Failure to Log…Correctly

There is supposed to be a standard of practice among Nitrox and mixed-gas fill stations (including your local dive store) that goes something like this. Before you are allowed to leave the fill station with your freshly filled Nitrox, Oxygen or Trimix cylinder, you must:

• Personally analyze (or witness the analysis of) your cylinder’s oxygen (and, if applicable) helium content.
• Label your cylinders as described on the preceding page.
• Enter a minimum of the date, cylinder description, FO2 and MOD in the fill station log and sign it.

You already know the reason for properly analyzing and labeling your cylinders. The fill station log provides a back-up for this information. It also relieves the dive operation of considerable liability by having you sign for what you at least thought was the cylinder’s O2 content and the depth at which this wonderful gas mixture could get you killed.

This system can break down for any of a variety of reasons, however:

• A surprising number of dive operations simply don’t bother with keeping a log — especially those that only dispense premixed Nitrox.
• Equally common are divers who seem willing to accept the dive operator or gas blender’s word that their cylinders actually contain the gas mix they asked for.

I’ve been mixing gas for over ten years now. And, although I’d like to think I’m pretty good at it, I make my share of mistakes. So does every other gas blender I know. This being the case, a diver would have to be not just stupid, but drooling, farm-animal stupid to simply take my word as to their cylinder’s content without checking it himself.

Even when divers analyze their own gas and complete and sign the fill station log, they frequently do so incorrectly.

Common mistakes include:

• Failure to Analyze Properly: Obviously, it does no good to log an FO2 value that is several percentage points off (any more than it does to label a cylinder with the wrong FO2). The only good thing here is that at least there will be some record of why your stupidity caused you to get bent or die.
• Logging the “Wishful Thinking” FO2: This is when you asked for, say EAN50, your analysis says what you got was EAN48 — but you log it as EAN50 any way. Doh! Let’s try this one more time. You label and log the actual FO2, regardless of whether or not it is what you originally wanted.
• Logging the “Wishful Thinking” MOD: This is a variation on the preceding error. You wanted, say, EAN50 (whose MOD is normally considered to be 70 feet — even though it’s actually between 72 and 73 feet). What you got was EAN48…but you logged it as an MOD of 70 feet any way, because you knew that was the MOD for EAN50 and, well, it was close enough — right?

Obviously, it is better to label and log an MOD that is shallower than the actual MOD than it is to use an MOD that is deeper than what it should be. The former is, at worst, overly conservative; the latter, on the other hand, can get you killed. But why not just be accurate, for heaven’s sake?

MOD tables are available from a variety of sources, and generally come with the training materials every entry-level Nitrox diver receives — frequently on the back side of the EAD tables. In other words, there is no excuse for not having them handy when you analyze gas, label cylinders and enter that data in the fill station log.

Everything you’ve read about in this article, all of these things that every diver should do — but all too often doesn’t do — well, they’re not there because some “expert” said so. They’re here because failure to do so can get you bent or killed. It’s that simple.

So what is it you want to be: A diver? Or a statistic?

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