Heat illness rarely arrives without warning. It builds over a shift — a roofer who stops sweating, a laborer who gets clumsy and short-tempered after lunch, a new hire who sits down and cannot get back up. Most of it is preventable with things every site already knows about: water close by, real breaks in real shade, the heaviest work moved to the cooler hours, and people who are new to the heat eased in rather than thrown in. This heat stress assessment puts those things on one page for one day. You record the conditions, the work and the clothing, check that water, rest and shade are actually in place, name who is new and how they will build up, agree what happens in an emergency, brief the crew, and get their names on the sheet. Fill it in here and download a PDF without creating an account.
Temperature is only half the picture
Two days with the same thermometer reading can carry very different risk. Humidity stops sweat from cooling the body; direct sun, hot roofs, asphalt and engines add heat from every side; still air takes away the breeze that helps. That is why the form asks for the humidity and the sun as well as the temperature, and for either the heat index or a wet bulb globe temperature (WBGT) reading if you have one. Both are typed in as read — from a weather service, the OSHA-NIOSH Heat Safety Tool app or an on-site meter. The form does not calculate them and does not treat any number as a legal line.
Then comes the part a weather report cannot know: how hard the work is and what people are wearing. Digging trenches in coveralls and a respirator on a warm, humid morning can be riskier than light work on a hotter, drier afternoon. Your overall read of the day's risk should weigh all of it together.
New and returning workers come first
A large share of serious heat illness happens in the first few days on the job, because the body takes time to adjust to working in heat — and it loses that adjustment again after a week or so away. OSHA's heat guidance puts particular weight on it. The form asks whether anyone is new to the heat or back from time off, and if so, opens a section to record how their exposure will build up over their first days, who keeps an eye on them, and their names. Answering that nobody has a build-up plan is flagged in the report.
Water, rest, shade — checked, not assumed
Every heat plan says water, rest and shade. The question on the day is whether the cooler is actually near the work and will last the shift, whether the shade is big enough for the people who need it at the same time, and whether breaks happen when the plan says they will rather than when the job allows. Each is a yes, no or N/A answer, and a No for water or shade goes to the top of the report.
The buddy system matters more than it sounds. People in the early stages of heat illness are often the last to notice it, because confusion is one of the first signs. Pairing people up, and telling them it is fine to call a break for their partner, catches what self-reporting misses.
Plan the emergency before you need it
Heat stroke is a medical emergency: call 911, start cooling the person at once and do not leave them alone. Cooling fast is what makes the difference, so the form asks what you would use — ice, a tub of cold water, a hose, wet towels and a fan — and whether it is actually on site. It also asks the practical questions that slow ambulances down on construction and farm sites: does everyone know the address or a landmark, is there phone signal, and who meets the crew at the gate.
On the phone, speak while you walk, and the document writes itself: read out the conditions, walk to the water and the shade, say what you see, and the plan fills in. Re-check the conditions after lunch in the log at the end.
The briefing and sign-on
The last part is the toolbox talk itself: tick what you covered — the warning signs, what to do, drinking before you are thirsty, the effect of alcohol, poor sleep and some medicines, and where the water and shade are — note what the crew suggested, and get everyone on the sign-on list. Keep it short. Five minutes on a hot morning that people actually listen to beats twenty that they do not.
Common questions
What is a heat stress assessment?
A short written look at how much heat a crew will face on a given day and what is in place to manage it: the weather, the work, the clothing, who is not yet used to the heat, water, rest and shade, monitoring, and the emergency plan. Many sites do one each morning during hot weather.
Is there an OSHA heat standard?
OSHA has long enforced heat hazards under its general duty to keep workplaces free of recognized serious hazards, and publishes heat illness prevention guidance and a national emphasis program. A dedicated federal heat rule has been in the rulemaking process; check its current status. Several states, including California, Washington and Oregon, have their own heat rules. This form records your assessment; it does not make you compliant with any of them.
Should I use the heat index or WBGT?
WBGT accounts for sun, wind and humidity as well as temperature, so it is the better measure for outdoor work in direct sun, but it needs a meter or a WBGT forecast. The heat index is easier to get and is widely used for planning. Record whichever you have, and say where the number came from.
What is acclimatization and why does it matter?
It is the body's adjustment to working in heat — sweating earlier and more efficiently, with less strain on the heart. It takes several days of gradually increasing exposure and fades after time away. Workers without it are at much higher risk, which is why new and returning workers get their own section.
What are the signs of heat exhaustion and heat stroke?
Heat exhaustion often shows as heavy sweating, headache, dizziness, nausea, weakness, cramps and thirst; move the person to a cool place, loosen clothing, give water and watch them. Heat stroke can bring confusion, slurred speech, fainting or seizures, and hot skin that may be dry or still sweating. It is an emergency: call 911 and cool the person immediately.
Does this work for indoor heat?
Yes. Kitchens, laundries, foundries, boiler rooms and warehouses without cooling can all be hot enough to cause heat illness. Choose the indoor option under sun and shade and list the heat sources.