School programs use heat index to modify activities

Credit: Mississippi High School Activities Association information

As of June 2023, it is mandatory that all MHSAA sports/band/spirit groups must stop any outdoor activities when the Heat Index reaches a temperature of 105 degrees.

A heat index is a scale that combines air temperature and relative humidity in an attempt to determine the human-perceived equivalent temperature.  In layman’s terms, it tries to combine these two important factors into a single number that better describes “how hot it feels.” The result is also known as the “felt air temperature” or “apparent temperature.” For example, when the temperature is 90°F with very high humidity, the heat index can be about 106°F.

The human body normally cools itself by perspiration, or sweating. Heat is removed from the body by evaporation of that sweat. However, relative humidity reduces the evaporation rate because the higher vapor content of the surrounding air does not allow the maximum amount of evaporation from the body to occur. Higher humidity results in a lower rate of heat removal from the body, hence the sensation of being overheated.  Because of this, heat index rather than temperature alone is a safer number to use in identifying safe outdoor activities.

While the changes made to activities based on environmental conditions will vary based on the sport, each school’s facilities and resources, and the conditioning of the participants in question, the following should be viewed as general guidelines to help with decision making.

Danger (Red):   Heat index 105 degrees or greater

• Mandatory stopping all outside activity and either move activities indoor or delay until conditions improve
• Indoor activity may need to be altered if air conditioning is not available
• Insure adequate access to water and other sources of rehydration
• Limit intensity and/or duration of outside activities (e.g. walking instead of running, low impact activities, breaks between exertions).
• Provide access to water during all activity and provide frequent breaks (at least hourly) specifically to rehydrate and cool down
• Increase vigilance in monitoring participants for necessary action.
• Limit overall activity time to 4 hours per day, with no more than 2 hours per session.
• Ensure at least a 3-hour recovery period between practices.

Heat Warning (Orange) Heat index 100-105 degrees

• If at all possible, move outside activities indoor. If not possible, further increase frequency of breaks and reduce intensity of practices/activities.
• Limit intensity and/or duration of outside activities (e.g. walking instead of running, low impact activities, breaks between exertions).
• Provide access to water during all activity and provide frequent breaks (at least hourly) specifically to rehydrate and cool down
• Limit activity to no more than 2 hours per session.
• Increase vigilance in monitoring participants for necessary action.
• Ensure at least a 3-hour recovery period between practices.

Standard Precautions (Yellow) Heat index 95 degrees to 100 degrees

• Limit intensity and/or duration of outside activities (e.g. walking instead of running, low impact activities, breaks between exertions).
• Provide access to water during all activity and provide frequent breaks (at least hourly) specifically to rehydrate and cool down
• Increase vigilance in monitoring participants for necessary action.
• Ensure at least a 3-hour recovery period between practices.