Heat index

The heat index provides information about how hot it feels outside in the shade. It is a measure of the air temperature in relation to the relative humidity for a particular day.

A heat index is listed each day in the newspaper to alert people of the risk for a heat-related illness. Direct exposure to the sun can increase the risk for a heat-related illness on days when the heat index is high. Babies, older adults, or anyone with a health condition may have more risk of problems with the heat because of their age and general health.

A heat index of:

  • 27°C (80°F) to 32°C (89°F) may cause fatigue.
  • 32°C (90°F) to 40°C (104°F) may cause heat cramps or heat exhaustion.
  • 41°C (105°F) to 54°C (129°F) may cause heat cramps or heat exhaustion, and heatstroke is possible.
  • 54°C (130°F) or higher may cause heatstroke.

Prevention measures during days of high heat index will help reduce the risk of a heat-related illness. When the outdoor humidity is greater than 75%, losing body heat by sweating is not as effective, so other measures to keep cool are needed.

Is it an emergency?

If you or someone in your care has chest pains, difficulty breathing, or severe bleeding, it could be a life-threatening emergency. Call 9-1-1 or the local emergency number immediately.
If you are concerned about a possible poisoning or exposure to a toxic substance, call Poison Control now at 1-800-567-8911.

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