Heat Illness & Cold Stress
Clothing & PPE for
Cold Weather Work
Cold Weather Work
OSHA Cold Stress Guide · ASTM F1720 · Layer System Required for Work Below 40°F
The right clothing is the most important cold stress prevention tool on an NYC winter construction site. No heater compensates for a worker in wet cotton jeans and a single sweatshirt. The layering system is not fashion — it is engineered thermal management, and getting it wrong leads directly to cold stress illness.
The Three-Layer System
- Base layer (next to skin): Moisture-wicking synthetic (polyester) or merino wool. Moves sweat away from skin. NEVER cotton — wet cotton provides zero insulation and chills the body rapidly
- Mid layer (insulation): Fleece, down, or synthetic fill. Traps warm air. Must retain some insulation value when compressed — down loses its effectiveness when wet; synthetic retains it
- Outer layer (shell): Wind-resistant and water-repellent. Must breathe — a non-breathable shell traps moisture from sweating inside the layers, defeating the system
Extremity Protection — The First Areas to Lose Circulation
- Head: a simple knit hat covers the ears and reduces body heat loss by up to 30%
- Hands: insulated work gloves rated to at least 10°F for most NYC winter work. Liner gloves allow fine motor tasks while maintaining protection
- Feet: wool or synthetic wool socks (not cotton), insulated steel-toed boots rated for cold weather. Waterproof boots for wet work
- Face: balaclava or neck gaiter protects the face during wind exposure; required above 10°F wind chill per NYC site safety best practice
Managing Layers During Work
- Workers who generate heat during heavy work should remove the mid layer to prevent sweating — a soaking wet mid layer provides no insulation during rest breaks
- Wet clothing must be changed at break time — carrying a spare set of base and mid layers is strongly recommended during winter work
- PPE compatibility: ensure Class E hard hat fits properly over a knit hat; high-visibility vest must fit over the outer shell
Discussion Questions
- Why is cotton the wrong choice for a base layer in cold weather? What should replace it?
- A worker is sweating heavily during concrete work. They remove their outer shell during the task. Why must they put it back on before taking a rest break?
- Down fill insulation vs. synthetic insulation — which is better for NYC winter construction and why?
- If your boots get wet from standing in a puddle, what should you do before the next work period?
Sign-Off
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