Heat Illness & Cold Stress
Understanding
Wind Chill
Wind Chill
OSHA Cold Stress Guide · NWS Wind Chill Index · Exposed Skin Danger Below -18°F WC
Wind chill is the perceived decrease in air temperature felt on exposed skin due to airflow. On an NYC high-rise site, winds can be 20–30 mph stronger at the 20th floor than at street level. A day that feels manageable at grade can be life-threatening at elevation. Every worker on exterior work must understand the wind chill table before stepping outside.
The Wind Chill Table — What It Means
- At 30°F air temp + 30 mph wind: wind chill = 15°F — exposed skin can freeze in 30 minutes
- At 20°F air temp + 20 mph wind: wind chill = 4°F — exposed skin can freeze in 30 minutes
- At 10°F air temp + 30 mph wind: wind chill = -8°F — exposed skin can freeze in 10 minutes
- At 0°F air temp + 15 mph wind: wind chill = -19°F — exposed skin freezes in under 10 minutes
- Wind chill affects exposed skin only — it does not affect the freezing point of water or metal
Assessing Wind Exposure by Floor Level
- Every 10 floors of elevation adds roughly 3–5 mph to wind speed on NYC buildings — above the urban canyon effect
- Corner exposures and open deck edges amplify wind significantly — monitor conditions independently per floor level
- OSHA has no specific wind speed work stoppage rule — the Competent Person and SSM must use professional judgment
- Suspended scaffold operations stop at 25 mph sustained winds regardless of wind chill
On-Site Wind Monitoring
- SSM should check NWS forecast (weather.gov) and wind chill advisory status before each shift during winter months
- A handheld anemometer in the field office allows real-time wind measurement at each floor level — recommended for all exterior high-rise work
- Document wind conditions and any work modifications in the SSM daily log (PL-001)
Discussion Questions
- The air temperature is 25°F and the wind on your floor is 25 mph. What is the approximate wind chill, and how long can exposed skin be in those conditions?
- Why might wind conditions at the 15th floor be significantly different from conditions at street level?
- At what wind speed must suspended scaffold operations be stopped?
- Who determines whether conditions are too dangerous to work exterior on this site, and what authority do they have?
Sign-Off
Project Address
Date
Time
Foreman / Supervisor
SSM / SSC Name & License No.
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