A heat wave is a period of two or more days in a row when apparent temperatures on the National Weather Service heat index exceed 105°F to 110°F (40°C to 43°C). The temperature standards vary greatly for different locales. Heat waves can be extremely dangerous. According to the National Weather Service, 175 to 200 Americans die from heat in an average summer. Between 1936 and 1975, as many as 15,000 Americans died from problems related to heat. In 1980, 1,250 people died during a brutal heat wave in the Midwest. in 1995, more than 700 people died in the city of Chicago from heat-related problems. A majority of these individuals were the elderly living in high-rise apartment buildings without proper air conditioning. Large concentrations of buildings, parking lots, and roads create an “urban heat island” in cities.