It gets very dangerous during the day in the late Summer. But the problem is that UPS trucks are not air conditioned as that would cost more so f' the workers, just get another one if one of the plebs dies. US labor Law has been owned by corpos for far too long.
I seem to remember the lack of AC was because the union contract they had said that if you equip any trucks with AC, you have to equip all of them. That may have made it legally dubious to roll out AC installs because there would be a transition period. Fortunately I believe UPS and their union have come to an agreement to fix this, this incident further proves it’s necessity.