They will need to use a WBGT device, which stands for "wet bulb globe temperature." It doesn't only look at heat index. Related articleWhat they're saying:The Korey Stringer Institute, based at the University of Connecticut, is named for the NFL player who died from heat stroke. If the WBGT is at 92, that means outdoor practice should be canceled. "It's really important to recognize that a heat index reading of say a 92, for example, that's not the same as saying it's 92 degrees outside.