> A sustained wet-bulb temperature exceeding 35 °C (95 °F) is likely to be fatal even to fit and healthy people, unclothed in the shade next to a fan; at this temperature human bodies switch from shedding heat to the environment, to gaining heat from it.
The important thing is that passive/evaporative cooling simply stops working. In fact, sitting in front of a fan would actually speed up your death. You'll also die shockingly quickly (20 or so minutes, even for healthy, fit adults).
The only thing that can save you is:
- air conditioning
- getting in a cold tub
- going somewhere cooler (obviously) like a basement or parking structure
There are two thing that make this frightening:
1. We have already, for the first time in history, started seeing spikes of wet-bulb temperatures that exceed these values. Fortunately so far they have been in uninhabited areas.
2. If we ever see these temperatures in a city, odds are that the electrical grid would fail on account of the strain by A/C units.
So picture this: a heat wave of this magnitude hits a large city. Bangkok, Phoenix, Melbourne. It lasts for 48+ hours. The grid fails on account of the strain. We're looking at a mass casualty event with millions of dead in a matter of hours/days.