How much heat can a person safely withstand? It depends.

Much less visible and dramatic than hurricanes, floods and tornadoes, heat is considered the silent killer, affecting the lives and health of people across the country. An average of 702 heat-related deaths occur each year in the United States, according to statistics from the Centers for Disease Control and Prevention (CDC).

Some groups of people need to be especially careful in hot weather. For example, city dwellers and those living on the upper floors of high-rise buildings or in heat-prone regions are most at risk of heat-related illnesses. People who have difficulty moving or who have health problems are particularly susceptible. The elderly and toddlers also deserve special attention in times of high heat and humidity.

NOAA’s National Weather Service (NWS) and Occupational Safety and Health Administration (OSHA) have also partnered to raise awareness among outdoor workers and their employers during excessive heat events. As part of this effort, NWS incorporates specific safety precautions for outdoor workers when heat advisories and warnings are issued.

A chart showing the signs of heat exhaustion and heat stroke, and what to do if detected. For the Spanish version of this graphic and other heat safety graphics, visit (NOAA National Weather Service)