Heat is testing the limits of human survivability. Here’s how it kills
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Philip Kreycik should have survived his run.

In the summer of 2021, the 37-year-old ultra-marathon runner used an app to plot a roughly 8-mile loop through Pleasanton Ridge Regional Park in California, a huge stretch of parkland threaded with trails.

On the morning of July 10, as temperatures crept into the 90s, Kreycik set off from his car, leaving his phone and water l