 When the heat index hits 80 degrees, employers must provide rest areas with water. At 90 degrees, employers must give workers 15-minute rest breaks every two hours and monitor them for signs of heat illness. The federal rule is modeled on state rules already in effect in a handful of states, including California and Washington. Business groups have called those rules burdensome and unnecessary, given they already have their own rules in place. Andrea Hsu, NPR News.