Iowa Heat Awareness Day – June 5, 2014

The Iowa Homeland Security and Emergency Management Division, and the National Weather Service have declared June 5, 2014 as Heat Awareness Day in Iowa. Extreme heat is a seasonal hazard in Iowa which is often underestimated. Did you know that heat is the number one weather-related killer? Understanding heat safety is important and can save lives.

Summertime in Iowa means two things: heat and humidity. These two weather parameters combine to create the Heat Index (Apparent Temperature), which is an accurate measure of how hot it really feels when relative humidity is combine with the actual air temperature. The combination of extreme heat and humidity conspire to tax the human body beyond its natural cooling abilities. Heat related deaths account for many deaths and injuries each year.

Vehicle Safety


Above: Thermometer set in car to record temperature
Bottom: High temperature recorded in car

Just how hot can the interior of a car become? To find out, last year we placed a thermometer inside a car parked outside in the sun during a full work day. The high temperatures on the day we conducted our experiment only reached 80°F. However! The interior temperature in the car reach 117°F! A car with the windows cracked showed a similar temperature rise. Even on a relatively mild day, the interior of a car can become dangerously hot for children or pets left unattended. Never leave children or pets unattended in a car, even for short periods of time. Remember: Beat the Heat, Check the Back Seat!


What is the Heat Index?

The Heat Index (HI) is sometimes referred to as the “apparent temperature” and is a measure of how hot it feels outside to the human body. The HI includes the influence of both the actual air temperature and relative humidity. The body dissipates almost 90% of its heat through sweat but sweating by itself does nothing to cool the body unless the water is removed by evaporation, and high relative humidity hinders evaporation.


To figure out the HI, reference the Heat Index Chart and find the intersection of the air temperature and relative humidity. The shaded zones on the chart correspond to the probabilities of developing heat-related disorders. Heat disorders are generally a result of the body’s inability to shed excess heat by sweating or a chemical (salt) imbalance caused by too much sweating. When heat gain exceeds the level the body can remove, or when the body cannot compensate for fluids and salt lost through perspiration, the temperature of the body’s inner core begins to rise and heat-related illness may develop. The table explains the risk to the body from continued exposure to excessive heat and is color coded to match the HI chart shown.



More information can be found:
Heat and Heat Safety (pdf)
NWS Des Moines Heat Safety
NWS Heat Safety (Español)