What is the effect of elevation on oxygen readings?

Recently we received a call from a customer who was in quite a panic.  They had taken their Model 901 O2 analyzer from Minnesota to Denver, and turned it on to see quite a difference in the ambient oxygen readings when powering the analyzer on.

While our calibration certificate states the elevation that our O2 analyzers are calibrated, certainly many customers don’t read the certificate that closely, or even realize the difference that a change in elevation can make.

But, it’s instructive to know that the difference between oxygen readings at some key altitudes:

Elevation (Feet) Pressure (mb) Pressure (atm) O2 Reading  
0 1013.2 1.000 21.31  
500 995.1 0.982 20.93  
1000 977.1 0.964 20.55  
1500 959.1 0.947 20.17  
2000 941.1 0.929 19.80  
5000 850 0.839 17.88

So, as this chart demonstrates, a difference of a few hundred feet will make little difference, especially when testing gas flushed packages with less than 1% oxygen.  But it might make a difference if the “span” of the analyzer is not adjusted upon arriving to a significantly different elevation.

The Quantek factory is at an elevation of 500 feet, so if you’re up in the mountains, you may notice that the oxygen reading is about 1% lower at 2000 feet when you receive your analyzer.  When testing nitrogen flushed packages, where the goal is to remove as much oxygen as possible, this may not be significant – it does not mean that a package with 1% oxygen will test as having 0% oxygen.

The difference is proportional – so even without adjusting the analyzer, a package with 10.0% oxygen will read 9.9%; a package with 0.5% oxygen will not show any difference.

Of course, it is always best to calibrate your analyzer upon receipt.  This is very easy – press the pump button to draw in room air, let the reading stabilize, then adjust it to 20.9%.