DIVE – Page 9 – Dive To Escape

If you’re considering Nitrox, you have either gotten to the stage in your diving where you want to dive more often in a day and you want to stay down longer, or you have seen all these tanks with the green and yellow ENRICHED AIR, EANx, or NITROX on them, and you're trying to figure out what this is all about. The long and short of it is, if you're considering becoming Nitrox certified, you won't regret it. Nitrox lets you dive longer, safer and with less fatigue. If you're considering getting nitrox certified you won't regret it. Now let's take a look at how diving this gas can do all those things. This article is not a substitute for getting officially trained and certified to dive enriched gasses. They do have their risk factors and official training from a certified instructor is necessary. What is nitrox Enriched Air, Nitrox, EANx are all different names for the same thing. They are all names for compressed gas with a higher percentage of oxygen than the standard air used for scuba diving. Standard breathing air is 21% oxygen and 79% nitrogen compared to Enriched air can be anywhere from 22% oxygen up to 40% oxygen and 60% nitrogen. If you remember your open water gas theory, you may recall that Nitrogen is one of the main contributing gases to nitrogen narcosis as you go deeper in the water column. If you are open water certified, you may have started to understand the advantages of diving enriched air when you learnt the percentage of nitrogen in your breathing air; because of both the decrease of nitrogen gas and the increase of oxygen, your bottom times are drastically affected. This is why diving with a computer will ease the use of enriched air because the computer will adjust your bottom times automatically based on the nitrox/oxygen ratios you are breathing. We will cover equipment needs later in this article. The image demonstrates the difference in Nitrogen content (yellow) and Oxygen content ( green) in breathing air vs different percentages of NItrox or Enriched Air. Why dive nitrox As I mentioned earlier, enriched gas or nitrox has an increased percentage of oxygen and a decrease in nitrogen and because of this, a diver diving nitrox can extend bottom times significantly ( insert a table comparing bottom times of air and nitrox). The increased bottom times for someone diving within recreational limits is one of the main reasons any diver would want to dive with nitrox/enriched air. Another good reason to dive with nitrox is that, when you are doing repetitive dives on the same day, diving enriched air can leave you less tired at the end of the day. The reduction in nitrogen decreases the metabolic load, making it easier for the body to breathe off (off-gas) the accumulated nitrogen in your body. Offgassing happens more quickly because there is less nitrogen in your blood due to the air you were breathing having less nitrogen gas in it. Also, because you have an increased bottom time, this can lead to a diver not pushing or diving close to the NDL (non-decompression limits). Since you have lots of bottom time, you can increase your safety factor if you so choose. This comes off more like dive propaganda though, because we all know if a diver has more bottom time, that means the diver will stay down longer. After all, that’s what we are doing this for, right?! Is diving Enriched air or Nitrox dangerous? Scuba diving is an inherently risky sport. So when adding Nitrox or enriched air to your arsenal of dive skills, we need to consider the safety factor of using a different mixture of gas to breathe other than air. Breathing a gas with less nitrogen than air has benefits that we have mentioned earlier because your body won't accumulate as much nitrogen from enriched air or nitrox as from air, and one can stay down longer. But what about the increased percentage of oxygen? How does that affect our safety factors? An increase in oxygen concentration can cause toxicity that breathing normal air won't cause within recreational limits. An increased percentage of oxygen does affect safety in two different ways. First, the depth one can dive to will be reduced because of the increased percentage of oxygen, because of the oxygen partial pressures that will be exerted on your body. Partial pressure refers to the part of oxygen in the air hence partial pressure. Partial pressure is typically measured in the atmosphere (ATA), and oxygen partial pressure (PO2 or PP02). The PADI ENriched air diver course gives divers a Maximum Oxygen Partial Pressure limit of 1.4 bar and a contingency limit of 1.6 bar; above that, a diver will experience oxygen toxicity. Some of the symptoms can appear gradually and get worse over time. These symptoms can include, but are not limited to: Tunnel Vision, visual disturbance Ear ringing Nausea Twitching or muscle spasms, especially in the face Irritability, restlessness Dizziness seizures In the worst situation, oxygen toxicity in the water at depth can be fatal because it can cause seizures. This is not to be taken lightly, as I have had the unfortunate experience of losing a dive buddy who was a friend and mentor to this exact situation. Diving with oxygen-enriched air is safe and enjoyable and recommended within your training limits and the training recommendations only. The onset of seizures does not have to come after the symptoms I mentioned earlier; seizures can spontaneously happen without any other symptoms if you exceed the limits of exposure at depth. Let's take a look at how depths affect Oxygen exposure: This table demonstrates the increase in bottom time when using Nitrox/Enriched Air for diving vs. using Breathing air. The deeper you dive, the more you will increase the atmosphere of oxygen you are immediately exposing your body to. As one has multiple same-day dives on Nitrox, your body will accumulate oxygen and will need time to off-gas also. The best way to monitor your oxygen exposure throughout multiple dives is by using a dive computer with a nitrox setting. Something else that plays a large safety factor for diving Nitrox is buoyancy control. This is because depth or, more specifically, exceeding the acceptable depth will make enriched air toxic. If you aren’t confident with your buoyancy control, I strongly suggest that you not dive enriched air in a no-bottom situation. I dive nitrox a lot in the summer in no-bottom conditions, so I know firsthand it can be so easy just to go a little deeper to see another artifact on the wreck or to follow a fish around the corner. Before you know it, you can be dangerously close to diving to a dangerous depth for the nitrox blend you’re breathing. One must be vigilant when diving enriched air, never to exceed the 1.4 ATA of pp02 and stay well within the 1.6 recommendation because the result of oxygen toxicity at depth cannot be understated. It can be fatal. Paying attention to your depth and not exceeding the limits of your dive plan within the training recommendation can’t be emphasized enough and wasn't mentioned enough when I did my nitrox course. Do I need specialized equipment to dive with ENriched air or Nitrox? As with so much in diving, new skills, new courses, or different dives will often lead to equipment upgrades, and I hope Dive To Escape has helped you save some money and not make some of the redundant and expensive mistakes that I have made. However, diving enriched air usually only requires some slight equipment modification and, hopefully, if you already own a dive computer, it’s compatible with diving Nitrox. When breathing gases with an increase in oxygen concentration, there are some things we need to consider due to the nature of oxygen being a fire accelerant. Oxygen won’t burn on its own usually, but it allows other things to burn better. Meaning when oxygen is exposed to certain carbon-based chemicals, it can cause them to ignite spontaneously. For this reason, most dive equipment usually is serviced to a minimum standard where it is safe, around up to 40% oxygen. Because of the increased risk, tanks that are visually and hydrostatically tested for enriched air situations will typically be labelled with a large green and yellow sticker stating that it meets the standard to use up to 40% oxygen safely. Another primary consideration is your dive computer. At one point, they taught enriched air divers to dive with a table, but as of the mid-2000’s the standard for anyone diving enriched air should be using a dive computer with an enriched air setting. This is great because the computer will do a pretty good job of tracking your oxygen exposure over repetitive dives, which will significantly help you reduce your chances of ever experiencing some of the milder symptoms of oxygen toxicity. Most enriched air dive computers also have a great feature that can help you plan your nitrox/enriched air dives because it will let you enter the specific percentage of oxygen you will be diving and it will tell you the depth you cannot exceed. Finally, the most significant advantage of enriched diving air with a computer is that the dive computer will continually monitor your depth and as your dive has multiple levels or depths, the computer will constantly be calculating your bottom time, and with nitrox, you will see that you can safely and significantly extend your dives. You do need training to dive ENriched air or nitrox. Hopefully, at this point of the article, I have given you a good reason why you want to dive into enriched air, as well as some of the safety precautions and concepts that you will be exposed to when you take the nitrox course, which I think anyone who plans to dive frequently should strongly consider. The Nitrox course is relatively short, with most of it being self-study, reading the PADI Nitrox manual. My instructor spent approximately 2-3 hours doing the chapter reviews in the book to make sure I understood the material in the book. Then, he showed me how to set my dive computer for the nitrox dives we were about to perform. One of the most valuable skills you will be taught in the nitrox course is requesting or ordering the desired nitrox mix (percentage of oxygen in the tank) and, most notably, checking or analyzing Nitrox once the tank has been filled. This helps make sure you get the concentration of oxygen you requested, limit shop liability, and help you enter the specific percentage of oxygen you will be breathing for your dive. I can not emphasize this skill enough; you need to analyze any enriched air before leaving the shops and using it. The importance of knowing what oxygen percentage you are breathing, so you never exceed the depth rating is critical. Enriched air has safety factors that need to be adhered to. You must plan your dive according to the enriched air you plan to breathe, therefore, it is critically important for you to know for sure that the air you are breathing is the air you planned to dive. This is why, the course will teach the procedure of tagging or labelling your tank with the gas you are requesting, anywhere from 22% oxygen to 40% oxygen. Once the tank is filled and before you take the tank, you will use an oxygen gas analyzer provided by the shop you are buying your enriched air from (you can get your own if you want) to verify what is in the tank. Then, you allow the tank that you are going to breathe to blow some air over the oxygen sensor, and it will give you a reading of the actual percentage of oxygen the tank was filled with. That way, you can make any necessary adjustments to your dive plan. For example, if you requested 32%oxygen and the gas blender got 28%, you can factor that into your dive plan as you may be able to go a little deeper than if you had got 32% to your contingency plan. Or you can just dive to the same depths as though you had 32% knowing your breathing 28%, which increases your safety factor. Or you can ask the shop to remix your tank, but it is normal for most shops to be within 1-3% of the requested percentage. Either way, it can not be emphasized enough that you, the person who will breathe the gas, should analyze it. In my experience, all the dive shops I have used require the diver to analyze the gas in the presence of the gas blender, and both people sign as witnesses to the diver knowing what gas they are breathing on their dive. Diving enriched air adds a minor technicality to diving. Still, given the bottom time increases and the reduction of dive fatigue for multi-dive days, you can’t go wrong with getting certified. 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