Penn State researchers found that the maximum wet-bulb temperature humans can endure is lower than previously thought — about 31°C wet-bulb or 87°F at 100% humidity — even for young, healthy subjects. The temperature for older populations, who are more vulnerable to heat, is likely even lower.
This is the best chart I've found, basically the purple/red line is where you're dead
https://www.dtn.com/wp-content/uploads/2019/03/heatindex_graph.png
This is the best chart I've found, basically the purple/red line is where you're dead https://www.dtn.com/wp-content/uploads/2019/03/heatindex_graph.png