I've worked in mines in the desert in South Australia where temps semi regularly hit 46-47 degrees.

It's OK (ish) because the humidity is low. But you can drink a litre an hour all day (11+ hours) and not need to pee. All that water goes somewhere.

The underground workings are often more dangerous, with lower temperatures but higher humidity. Once wet bulb temps get above 34 degrees underground personnel need to retreat from the area and the only work that can be done there then is work to fix the ventilation.

There's heat stress meters that measure wet and dry bulb temperatures and airflow, and can basically compute cooling power in watts. Not enough cooling power -> everyone out.

It's dry as a bone here right now. (That's good)

Also means it's all a big tinderbox. (That's bad)

Isn't this called wet bulb or something and lethal?

Actually at 100% humidity the highest survivable temperature for a human is 35 C° wet bulb temperature.
But that is with everything else being perfect, being healthy, in the shade, and perfectly hydrated, and zero physical activity.
A more realistic maximum survivable wet bulb temperature is closer to 30 C°. But 35 C° is the absolute maximum, where above that everybody dies.

Yup. Wet-bulb conditions are no joke and can kill, making functioning A/C a life-saving technology if not an outright requirement for survival.

South Australia doesn't have humidity.

This temperature happens a lot in Taiwan and is also 100% humidity. It's not comfortable.