Columbus Mayor Michael Coleman has ordered fire hydrants be opened today and Friday at Beatty Recreation Center, Driving Park, Linden Park and Westgate Park from 1 p.m. to 4 p.m. It's part of what he calls "operation cool down", to help area residents beat this week's high heat. Columbus is under a heat advisory through Friday night, and Cleveland Clinic physician David Frid notes excessive heat puts extra strain on the human heart.