Mark's Dive Log

This time a year ago I was busy chewing through the PADI Tec Deep Diver course work and thinking about how much information we were expected to know. We learned fun acronyms like "Being Wary Reduces All Failures", "a Good Diver's Main Objective Is To Live", and NOTOX. We learned how to plan gas consumption for divers with different breathing rates and tank sizes. We learned how to calculate decompression stops using gasses with different oxygen content. Most importantly, we learned how dangerous tech diving can be and how to minimize the risks, i.e. how to be safe.

One thing I quickly realized was that regardless of how much more depth or bottom time we would get by learning how to do decompression diving, my primary reason for getting into tech diving was still not being met. I got into tech diving to be able to dive wrecks in the Great Lakes.

The Great Lakes have some of the most well preserved shipwrecks in the world. The combination of fresh water, depth, and temperature allow wooden shipwrecks to remain intact long after they would have deteriorated or been destroyed in other environments. While studying for the class, I quickly realized that the 165' mark that the DSAT Tec Deep certification trains you for was insufficient to reach some of the best wrecks including the Daniel J. Morrell (a 587' freighter that sank in two halves five miles apart, the bow at 213' and the stern at 225') and the Roy A. Jodrey (a bulk freighter similar to the more famous Edmund Fitzgerald that sank a year later).

So that meant that I was destined to do the second half of the DSAT curriculum: Tec Trimix. The DSAT Trimix course teaches you how to plan and execute dives to 240' and beyond using gas blends of Oxygen, Nitrogen, and Helium.

If you're like me, the first time you heard of diving with helium, you thought someone was pulling your leg. As it turns out, helium has been in use in diving since the 1960s. Initially helium was used to replace the nitrogen in air (a mixture known as heliox) to eliminate nitrogen narcosis. Unfortunately, that introduced a new problem: HPNS (High Pressure Nervous Syndrome) when diving at depths around 400 feet. To counteract this, divers began to add nitrogen back into the mix to act as a mild depressant. Thus trimix was born.

So, the use of helium as a dive gas has been around for a while, and it allows you to dive deeper than an oxygen equivalent nitrox (nitrogen and oxygen) blend, but it comes at a price. Actually, it comes with several prices, including the cost. More important than that is the extra decompression time. Then the cost of a drysuit inflation system since you can't use trimix in your drysuit (helium doesn't provide enough thermal protection). Oh yeah, your deco stops have to be even more precise than with nitrox tech diving. And did I mention the cost of the gas? Oh, and sometimes you may be diving with a mix that doesn't have enough oxygen to support life at the surface. And you may be diving with three, four, or more decompression/stage/travel bottles. Using the wrong one at the wrong time could result in death. Not to mention just lugging all of that bulk through the water.

So why do it?

To get to the bottom. Honestly, the risks are manageable (even if they aren't eliminated) and replacing some of the nitrogen with helium makes you safer at depth because you aren't as narced as you would be with nitrox or air. And diving with hypoxic mixes (gas blends with less than 21% oxygen) reduces your oxygen exposure for even more safety. So you trade one set of risks for another. But you'll get to dive places that most people can't even dream about.

As for the inherent relative risk of diving to 245 feet versus 165 feet? Does it really matter? You can't go straight to the surface from either depth, so screwed is screwed. If you have an emergency that you can't handle the result will be the same whether you are 245 feet or "only" 165.

And to think that 130 feet used to be scary.