I have to interject here because I think this is a slightly dangerous claim.

Balloon helium is just helium, broadly, at 98%+ concentration. It has a tiny amount of atmospheric gas, mostly nitrogen, in it as there is no need to go too far with purifying it, but there is zero intention of making it any safer to inhale. It is basically accidental contaminants.

If you inhale 98%+ helium, the diffusion gradient reverses and oxygen floods out of your blood. Did this once as a kid and actually blacked out. This is functionally just as true at 98% helium with some nitrogen and a tiny amount of oxygen as it is with 99.9999% helium. The difference for inhalation is a wash.

Inhaling helium is not advised. The protection we have, such as in my case, is that invariably our rapid physiological response stops us from inhaling helium and oxygen can return.