What Does Nitrox Do For Diving?

Nitrox diving is a type of recreational scuba diving that uses an oxygen-rich gas mixture instead of regular air. This creates several benefits, such as reducing nitrogen buildup and increasing dive time. Nitrox typically contains 32% to 40% oxygen, meaning that the amount of oxygen added to the air is either 32% or 40%. Nitrox diving increases the no-stop dive time for longer dives and shorter surface intervals, all else being equal and gas supply allowing.

While not entirely without risk, nitrox diving offers huge advantages for moderate depth diving when done carefully and correctly. With mentoring from an experienced nitrox instructor, nitrox can help divers spend more time at depth compared to diving with air, resulting in a more enjoyable scuba vacation. Nitrox diver absorbs less nitrogen for a given depth and dive time than a diver who uses air, resulting in less nitrogen to absorb.

One of the main reasons many people choose to dive with Nitrox is that it allows them to stay underwater longer. As they know from their Open Water certification, diving with Nitrox reduces the risk of decompression sickness. However, it is not entirely true to say that diving with Nitrox is safer than with air. Nitrox diving is a popular choice for those looking to improve their diving experience and enjoy a more enjoyable experience.

When should you dive with Nitrox?

The moments when nitrox will make the greatest difference is when you are doing multiple dives over multiple days and are getting close to some of the no-decompression limits your personal dive computer is telling you about.

As stated, when you dive using nitrox you can take advantage of increasing your maximum allowable bottom time. This happens because the extra oxygen added to your breathing gas when it was filled has displaced nitrogen. Because there is less nitrogen in the mix to be absorbed by your body you can spend longer at depth before you reach the nitrogen limit – which is the decompression limit. Secondly, since you are absorbing less nitrogen on a given dive, your surface intervals can usually be shortened.

Being on a live-aboard, hundreds of miles from home where you are doing 3 to 4 dives a day will allow you to see a huge difference if you can compare yourself to those diving on regular air. You have paid a lot of money to get there and you want to make each and every dive count. You do not want to get back in the water for the fourth dive so you can zip about at 50ft/15 meters just because you have reached your no-deco limits for the day – especially when the schooling hammerheads are hanging out around 70ft/21 meters. That is where you want to be… for as long as possible.

Does diving with Nitrox feel different?

You’ll Feel Less Tired. There Is a theory that divers feel less tired after diving with nitrox tanks. Studies have shown that is really a placebo effect, and it doesn’t make a difference. However, many divers will say that they feel better after diving with nitrox.

You Can Go Deeper. Although those green and yellow tanks can look more ‘professional’ the depth levels when using an enriched gas mix is actually shallower than when using air, due to the risks of oxygen toxicity when using a higher oxygen blend at depth.

More Than Just Air!. This blog is just an overview of why diver’s really love the nitrox course speciality, but there’s more to it than using a different tank. There are many considerations when using an enriched air mix, which you’ll learn during your Nitrox Course.

What is the advantage of diving with Nitrox?

Shorter Surface Intervals. A diver using Enriched Air Nitrox absorbs less nitrogen on any given dive than a diver using air.

With less nitrogen in your body, the time required to ‘off gas’ in between dives is decreased. Giving you less time needed to kill in between dives and getting you back in the water sooner!

Longer Bottom times on Repetitive Dive Times. If you like to do multiple dives in a day… we’re looking at you!

When you plan to dive for multiple days, it makes sense to introduce less Nitrogen into your body. The less Nitrogen you use, the more time your body is allowed at any given depth. A diver using Enriched Air Nitrox will have a longer bottom time allowance on a repetitive dive than a diver using air because the EAN diver has absorbed less nitrogen.

What is the downside of Nitrox?

Oxygen Toxicity and Depth Limits. While Nitrox diving comes with many advantages, such as an increased bottom time for no decompression dives, it also has a few of its own concerns. One of the main ones is oxygen toxicity that can occur due to the increased levels of oxygen in the mix.

2. Shorter Surface Intervals.For those divers that are in a hurry to get back in, another benefit of breathing Nitrox is shorter surface intervals. A diver using Nitrox absorbs less nitrogen on a given dive than one who uses air. This can make a remarkable difference in the time it takes to off-gas on the surface. For example, a diver using air will be in pressure group H after a 45 minute dive to 60 feet (18.3 meters). This means that he will have to wait for a minimum of 5 hours and 17 minutes to repeat the same dive. A diver using EAN32, on the other hand, will be in pressure group G after a 45 minute dive to 60 feet (18.3 meters), which means that he can repeat the same dive after only 53 minutes on the surface (according to NOAA’s no decompression dive tables).

3. Longer Repetitive Dive Times.Nitrox proves to be especially useful for divers, who want to perform more than one dive per day. Due to having absorbed less nitrogen on the first dive, Nitrox divers will have a longer allowable bottom time on a repetitive dive. For example, after a dive to 60 feet (18.3 meters) for 45 minutes a diver using air can stay at 60 feet for only 14 minutes if he reenters the water in half an hour. Whereas, a diver performing the same series of dives on EAN32 will be able to stay at 60 feet for 43 minutes on his second dive (according to NOAA’s no decompression dive tables).

4. Reduced Post-Dive Exhaustion.Although it is not scientifically proven, many divers claim to be less tired after dives on nitrox. One of the widely accepted theories, explaining this phenomena is that lower nitrogen levels reduce the amount of microbubbles in the diver’s bloodstream, thus reducing the post-dive lethargy.

How long can you stay underwater with Nitrox?

•Less time between divesAnother great benefit of diving with Nitrox is that it allows divers shorter surface intervals. This means we need to wait less time before getting back in the water. When we dive with Nitrox we absorb less nitrogen while we are underwater, therefore, there is a lesser amount of residual nitrogen in our body to off gas between dives. For example, diving with air at 60 feet (18.3 mt) for 45 minutes will put us in pressure group H. We will have to wait no less than 5 hours and 17 minutes in order to make another dive at the same depth for the same time. Using Nitrox at 32% for the same dive instead of air will put us in pressure group G. Which means we will be able to make the same dive at the same depth for the same time after only 53 minutes on the surface.

•More diving during your holidayMany diving resorts and liveaboards offer free Nitrox to those clients certified to use it. Diving repeatedly with enriched air will make your body accumulate less residual nitrogen. This will allow you to dive more frequently and safer during your vacation. Using enriched air during your dive could potentially gain you hours of additional dive time over the course of the same week holiday.

•Less tiringEven if it has not been scientifically proven, it is well established amongst divers, the belief that diving with Nitrox will reduce your post dive fatigue. Many divers claim to feel less tired after diving with enriched air. This theory could be explained with the fact that less nitrogen in a diver body also reduces the amount of microbubbles in body tissues which could have a direct consequence on diver fatigue.

Why doesn’t everyone dive with Nitrox?

When breathing normal air on a dive, we would have to descend to depths below 200 feet before oxygen toxicity becomes a problem. However, using enriched air or oxygen on a dive can cause us to reach depths that are potentially dangerous well within traditional recreational depth limits. For this reason divers must be properly trained to use enriched air to avoid a life-threatening accident.

The example above further highlights why divers making very deep dives will not be able to use enriched air at depth. If the diver were to descend to 130 feet, the maximum operating depth would be exceeded and there would be a risk of oxygen toxicity.

Can you stay down longer with Nitrox?

Nitrox’s Magic: More Oxygen, Less Nitrogen. The magic of Nitrox lies in its reduced nitrogen content compared to standard compressed air. Excessive nitrogen buildup can lead to decompression sickness (DCS), a potentially dangerous condition. Nitrox minimizes this risk by decreasing the nitrogen component and increasing the oxygen content relative to air, which translates into extended bottom time. More oxygen means less nitrogen, and less nitrogen means you can stay down longer.

However, it’s crucial to recognize that Nitrox diving introduces its own set of considerations and risks, distinct from those of traditional air diving. Navigating these waters requires a keen understanding of Nitrox and the ability to apply that knowledge safely.

Discover the World of Nitrox with SDI’s Computer Nitrox Course. To equip divers with the skills and knowledge necessary for safe and enjoyable Nitrox diving, Scuba Diving International (SDI) offers the Computer Nitrox course. This comprehensive program delves into the risks associated with Nitrox diving and provides invaluable guidelines to help manage those risks.

How deep can you dive on 32% Nitrox?

The two most common recreational diving nitrox mixes are 32% and 36%, which have maximum operating depths of about 34 meters / 110 feet and 29 meters / 95 feet respectively when limited to a maximum partial pressure of oxygen of 1.4 bar.

Nitrox with more than 40% oxygen is uncommon within recreational diving. There are two main reasons for this: the first is that all pieces of diving equipment that come into contact with mixes containing higher proportions of oxygen, particularly at high pressure, need special cleaning and servicing to reduce the risk of fire. The second reason is that richer mixes extend the time the diver can stay underwater without needing decompression stops far further than the duration of typical diving cylinder. For example, based on the PADI nitrox recommendations, the maximum operating depth for Nitrox45 would be 21 meters / 70 feet and the maximum dive time available at this depth even with Nitrox36 is nearly 1 hour 15 minutes: a diver with a breathing rate of 20 liters per minute using twin 10 litre, 230 bar (about double 85 cu. ft.) cylinders would have completely emptied the cylinders after 1 hour 14 minutes at this depth.

Nitrox, usually containing 50% to 80% oxygen, as well as pure oxygen, is common in technical diving as a decompression gas, which eliminates inert gases, such as nitrogen and helium, from the tissues more quickly than leaner oxygen mixtures eliminate them.

In deep open circuit technical diving, where hypoxic gases are breathed during the bottom portion of the dive, a Nitrox mix with 50% or less oxygen called a “travel mix” is sometimes breathed during the beginning of the descent in order to avoid hypoxia. Normally, however, the most oxygen-lean of the diver’s decompression gases would be used for this purpose, since descent time spent reaching a depth where bottom mix is no longer hypoxic is normally small, and the distance between this depth and the MOD of any nitrox decompression gas is likely to be very short, if it occurs at all.

What is the 40% rule in Nitrox diving?

If the dive shop has Nitrox in banks, or uses a compressor with either a membrane system or Nitrox mixing stick to create the Nitrox, then the dive shop may generally believe the cylinder being filled does not need to be O2 clean to be filled with Nitrox up to 40%. (That is, the standard practice is to apply what is known as the 40 per cent rule.) In this case the shop will be decanting Nitrox which is already mixed at a fraction of Oxygen (FO2) less than 40% into the tank. More dive shops are beginning to bank Nitrox and have it ready to decant into customers cylinders. Some dive shops keep more Nitrox banked than they do air. Using this method the cylinder and valve never see more than 40% Oxygen. If the dive shop is following the 40% rule, they will not require the cylinder and valve to be Oxygen cleaned, as the tank and valve only ever “sees” Nitrox below 40%.

At The Scuba Doctor we use partial pressure blending for Nitrox and Trimix fills, so your cylinders and valves need to be O2 clean when getting these fills because they will see 100% Oxygen.

What if I want a Nitrox fill over 40%?. This question is asked because many people in the dive industry simply refer to and follow the 40 per cent rule.

What is the 40% rule in nitrox diving?

If the dive shop has Nitrox in banks, or uses a compressor with either a membrane system or Nitrox mixing stick to create the Nitrox, then the dive shop may generally believe the cylinder being filled does not need to be O2 clean to be filled with Nitrox up to 40%. (That is, the standard practice is to apply what is known as the 40 per cent rule.) In this case the shop will be decanting Nitrox which is already mixed at a fraction of Oxygen (FO2) less than 40% into the tank. More dive shops are beginning to bank Nitrox and have it ready to decant into customers cylinders. Some dive shops keep more Nitrox banked than they do air. Using this method the cylinder and valve never see more than 40% Oxygen. If the dive shop is following the 40% rule, they will not require the cylinder and valve to be Oxygen cleaned, as the tank and valve only ever “sees” Nitrox below 40%.

At The Scuba Doctor we use partial pressure blending for Nitrox and Trimix fills, so your cylinders and valves need to be O2 clean when getting these fills because they will see 100% Oxygen.

What if I want a Nitrox fill over 40%?. This question is asked because many people in the dive industry simply refer to and follow the 40 per cent rule.

How long after diving with Nitrox can you fly?

To be more exact, the studies carried out by DAN (Divers Alert Network) have obtained great acceptance by the diver community. These studies apply to flights ranging between altitudes of 2,000 feet / 610 meters and 8,000 feet / 2,439 meters) and only for sport diving. Neither professional diving nor Nitrox diving adheres to these recommendations:

• After single no-decompression dives, a minimum pre-flight surface interval of 12 hours is suggested.
• After multiple no-decompression dives per day or multiple days of diving, a minimum pre-flight surface interval of 18 hours is suggested.
• For dives requiring decompression stops, there is little experimental or published evidence on which to base a recommendation
• for decompression diving, a preflight surface interval substantially longer than 18 hours appears prudent.

To help divers in these calculations, dive computers are a great ally. These devices, currently, can calculate the optimal waiting time to fly after diving and do these calculations based on the dives you have made. If you do not have your own dive computer and you must rent one, use the same one for all the dives you will do. In this way, you will ensure that the calculations of the device are not biased.

Diving After Flying. Although there should not be any problem to dive after flying, remember to hydrate properly during the trip. Since dehydration is a factor that makes it difficult to eliminate inert gases and as you know, nitrogen is one of them. Besides, long-distance trips can cause sleep disturbances and jet-lag. Follow our advice and give yourself some time to recover from the trip before the first dive.

How long can you dive at 100 feet with Nitrox?

Imagine you’re doing a deep dive to 100 feet. Based on the Recreational Dive Planner (RDP), you hit your no decompression limit (NDL) at 20 minutes on a typical air dive. But, diving nitrox changes this. Because you’re breathing less nitrogen, less dissolves into your body—all else being equal—allowing a longer no-decompression limit. Using EANx32, for example, your no stop limit is 30 minutes at 100 feet.

For tables diving, you either use special tables for the blend you’re using, or air tables with an Equivalent Air Depth (EAD) that adjusts your limits. If, for example, you are at 70 feet diving EANx36, your EAD is 50 feet because you’re absorbing nitrogen as if you were 20 feet shallower with air. Using the RDP, your single dive no stop time doubles from 40 minutes to 80 minutes. Using EANx with a computer (which is most common today), the EANx advantage plus a multilevel profile means most dives—even repetitive dives—are limited by how much gas you have, not by no stop time.

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