Analyze your tanks
How often when you get your tanks filled or rent tanks do you analyze your tank? How certain are you that the tank you are renting does not have any trace of nitrox or other gases in it? Have you ever made sure that they clear the fill whip before starting to fill your tanks?
Even if you are not a certified nitrox diver it is critical to always analyze your mixture before diving with it. This is a simple task that can save your life. Every day in the dive industry we read about accidents and deaths that result from failure to take 2 minutes more and analyze your tank. Most shops have a nitrox analyzer and many more are starting to carry a c02 analyzer as well. Take the time to check them. If you do not know how to use an analyzer ask the staff to help you. If the staff says there is no need insist on doing so.
The reason to do this is that oxygen becomes poisonous at a depth greater than 20 feet (can be shallower based on the person and other factors). If your tank contains the wrong mix for the depth you are planning you run a chance of oxygen toxicity and a CNS hit. This is usually in the form a grand-mal convulsion, which can lead to your death from drowning. There is a lot more involved with this and additional reading can further educate you on the issues. I would suggest this article: http://www.diverite.com/education/rebreather/tips/oxygen%20toxicity%20signs%20and%20symptoms/ as well as searching Google for CNS hit / Clock and Oxygen toxicity.
There is one exception to analyzing your tanks and I hesitate to say what the exception is, though I feel it does need mentioned as if I don’t someone else will. There are some fill stations that only fill air and are not capable of doing mix gasses. In this scenario the chances that the tank you rent from them having nitrox or a mixed gas is pretty much 0%. However if you have your own tank with a nitrox mix already in it and have it topped off you will still have a percentage of nitrox in the tank. In this case you should analyze it before diving with it to avoid issues. No matter what the case is, if a c02 analyzer is available I would strongly suggest using it. C02 issues usually occur from poor air intake and poor compressor maintenance. Though there are other things that can cause it.
In short analyze your tanks all the time even as a recreational non nitrox certified diver. This short process can save your life.
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