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Analyzing and Checking Gases – NACD Journal 3rd Quarter, 2005

You know the feeling of pleasure that comes when you fin over a low silty clay bottom, look back and it’s as clean as a whistle. That moment when everything falls into place during a cave dive, the little inward grin of satisfaction that comes after you lay in that “perfect” jump reel, the post-dive buzz after visiting somewhere you haven’t been before. These, at least to me, are some of the more important of the various reasons that motivate me to cave dive, apart from the fact that it’s just plain fun!

I’ll always remember swimming Peacock 3 for the first time, gliding over the “sand slide restriction”, marveling at the darkness of the walls, the organic growth hanging from the ceiling, jump lines appearing out of nowhere, a dive very different from the clear waters of Ginnie but definitely one of the better dives I’ve done in my short cave diving career. It was awesome to finally take the jump over to Hendley’s Castle and drop down, gently scull through the bedding plane at 130 feet or so. I remember my Nitek He beeping as I crossed over the 1.4 ppO2 threshold so, as my buddy and I had discussed previously, we turned around at the end of the bedding plane and headed back up. The drop after the bedding plane looked incredibly tempting but we didn’t have the mix for it, after all the cave will still be there tomorrow, the next week and long after we have all moved on. A couple of weeks ago I was hovering above and looking into “The Pit” at D2 and literally felt my jaw drop at the clarity of the water. It was an indescribable feeling to be surrounded by such wondrous formations, to be completely overwhelmed by the prettiness of such a cool tunnel dropping out of sight at the very bottom of such a massive cave. We were well above thirds but due to the limitations of our END (Equivalent Narcotic Depth) the guide and I decided (as per our pre dive plan) to leave it for another day. The point here is that while we all work our way up to, and enjoy doing these types of dives, one must always be aware of the limitations of what one is breathing. There is no place for complacency and self satisfaction in cave diving and this is even more pronounced when it comes to our breathing mixes.

Working as a professional gas blender, (okay, okay being a tank monkey!!) I talk to a lot of cave divers with varying skill and experience levels and one of the more common questions I get asked is “What are you blowing today?” Even though I know we have our usual 32% on tap, I always give my standard answer “Oh I don’t know, I guess somewhere between 21% and 40%”. The reason I say this is I want people to check their gas, I see too many people fill out our gas log and “presume” we’re giving them 32%. I’ve also been asked “What’s the MOD (Maximum Operating Depth) of 32%?” One time I told a gentleman “198 feet” and he wrote it down in my log book!! Needless to say we had a little chat about MODs…..

People, I work at the gas station and I always check my Nitrox percentage every time I fill my tanks, whether they’re back gas, stage bottles or deco bottles.  A good cave dive begins with good planning and if you don’t know what’s in your tanks how can you plan your dive? I’ve shown up at a deep site and watched someone swear they had 32% as their deco gas, but after analyzing it, due to some insistence on a friend’s part, it turned out to be 42%! Considering that it’s an accepted practice during decompression to get on our deco gas with our ppO2 at 1.6, if you work through the math, 42% at 130 ft gives one a ppO2 of 2.1! Maybe you’re comfy with that, but I’m definitely not….

Anyways, here’s a quick refresher for those who’ve forgotten…..MOD = ((Desired PPo2/Fo2) – 1) x 34 (or 33 in salt water) as in ((1.4/.32) -1) x 34 = 114. Got it? If not, swing by my shop and I’ll explain it better. While we’re on the subject, we all know cave diving’s an expensive sport, so please take the time to drop the $25 to $1000 that it takes to buy/build your own gas analyzer. This is just my opinion, but if you’re diving nitrox you really should own a nitrox analyzer, and if you’re diving trimix you should invest in a helium analyzer, and the key here is to know how to use and calibrate it. How many people reading this know that if you calibrate your sensor on a hot muggy North Florida summer day (90deg/80%humidity) and are not using an air bottle, you will want to calibrate your O2 to 20.1% instead of 20.9%? I constantly try and explain this to people as they wave our shop analyzer around in the air. Think about this for a moment, would you cave dive without a safety reel? Would you let someone else check your valves in water? Would you want me to tell you what kind of gas you’re diving today? Do you trust the tank monkey with your life?

I don’t mean to go on about this, but it’s very basic stuff that should have been covered in your cave and gas courses. Sure we all get a little bit lazy at times, but knowing your gas percentage and how to analyze it is extremely critical stuff. For example, on a recent dual fatality, the divers involved had an END of over 150 ft, which had to only compound whatever problems they were already trying to deal with. Well, thanks for taking the time to read my viewpoint, please make sure you know what gas you’re diving and hopefully I won’t have to keep re-calibrating our shop analyzer all the time!! Anyways, as always try to slow down and think a little bit before you act, keep your cave diving safe and please take good care of our underwater cathedrals.

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