Heat illness is a leading cause of weather-related worker deaths. Enter the temperature and humidity to get the heat index (what it feels like) and the corresponding OSHA risk level with protective-measure guidance.
OSHA heat-index risk levels
| Heat index | Risk | Protective measures |
|---|---|---|
| Below 91°F | Lower (Caution) | Water, rest, shade; acclimatize new workers |
| 91–103°F | Moderate | Active rest breaks, hydration schedule, buddy system |
| 103–115°F | High | Frequent breaks in shade/AC, adjust work, monitor closely |
| Above 115°F | Very High to Extreme | Reschedule non-essential work; strict work/rest cycles |
Gear for hot, high-visibility work
FAQ
Does the heat index account for sun and exertion?
No. The heat index assumes shade and light wind. Direct sun can add up to ~15°F, and heavy exertion or PPE raises effective heat load further — treat the result as a minimum.
What is acclimatization?
Gradually building heat tolerance over 1–2 weeks. New and returning workers are at highest risk; OSHA recommends ramping workload (the “20% rule”) for the first days.
Estimate using the NWS heat-index (Rothfusz) equation; risk bands per the OSHA-NIOSH Heat Safety Tool. Add ~15°F for full-sun exposure. Not a substitute for a heat-illness prevention program, WBGT monitoring, or medical guidance.
More free safety tools
→ See all 18 free safety tools
Hearing Protection NRR Calculator · Respirator Cartridge Selector · OSHA PPE Hazard Assessment · Fall Clearance Calculator · Glove Chemical Compatibility · Hi-Vis Class Selector · Cut-Resistance Level Selector · Silica Exposure / OSHA Table 1 · Noise Dose Calculator · Eyewash & Safety Shower Checker · Confined Space Entry Checklist · Welding Lens Shade Selector · Ladder Safety Calculator · Lockout/Tagout Checklist · Hand-Arm Vibration Calculator · Work Glove Size Calculator · Forklift Daily Inspection Checklist
Built and reviewed by the WC Safety editorial team (Steven Eaton). We curate and review industrial PPE against ANSI, NIOSH and OSHA standards.