Information current as of October 2026. Heat regulations are changing, so check OSHA's heat page and your state agency for the latest requirements.
Construction crews work in direct sun, wear layered PPE, and do heavy physical work. That combination makes heat one of the biggest daily risks on site. This guide covers how to plan for it, what to do each day, and where cooling gear fits.
For the regulatory side, see our OSHA heat illness prevention guide.
Why construction sites run hot
Concrete, steel, and asphalt absorb sun all morning and give it back all afternoon. The heat at chest height on a slab is often higher than the forecast.
Shade is limited until the structure goes up. And the crew is layered before the heat even starts: hi-vis, a harness, a hard hat, sometimes long sleeves. Each layer holds heat in.
Know the warning signs
Heat exhaustion: heavy sweating, weakness, dizziness, headache, nausea, cool and clammy skin. Move the person somewhere cool and give water.
Heat stroke is an emergency: confusion, slurred speech, fainting, or seizures. Call 911 and start cooling the person right away.
Build a site heat plan
A written plan keeps every crew doing the same thing. At minimum:
- Name one person responsible for heat on each site
- Check the forecast and heat conditions every morning
- Set work and rest schedules for hot days
- Provide water and a shaded or cool rest area
- Train workers and supervisors on the warning signs
- Write down the emergency steps, including the site address for 911
Water, rest, and shade
Water. Cool water within easy reach of every crew. For moderate work in moderate heat, NIOSH suggests about one cup every 15 to 20 minutes. Don't wait until workers are thirsty.
Rest. Scheduled breaks, longer and more frequent as conditions get hotter.
Shade. Portable canopies, trailers, or any cool area where workers can recover out of the sun.
Acclimatization: the highest-risk period
Almost half of heat-related deaths happen on a worker's first day on the job or first day back after a long absence. A worker who feels fine on day one can still get sick on day two.
Use the Rule of 20 Percent for new workers:
- Day 1: 20% of a normal day in the heat
- Each following day: add 20% until they reach a full schedule
For an 8-hour day, that's no more than 1 hour 40 minutes on day one. Workers who have done the job before and are returning can start at 50% and build up over about four days.
Watch new workers closely. Don't treat acclimatization as a formality.
Adjust the work, not just the workers
- Start earlier and do the heaviest tasks in the cooler morning hours
- Rotate crews between hot and cooler tasks
- Use a buddy system so someone is watching each worker
- Use equipment for heavy lifting where you can
PPE and heat
Hi-vis, harnesses, and hard hats are required on most sites, and they also add heat load. Where you have a choice, pick breathable fabrics and gear that doesn't add layers.
Personal cooling gear can help. Fan-cooled vests and jackets move air across the body so sweat evaporates, and some are built to work with a harness. If you go this route, check the ANSI class, harness compatibility, and battery certification before you order. Our cooling vest buyer's guide covers each of those.
Two limits to keep in mind. Fan-cooled gear works less well in sustained very high humidity. And it supplements water, rest, shade, and acclimatization. It doesn't replace them.
Daily site checklist
- Forecast and heat conditions checked
- Water stocked at every work area
- Shade or cool-down area set up
- New and returning workers on an acclimatization schedule
- Workers and supervisors know the warning signs
- Emergency plan and site address posted
- Hot-weather schedule and rest breaks in place
FAQ
How much water should a construction worker drink in the heat?
For moderate work in moderate heat, NIOSH suggests about one cup (8 oz) of cool water every 15 to 20 minutes. Needs go up with hotter conditions and heavier work.
How long does heat acclimatization take?
New workers should build up over about a week using the 20 percent rule. NIOSH describes a 7 to 14 day range for full adaptation.
Does PPE make heat stress worse?
It can. Protective clothing and PPE add heat load, which is why breaks, water, and acclimatization matter even more when PPE is required.
Can cooling gear replace breaks and shade?
No. It supplements them.
This article is general information, not legal advice. Requirements vary by state and industry, so confirm with your safety manager or legal counsel.
Talk to us about your crew
Volume pricing, Net 30 terms available for qualified business accounts, and complete compliance documentation for your approval process.
