|It is not a realistic possibility given the laws of physics|
Posted by Dr. Strangelove on August 24, 2005 at 16:49:41:|
In Reply to: Re: Care to be specific about what's wrong? posted by Chuck Tribolet on August 24, 2005 at 11:15:53:
The idea of "spontaneous oxygen explosions" goes against any theory of physics that is ever implicated in the various cautionary tales against partial-pressure nitrox blending. It's the pressurization of oxygen in high concentrations that creates the risk of combustion by hydrocarbons which -- in the form they are found in air and rubber o-rings and lubricants -- are essentially incompletely combusted fuels to begin with.
So in the presence of highly concentrated, high-purity oxygen these hydrocarbons may -- again, essentially -- "complete" their combustion. I am far too lazy to go find or draft the algebraic expressions involved but you can calculate, based on the temperature, pressure, the percentage of oxygen in the mix, and the density of the hydrocarbon "fuel," the point after which combustion becomes likely.
Once the pressurized oxygen is through the line and valves and into the tank, the risk of combustion approaches essentially zero assuming the typical recreational nitrox range of 32 to 40 percent oxygen. Which is why shops with membranes don't concern themselves with oxygen cleansing because EVEN UNDER PRESSURE at those percentage concentrations of oxygen combustion is algebraically impossible (or at least so unlikely as to be the practical equivalent). Possibly this could change if you elected to fill the tank on the surface of Venus but we can assume not.
So it is not possible for there to be spontaneous oxygen combustion at discrete locations inside of a filled tank because the temperature, pressure and concentration of oxygen present does not differ materially among various "spots" inside a filled scuba tank.
Another way of saying it is that if such combustion took place, then the conditions which allowed it would exist not just at the spot of the spontaneous combustion but also at every other spot inside the tank (for the reasons stated above) and thus the tank would in all likelihood have to explode -- unless of course it was only lightly filled and was thus able to withstand the increased temperature and pressure resulting from the combustion.
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