Nitrox: Selecting Your Best Mix

Nitrox has come a long way over the years; from being a forbidden gas to the most commonly used breathing gas by divers. Despite the number of divers using nitrox, there are still some misconceptions about how nitrox can best benefit you during your dives and what the best mix is for your dive. In this article we are going to focus on the best mix, which will also address some of the benefits.

Environmental Conditions for Nitrox

Before we get to the formulas for how to figure out this best mix, we should talk about some factors that effect this decision. First, you need to know the environmental conditions such as: current, visibility, and temperature. All these factors affect your metabolic rate, which increases your uptake of nitrogen. Without taking these factors into consideration when deciding your best mix, you: a) may put yourself at risk or b) not chose the optimum percentage of oxygen.

PO2 for Diving Nitrox

Now that we have determined some of the environmental factors, it’s time to look at PO2’s. For recreational diving the maximum PO2 is 1.6. For a diver to choose a 1.6 PO2, all environmental conditions must be perfect: good visibility, no current, warm water temperatures, a low workload for the diver and the planed bottom time of the dive cannot exceed 45 minutes. If any of these factors are not perfect, you must lower the PO2. As an example, if your dive involves current, low visibility, etc. it would be best to set your PO2 to a maximum of something less than 1.3.

Atmospheric Pressure

The final decision making factor is depth. Because all formulas use absolute pressure, you must always factor in atmospheric pressure, or the pressure of the air on the water. The formula for determining best mix, PO2 and maximum depth is commonly referred to as Daltons Diamond (also known as a T formula). To determine best mix you must know the depth of your dive and the PO2 you want to use.

As an SDI Computer Nitrox diver, you have learned how to program your mix and PO2 into the dive computer and let it determine your maximum depth. Most computers will give an audible and visual alarm should you get close to or exceed your maximum PO2. Knowing the formulas above gives you a better understanding of how your computer works and should you decide to get involved in the technical side of diving, the above information introduces you to the basic formula for all future technical courses.

Now that we have discussed many of the variables that affect nitrox diving and determining your best mix, it is important to understand that not all dives are the same, so saying that one mix fits all would be incorrect. It is important to plan your dive or dives ahead of time and get the proper mix(s) in your cylinder(s). Equally as important is verifying the mixes you received, logging them at the dive center, labeling the cylinder(s) and then just before the dive, analyzing again.

The single most important things are that you are safe and having fun. Having some conservancy in your dive planning is a good move, and it will help ensure another day of diving.

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