Help why helium purity??

[mouseteacup]

I've seen sources (forget where unfortunately) saying that for the exit bag method, you should use helium with a purity above 99%. Why is that? Wouldn't 99% purity be enough?

 

[Black Sheep One]

Many moons ago, one could walk into your local big box mart and buy a Helium party balloon tank. It would be near 99% Helium. Party kids would inhale it to make funny sounds. They would also die . The parents would file wrongfull death lawsuits. So the later tanks were now filled with 80% Helium and 20% Oxygen. No more wrongfull death lawsuits. Because the air is 20.9% Oxygen, these tanks will not kill you. If your goal is to die, well Houston we have a problem.. 99% Helium should kill.

 

[ClownWorld2023]

99% should work fine.

For other gases, purities of 2.8 and higher are common.