If a full cylinder / tank of N2O has 750 to 800 psig.

And 90 percent or more of the medical gas manifolds switch over to the secondary changeover side at 140 to 150 psig.

The math would be that around 20 percent of the cylinder / tank pressure is being return the medical gas supplier.

SO What !

Well at that point (to the best of my knowledge). The medical gas supplier is blowing off to the earth atmosphere the leftover 20 percent gas N2O.

Al,

I don't think it's fair to say 20% is of a full cylinder is lost when the supplier refills. These tanks fill at 50 lbs and are probably somewhere around 400 cubic foot of gas.  The leftover in the tank may be 20% of the gas volume but not the total amount consumed.  I'm pretty sure thats what you meant but I just wanted to clarify.

To be honest I didn't really care for the articles and felt like they were propaganda driven.  I also took offense at the "Highly Inefficient Piped System".  My data shows no such thing.

In my short google searching I found that most if not all (99.996%) of the N2O inhaled leaves the body un-metabolized in its original state.  

If the point of the article was to save the planet, try and find a different/safer anesthetic gas, or focus on capturing it as it is exhaled through the WAGD system if it is so terrible.  Don't scapegoat piped medical gas systems for being inefficient and wasteful.

Al,

My point was:

20% of a full 50 lb bottle is 80 cubic ft. (20% of 400 CuFt)

20% of an empty -gas only- filled bottle is much much less.  Someone here smarter than me can tell us the volume inside an H-Cylinder and convert 150psi and an unknown volume to CuFt.  I'd bet it's just about 15 CuFt.

My personal data is that Nitrous Oxide leaks are pretty rare compared to Oxygen and Vacuum.  Most employee overexposure to N2O we see is related to procedures not leaks in the piped gas system.  I'd be happy to pass any info.  Cary, just shoot me an email with what you're looking for.

Google solved the Metabolism question.  I'm not smart enough to know if it is correct or not.....  The big point there is even if the gas is all used in anesthesia to patients with "zero loss"; if it is exhaled to the atmosphere in its original state with no chemical change (through the WAGD system) what's the point of talking about leaks in the system?  

This would mean that every CuFt of N2O produced hits the atmosphere unless it is captured.

It this a big deal?  I don't know....