The normal range for core temperature is 36.5°C-37.5°C but in reality we can exceed these temperatures. An extreme but survivable core temperature would be about 41°C, beyond which you’d expect to see organ and brain damage as the body effectively cooks itself very gradually. Scans of people’s brains after suffering heat injuries demonstrate that tissue is damaged as if it’s been cooked! If our core temperature exceeds our safe limit then we may collapse from heat exhaustion.