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Why Johnny Can’t Analyze

The very first body recovery I worked after moving to north-central Florida’s cave-diving country in 1989 wasn’t a cave diving accident at all. It was a Nitrox-related fatality caused, to a large degree, by the victim’s failure to accurately analyze his breathing mixture prior to the dive.

No Oxygen!

Which reminds me: Why do we call it Oxygen Enriched Air? It’s the reduced nitrogen that provides the benefit, not the increased oxygen content … which can kill you if you are not careful. It would be more accurate to call it Oxygen Poisoned Air or, baring that, at least call it something like Nitrogen Diminished Air.

In any event, at the time, it was widely held that 1.6 atmospheres was a perfectly acceptable limiting PO2 for the working phase of a dive (today most of us limit this to 1.4 atmospheres or less, using 1.6 only for deco). As a result, the victim in this case thought that EAN36 would be a great mix for this dive as it would give him an MOD of 114 feet (based on a PO2 of 1.6 atmospheres) — and, according to the NOAA table, a single-dive exposure limit of two hours in the cave he and his buddy planned to dive (based on a PO2 of 1.5 atmospheres).

It was a nice theory. There were a couple of problems, however:

Dunce Cap

Had the victim’s gas analysis been accurate, he might have scraped by at those values. Unfortunately, his actual FO2 (determined by the recovery team after the fact) was 40.1 percent. This made his MOD 99 feet (a depth he exceeded several times during the dive). He was also five-minutes past his planned single-dive time limit of 45 minutes when he toxed and drowned.

The bottom line is: If you don’t know how to properly analyze your gas mixture, you can die. It’s as simple as that.

Given this, you would think Nitrox and technical divers would take gas analysis more seriously. Unfortunately, many don’t. In my capacity as manager of one of Florida’s most popular technical diving training sites, I routinely see things that completely floor me, including:

Nitrox Tank

Are you guilty of any of the above (or, worse, perpetuating this behavior in students)? If so, you will want to read what follows.

Failure to analyze at all »