How long can a human stay afloat safely in mid air?

Question

in a chair lifted by helium balloons

Answer 1

Depending on the altitude and their food and water supply, indefinitely. But eventually the helium will escape from the balloons and they will come back down to earth.

Answer 2

A man in southern California did it with large helium filled balloons tied to a lawn chair. He took a small pellet pistol along with him and his plan was to shoot the balloons one at a time to come down. He dropped the pistol and it fell to Earth. He managed to come down and survived the flight although he was fined by the FAA for creating a flight hazard. He proved it could be done.

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A recent attempt by a priest in New Zealand was not so lucky. His flight was part of a publicity stunt for the benefit of charity. He was blown off course by strong winds, was lost and never found again, and is presumed to be dead.

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I don't recommend you try it because it could have fatal results.