You’ve probably already seen some scuba divers wearing green and yellow stickers on their tanks while others continue to use the traditional gray tanks without any stickers. You might be wondering, “What’s the difference?” So let’s get into the Nitrox, and compare Nitrox vs. air for scuba diving!
You can learn a lot about a scuba tank by its color! The 21% oxygen and 79% nitrogen air in normal scuba tanks is the same air you breathe on land. However, the air in scuba tanks has been compressed to a considerably higher pressure than the air you breathe when you are above the water; without this compression, your dive would last much, much shorter.
Meanwhile, enriched air, often known as Nitrox or EANx, is a breathing gas with a higher oxygen concentration than ordinary air. It is frequently stored in tanks marked with a green and yellow tank band. That said, what is Nitrox? How well do you understand it?
Enriched air Nitrox (EANx) is a word used to describe any nitrogen/oxygen gas mixture that contains more oxygen than the standard 21%. For instance, 32 and 36% oxygen are both common; these percentages are referred to as Nitrox 32 or EAN32, respectively.
Tanks loaded with EAN are identified with a yellow and green tank band at the top, just below the crown, to distinguish them from air cylinders.
However, the proportion of oxygen mix is indicated on a label or tag, which is significant because it impacts your maximum depth and no-stop dive time.
As we stated earlier, because enriched air contains more oxygen than regular air, its nitrogen content is lower. Consequently, you breathe in less nitrogen during the dive than you would if you were breathing standard air.
In Open Water Diver training, you’ll discover that the water pressure during a dive causes the nitrogen in the air you breathe to dissolve in your blood and tissues. More nitrogen dissolves at more tremendous pressures (deeper dives) and longer periods at lower pressures (bottom time).
Decompression sickness (DCS) refers to a situation where excessively dissolved nitrogen start forming bubbles in your body as a form of exit solution. By staying within the no-stop limitations, you can reach the surface without stopping (but make your safety stop) because the amount of dissolved nitrogen is theoretically limited. If you go over this limit (as tec and commercial divers do), you must make the required decompression stops when you ascend to minimize the danger of DCS.
For instance, a professional diver on air at 100ft reaches no decompression after 20 minutes, according to the Recreational Dive Planner. The diver could stay at 60ft for a maximum of 55 minutes. However, these figures aren’t the same with Nitrox, and we’ll explain as we go further. The recommended depth for inexperienced divers is 60ft with a 15ft safety stop.
If all else is equal, less nitrogen dissolves into your body since you inhale less of it, allowing a longer no-decompression limit. The equivalent air depth (EAD), which is a shallower depth at which nitrogen would dissolve at the same rate if the air were used, can be used to calculate this. If your EAD, for instance, is 90ft at 105ft with EANx32, then you absorb nitrogen like you were 15ft shallower. This results in a 66% increase in bottom duration from the diver’s normal no-decompression limit of 15 to 25 minutes.
What do you do in a situation when you have enough oxygen in your tank to keep diving but have consumed all of the nitrogen you can for a dive? You might have to stop the dive because of your no-decompression limitations (NDL).
The NDL or No-Stop time for 18 meters is 56 minutes, according to the Recreational Dive Planner chart. However, Nitrox modifies this figure!
Due to the higher oxygen content, diving using Nitrox minimizes the amount of nitrogen that enters the body. As mentioned earlier, your NDLs will be lengthened with Nitrox, allowing you to extend your dive and get more bottom time in the same scenario as before.
In the 50 to 100-foot range, Nitrox is most effective. For dives shallower than 50ft, no-stop times are frequently so long that you’ll exhaust your tank before the diving period expires. Your no-stop time limit for your first dive with EANx36 at 60ft is 80–90 minutes or more (depending on your computer). So your gas supply, not your decompression limit, will determine how long you can dive without stopping.
While it is always advisable to dive into your comfort zone (depth) if you’re not a professional, you can always stretch your boundaries and dive longer with caution. However, it is a common notion that experienced divers prefer Nitrox diving to go past air restrictions without ever getting close to the no-stop limits. Like air, this does not provide complete safety, but for most divers, remaining within limits lowers the danger of DCS.
Although Nitrox has its benefits, there are certain risks associated with using it. Just like oxygen, Nitrox can be dangerous in large doses. The effects of oxygen toxicity on the central nervous system include convulsions or seizures, visual distortions, ringing in the ears, nausea, twitching, irritability, and dizziness.
Convulsions or seizures are the most dangerous of these symptoms while diving. In diving, oxygen toxicity happens once you surpass safe limits of partial pressure. When they do occur underwater, they do so suddenly and can result in drowning if the diver loses the regulator while convulsing. If you travel deep enough, any amount of Nitrox can be harmful, but with air, you have to go far deeper than the recommended depths for this to be likely.
With Nitrox, the recreational diving depth is 60ft. And the maximum depth decreases with increasing oxygen content; the maximum depth is equal to the depth at which the PPO2 would be 1.4ata. Another sort of oxygen exposure can result from prolonged exposure to high oxygen levels.
There were few tables and no EANx dive computers available when enriched air was initially being used for recreational diving. Consequently, divers had to calculate everything using a pencil and calculator.
However, in modern recreational Nitrox diving, NO ONE does this anymore. You simply check the maximum depth on a chart and enter your EANx mix into your computer, and it will calculate your oxygen exposure and alter your no-stop duration. Finishing the dive due to low gas, cold, hunger, or the need to use the lavatory is practically a given while diving EANx with a computer on a multilevel profile. You have to learn how to analyze your mix, which is not difficult.
However, to use that information effectively and securely, you must comprehend what your computer is doing for you.
For instance, partial pressures are used to determine the pressure portion of the oxygen limit. The oxygen content of the EANx can be calculated by multiplying it by the absolute pressure (in atmospheres or bar). For instance, an individual inhaling air (21% O2) at 132ft (5ata) is breathing oxygen at a partial pressure of 1.05. At the surface, this would be the same as breathing 105% oxygen. In other words, you cannot breathe that PPO2 at the surface even when you’re on pure oxygen.
The formula for determining PPO2 is as follows: 5ata times 0.21% oxygen equals 1.05 PPO2.
Dropping the decimal makes it simple to calculate the surface equivalent percent.
The depth limit is determined by calculating the depth at which a mix would have a PPO2 of 1.4 as follows: Maximum Depth: *(1.4% mix – 1) X 33
The mix percentage is entered using a decimal (32% would use 32).
Expert divers are trained in further associate risk management; however, they frequently dive to partial pressures of oxygen up to 1.6 PPO2.
Sometimes it seems enriched air is a panacea for all diving problems. Let’s take a moment to dispel a few myths since that is not the truth.
If breathing less nitrogen results in less narcosis, then narcosis should be less prevalent. The problem is that you have to cease taking Nitrox at the same depth that you start to worry about narcosis (between 100 and 130ft) due to the possibility of oxygen toxicity. You’re one step up and one step back, even if oxygen is regarded to be roughly as narcotic as nitrogen (not always, but typically — it gets complicated).
This may also seem logical at first sight. If each breath contains more oxygen, you probably won’t need to take another one as frequently, and your gas consumption rate will be lower. Unfortunately, that is not how it works because most of the oxygen you breathe is exhaled and unused. The need to expel carbon dioxide triggers the subsequent breath, which is unaffected by the contents of your tank.
According to this notion, off-gassing nitrogen is a primary contributor to diving tiredness; thus, using less of it should make you feel less exhausted. Meanwhile, there’s no concrete proof that this notion is true. Several diving pieces have debunked this perception.
Some divers identify diving deep with those serious, “techie,” green-and-yellow cylinders. EANx adds a smaller depth floor, and there are substantial consequences for diving below it, including the possibility of death. On a regular air mix, many of us would take the chance of pursuing that eagle ray down to 150ft, but not on Nitrox. However, some people may mistake EANx for a deep diving gas because tec divers use it to decompress in the shallows after a deep dive.
The pre-mixes typically sold at dive shops—32 or 36%—make life easy. Take the tank, examine the mixture, confirm the maximum depth, and input the information into your computer.
However, you can use other mixtures. As long as it’s under the recreational limit of 40%, your dive shop will probably blend a tank with whatever amount you require for your dive. You can get the best value for your money with custom blends. For instance, using EANx32 at 70ft results in an EAD of 56ft and a table NDL of 55 minutes, whereas using EANx40 results in an EAD of 45ft and a table NDL of 100 minutes, providing more dive for your money.
Dive shops frequently keep the EANx blend on hand in locations where a specific mix is very beneficial due to depth.
The National Oceanic and Atmospheric Administration (NOAA) and the U.S. Navy claim that typical dive equipment is suitable for oxygen concentrations up to 40%. There has never been a gear-related incident with recreational diving equipment used within recreational Nitrox restrictions because this is also the upper limit for Nitrox diving. (Note: Some producers follow a stricter norm. Always adhere to a manufacturer’s instructions for their equipment).
Despite what many people think, oxygen does not burn. However, it does increase the flammability of everything it comes into contact with; the more oxygen present, the easier it is for most things to ignite and the faster they burn. Only one piece of equipment is exempt from this rule: the scuba tank.
One explanation is that a typical method of creating Nitrox (particularly custom mixes) calls for first filling the tank with pure oxygen and then with air that has been specifically filtered to make it compatible with oxygen.
The components (O-rings, valve seats, and any lubricants) must be rated for use with pure oxygen because the tank contains only pure oxygen during mixing. As a result, they must comply with oxygen service standards. Additionally, the tank needs to be cleaned specifically, which is done yearly.
The second reason is that the tank needs to be marked to prevent accidental air diving. The cylinder’s distinctive EANx band is located at the top, making it easy to see even when surrounded by other cylinders.
Normal air, or purified air with 21% oxygen, is called Normoxic Nitrox.
Enriched air, or enriched air Nitrox (EAN): any mixture containing greater than 21% oxygen.
Equivalent Air Depth, or EAD. The link between the depths at which inhaling air would result in a comparable absorption rate of nitrogen at a given depth.
Oxygen partial pressure, atmospheric pressure, and the percentage of oxygen equal PPO2 (or PO2). MOD, or maximum depth: Maximum depth: *(1.4% mix – 1) X 33
Best Mix: (Depth + 33) / 33) / 1.4 = best mix.
Enriched air Nitrox is a fantastic technique to lengthen your dive and maximize your experience. It can make you less exhausted after a dive and lower your risk of getting “the bends,” commonly known as decompression sickness. Enriched Air Nitrox with higher oxygen content aids in reducing nitrogen absorption and nitrogen buildup in your body tissues.
Compared to other popular diving gas combinations, enriched air Nitrox is unique. To prevent issues, you’ll need to know how to utilize it correctly. Using enriched air lowers your risk of decompression, which is its main advantage. When diving with enriched air, you will spend more time at the bottom and less time at the top. You’ll have more time to research aquatic life and sunken ships as a result.
Oxygen poisoning is the main issue with enriched air diving. Short-term memory loss, confusion, joint discomfort, and excessive weariness are all possible signs of oxygen toxicity. Decompression sickness can also be more likely to occur when diving too deep or with too much nitrogen. However, your decompression safety should not be a concern if you speak with your dive instructor before diving.
Divers can enhance their decompression safety margin when Nitrox diving as opposed to air, among other advantages. However, you must first grasp the variations in breathing gas mixtures as well as the dangers of inhaling air with a high oxygen content before using Nitrox.
Also, you have to understand that Nitrox is a type of metabolizable gas that takes the place of nitrogen. Nitrogen can be harmful, and divers who breathe it excessively risk developing decompression sickness (DCS).
Additionally, divers can raise the percentage of oxygen in their breathing gas by adding more to the limited amount of oxygen in Nitrox. For decompressing stops, a 50/80 mix of Nitrox and oxygen is typical. This mixture won’t be as effective as one that has only oxygen. Also, it makes oxygen toxicity more likely.
That said, contrary to the common perception that divers can go deeper and stay longer with Nitrox, with air diving, divers can actually stay longer and deeper with air diving. Air diving allows you to reach a maximum operable length (MOD) of 56m/184ft. Meanwhile, for Nitrox diving (32% and 36% mixes), the MOD of 34m/110ft and 29m/95ft, respectively. And it is limited to a maximum partial pressure of oxygen of 1.4 bar.
The choice between air and Nitrox for scuba diving ultimately comes down to personal tastes and dive goals. Both options have advantages and considerations in particular. While Nitrox is often perceived as the option for professional diving, air is still a safe and affordable option for recreational dives. Nitrox is great but can only take you up to a certain point, while air diving offers more advantages for deeper and longer bottom periods. But keep in mind that Nitrox offers lesser nitrogen-related dangers.
However, regardless of their preference, you’ll want to put safety, training, and good gas management first. The ideal option ultimately depends on the particular dive strategy, diver experience, and environmental aspects. The distinction between these two possibilities may become hazier as technology develops, but divers must remain knowledgeable, safe and make wise choices to guarantee a satisfying and secure underwater experience.