CREWTALKS

Heat Index & Work Safety Calculator

🌡

What This Tool Does

Heat illness is one of the leading causes of worker death and injury on construction sites. This calculator uses the official NOAA heat index equation to show what the temperature actually feels like to a worker's body — not just the thermometer reading. It then maps that to OSHA's Heat Illness Prevention Action Levels so supervisors and workers know exactly what precautions are required before anyone steps onto the job site.

How To Use This Tool
1
Set today's temperature
Drag the left slider to match the current or forecasted air temperature at your job site.
2
Set the humidity
Drag the right slider to match the relative humidity. Check your local weather app or a job-site hygrometer.
3
Read the risk level
The center display shows the heat index and color-coded OSHA risk level. The info bar below tells you exactly what to do.
4
Review the full guidance
Scroll down for work/rest ratios by exertion level, a full reference chart, and symptoms every crew member should know.
💡 Tip for supervisors: Run this at the morning toolbox talk. If the heat index will cross a threshold during the shift, plan your work schedule around it — front-load heavy tasks in the early hours.
Live Calculator
🌡 Air Temperature 90°F
70°F120°F
Feels Like (Heat Index)
—°F
—
💧 Relative Humidity 60%
10%100%
Risk Level
—
Water
—
Rest Breaks
—
Buddy System
—
OSHA Heat Illness Prevention — Action Levels
LOWER RISK < 91°F

Normal working conditions with basic hydration and awareness.

  • Drink water regularly (every 15–20 min)
  • Take normal scheduled breaks
  • Wear lightweight, light-colored clothing
  • Know the signs of heat illness
  • Allow new workers to acclimatize over 1–2 weeks
MODERATE 91–103°F

Implement heat illness prevention program and added precautions.

  • Water every 15 min — don't wait until thirsty
  • Rest in shade between tasks
  • Use buddy system — watch coworkers
  • Set up shaded rest area near work zone
  • New workers: limit to 2 hrs at start
  • Pre-shift safety talk on heat illness
HIGH RISK 103–115°F

Active controls required. Workers need regular supervised rest.

  • Mandatory buddy system — no solo work
  • Water & electrolytes every 15 min
  • 5+ min shaded rest per 20 min work
  • Designate heat safety monitor on site
  • Have cool water/ice on hand
  • Know location of nearest ER
  • Limit heavy exertion to early morning
EXTREME > 115°F

Stop non-essential work. Serious heat stroke risk for all workers.

  • Reschedule non-essential tasks
  • Essential work: maximum 15 min on / 45 min off
  • Continuous supervisor monitoring required
  • Ice packs and cooling station on site
  • Emergency action plan reviewed by all
  • Call 911 immediately for any symptoms
Heat Index Reference Chart

The heat index combines air temperature and relative humidity to show what the temperature feels like to the body. Your current reading is highlighted in the chart below. Source: NOAA National Weather Service Rothfusz equation.

Lower (<91°F)
Moderate
High
Extreme
Air Temperature (°F) →
Highlighted cell = your current temp & humidity · Hover any cell for details
Work / Rest Ratios by Exertion Level

Per Hour of Work (NIOSH / ACGIH Guidelines)

Recommended work & rest minutes for each risk level

Work Intensity Moderate Risk High Risk Extreme Risk
🪑 Light
Standing, light assembly		 45 / 15 30 / 30 15 / 45
🔨 Moderate
Framing, digging, demo		 30 / 30 15 / 45 STOP WORK
💪 Heavy
Concrete, roofing, iron		 15 / 45 STOP WORK STOP WORK

Additional Risk Multipliers

These factors increase the effective heat stress on workers

FactorIncreases Risk By
Direct sunlight +10–15°F effective heat
No acclimatization (first 1–2 weeks) Treat as 1 level higher
Wearing full PPE / heavy clothing Treat as 1 level higher
Previous heat illness Significantly higher risk
Certain medications (diuretics, etc.) Treat as 1 level higher
Heart / kidney / diabetes conditions Significantly higher risk
Recognize Heat Illness — Act Fast

Symptoms & Emergency Response — Know Before It Happens

⚠ Heat Cramps & Heat Syncope
  • Painful muscle cramps (legs, abdomen)
  • Heavy sweating during intense work
  • Brief fainting or dizziness
  • Pale, moist skin
  • Nausea
Response: Move to cool area, sip water with electrolytes, rest. Return to work only if fully recovered and no other symptoms.
🚨 Heat Exhaustion
  • Heavy sweating
  • Cold, pale, clammy skin
  • Fast, weak pulse
  • Nausea or vomiting
  • Headache, dizziness, weakness
  • Fatigue and confusion
Response: Move to A/C or shaded area, loosen clothing, apply cool wet cloths, have them sip water. Seek medical attention. Do NOT return to work same day.
🆘 Heat Stroke — CALL 911
  • High body temp (103°F+)
  • Hot, red skin — may be dry OR wet
  • Rapid, strong pulse
  • Confusion, slurred speech
  • Loss of consciousness
  • Seizures
CALL 911 IMMEDIATELY. Cool the person by any means — ice packs to neck/armpits/groin, cool water immersion, fan. Do NOT give fluids if unconscious.
Sources: OSHA Heat Illness Prevention Campaign · NOAA National Weather Service Heat Index Equation · NIOSH Criteria for a Recommended Standard (Occupational Exposure to Heat and Hot Environments) · ACGIH TLVs for Heat Stress and Heat Strain.  |  Always consult current OSHA guidelines and your company safety plan. This tool is for reference only.