Grades of helium: the differences and uses - Zephyr Solutions
Grade 4.7 (4.7 helium = 99.997% purity) A "Grade-A" industrial helium, 99.997% helium is mostly used in cryogenic applications and for pressurizing and purging, but is also used as a control atmosphere in manufacturing, as a cover gas during welding, in breathing mixtures for divers, and leak detection. Grade 4.6 (4.6 helium = 99.996% purity)
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