dangerous triple digit temperatures. in phoenix, first responders race to save lives as the city is expected to hit its 24th straight day of temperatures of 110 degrees or higher. the nights are just as brutal, not dipping below 90. i guess we have to be vampires in this kind of weather. reporter: nationwide extreme heat kills more than 700 people every year. for paramedics working those 911 calls, the priority is cooling people down with icy cold ivs, wet towels and ice packs. put them under the armpits, inside the shirts, put them in the groin area. reporter: july is shattering heat records. more than 3,500 so far. cities including las vegas, austin and miami are on a streak of dangerous temperatures. at some point your body is not made to function in these temperatures. heatstroke has a mortality rate of 10% or more.