Which two nitrox mixtures are referred to as NOAA Nitrox I and NOAA Nitrox II?

The correct answer identifies the two specific nitrox mixtures designated as NOAA Nitrox I and NOAA Nitrox II. NOAA Nitrox I refers to a nitrox mixture that contains 32% oxygen, while NOAA Nitrox II consists of a mixture containing 36% oxygen. These mixtures are recognized for their enhanced safety margins during dives compared to air, particularly at increased depths.

NOAA establishes these mixtures primarily for recreational and research diving purposes, allowing divers to reduce their nitrogen absorption and extend their bottom time, thus minimizing the risk of decompression sickness. The selection of these specific percentages reflects an optimal balance between oxygen content and the associated risks of oxygen toxicity at deeper depths.

Other mixtures that might be mentioned in the context of nitrox dive training or equipment, such as those with 30% and 34% oxygen or varying levels of oxygen content like 28% and 40% or 36% and 38%, do not align with NOAA's defined standards for Nitrox I and II.