Every construction worker exposed to hot or humid conditions, direct sun or heavy physical work needs heat stress training, along with the supervisors who plan work schedules. New and returning workers who are not yet acclimatized face the highest risk, as do crews working near hot equipment, roofing or asphalt.

Heat stress is enforced federally under the OSH Act's General Duty Clause, and OSHA has proposed a dedicated heat injury and illness prevention standard. California, Washington, Oregon and Maryland already have state heat rules that require measures such as training, water, shade and rest. Check which rules apply in each state where crews work.

Heat exhaustion causes heavy sweating, weakness, dizziness, headache, nausea and cool, clammy skin. Heat stroke is a medical emergency marked by confusion, slurred speech, fainting or seizures, and very high body temperature. Call 911 for suspected heat stroke and cool the worker immediately with water or ice while waiting.

Construction workers can prevent heat-related illness by drinking water frequently, taking rest breaks in shade, wearing light breathable clothing, and building up heat tolerance gradually over the first week or two. Supervisors should schedule heavy tasks for cooler hours and use a buddy system so coworkers watch each other for symptoms.

Acclimatization is the process of gradually building tolerance to working in heat, usually over one to two weeks. It matters because many heat-related deaths happen in a worker's first few days on the job. NIOSH recommends that new workers start at no more than 20 percent of normal heat exposure on day one.