JACKSONVILLE, Fla. – The Highway 82 Fire in Brantley County, Georgia, is now up to 32% contained. Weather conditions have been more favorable over the past day for containment.
Several factors lead to a fire becoming larger. They include drought, overgrown forests, wind and extreme heat.
Most of our area is in an exceptional drought, and the wind has been elevated over the past few days, which has made containment difficult.
It has also been very dry, and you may have heard of the term “relative humidity.”
The humidity has been critically low over the past few days, generally below 30%. What exactly is relative humidity, and how does it impact how a fire spreads?
There’s water vapor in our atmosphere because of a process called evaporation.
This is when water changes from a liquid to a gas.
Water “evaporates” from the oceans, lakes, rivers, plants and the ground.
The relative humidity is one metric used to measure the amount of water in the air as a percentage. In other words, when the air is completely full of water vapor, that would be 100%.
Warmer air can hold more moisture than cold air, so if you have the same amount of absolute humidity, colder air will have a higher relative humidity and warm air will have a lower relative humidity.
The relative humidity can dampen or dry out potential fuel, basically anything that is combustible.
We had several days last week and this week where the relative humidity was below 30%. That means it was very dry, which helped the fire expand rapidly.
You may be wondering how exactly the relative humidity percentage differs from the dew point.
Dew point is another metric that measures the amount of moisture in the air.
The dew point marks the temperature at which water vapor turns into liquid water droplets.
If the dew point is less than or equal to 55, it is dry and comfortable. Between 55 and 65, you will likely notice the air becoming sticky.
Over 65 is when there’s a lot of moisture in the air, and it is more uncomfortable.
Humidity plays a critical role in whether a fire spreads or becomes more contained, but it’s not the only thing.
That’s why officials look at a combination of humidity, wind speed and direction, among other factors, to come up with the best plan on fighting a fire.