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.
By Michael Thornton and Josh Thornton
Switching your diving gas in 8 easy steps
Safe technical diving begins with awareness. The first step is being aware of yourself. As you gain experience and comfort you become aware of yourself and your gear. The highest level of awareness is when you are aware of yourself, your gear, and your surroundings including your dive team. When you add complications, emergencies or any kind of stress your awareness will diminish.
Not being aware of you, your gear or your surroundings during something as critical as a gas switch can be fatal. It is important to follow a strict protocol while staying aware during any gas switch to minimize risk.
As with most diving skills there is more than one way to do things. By establishing a set protocol and adhering to it every time, the risk of making a mistake is reduced. The most common problems that arise during a gas switch are losing control of your buoyancy and changing depths unintentionally or breathing the incorrect gas mixture for the respective depth.
All deco bottles should be pressurized but with valves closed when not in use. This prevents losing gas unintentionally and minimizes the risk of breathing off of the incorrect regulator. Pressurizing is necessary to keep water out of the system and your gear working.
When performing a gas switch, the following steps will help:
- Confirm you are at the correct depth to make the planned switch and achieve neutral buoyancy. (Also have team verify)
- Identify the correct cylinder by verifying the MOD marking on the cylinder. (Also have team verify)
- Deploy the second stage and follow the hose back to the first stage to verify you have the correct second stage.
- After you have confirmed you have the correct second stage and cylinder, open the valve.
- Purge the second stage to remove any debris that may have entered during the dive, and confirm functionality.
- Swap regulators and breathe. (Signal team you are okay)
- Clip off primary regulator.
- Change gases on your computer(s). (Signal this and confirm it with your team)
As a team you should discuss where your cylinders will be mounted. Some common mounting protocols are: 1) rich mixes on the right and lean mixes on the left or 2) all cylinders on the left side and rotate them for easy access at the appropriate depths. Whichever protocol you choose make sure you can easily access all of the cylinders and verify with visual and tactile methods the various cylinders. Team gas switching protocols call for individuals to verify proper gas switches within the team. Some teams prefer to complete the switch one at a time to allow maximum control.
Labeling the cylinder near the neck allows the diver to see it (and in turn, verify the mix). An additional label on the side near the bottom of the cylinder allows the team to see the markings as well.
When switching from one deco/stage gas to another it is important to follow the same verification procedures listed above. To avoid confusion, switch to your back gas. This will allow you to stow the regulator from the first deco/stage cylinder and turn off the valve prior to deploying the second deco/stage regulator.
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.