Heat Index Calculator
Calculate the heat index (apparent temperature) from temperature and humidity. Get safety warnings, health risk assessments, and recommendations for hot weather conditions.
Heat Index Calculator
Calculate the heat index (apparent temperature) and assess heat-related health risks
Understanding Heat Index
What is Heat Index?
Heat index, also known as apparent temperature, is a measure of how hot it feels when relative humidity is factored in with the actual air temperature. It represents the temperature the human body feels when heat and humidity combine.
The heat index is calculated using the air temperature and relative humidity to determine the perceived equivalent temperature. This is important because the human body cools itself through perspiration, and high humidity reduces the effectiveness of sweating.
Why It Matters
- • Helps assess heat-related health risks
- • Guides outdoor activity planning
- • Informs workplace safety decisions
- • Essential for heat emergency preparedness
- • Used in weather warnings and advisories
- • Important for athletic and military operations
Heat Index Risk Categories
Normal
No special precautions needed. Normal outdoor activities are safe.
Caution
Fatigue possible with prolonged exposure and physical activity.
Extreme Caution
Heat exhaustion and heat cramps possible with prolonged exposure.
Danger
Heat exhaustion and heat stroke likely with prolonged exposure.
Extreme Danger
Heat stroke imminent. Emergency cooling required.
Heat-Related Health Conditions
Heat Cramps
Heat Exhaustion
Heat Stroke
Heat Safety Guidelines
Before Heat Exposure
- • Check weather forecasts and heat index predictions
- • Plan outdoor activities for cooler parts of the day
- • Ensure adequate hydration before going outside
- • Wear appropriate clothing (light colors, loose fit)
- • Identify cooling centers and shaded rest areas
- • Review emergency action plans
During Heat Exposure
- • Drink water every 15-20 minutes
- • Take frequent breaks in shade or air conditioning
- • Monitor yourself and others for heat symptoms
- • Avoid alcohol, caffeine, and heavy meals
- • Use cooling towels, ice packs, or misting fans
- • Adjust activity intensity based on conditions
Special Populations at Risk
| Population | Risk Factors | Special Precautions |
|---|---|---|
| Infants & Children | Less efficient temperature regulation, higher surface area | Never leave in vehicles, frequent hydration, limit outdoor time |
| Elderly (65+) | Decreased sweating, medications, chronic conditions | Welfare checks, air conditioning access, medication review |
| Outdoor Workers | Prolonged exposure, physical exertion, protective equipment | Mandatory rest breaks, hydration programs, heat acclimatization |
| Athletes | High intensity exercise, competitive pressure, equipment | Modified training schedules, cooling strategies, heat illness protocols |
Heat Index Limitations
Important Considerations
- • Heat index assumes shade and light wind conditions
- • Direct sunlight can add 15°F to the heat index
- • Most accurate for temperatures above 80°F (27°C)
- • Individual heat tolerance varies significantly
- • Medications can affect heat tolerance
- • Acclimatization improves heat tolerance over time
Other Factors to Consider
- • Wind speed and direction
- • Solar radiation and cloud cover
- • Individual fitness and health status
- • Clothing and equipment worn
- • Duration and intensity of activity
- • Hydration status and electrolyte balance
Frequently Asked Questions
How accurate is the heat index?
The heat index is most accurate for temperatures above 80°F with moderate to high humidity. It assumes shade and light wind conditions. Direct sunlight can make conditions feel 15°F hotter.
Why does humidity make heat feel worse?
The human body cools itself through evaporation of sweat. High humidity reduces the rate of evaporation, making it harder for the body to cool down, which makes the temperature feel hotter.
At what heat index should outdoor activities be cancelled?
Many organizations cancel outdoor activities when the heat index reaches 105°F (41°C). For children, elderly, or high-risk individuals, activities may be cancelled at lower heat indices.
How can I protect myself from extreme heat?
Stay hydrated, limit outdoor activities during peak heat, wear light-colored loose clothing, use sunscreen, take frequent breaks in shade or air conditioning, and never leave anyone in vehicles.
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