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.
Your open water course just can’t cover everything there is to know and I’m here to provide a few answers.
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.
We get questioned a lot on what the difference is between SDI, TDI and ERDI courses, so we decided to put it out there where it’s easy for everyone to find when they start doing research.
There are many factors that can help a diver at any level conserve breathing. The following are six basic suggestions that may help you reduce your gas consumption.
Sport and technical diving have differences, such as going deeper and staying longer. Most people who are curious or want to technical dive shouldn’t be discouraged by bad attitudes.
The best way to prepare and plan is to follow three core tips when diving Nitrox. 1. Analyze 2. Label 3. Set Computer
This article will discuss 3 mistakes that are common for new divers, how to avoid them, and how an experienced diver could easily end up making the same mistake..
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