What is the maximum operating depth


Scuba diving is one of the most stimulating outdoor activities. It not only helps tone muscles but also aids in breathing. This is a comprehensive physical fitness alternative that also helps improve mind and body coordination. Like with all water sports, it is important to appreciate the importance of safety in scuba diving. One of the most important considerations has to be Nitrox Maximum Operating Depth (MOD). If you are a scuba diver using air, it is important to understand what MOD entails in order to avoid accidents when diving.

Why Should a Diver Calculate a Maximum Operating Depth?

Breathing high concentrations of oxygen can cause oxygen toxicity, which is usually fatal when diving. The concentration (or partial pressure) of oxygen in a diver’s breathing gas increases with depth. The higher the percentage of oxygen, the shallower the depth at which it becomes toxic. Divers calculate a MOD to be sure that they do not descend beyond the depth at which the oxygen in their tank may become toxic.

Despite oxygen being an all-important gas for us human beings, breathing in extremely high concentrations of it can be rather fatal for divers. This is because doing so will result in oxygen toxicity. There are two types of oxygen toxicity: Pulmonary oxygen toxicity and central nervous system (CNS) toxicity.

Pulmonary oxygen toxicity is caused by exposure to elevated partial pressures of oxygen for long periods of time resulting in a burning sensation in the trachea, coughing, shortness of breath, and eventually lung failure. On the other hand, CNS toxicity is caused by exposure to oxygen partial pressures greater than 1.6 ATA and can result in convulsions, pulmonary barotrauma, or even death. In any case, you’ll want to make sure that you don’t expose yourself to any of these types of oxygen toxicity.




Should I Calculate My Mod on Every Dive?

A diver should calculate the MOD for his dive whenever he uses enriched air nitrox, trimix or pure oxygen. Technical divers who engage in deep air diving must also calculate MODs. A scuba diver who breathes air and who remains within recreational dive limits need not calculate a MOD for his dive. In fact, on most recreational dives the maximum depth will be limited by factors such as the no-decompression limit, narcosis, and the experience level of the diver instead of the MOD.

How is MOD calculated? Start by calculating the percentage of oxygen in your tank. Once this is done, determine the maximum partial pressure of oxygen with the recommended limit being 1.4 ata. The formula for MOD is:

                  {(maximum partial pressure of oxygen / percentage of oxygen in tank) – 1} x 33 ft

The formula is simple but while you know your MOD, it is also important to consciously stay above your depth limit. Luckily, you can now use a dive computer to alert you in case you exceed your MOD or oxygen partial pressure limit levels. Alternatively, you should clearly write the MOD of the gas in tank so that other divers can alert you in case you exceed MOD. Go ahead and calculate MOD for your next dive and make sure you stay above the depth limit.

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 gasses. Most computers are 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 gasses should 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.

On today’s dive boats, you’d be hard-pressed not to see one or two of the telltale green and yellow tanks that announce the presence of nitrox, or oxygen-enriched air, which has been used in recreational diving for decades. Every major training agency has a nitrox training program in one form or another. We’ll explore what nitrox is, what the risks are and what its practical uses are for the everyday diver.

But what is nitrox?

In recreational diving terms, enriched air nitrox (EAN) refers to any nitrogen/oxygen gas mixture with an oxygen concentration higher than the 21 percent found in normal air–32 percent oxygen is the most common–and tanks filled with EAN are often clearly marked with a nitrox tank band and have the mix percentage written somewhere near the tank valve. It is this higher percentage of oxygen, and the proportionately lower percentage of nitrogen, that allows divers to lengthen no-decompression limits, shorten surface intervals and get an added safety buffer for decompression sickness in certain diving circumstances.

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Knowing your scuba MOD is crucial to ensure that you have a safe diving adventure. As can be seen above, calculating your maximum operating depth isn’t really that difficult. Sure there are MOD cheat sheets available online that you can use, but knowing how to do it and doing the calculations yourself makes you much more confident about the resulting number. And if you’re having doubts about your calculations, check in with your diving buddy or diving instructor for confirmation. After all, it’s better to be safe than to be sorry.

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