Tank oxidation contributes to death

[Rick Murchison]

Genesis once bubbled...
Even so, 1% O2? How?

Think "Helium." Unless told to do so, it isn't somerhing they'd test for, and it's oderless, tasteless etc...
If the guy was a homebrewer...
Rick

 

[Genesis]

Let's assume that he had "missed" putting the O2 in on a Trimix fill.

He'd be grossly under O2 percentage, but still not have less than 1% in the tank....

If I saw a less than 1% reading on my O2 analyzer, I certainly wouldn't stop there and call it a day. I'd first make sure the sensor was actually connected , and if it was, you can bet I'd want a FULL analysis on the contents of the tank.

But even if you DO stop there, and say "well that obviously would kill you", thus satisfying the "cause of death" problem, to then go on to list "contributing factors" is beyond stupid and only serves to damage the reporter's credibility. There ARE no contributing factors - the diver breathed a gas that had (effectively) no oxygen in it!

 

[John C. Ratliff]

I looked over my personal files, and so far have been unable to find the reference I remember. I did do a search an the net, and came up with this website:

YMCA SCUBA

I believe the death I remember was to a fellow who had an old tank he had not used in years, and simply wanted to go under a dock to find something. He was only under a little while, and the bubbles stopped coming up. He was dead when they brought him to the surface. Again, this is from long-ago memory, and therefore not really reliable. I'll search again.

I think that this type of oxygen depletion could occur in steel tanks, but not aluminum. The corrosion process is different in the two, and in steel it accelerates with time, whereas aluminum is self-limiting by the scale. I'll get a better handle on the corrosion process, and see whether the other's perception that this simply could not happen is true. My mind says it is possible, but I cannot prove it right now.

SeaRat

 

[John C. Ratliff]

I have so far searched through a number of references, including the Proceedings of IQ6-9, the 1971 and 1975 Unites States Underwater Fatality Statistics, and several books, without success. I did find the following references though:

We occasionally run into a classic example which needs to be mentioned. In one fatality the victim was using a 38 cubic foot surplus oxygen cylinder. The investigator reported as the follaws: "The regulator had rust and salt water residue in the first stage. The tank contained five quarts of rusty salt water with one-half inch of rust sediment." In this instance the victim was probably doomed before entering the water. If he didn't "buy it" on this dive he probably would on the next dive, if the tank didn't explode the next time it was charged.

John J. McAniff, "National Accident Data Analysis," Proceedings of the Eighth International Conference on Underwater Education, IQ8, Sponsored by the National Association of Underwater Instructiors, Nov. 5-7, 1976, Addendum, pg 45.

Another reference to the same accident states:

The only case in which the condition of the air supply gear was definitely implicated in a death involved a 38 ft3 surplus report: "The regulator had rust and salt water residue in the first stage. The tank had five quarts of rusty salt water in it, with one half inch rust sediment present." Since this tank had 700 lb/in2 remaining and the victim was diving alone, oru presumption is that the victim performed some moneuver in the water that dumped residue into his regulator and either locked it up or flooded his mouth and lungs with rust and water...

United States Underwater Fatality Statistics 1975, March 1977, pg 27

It is possible that I heard at one of the conferences that the air had been tested bad after these reports were published, but that remains unconfirmed.

For those of you who feel that the corrosion reactions of iron in water are "simple chemistry," take a look at this site:

Equilibrium Reactions of Iron in Water

Add salt water, and the corrosion effect is much enhanced:

Iron corrosion in (salt) water

To me, this means that a decrease in oxygen content, perhaps enough to jeopardize life, is a viable possibility with the introduction of salt water into the tank, and given enough time. Notice in the referenced reaction (see the iron corrosion in (salt) water page, above), there are several steps that use oxygen, and that it seems to be an accelerating process that is quite complex.

SeaRat

 

[100days-a-year]

Actually that seemed to imply that more Fe is bound up than O.That still doesn't explain where the 18ozs or so of 02 went .There wasn't any mention of 5 to 10 lbs of rust which is what the range of formulae give us.The rust blocking the 1st stage is much more likely.

 

[John C. Ratliff]

There are two reactions of interest to me to look at. I'll preface this by saying that I'm not a chemist, but these are interesting.

The first is the reaction of oxygen with the water:

The electrons provided from both oxidation steps are used to reduce oxygen as shown.

O2 (g) + 2 H2O + 4e- ------> 4 OH-

In this one, we loose oxygen as a gas to the water, in the form of hydroxide ions. It is possible to react a lot of oxygen with the water and loose it in this manner. Then we come to the rust formation:

The ferric ions then combine with oxygen to form ferric oxide [iron (III) oxide] which is then hydrated with varying amounts of water. The overall equation for the rust formation may be written as :

4Fe+2 (aqueous) + O2 (gas) [4 + 2 H20] -----> 2Fe2O3 X 2H2O (solid) + 8 H+ (aqueous)

It seems that the oxygen not only forms with the iron, but also with the water and with water that is bound with the iron in solid form.

Now, if you look at those 8 hydrogen ions, they again can combine with the oxygen in the air to form hydroxide, and begin the process over, accelerating as it goes. This would take care of 4 O2's, which adds up over time to a decreased oxygen content in the tank's air.

That's what I see from the formulas. Again, I'm not a chemist, and if there are any of you out there who are, please educate us.

SeaRat