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NOAA, the National Oceanic and Atmospheric Administration, has recognized two standard Nitrox mixes: EAN 32 (32% oxygen and 68% nitrogen) and EAN 36 (36% oxygen and 64% nitrogen) as safe to use for recreational diving. These blends are often referred to as "NOAA Nitrox" and they are the most common Nitrox mixes used in recreational diving.
NOAA recognized these two blends because they have been found to provide a balance between increased bottom time and reduced risk of decompression sickness. EAN 36, which has a lower percentage of oxygen, is suitable for shallower depths, where divers are less likely to experience decompression sickness and can stay underwater for longer periods of time. EAN 32, which has a higher percentage of oxygen, is more suitable for deeper dives, where the increased oxygen content can help to reduce the risk of decompression sickness.
Additionally, these blends are well-suited for the most common depths that recreational divers typically dive, and have been extensively studied and are backed by scientific research, which NOAA uses as the basis for their recognition. They are also easy to find and can be used with most of the diving equipment.
The use of Nitrox allows for longer no-decompression bottom times than diving with air. This is because the increased oxygen content in Nitrox reduces the amount of nitrogen absorbed by the body, which reduces the risk of decompression sickness.
The maximum operative depth (MOD) is one of the factors that is taken into consideration when selecting a Nitrox blend. The MOD is the maximum depth at which a particular Nitrox blend can be used safely. EAN 32 has a MOD of about 131 feet (40 meters) and EAN 36 has a MOD of about 108 feet (33 meters).
It's important to remember that divers should always use the appropriate Nitrox blend for their dive and stay within the MOD to avoid the risk of oxygen toxicity.
There have been some individuals and organizations in the past who have questioned the safety and efficacy of Nitrox in recreational diving. Some have argued that Nitrox is not necessary for recreational diving, as the risk of decompression sickness is already low when using air. Others have raised concerns about the potential risks of oxygen toxicity associated with Nitrox.
However, as the use of Nitrox has become more widespread and research on its benefits and risks has continued, these criticisms have largely been debunked. Nitrox has been found to be safe and effective for use in recreational diving when used properly, and it is now widely accepted and used in the diving community.
It's important to note that Nitrox is not a panacea, it's just a tool that can help divers to increase their bottom time and to reduce the risk of decompression sickness. Divers still need to be aware of the risks and to follow the guidelines, diving with Nitrox should be part of a good dive plan, taking into account the diver's level of training, the dive site and conditions, and the equipment used.
