba diving that exceeds the scope of recreational diving . Technical divers require advanced training, extensive experience, specialized equipment and often breathe breathing gases other than air or standard nitrox....
, the maximum operating depth (MOD) of a breathing gas
Breathing gas

Air is the most common and only natural breathing gas. Other artificial gases, either pure gases or mixtures of gases, are used in breathing equipment and enclosed habitats such as Scuba set, surface supplied diving equipment, recompression chambers, submarines, space suits, spacecraft and anaesthetic machines....
 is the depth at which the partial pressure
Partial pressure

In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
 of oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
 (ppO2) of the gas mix exceeds a safe limit. This safe limit varies depending on the diver training
Diver training

Diver training is the process of developing skills and building experience in the use of diving equipment and techniques so that the diver is able to diving activities safely and have fun....
 agency, the level of underwater exertion planned and the planned duration of the dive, but is normally in the range of 1.2 to 1.6 bar
Bar (unit)

The bar , decibar and the millibar are units of pressure. They are not SI units, nor are they cgs units, but they are accepted for use with the SI....
.

The MOD is significant when planning dives using gases such as nitrox and trimix
Trimix

Trimix is a breathing gas, consisting of oxygen, helium and nitrogen, and is often used in deep commercial diving and during the deep phase of dives carried out using technical diving techniques....
 because the proportion of oxygen in the mix determines the maximum safe depth for breathing that gas. There is a risk of oxygen toxicity
Oxygen toxicity

Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen at elevated partial pressures. It is also known as oxygen toxicity syndrome, oxygen intoxication, hyperoxia, or the Paul Bert effect and Lorrain Smith effect, after the researchers who pioneered its discovery and desc...
 if the MOD is exceeded. The tables below show MODs for a selection of oxygen mixes. Note that 21% is the normal air.

Safe limit of partial pressure of oxygen


The maximum single exposure limits recommended in the NOAA Diving Manual are 45 minutes at 1.6 bar
Bar (unit)

The bar , decibar and the millibar are units of pressure. They are not SI units, nor are they cgs units, but they are accepted for use with the SI....
, 120 minutes at 1.5 bar, 150 minutes at 1.4 bar, 180 minutes at 1.3 bar and 210 minutes at 1.2 bar.

Formulas

To calculate the MOD for a specific ppO2 and percentage of oxygen, the following formulas are used:

In feet


In which ppO2 is the desired partial pressure in oxygen and the FO2 is the decimal value of the fraction of oxygen in the mixture. For example, if a gas contains 36% oxygen and the maximum ppO2 is 1.4 bar, the MOD (fsw) is x [(1.4 / 0.36) - 1] = .

Note that the formula simply divides the total partial pressure of PURE oxygen which can be tolerated (expressed in bar or atmospheres) by the fraction of oxygen in the nitrox, to calculate to total atmospheres pressure this mix can be breathed at (obviously 50% nitrox can be breathed at twice the pressure of 100% oxygen, so divide by 0.5, etc.). Of this total pressure which can be tolerated by the diver, 1 atmosphere is due to the earth's air, and the rest is due to depth in water. So the 1 atm for the air is subtracted out, to give the rest of the pressure added by water (in atmospheres). The remaining part in each formula merely converts pressure in atm produced by depth in water, to the depth. It does this by multiplying by the appropriate amount of depth to produce an atmosphere of pressure: of salt water (fsw) or 10 meters of salt water.

In metres


In which ppO2 is the desired partial pressure in oxygen and the FO2 is the decimal value of the fraction of oxygen in the mixture. For example, if a gas contains 36% oxygen and the maximum ppO2 is 1.4 bar, the MOD (m) is 10 metres x [(1.4 / 0.36) - 1] = 28.9 metres.

MOD table in feet


Maximum Operating Depth (MOD) in feet of sea water for ppO2 1.2 to 1.6
MOD (fsw)% oxygen
3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 50 55 60 65 70 75 80 85 90 100
Maximum ppO2 (bar) 1.6 1727 847 553 407 319 260 218 187 162 143 127 113 102 92 84 72 63 54 48 42 37 33 29 25 19
1.5 1617 792 517 379 297 242 202 173 150 132 117 104 93 84 77 66 57 49 43 37 33 28 25 22 16
1.4 1507 737 480 352 275 223 187 159 138 121 107 95 85 77 69 59 51 44 38 33 28 24 21 18 13
1.3 1397 682 443 324 253 205 171 145 125 110 97 86 77 69 62 52 45 38 33 28 24 20 17 14 9
1.2 1287 627 407 297 231 187 155 132 113 99 87 77 68 61 55 46 39 33 27 23 19 16 13 11 6


These depths are rounded down to the nearest foot.

MOD table in metres

Maximum Operating Depth (MOD) in metres of sea water for ppO2 1.2 to 1.6
MOD (msw)% oxygen
3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 50 55 60 65 70 75 80 85 90 100
Maximum ppO2 (bar) 1.6 523.3 256.7 167.8 123.3 96.7 78.9 66.2 56.7 49.3 43.3 38.5 34.4 31.0 28.1 25.6 22.0 19.1 16.7 14.6 12.9 11.3 10.0 8.8 7.8 6.0
1.5 490.0 240.0 156.7 115.0 90.0 73.3 61.4 52.5 45.6 40.0 35.5 31.7 28.5 25.7 23.3 20.0 17.3 15.0 13.1 11.4 10.0 8.8 7.6 6.7 5.0
1.4 456.7 223.3 145.6 106.7 83.3 67.8 56.7 48.3 41.9 36.7 32.4 28.9 25.9 23.3 21.1 18.0 15.5 13.3 11.5 10.0 8.7 7.5 6.5 5.6 4.0
1.3 423.3 206.7 134.4 98.3 76.7 62.2 51.9 44.2 38.1 33.3 29.4 26.1 23.3 21.0 18.9 16.0 13.6 11.7 10.0 8.6 7.3 6.3 5.3 4.4 3.0
1.2 390.0 190.0 123.3 90.0 70.0 56.7 47.1 40.0 34.4 30.0 26.4 23.3 20.8 18.6 16.7 14.0 11.8 10.0 8.5 7.1 6.0 5.0 4.1 3.3 2.0