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.
In reality, Trimix is a risk management breathing mixture utilized by divers typically seeking to offset the consequences of diving normoxic air or nitrox mixtures at a planned diving depth by replacing much of the nitrogen and some of the oxygen with more benign inert gases like helium.
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.
Knowing that we are going to have some sort of equipment malfunctions, environmental/navigation emergencies, and will just simply make mistakes at some point in our technical diving careers, how do we avoid becoming a diving fatality statistic?
by Jon Kieren:
Technical diving is inherently dangerous. Diving in environments that restrict your access to the surface requires your foundational scuba diving skills to be second nature so when an emergency arises you can focus on solving the problem and aborting the dive. Whether you are just starting your TDI Intro to Tech Course, or have over 200 Advanced Trimix dives, these six essential skills should be practiced on every dive.
- Predive Check, Descent/Bubble Check, and S-Drill – While there are three skill sets listed here, we group them together because the overall objective is the same for all three: start the dive properly equipped and with fully functioning equipment.
- Predive Check – Once fully dressed for the dive, as a team, each diver runs through their own equipment to verify primary cylinders are full and valves open with turn pressures verified, stage/deco cylinders are full with regulators pressurized but valves turned off, BCD inflates AND holds gas, dive computers/gauges are turned on and functioning properly, mask/fins/weights/etc. are donned and in good condition to dive.
- Descent/Bubble Check – Depending on conditions and site, either on the surface or on the initial descent, the team inspects each other’s equipment looking for leaks and trapped or entangled equipment.
- S-Drill – Each team member takes turns conducting the proper gas sharing procedure with another teammate.
- The dive does not start until all of these checks have been conducted, any complication must be resolved before continuing the descent.
- Trim/Buoyancy/Finning – It’s not just for looks. The importance of being able to hold your position in the water column and prevent silting-out an environment cannot be overstated; and everyone can use a little practice. Every dive, try to spend some time focusing on different finning techniques and trim/buoyancy control. Grab the GoPro and let your buddies film you so you can get some valuable feedback on what you actually look like in the water as well.
- Valve Drills – On every single dive, you should practice shutting down and re-opening each valve. Make sure do to this with a teammate so they can verify each valve gets re-opened. Depending on your exposure protection and recent diving activity, you may find it more difficult to reach your valves than you remember. It is important to work on this flexibility and muscle memory on a regular basis, because when you really need it is not the time to realize that you cannot reach a valve.
- Remove and Replace Stage/Deco Cylinders and Bottle Swapping – It is important to occasionally practice removing and replacing stage/deco cylinders in order to maintain this muscle memory. Even if the dive does not require you to stage a cylinder, practicing this skill often will speed up and smooth out the process on the dives where it is required. Going over your bottom time because you were fumbling with a stage cylinder is both embarrassing and dangerous. You should also practice swapping bottles with teammates. This can be done while decompressing by swapping stages or lean deco gasses that you are finished with between your teammates. This increases team awareness, communication, and equipment familiarity. It is extremely important to check that no hoses or equipment have been trapped by the stage/deco bottle any time you replace one.
- Lift Bag/SMB Deployment and Reel Skills – Both deploying a lift bag/SMB and running a reel are skills that deteriorate quickly when not practiced regularly, and sloppy work in these skills can be extremely dangerous. Practice these skills as often as you can, if you don’t use it, you’ll lose it.
- Post Dive Briefing – It is extremely important to debrief every single technical dive. Discuss the highs and lows of the dive, where communication was good, where it was bad, and what areas can be improved upon for the next dive. You cannot see yourself in the water, so it is important everyone in the team provides some constructive criticism. This is often done with friendly banter, but it is important to remember that this feedback will help you improve your diving and safety.
While this is not intended to be an all-inclusive list of skills to be practiced for technical diving, these six skills are applicable to most technical diving scenarios, and can be easily practiced on just about every dive. What other skills do you like to practice regularly?
Why do divers do stupid things? Well the short answer is because they are stupid. Now I know that the majority of the readers of this article are going to be divers and it’s not usually a good idea to start off by insulting your audience but bear with me.
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