As the dog days of summer approach and the heat index lingers around triple digits in the South, it’s always a good idea to take precautions.

The heat index was developed to help determine the risk of heat-related illnesses for outdoor workers, what protective actions are needed and when they should be taken. The index combines air temperature and relative humidity to measure how hot the weather feels, according to the United States Department of Labor. It’s important to note that the heat index values were devised for shady and light wind conditions. Exposure to full sun can increase index value as much as 15 degrees Fahrenheit.

Below is a summary of risk levels — Lower (less than 91 degrees), Moderate (91 to 103 degrees), High (103 to 115 degrees), Very High to Extreme (greater than 115 degrees) — and associated protective measures that are prescribed by the Occupational Safety and Health Administration.