Why is there an altitude limit for helium drives? If the HDA is a sealed environment, then how can the external air pressure have any effect on the internal operation?

HGST Ultrastar He8 SATA OEM Specification:
https://www.hgst.com/sites/default/files/resources/UltrastarHe8_OEMSpec_SATAmodels_v1.6.pdf

If the answer is to do with the pressure limits of the gas tight seal, then why is there such a huge disparity between the operating and non-operating limits?

And what is the reasoning behind this statement:

"Maximum storage period within shipping package is one year"

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Don't quote me on this as I'm not sure but the big gap is to consider humidity and other factors. Perhaps the performance is also impacted upon 3k or higher due to air pressure but may still be functional?

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How can the external air pressure affect the helium environment? AISI, the analogy is a pressurised cabin on an aeroplane when flying at 10,000 metres. The passengers continue to function as human beings as if they were at sea level.

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