Free calculator
Check the heat index before the crew starts.
Enter the air temperature and the humidity where the crew is working. You'll get the heat index and what the risk level means for the shift.
Also calledHeat index for outdoor workers, Apparent temperature calculator, Heat stress calculator
The National Weather Service says full sun can add up to 15°F to the heat index. Check the forecast and measure on site.
Result
Heat index
--°F
Enter a temperature and humidity.
A guide, not a medical tool. Follow your company’s heat illness prevention plan, and get medical help for anyone who shows signs of heat illness.
This does arithmetic on what you type. Nothing leaves your browser. Check the result against your own rules and procedures.
How it's calculated
- This uses the National Weather Service method. At milder temperatures it uses a simple formula. When the heat index reaches about 80°F, it switches to the full regression equation, with the NWS adjustments for very dry and very humid air.
What it can't tell you
- Full sun can add up to 15°F to the heat index. Measure where people are actually working.
- It doesn't account for heavy gear, hard physical work, a worker new to the heat or someone who's unwell.
- It's a guide. Follow your company's heat illness prevention plan, and get medical help for anyone who shows signs of heat illness.
Run this in the field.
Assign the heat check and the water-and-rest routine to the crew each morning, and see who has done it.
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Common questions
- What is the heat index?
- It's how hot it feels to the body when humidity is combined with air temperature. High humidity slows the evaporation of sweat, so the same temperature feels hotter.
- What heat index is dangerous for outdoor work?
- Risk rises as the number rises, and it depends on the work, the gear and the person. Many safety programs use bands like lower, moderate, high and very high. Use your own plan's triggers, and treat any sign of heat illness as serious.
- Does this replace a heat illness prevention plan?
- No. It helps you decide what level of controls a day needs. Water, shade, rest, acclimatization and a way to call for help are the plan's job.
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