Temperature and Heat Index, Your Body Knows the Difference

It's not the heat it's the humidity. We have all either heard this and or said this before. My first reaction is who cares I'm hotter than Chewbacca in a sleeping bag. A more accurate phrase would be it's not the heat it's the heat index. This is because heat and humidity combine to form the heat index. The heat index is a measure of how the air affects the human body. Higher temperatures and higher relative humidity equals a higher heat index, which means you feel more inclined to make like a goose and migrate. Understanding the heat index can help you understand the potential dangers to your body and how to deal with them.

Relative Humidity
In order to understand heat index you must understand relative humidity.Humidity (specific humidity) is simply a measure of how much water vapor is in a parcel of air. Relative humidity is humidity's second cousin by marriage. Seriously, it is the humidity relative to the heat.The higher the heat the more water vapor it will take to saturate the air. So if we compare cooler air with warmer air, both having the same amount of water vapor in them, the cooler air will have a higher relative humidity.

Figuring heat index

The heat and humidity are combined to form the heat index. Higher heat and relative humidity equals a higher heat index. The accompanying chart shows this relationship and the levels of danger associated with the varying heat indexes produced. This is figured using an equation that can be seen at campbellsci.com for those of us who just need to know. Something to be aware of is that the heat index is figured using official temperature stations. These stations are not in the direct sun. Direct sun can increase the heat index 15⁰ F or more!

Why we need the heat index

The heat index is a more accurate measure of the affects on your body then temperature alone. One of the reasons is it affects perspiration, the bodies natural cooling system. When your body gets hot you perspire. This is good for both you and the deodorant manufacturers. Energy is used to make the perspiration evaporate causing your body temperature to cool. The problem arises when heat indexes are high and evaporation is not very efficient. This is because with relative humidity levels already high there is not much room left in the air for your sweat to evaporate.

Another reason we need the heat index is that it can indicate when smog levels will rise. According to Mirriam-Websters Online Dictionary smog is "a fog made heavier and darker by smoke and chemical fumes". Fog will form when relative humidity is high enough that the air reaches its' saturation point. Hot air filled with smog can be particularly dangerous for those with lung disorders like asthma or COPD.

Basic high heat index precautions
Heat exhaustion or Heat Stroke are real possibilities when heat index levels are high. The best way to deal with this is to get to a much cooler place and rest. If this is not possible fan yourself with anything available. Fanning will make wind that will carry some of the water vapor away from you allowing new evaporation to take place. The drinking of water can not be stressed enough when we have a high heat index. Not being prepared or having the means to be prepared is the biggest reason we have deaths from heat waves. If you know you may be vulnerable to high heat take it extra seriously. If you do not have air conditioning find a place to go that does.

So the next time someone says it's not the heat it's the humidity. Just smile and say "actually it's the heat index you knucklehead". Or maybe not.