### What Is a Maximum Operating Depth?:

### Why Should a Diver Calculate a Maximum Operating Depth?:

### In What Situations Must a Diver Calculate a Maximum Operating Depth?:

### How to Calculate a Maximum Operating Depth:

1. Determine the percentage of oxygen in the your scuba tank.

If you are diving on air, the percentage of oxygen in your tank is 0.21. If you are using enriched air nitrox or trimix, use an oxygen analyzer to determine the percentage of oxygen in your scuba tank.2. Choose a maximum partial pressure of oxygen for your dive.

Most scuba training organizations recommend that divers limit the concentration of oxygen (called the partial pressure of oxygen) to 1.4 ata. However, a diver may lower or raise this number depending upon the type of diving and the purpose of the breathing gas. In technical diving, for example, pure oxygen is frequently used at partial pressures higher than 1.4 ata for decompression stops.3. Calculate your maximum operating depth using this formula:{(maximum partial pressure of oxygen / percentage of oxygen in tank) - 1} x 33 ftExample:Calculate the MOD for a diver breathing 32% oxygen who plans to dive to a maximum oxygen partial pressure of 1.4 ata.Step one: substitute the appropriate numbers into the formula.

{(1.4 ata / .32 ata)- 1 } x 33 feetStep two: do the simple arithmetic.{ 4.38 - 1 }x 33 feet3.38 x 33 feet111.5 feetIn this case, round the 0.5 decimal down, not up, to be conservative.111 feet is the MOD

### Cheat Sheet of Maximum Operating Depths for Common Breathing Gasses:

**Air**. . . . . . . . . . . 21% Oxygen . . . .

**MOD 187 feet**

**Nitrox 32**. . . . . . 32% Oxygen . . . .

**MOD 111 feet**

**Nitrox 36**. . . . . . 36% Oxygen . . . .

**MOD 95 feet**

**Pure Oxygen**. . . 100% Oxygen . . .

**MOD 13 feet**

### Putting a Maximum Operating Depth into Use:

While understanding how to calculate a MOD is great, a diver must also make sure that he stays above his depth limit during a dive. One good way for a diver to ensure that he does not exceed his MOD is to use a dive computer that can be programmed for nitrox or mixed gases. A computer can be programmed to beep or otherwise notify the diver if he exceeds his MOD or partial pressure limits.

In addition, a diver using enriched air or other mixed gas should also label his tank with the MOD of the gas inside. If the diver accidentally exceeds the MOD written on his tank, his buddy may notice the written MOD and alert him. Writing the MOD on the tank, along with other information about the gas the tank contains, also helps to prevent a diver from mistaking the tank for one filled with air.

Now you can calculate a maximum operating depth for a breathing gas containing any percentage of oxygen. Safe diving!

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