"Extreme Heat" seems to be 37-40 degrees Celsius which is bafflingly mundane to me as an Australian who grew up in rural New South Wales. We'd pack 30 kids and a teacher into an un-airconditioned classroom with just a ceiling fan and the windows open in that temperature. I imagine the buildings there just aren't built to support that heat plus the body height of hundreds or thousands of attendees?
the British are notoriously sensitive to heat. They'll call 30 Celsius weather a heat wave.
Last summer my house got to 39, and I didn't have AC (it was broken). I think I'm still recovering.