Thank you! It is really important to emphasize that heat and humidity have both to be taken into account. To quote a relevant passage from the article you linke

Thank you! It is really important to emphasize that heat and humidity have both to be taken into account. To quote a relevant passage from the article you linked: > Concern often centres on the “threshold” or “critical” WBT for humans, the point at which a healthy person could survive for only six hours. This is usually considered to be 35C, approximately equivalent to an air temperature of 40C with a relative humidity of 75%. (At the UK’s 19 July peak temperature, relative humidity was approximately 25% and the wet-bulb temperature about 25C.) (WBT is Wet Bulb Temperature)