Heat Index & Work/Rest Schedule Calculator

How It Works

1. Enter Conditions

   Enter dry-bulb air temperature and relative humidity. The app applies the NOAA/NWS low-range and Rothfusz heat-index branches in degrees F.

2. Flag Worker and Site Conditions

   Select workload, acclimatization status, and whether full sun or radiant heat is present. These flags add warnings because heat index alone does not capture total heat stress.

3. Review the Screen

   Use the OSHA/NIOSH risk tier, source warnings, and planning prompt as a first-pass discussion item before setting site controls.

4. Verify Before Action

   Use WBGT, current OSHA/NIOSH/state-plan guidance, employer procedures, and qualified safety or industrial-hygiene review before establishing work/rest cycles.

Built For

• Safety teams documenting an initial heat-index screen before reviewing a site heat plan
• Supervisors comparing morning and afternoon weather windows before moving heavy tasks to cooler hours
• EHS staff flagging new or returning workers who need acclimatization review
• Outdoor crews checking whether full sun makes a shade-only heat-index value insufficient
• Warehouse or process-area supervisors recognizing when radiant heat makes WBGT measurement more appropriate
• Event planners preparing water, shade, monitoring, and emergency-response questions for hot-weather work

Features & Capabilities

NOAA/NWS Equation Path

Uses the official low-range simple branch, Rothfusz regression, and humidity correction logic for heat-index arithmetic.

OSHA/NIOSH Risk Tier Screen

Maps heat index to lower, moderate, high, and very high/extreme protective-measure tiers with visible source warnings.

WBGT Boundary Warnings

Shows why heat index does not replace WBGT for radiant heat, full sun, PPE, heavy work, or site-specific occupational heat-stress decisions.

Acclimatization Prompt

Flags new and returning workers for OSHA/NIOSH Rule-of-20-Percent review instead of hiding that risk inside a fake heat-index adjustment.

Source-Aware Export

CSV and PDF exports carry warnings, assumptions, source pointers, first-aid reference notes, and formula basis.

Assumptions

• Air temperature is dry-bulb temperature and relative humidity is percent RH
• Heat index is calculated with the NOAA/NWS low-range and Rothfusz equation path
• Risk tiers are heat-index protective-measure screens, not enforceable work authorization
• Workload, PPE, radiant heat, air movement, rest-area temperature, and individual medical factors are not measured
• The full-sun caveat is a warning only and does not replace WBGT

Limitations

• Does not measure WBGT, globe temperature, air speed, radiant heat, or heat strain
• Does not reproduce current ACGIH TLV heat-stress tables or set WBGT-based work/rest cycles
• Does not determine OSHA, state-plan, Cal/OSHA, Washington, Oregon, agriculture, maritime, construction, or employer heat-program compliance
• Does not evaluate PPE/clothing correction factors, medications, fitness, prior heat illness, pregnancy, age, or other personal risk factors
• First-aid text is reference context only and does not replace emergency medical care

References

• NOAA/NWS Weather Prediction Center Heat Index Equation
• CDC/NIOSH OSHA-NIOSH Heat Safety Tool App page
• OSHA Heat Hazard Recognition
• OSHA Water. Rest. Shade.
• OSHA Protecting New Workers
• NIOSH Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (2016)
• ACGIH TLV/BEI source pointer for authorized current heat-stress guidance

Frequently Asked Questions