Heat Dome Safety Calculator
OSHA Heat Stress Work/Rest Guidelines by WBGT
Recommended work/rest cycles per hour for acclimatized workers. Non-acclimatized workers should use one level higher precaution.
| WBGT (°F) | Risk Level | Light Work | Moderate Work | Heavy Work | Very Heavy |
|---|---|---|---|---|---|
| < 78 | Low | Continuous | Continuous | Continuous | 50 min / 10 rest |
| 78-82 | Moderate | Continuous | Continuous | 50 / 10 rest | 40 / 20 rest |
| 82-85 | High | Continuous | 50 / 10 rest | 40 / 20 rest | 30 / 30 rest |
| 85-88 | Very High | 50 / 10 rest | 40 / 20 rest | 30 / 30 rest | 20 / 40 rest |
| 88-90 | Extreme | 40 / 20 rest | 30 / 30 rest | 20 / 40 rest | STOP WORK |
| > 90 | Deadly | 30 / 30 rest | 20 / 40 rest | STOP WORK | STOP WORK |
How We Calculate This
This heat dome safety calculator (wbgt) uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
How to Convert Oven Recipes to Air Fryer
This calculator estimates the Wet Bulb Globe Temperature (WBGT), the gold standard for assessing heat stress risk. WBGT accounts for temperature, humidity, wind, and solar radiation — not just temperature alone.
The basic rule:
- WBGT approximation = 0.7 × wet bulb temp + 0.2 × globe temp + 0.1 × dry bulb temp
- Simplified estimate uses temperature, humidity, wind, and sun exposure as proxies
- OSHA work/rest guidelines based on WBGT thresholds and work intensity
- Hydration recommendations: 1 cup (8 oz) every 15-20 minutes in high heat
WBGT is more accurate than the standard heat index because it accounts for wind and sun exposure. A day with 90°F and 80% humidity in full sun can have a WBGT over 88°F — extremely dangerous. When in doubt, reduce activity and increase rest breaks.
When Would You Use This Calculator?
This heat dome safety calculator (wbgt) is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
What is WBGT and why is it better than heat index?
Wet Bulb Globe Temperature (WBGT) measures heat stress by combining air temperature, humidity, wind speed, and solar radiation. Heat index only uses temperature and humidity. WBGT is the standard used by OSHA, the military, and NIOSH for outdoor worker safety because it better reflects actual heat stress on the body.
At what temperature should you stop working outdoors?
There is no single cutoff — it depends on WBGT and work intensity. OSHA guidelines suggest stopping heavy work when WBGT exceeds 90°F, moderate work above 92°F, and even light work above 95°F. Below these, use work/rest cycles. Acclimatized workers have slightly higher tolerances.
How much water should I drink in extreme heat?
OSHA recommends 1 cup (8 oz) of water every 15-20 minutes during moderate to heavy outdoor work in heat. That is about 1 quart per hour. Do not exceed 48 oz per hour (risk of hyponatremia). Add electrolytes if sweating heavily for more than 2 hours. Start hydrating before going outside.
What are signs of heat stroke vs heat exhaustion?
Heat exhaustion: heavy sweating, weakness, nausea, dizziness, cool/pale skin. Move to shade, hydrate, cool with water. Heat stroke: body temp above 103°F, hot/red/dry skin, confusion, loss of consciousness. Heat stroke is a medical emergency — call 911 immediately and cool the person aggressively.
Does humidity make heat more dangerous?
Absolutely. High humidity prevents sweat from evaporating, which is your body's primary cooling mechanism. At 95°F with 30% humidity, your body can cool itself reasonably well. At 95°F with 80% humidity, sweat barely evaporates and heat illness risk skyrockets. Humidity is often the most dangerous factor.
What are OSHA's heat safety requirements?
OSHA requires employers to provide water, rest, and shade when heat index exceeds 80°F. Above 90°F: mandatory rest breaks, buddy system, and acclimatization plan for new workers. OSHA's 2024 proposed rule would require specific work/rest schedules, cooling measures, and emergency response plans based on WBGT levels.