The great majority of the gaseous helium that has been supplied to helium customers in recent years has been Grade 5 helium, which means that it is 99.999 percent pure.
In fact, the typical purity of standard commercial grade helium has migrated over the years from 99.995 percent purity (Grade 4.5) to Grade 5, despite the fact that several of the major helium applications would be perfectly fine using helium of lesser purity.
So why do many helium customers purchase higher purities than they require? The simple answer is that the great majority of helium sold globally starts out as extremely pure liquid helium that is filled into bulk liquid ISO containers for cost-efficient transportation to world markets, despite the fact that most end-user demand is for helium in gaseous form. The typical liquid helium ISO container holds approximately one million standard cubic feet (SCF) of helium, while the largest tube trailer or skid utilized to transport gaseous helium only holds about 180,000 SCF. This means that transportation of bulk liquid helium is more efficient than transportation of bulk gas by a factor of more than five. While the purity of liquid helium is not directly measurable due to its extreme cold, it easily exceeds Grade 5 purity. Since the global helium supply chain has developed around bulk liquid transportation, and high purity helium is readily available, it follows that Grade 5 helium has become the standard commercially sold product. In fact, it would add operational complexity and cost for most helium suppliers to offer helium of lesser purity.
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