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Maximum Operating Depth (MOD) Calculator

Disclaimer: I take no responsibility for the accuracy of the calculations and data below. Always verify against other sources.

This calculator can be used to find the maximum operating depth (MOD) in metres and feet at the provided partial pressure of oxygen (ppO2) in bar with various fractions of oxygen (FO2%). Just enter values for "Fraction of Oxygen (FO2)" and "Partial Pressure Oxygen (ppO2)" and click on the "Submit" button.

MOD Calculator
* Indicates required field

e.g. 1=100%, 0.21=21% etc.

e.g. 1.2 to 1.6 bar

Diving a Fraction of Oxygen (FO2) of .32 or 32%
at a Partial Pressure Oxygen (ppO2) of 1.4 bar
your Maximum Operating Depth (MOD) rounding shallower is:

33.7 metres

in imperial units:

111 feet


Disclaimer:
This calculator provides information about gas use in scuba diving. UNDER NO CIRCUMSTANCES is there any implication that any gas mixture is safe or even life supporting at any depth. If you have not recived training in technical scuba diving, Nitrox, Trimix or Heliox you should not attempt to use any of these results. Improper use of gasses in diving can result in injury or DEATH.


MOD Table (metric)

The table below show the maximum operating depth (MOD) in metres at typical values for the partial pressure of oxygen (ppO2) in bar with various percentages of oxygen (O2%).

Maximum Operating Depth (metres)
FO2 / O2% Maximum ppO2 (bar)
1.6 1.5 1.4 1.3 1.2
0.1 / 10% 150.0 140.0 129.9 119.9 109.9
0.11 / 11% 135.4 126.3 117.2 108.1 99.0
0.12 / 12% 123.3 115.0 106.6 98.3 89.9
0.13 / 13% 113.0 105.3 97.6 89.9 82.3
0.14 / 14% 104.2 97.1 89.9 82.8 75.7
0.15 / 15% 96.6 90.0 83.3 76.6 69.9
0.16 / 16% 90.0 83.7 77.5 71.2 64.9
0.17 / 17% 84.1 78.2 72.3 66.4 60.5
0.18 / 18% 78.8 73.3 67.7 62.2 56.6
0.19 / 19% 74.2 68.9 63.6 58.4 53.1
0.2 / 20% 70.0 65.0 59.9 54.9 49.9
0.21 / 21% 66.1 61.4 56.6 51.9 47.1
0.22 / 22% 62.7 58.1 53.6 49.0 44.5
0.23 / 23% 59.5 55.2 50.8 46.5 42.1
0.24 / 24% 56.6 52.5 48.3 44.1 39.9
0.25 / 25% 54.0 50.0 46.0 41.9 37.9
0.26 / 26% 51.5 47.6 43.8 39.9 36.1
0.27 / 27% 49.2 45.5 41.8 38.1 34.4
0.28 / 28% 47.1 43.5 39.9 36.4 32.8
0.29 / 29% 45.1 41.7 38.2 34.8 31.3
0.3 / 30% 43.3 40.0 36.6 33.3 29.9
0.31 / 31% 41.6 38.3 35.1 31.9 28.7
0.32 / 32% 40.0 36.8 33.7 30.6 27.4
0.33 / 33% 38.4 35.4 32.4 29.3 26.3
0.34 / 34% 37.0 34.1 31.1 28.2 25.2
0.35 / 35% 35.7 32.8 30.0 27.1 24.2
0.36 / 36% 34.4 31.6 28.8 26.1 23.3
0.37 / 37% 33.2 30.5 27.8 25.1 22.4
0.38 / 38% 32.1 29.4 26.8 24.2 21.5
0.39 / 39% 31.0 28.4 25.8 23.3 20.7
0.4 / 40% 30.0 27.5 24.9 22.4 19.9
0.41 / 41% 29.0 26.5 24.1 21.7 19.2
0.42 / 42% 28.0 25.7 23.3 20.9 18.5
0.43 / 43% 27.2 24.8 22.5 20.2 17.9
0.44 / 44% 26.3 24.0 21.8 19.5 17.2
0.45 / 45% 25.5 23.3 21.1 18.8 16.6
0.46 / 46% 24.7 22.6 20.4 18.2 16.0
0.47 / 47% 24.0 21.9 19.7 17.6 15.5
0.48 / 48% 23.3 21.2 19.1 17.0 14.9
0.49 / 49% 22.6 20.6 18.5 16.5 14.4
0.5 / 50% 22.0 20.0 18.0 15.9 13.9
0.51 / 51% 21.3 19.4 17.4 15.4 13.5
0.52 / 52% 20.7 18.8 16.9 14.9 13.0
0.53 / 53% 20.1 18.3 16.4 14.5 12.6
0.54 / 54% 19.6 17.7 15.9 14.0 12.2
0.55 / 55% 19.0 17.2 15.4 13.6 11.8
0.56 / 56% 18.5 16.7 14.9 13.2 11.4
0.57 / 57% 18.0 16.3 14.5 12.8 11.0
0.58 / 58% 17.5 15.8 14.1 12.4 10.6
0.59 / 59% 17.1 15.4 13.7 12.0 10.3
0.6 / 60% 16.6 15.0 13.3 11.6 9.9
0.61 / 61% 16.2 14.5 12.9 11.3 9.6
0.62 / 62% 15.8 14.1 12.5 10.9 9.3
0.63 / 63% 15.3 13.8 12.2 10.6 9.0
0.64 / 64% 15.0 13.4 11.8 10.3 8.7
0.65 / 65% 14.6 13.0 11.5 9.9 8.4
0.66 / 66% 14.2 12.7 11.2 9.6 8.1
0.67 / 67% 13.8 12.3 10.8 9.4 7.9
0.68 / 68% 13.5 12.0 10.5 9.1 7.6
0.69 / 69% 13.1 11.7 10.2 8.8 7.3
0.7 / 70% 12.8 11.4 10.0 8.5 7.1
0.71 / 71% 12.5 11.1 9.7 8.3 6.9
0.72 / 72% 12.2 10.8 9.4 8.0 6.6
0.73 / 73% 11.9 10.5 9.1 7.8 6.4
0.74 / 74% 11.6 10.2 8.9 7.5 6.2
0.75 / 75% 11.3 10.0 8.6 7.3 5.9
0.76 / 76% 11.0 9.7 8.4 7.1 5.7
0.77 / 77% 10.7 9.4 8.1 6.8 5.5
0.78 / 78% 10.5 9.2 7.9 6.6 5.3
0.79 / 79% 10.2 8.9 7.7 6.4 5.1
0.8 / 80% 10.0 8.7 7.4 6.2 4.9
0.81 / 81% 9.7 8.5 7.2 6.0 4.8
0.82 / 82% 9.5 8.2 7.0 5.8 4.6
0.83 / 83% 9.2 8.0 6.8 5.6 4.4
0.84 / 84% 9.0 7.8 6.6 5.4 4.2
0.85 / 85% 8.8 7.6 6.4 5.2 4.1
0.86 / 86% 8.6 7.4 6.2 5.1 3.9
0.87 / 87% 8.3 7.2 6.0 4.9 3.7
0.88 / 88% 8.1 7.0 5.9 4.7 3.6
0.89 / 89% 7.9 6.8 5.7 4.6 3.4
0.9 / 90% 7.7 6.6 5.5 4.4 3.3
0.91 / 91% 7.5 6.4 5.3 4.2 3.1
0.92 / 92% 7.3 6.3 5.2 4.1 3.0
0.93 / 93% 7.2 6.1 5.0 3.9 2.9
0.94 / 94% 7.0 5.9 4.8 3.8 2.7
0.95 / 95% 6.8 5.7 4.7 3.6 2.6
0.96 / 96% 6.6 5.6 4.5 3.5 2.4
0.97 / 97% 6.4 5.4 4.4 3.4 2.3
0.98 / 98% 6.3 5.3 4.2 3.2 2.2
0.99 / 99% 6.1 5.1 4.1 3.1 2.1
1 / 100% 6.0 5.0 3.9 2.9 1.9

Note that 21% is the normal air. The O2% values more commonly used in technical diving are highlighted. All MOD values are rounded shallower.
 


Disclaimer:
This table provides information about gas use in scuba diving. UNDER NO CIRCUMSTANCES is there any implication that any gas mixture is safe or even life supporting at any depth. If you have not recived training in technical scuba diving, Nitrox, Trimix or Heliox you should not attempt to use any of these values. Improper use of gasses in diving can result in injury or DEATH.


Explanation

In technical diving, the maximum operating depth (MOD) of a breathing gas is the depth at which the partial pressure of oxygen (ppO2) of the gas mix exceeds a safe limit. The safe limits prescribed for ppO2 vary across diver training agencies, the level of underwater exertion planned and the planned duration of the dive. Typically we use 1.4 bar for back or working gas, and 1.6 bar during decompression stops when we don't swim around or exert ourselves.

The MOD is significant when planning dives using enriched air nitrox (EAN) and mixed gases like trimix (i.e. helium, nitrogen, oxygen) because the proportion of oxygen in the mix determines the maximum safe depth for breathing that gas. There is a risk of oxygen toxicity if the MOD is exceeded.


Formulas

To calculate the maximum operating depth (MOD) for a specific ppO2 and percentage of oxygen, the following formulas are used:

Metric - metres

MOD formula metric

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 32% oxygen and the maximum ppO2 is 1.4 bar, the MOD (m) is 10 metres x [(1.4 / 0.32) - 1] = 33.7 metres.

Imperial - feet

MOD formula imperial

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 32% oxygen and the maximum ppO2 is 1.4 bar, the MOD (feet) is 33 feet x [(1.4 / 0.32) - 1] = 111 feet.

Note:
The formulas above simply divide the total partial pressure of PURE oxygen (ppO2) which can be tolerated (expressed in bar or atmospheres) by the fraction of oxygen (FO2) in the gas, to calculate to total atmospheres pressure this mix can be breathed at (obviously 50% oxygen 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: 33 feet of salt water (fsw) or 10 meters of salt water (msw).

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Last modified: Friday, 18 February 2011

 


 
 
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