Heat Stress — How Your Body Overheats

You lose heat four ways: sweating (and the sweat evaporating), radiating heat off your skin, air moving across you, and contact with cooler surfaces. Sweat evaporating is the big one. When humidity is high, sweat can't evaporate, so it just drips and you get almost no cooling out of it.

Heavy work is a heat source too. The harder you push, the more heat your muscles make. Add sun, hot surfaces, and no breeze, and heat piles up faster than your body can move it out.

Heat builds inside faster than you can shed it, and your core temperature rises. Early on you feel it as thirst, tiredness, and irritability. Push past that and you slide into cramps, then heat exhaustion, then heat stroke.

The danger is that it creeps up. You're focused on the work, you feel a little off, and you talk yourself into finishing the task. That's how people end up down. Treat early signs as a stop-work signal, not something to power through.

There's no specific federal OSHA heat standard. OSHA enforces heat hazards under the General Duty Clause, Section 5(a)(1) of the OSH Act, which requires a workplace free of recognized hazards likely to cause death or serious harm. A federal heat rule was proposed but is not final, so the numbers here are OSHA and NIOSH guidance, not a legal exposure limit.

Guidance or not, the physiology is real. Water, rest, shade, and building up to the heat are what keep crews upright. → see Water, Rest, and Shade and Acclimatization for the specifics.