... of its unique properties, such as its low boiling point, low density, low solubility, high thermal conductivity, or inertness. ... pressure nervous syndrome. At these depths the low density of helium is found to considerably reduce the ... used to cool certain metals to the extremely low temperatures required for superconductivity, such as insuperconducting ... .9999% O2 +Ar≤0.2,N2 ≤0.4,CO≤0.1,CO2 ≤0.1,CH4 ≤0 ...