Here are a few items you can include in your logbook to help you stay organized and honest, track progress, and work on self-improvement as a diver.
Having the correct weight makes it easier to get neutrally buoyant. It also helps with air consumption and it means you have to haul less weight to and from the dive site. Before we can determine our weighting requirements, we have to look at what factors are affecting us.
This article touches upon efficient ways to operate the ‘cursed’ clip and offers a few ideas on handling known as ‘Clip Management’.
One of the easiest ways to have a better experience underwater is by streamlining our gear and our bodies.
This article is the first of three that will address the differences in generations in the industry: Things divers born after 1985 will not understand. A presentation at DEMA titled Inside the Millennial Mind – How to connect with #Millennials to increase business, presented by Lauren Kieren (Millennial) and myself (old guy). Finally an article by Lauren titled, Things divers born before 1985 will never understand.
By Joel Silverstein:
Video Credit: Courtesy Capt. Billy Deans
***NOTE:*** This video was recorded over 20 years ago.
The Witches Brew – Trimix and Nitrox Gas Mixtures
So you’re planning on going diving this weekend and need to get your cylinders filled with nitrox. Imagine that you have a choice of getting that mix from one of only six dive centers in the United States. You can go to Long Island, New York; Gloucester City, New Jersey; Key Largo or Key West, Florida; Santa Cruz, California; or Bellingham, Washington to get those tanks filled. That’s right, back in the early days of technical diving we had a choice of six dive centers in the US that would fill our tanks with oxygen enriched air. If you were an active nitrox diver, the ability to obtain breathing gas was very limited. Getting gas required logistics far beyond that of driving to the local dive shop. Yet, that did not stop people from getting the coveted breathing gas. If you were near these dive centers, it was easy. If not, creativity crept in.
Tell any diver they cannot have something and soon they will make it themselves. It did not take long for divers to start mixing gas in their garages. Dive shop owners were strongly against this practice, and the industry frowned upon it just as loudly. Yet divers were mixing gas at home more than most could have imagined. Some divers were very successful at home brewing, but others were sloppy and dangerous. Most anyone with simple math skills could calculate proper proportions of oxygen and air to make a nitrox mixture. However, mixing nitrox gas was more complex than transfilling some oxygen and topping it up with air. It required oxygen, hoses, fittings, gauges, flow meters, an oxygen analyzer, and an air compressor. In addition, it took an understanding of cleaning for oxygen-service, gas system design, heat exchange, and the dangers of adiabatic compression. Most people could put the first parts together, but it was the oxygen compatible air and oxygen cleanliness that were the missing links for many. Some divers would fill their scuba cylinders at home with a specific amount of oxygen and then have them topped off with air at the local dive shop. On the surface, this seemed a logical solution, but it violated every rule of gas mixing, and it put many people at undue risk. In some situations, it resulted in serious accidents. If they were cutting corners in one part of this process, what else was not as good as required?
For divers who wanted to do it right, they sought out training from experts like former NOAA Diving Officer, Dick Rutowski in Key Largo, Captain Billy Deans in Key West, or ANDI co-founder, Ed Betts on Long Island.. The courses offered were comprehensive and usually took two to four days to complete. For those who could not get to these rare training events, the early CompuServe internet forums were a major source for gas mixing discussions. In addition, divers would share information they garnered from the Navy and NOAA diving manuals, as well as from the commercial diving industry. Along with all the seriousness and challenges that were facing technical diving in the early days, deep diving pioneer, Capt. Billy Deans created a video that parodied decompression table creation, breathing gas analysis and gas mixing. It gives today’s divers and gas mixers an idea of what we were up against back in the early days of recreational mixed gas diving.
It was not until Technical Diving International introduced the first TDI Gas Blender Course and textbook written by Jan Neal, that gas-mixing methodology became readily available to divers worldwide. Neal’s materials legitimatized recreational gas mixing and formed the basis for what we do today in teaching divers about mixing gases for diving. The dive industry as a whole has benefited from the contributions of divers over the years to gas mixing.
Learning about mixing gas is much easier today than it was twenty years ago. A whole industry has emerged that has made the tools of the trade much easier to get; between training, gas analyzers, gas boosters, compact compressors, filtration systems and a host of other items. While divers are able to get gas mixes from most any dive center around the world, there are those who still like to mix on their own and the right stuff is easy to get. Like in most every industry, great ideas and techniques are the product of a few brave individuals who sought out knowledge and adventure, many times from the workbench in their garage.
Joel Silverstein is the author of three books on nitrox, a major contributor to the NOAA Diving Manual, and TDI Instructor Trainer # 125. Since 1989 he has mixed more than two million cubic feet of breathing gas. Contact: firstname.lastname@example.org
By Jon Kieren
There are many factors that need to be considered when choosing decompression gasses for a dive. The dive profile, logistics, environment/site conditions, and personal preference all come into play; how do these factors affect our decision? First, we need to take a brief look at why we use different gasses for decompression to begin with, and then how the factors previously listed affect our gas choices. For big dives with extensive decompression obligations, it’s often a balancing act between oxygen exposure and off gassing.
Why switch gas anyway? This takes a brief lesson in decompression theory to explain; we’ll focus mainly on the off gassing portion of the dive. The rate of off gassing is related to the partial pressure within the tissues of the body and the partial pressure of the gas being breathed. When the partial pressure of the inert gas (mainly nitrogen and helium) in the lungs (the gas we are breathing) is LOWER than the partial pressure of the inert gas absorbed in our tissues, the gas will move from the area of high pressure (our tissues) to the area of low pressure (our lungs) and be expelled when we exhale.
There are two ways we can reduce the partial pressure of the inert gas in our lungs. First, is by ascending and letting Boyle’s law take over. As the gas expands as we ascend due to reduced ambient pressure, the partial pressure of the gas drops. This works but is not the most effective method. If we ascend too far or too fast and the ambient pressure decreases too rapidly, bubbles can form causing decompression sickness. The second method of reducing the partial pressure of the inert gas in our lungs is to reduce the fraction of the inert gas in our breathing mixture. In order to reduce the fraction of inert gas in the mix, we increase the fraction of oxygen. By switching to an oxygen rich gas on the ascent, we reduce the partial pressure of the inert gas in our lungs and increase the rate and efficiency of off gassing. So, more oxygen=less inert gas=faster/more efficient deco. Got it?
Okay, so if a higher fraction of oxygen is better for decompression, why don’t we just use 100% oxygen for the entire ascent? It would sure reduce our decompression times by a significant amount, wouldn’t it? Well, unfortunately we have to be cautious of the pesky oxygen free radicals caused by breathing high partial pressures of oxygen. If these oxygen free radicals are left to cause damage faster than the body can repair it, oxygen toxicity can become a serious concern. In short, the higher the oxygen content in the breathing gas, the shallower it must be breathed. As an example; for sport and technical diving applications, the maximum operating depth of oxygen is 6 metres/20 feet; and the maximum operating depth of 50% nitrox is 21 metres/70 feet. Here’s where we begin our balancing act.
We now need to consider the other factors that will affect our gas choice. First of all is logistics. What gasses are actually available? Many technical dive facilities have their decompression gasses pre-mixed, so you may be limited to what they have available or are willing to blend (gas blending can be a time consuming process). Also, there are many places in the world where 100% oxygen is not available, or can only be filled to roughly 150 bar/ 2000psi, depending on the fill station’s equipment. Once you know what your options are, you need to look a bit closer at the environment you’ll be diving in and how you will conduct your last decompression stop.
Many divers will vary the depth they plan to conduct their final decompression stop based on the environment they will be diving in. In a perfect world, we would always conduct our last stop at 3 metres/10 feet. Unfortunately, this is not a perfect world. Rough seas and overhead environments may make it difficult or impossible to conduct your last stop at 10 ft, so it may need to be conducted a bit deeper at 6 metres/20 feet. Conducting this last stop on 100% oxygen could now be problematic as you will be exposed to a much higher partial pressure of oxygen for the duration of the final decompression stop. Add rough seas to this in open water, and it could be very difficult to remain at a safe depth on oxygen. This is an instance where reducing the oxygen content may be wise. While a lower fraction of oxygen will not be quite as effective as a decompression gas on this final stop, it can significantly reduce the diver’s oxygen exposure. If you are making multiple gas switches in order to maximize the partial pressure gradient for the entire ascent, you will also need to look at the environment to decide what gasses to carry. A good example of this would be a cave dive. If you were planning your dive to switch to 50% at 21 metres/70 feet, but you know that there is a restriction in the cave at 21 metres/70 feet making it difficult to conduct a proper gas switch, you have a few options. First, would be carry the same gas, but decide to switch to it at a shallower depth where there is not a restriction. This would work fine, but would not be as effective for your decompression. You could also choose to bring a different decompression gas. A leaner nitrox mix could be switched to a bit deeper, but would not be as effective for the shallower stops. A richer nitrox mix would be more effective in the shallower stops, but you would not be getting the advantages of a decompression gas until later in the decompression schedule. Using desktop/mobile decompression software makes running these alternative options quick and easy so you can see immediately how your choice will affect your decompression plan.
After looking at all of the scenarios above, sometimes it just comes down to personal/team preference. Many divers and dive teams choose to use a standardized set of decompression gasses. This policy helps keep things simple and consistent. If a diver always carries 50% and oxygen for decompression, then they are always making gas switches at 21 metres/ 70 feet and 6 metres/20 feet. This standardized method streamlines the dive planning considerably, is consistent, and works well for many applications.
While this is not a complete discussion on decompression gas planning, it’s a good example as to what type of considerations we need to take into account when choosing our deco gasses. These points, along with others, are covered in depth in the TDI Decompression Procedures, Extended Range, Trimix, and Advanced Trimix courses and course materials. For more information on these courses, please visit TDI courses section
by Cris Merz:
The fantastic stories about voodoo gas seem to have mellowed out a little in the last 20 years. From, “It’ll kill you” to “You will have soooo much energy after the dive”, it never ceases to amaze how nitrox, as a topic for discussion, has always been a leader in misconceptions.
With many reasons in favor of diving nitrox, the reasons for doing so may hold a little more scientific value today than they did 20 years ago.
Few advances in the realm of diving have had a more profound impact during the past two decades than the widespread availability of Enriched Air Nitrox. And nothing has made the switch from diving air to diving nitrox more straightforward or more enjoyable than nitrox programmable dive computers.
Simply put, nitrox – air with additional oxygen content – allows divers to enjoy longer bottom times (and shorter surface intervals) than their air-breathing dive buddies, while staying within the limits that were stressed in their open water training.
Nitrox makes this possible because it contains reduced levels of nitrogen compared to air and less nitrogen translates into more bottom time! But of course there is a price to pay. Diving nitrox does present risks that are not present while diving air and these risks require divers to take additional steps during their pre-dive planning and then adhere to that dive plan.
The number one reason for diving nitrox is safety. When diving with a greater amount of oxygen (32% or 36%) in the mix, rather than air (21%), you decrease the risk of decompression sickness because you’ve lowered the amount of nitrogen you are breathing in at depth – and as we know, nitrogen is the number one culprit associated with decompression sickness.
When should we dive nitrox? Well, whenever the opportunity presents itself. It may not make a great difference but it certainly will not hurt. Unless you go diving beyond the Maximum Operating Depth (MOD) of the mix in your tank, it is beneficial to you every time, though sometimes those benefits are much greater than others based on your diving profile.
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.
Despite having depth limits to be aware of due to the risk of oxygen toxicity, and perhaps some additional costs for the fills, the benefits of nitrox will play a role in your steps to keeping your dives within safer limits than if you were on air.
If you are not yet nitrox certified, find out more about diving with enriched air from your local SDI or TDI instructor.
You will discover that diving nitrox is not rocket science. The concepts are straightforward and easy to understand. Of course, like most things relating to diving, the subject does have another side and if the science and technology behind the basic concepts of nitrox interest you or if you find yourself wondering how nitrox with higher levels of oxygen than 40 percent would affect your diving, you may want to consider continuing on to Technical Diving International’s (TDI’s) Advanced Nitrox Diver course.
Any time you fill a tank with nitrox, it must be identified as such. This will help to prevent accidents in the event that someone uses a tank filled with nitrox without taking the proper precautions.
by Jon Kieren
People make mistakes, it’s human nature. I make them all the time. I’m sure that even after this article has been edited several times and published someone out there will find at least a couple of typos and call us out on it. A typo is one thing. However, a simple mistake in the blending process can result in a diver breathing a mix with significantly more or less oxygen than they had expected, causing serious injury or death. If we KNOW that people make simple mistakes so often, then why do so many nitrox divers today NOT analyze their gas before diving? There are two primary reasons: either they don’t understand why it’s so important (a topic that is covered in every nitrox course), or they have just become complacent. This article will discuss both scenarios and how to avoid them.
Why is it so important to analyze your breathing gas? Simply, it can kill you if it’s wrong. If the oxygen content is less than the diver had expected, they can end up with unexpected and unknown decompression obligations.
Example – You make a dive to 30 metres/100 feet assuming you’re breathing 32% nitrox. You spend 39 minutes on the bottom and surface with no decompression obligation. Unfortunately, the nitrox tank you were diving was accidentally filled with air (21% oxygen), and in reality you just blew off 26 minutes of decompression. A significant error that is almost sure to result in Decompression Sickness. This situation can be made significantly worse by conducting repeated dives.
What if the oxygen content is HIGHER than you expected? Should be better off then, right? As far as decompression obligations are concerned, yes. However, a far greater risk in diving nitrox is Oxygen Toxicity and can cause severe convulsions (not a good situation underwater).
Example – Using the same dive as above, assuming you were on 32% nitrox at 30 metres/100 feet, your partial pressure of oxygen (PO2) would be close to its upper limit at about 1.3 ata. If that nitrox mix was in fact a 50% nitrox mix, your PO2 would now be over 2.0 ata and would be considered extremely dangerous.
The examples above are not the only concerns of breathing the wrong gas at the wrong depth; a thorough nitrox course will cover the others, as well as how to avoid them. So if you have to be Nitrox certified to dive nitrox, and the risks and proper procedures for avoiding those risks are covered in the course, why do people still end up breathing the wrong gas? The simple answer is: complacency. Over time, divers become complacent with their gas analysis procedures and start to skip it altogether, which means they end up in the water with absolutely no idea what they are breathing. Pretty scary.
Normalization of deviance is a term used by astronaut Mike Mullane (*Mullane 2014) to describe the process of complacency in safety procedures. In brief, it explains how humans have the tendency to take shortcuts due to different factors including time, peer pressure, etc. Once this shortcut is taken and nothing bad happens, the brain will incorrectly assume that the shortcut is “safe”. This shortcut now becomes the norm, and we have completely eliminated a critical step in a procedure. This applies to diving at every level. How many times have you seen divers jump in the water without doing a proper predive check? It is taught and its importance stressed in every open water course, yet it gets skipped every day because so many divers have “gotten away with it” they assume it’s safe to dive without making predive checks and then eliminate it from their procedure. Unfortunately, it also results in emergencies from divers forgetting to turn on their air and inflate their BCDs.
The same happens to nitrox divers. Maybe one day they are in a rush and forget to analyze their gas at the fill station. They get to the dive site and realize that they forgot to analyze but now do not have access to an analyzer. They are left with two choices, either not dive today or dive without analyzing their gas. The diver has been getting fills from that fill station for years and has never gotten the wrong mix, so they decide to dive anyway and assume the fill is correct. Nothing bad happens, so they now believe this shortcut is safe. “If I get my fills from XZY Dive Center, I know that it will be correct and I do not need to analyze my gas”. They have eliminated the most critical step in diving nitrox, and this is now the norm.
We know people make mistakes, and that’s why we have safety procedures in diving. These procedures help us catch the little mistakes before they create catastrophic emergencies. When diving nitrox, analyze every tank before every dive without exception. It could save your life.
* Mullane, Mike. (March 2014). Stopping Normalization of Deviance.