Heat Index Screening for Workplaces
Heat index joins air temperature and relative humidity. It estimates how hot the body feels in shade and light wind. That value matters on jobsites. Humidity slows sweat evaporation. Sweat then cools the body less. The worker may gain heat faster than the body can release it.
This calculator is built for screening. It is not a medical device. It is not a full industrial hygiene survey. It gives a fast planning number. Supervisors can compare the result with OSHA style worksite risk bands. They can also add a sun allowance when work happens in direct sunshine.
Why OSHA Planning Matters
Heat stress can rise during common tasks. Carrying materials, digging, roofing, paving, and loading all create metabolic heat. Heavy clothing and impermeable gear trap heat. New workers and returning workers often need gradual acclimatization. A safe plan should include water, shade, rest, training, buddy checks, and emergency response.
The calculated value should be read with site knowledge. A shaded weather station may not match a roof, trench, kitchen, foundry, or asphalt surface. Radiant heat, blocked wind, hot equipment, and reflected sunlight can raise exposure. When those factors are present, use stronger controls.
Formula Used
The tool uses the Rothfusz heat index regression when conditions support it. The formula uses temperature in Fahrenheit and relative humidity percent. For lower apparent temperatures, it uses the simpler average method often used before applying the regression. Dry air and very humid low temperature adjustments are included.
The calculator also estimates dew point with the Magnus method. Dew point helps explain moisture load. A high dew point means the air already holds much water vapor. Cooling by sweat becomes harder.
How to Use This Calculator
Enter the air temperature. Select Fahrenheit or Celsius. Add relative humidity from a weather meter or trusted report. Choose the sun or radiant heat option. Pick workload, clothing, acclimatization, and shift length. Press Calculate. The result appears above the form. Review base heat index, adjusted worksite heat index, risk bands, and suggested controls. Export the result as CSV or PDF for records.
If the advisory rises, reduce pace early. Move tasks, add breaks, or stop nonessential work before symptoms appear in any nearby worker.