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Modify or Cancel Games or Practices In High Heat or Humidity

Measure Apparent Temperature with Wet Bulb Thermometer

Whether to cancel or modify games or practices in high heat or humidity depends on the air temperature and the humidity (apparent temperature), which can be measured with a wet bulb thermometer (1).   In deciding when to cancel or modify games or practices due to high heat or humidity, keep in mind the following:

  • Hot, dry weather can be extremely dangerous. Because sweat evaporates very quickly in such conditions, your child won't feel sweaty, and neither you nor your child may recognize how much water he or she has lost.
  • As the relative humidity increases, the effectiveness of sweating in cooling the body decreases.
  • When the relative humidity is high, sweat drips off the skin so that the cooling benefit of evaporation is lost even at cooler temperatures, resulting in a build-up of body heat.

Modify or cancel games or practices based on the air temperature and the humidity (apparent temperature), which can be measured with a wet bulb thermometer available at hardware stores, as follows:

  • For wet bulb readings below 66 F (or when the relative humidity is 95% or higher, regardless of wet bulb reading), no precautions are needed, but watch closely children who are prone to heat illness.
  • If the wet bulb temperature is between 66 F and 78 F (or when the relative
    humidity is 95% or higher, regardless of wet bulb reading), be cautious. Insist on unlimited amounts of water (preferably iced), and that all athletes be monitored closely for symptoms of heat illness.
  • For wet bulb temperature readings above 78 F (or when the relative humidity is 95% or higher, regardless of wet bulb reading), modify practicebecause there is a real danger for serious heat illness, such as heat stroke. Keep practice light, modify or eliminate some drills, and allow athletes to work out in minimal gear. Water breaks in the shade should be mandatory. Do not allow children who lose weight during exercise to participate.

Editor's Note: While limiting or cancelling practices may be possible in some areas in the United States, in many others it is not possible. For instance, a 1991 study of environmental conditions in Alabama over a 5-year period found that there was no time in the month of August when it was considered safe for football practices or games. Similar results were noted for the southern half of that state in the month of September. Where cancelling or modifiying practices or games because of high heat or humidity is impossible, taking others steps to reduce the risk of heat illness, especially for football players, should be taken.

1. Bergeron MF, Rice SG, DiLaura Devore C & Council on Sports Medicine and Fitness and Council on School Health.  Policy Statement - Climactic Heat Stress and Exercising Children and Adolescents. Pediatrics 2011; 128(3) (published onine August 8, 2011). 

Revised August 8, 2011

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