The hottest deserts in the world are.... dangerous [[side note: where are the hottest ones, anyway? And what is the measure? All-time hottest temperatures? Hottest averages? Most days over 120? Other?]] [[Death Valley is pretty hot and dangerous, but so is the Namib and parts of the Sahara....and others....]].
Where does one draw the line on exposure times, and modes of exposure?
[[side note: I knew someone who had experienced sunstroke or overexposure to the sun when he was a young man. He still had residual problems and limitations, even many years later. He had to be much more careful with himself than otherwise.]]
And what about humidity? I just reread an account of someone's bike journey through the Amazon basin. It was not as hot as many deserts, but it was much more humid. He drank up to 15 liters per day (mostly water).
So I guess are two (at least) issues here.
The first is sun exposure. How do you know when you've crossed the line?
Or, how do you know when you are approaching that line?