Hourly heat planning table
Enter hourly conditions or load a local forecast. The planner uses shaded Heat Index values and optional sun adjustments.
| Time | Temperature | Humidity | Heat Index | Sun-adjusted value | Risk | Planning note |
|---|---|---|---|---|---|---|
| No hourly results yet. | ||||||
Saved assessments and comparison
Saved locally in this browser. No calculator data is sent to a database.
| Reference | Date | Site | Heat Index | Risk | Workload |
|---|---|---|---|---|---|
| No saved assessments. | |||||
Formula used
Heat Index = -42.379 + 2.04901523T + 10.14333127RH
- 0.22475541TRH - 0.00683783T² - 0.05481717RH²
+ 0.00122874T²RH + 0.00085282TRH²
- 0.00000199T²RH²
T = air temperature in degrees Fahrenheit
RH = relative humidity as a percentage
Effective WBGT = measured WBGT + clothing adjustment factor
The calculator first uses the National Weather Service Heat Index method. It then applies selected sunlight and radiant-heat additions. Workplace factors can escalate the displayed risk band.
Workload, clothing, acclimatization, and controls are evaluated separately. These modifiers do not create an official exposure limit. On-site WBGT measurements remain the preferred workplace method.
How to use this calculator
- Choose Heat Index, workplace, or WBGT assessment mode.
- Enter on-site temperature and humidity whenever possible.
- Select sunlight, airflow, clothing, workload, and acclimatization.
- Add worksite details for a useful printed record.
- Review warnings, immediate actions, and monitoring guidance.
- Use the hourly planner before the hottest work period.
- Save, copy, export, or print the completed assessment.
Example assessment data
| Scenario | Temperature | Humidity | Sun | Workload | Acclimatization |
|---|---|---|---|---|---|
| Outdoor maintenance | 90°F | 55% | Partial sun | Moderate | Fully acclimatized |
| New roofing worker | 92°F | 60% | Direct sunlight | Heavy | New worker |
| Indoor hot process | 88°F | 65% | Shade | Heavy | Returning worker |
Heat illness symptoms and first aid
Heat stroke
Warning signs include confusion, slurred speech, seizures, or unconsciousness. Call emergency services immediately. Start rapid cooling while help arrives.
Heat exhaustion
Signs include headache, nausea, dizziness, weakness, thirst, and heavy sweating. Move the worker to a cool area. Obtain medical evaluation promptly.
Cramps, syncope, and rash
Stop activity when symptoms appear. Cool and hydrate the worker. Seek medical help when symptoms persist or worsen.
Frequently asked questions
Is Heat Index enough for workplace safety?
Heat Index is a useful screening tool. It excludes workload, radiant heat, and many clothing effects. WBGT is usually more suitable for detailed assessment.
Why does direct sunlight change the result?
Weather Heat Index values assume shaded conditions. Direct sunlight can substantially increase worker heat exposure. The calculator allows up to 13.5°F addition.
What does the workplace-adjusted risk mean?
It combines environmental risk with selected job factors. The adjustment is a conservative planning aid. It is not an official OSHA exposure limit.
How is WBGT clothing adjustment applied?
The selected clothing factor is added to measured WBGT. This creates an effective WBGT value. Vapour-barrier clothing needs specialised professional review.
How should new workers acclimatize?
New workers generally start with limited hot-work exposure. Their exposure increases gradually over several days. Close supervision should continue during acclimatization.
How much water should workers drink?
Moderate heat work often requires frequent small drinks. The calculator estimates 8 fl oz every 15–20 minutes. Individual and medical needs can differ.
Can local weather replace on-site measurements?
Local forecasts help with early planning. They may miss indoor heat, radiant sources, and blocked airflow. Confirm conditions at the actual work location.
What happens when symptoms are selected?
The calculator increases the displayed urgency. Symptoms always take priority over calculated values. Follow first-aid and emergency procedures immediately.
Does this calculator prove OSHA compliance?
No calculation alone proves compliance. Employers must assess actual hazards and apply effective controls. Qualified professionals should review complex or severe conditions.
Where is saved assessment history stored?
History is stored in the current browser. It does not use a server database. Clearing browser storage can remove saved records.