4.2 Heat and cold stress

1 What the law requires right now

There is no final federal OSHA standard for heat, and none for cold. What applies is Section 5(a)(1) of the Occupational Safety and Health Act — the General Duty Clause — which requires each employer to furnish a place of employment free from recognized hazards that are causing or are likely to cause death or serious physical harm. OSHA says so directly on both its heat and cold stress pages, and it has cited employers for heat under that clause.

A rulemaking is underway. OSHA's proposed Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings rule was published in the Federal Register on August 30, 2024; the informal public hearing concluded on July 2, 2025, and the post-hearing comment period ended October 30, 2025. As of August 2026 the proposal has not become a final rule, so nothing in it is enforceable on its own. Several states run their own heat rules through State Plans — OSHA names Washington, Minnesota, California, Oregon and Colorado — and those are enforceable where they apply. Check your state.

One measurement note that matters if anyone ever investigates an incident: OSHA's Technical Manual chapter on heat stress establishes that OSHA uses WBGT — wet bulb globe temperature — to determine whether a heat hazard was present, not the heat index from the weather app. The heat index is a screening tool; our heat index and work/rest calculator explains where each one belongs.

2 Acclimatization: the risk factor nobody schedules for

The body adapts to heat over days, by sweating earlier, sweating more, and holding on to salt. Someone who has not worked in the heat recently has none of that adaptation. OSHA's guidance treats workers as unacclimatized if they have been doing the job for less than one to two weeks, and lists lack of acclimatization alongside heavy physical activity, hot conditions, and clothing that holds in body heat as the main occupational risk factors.

That is why heat fatalities cluster in specific, predictable circumstances: the first days of a heat wave, and the first days of a new worker on the crew. A veteran who was on vacation for two weeks is, physiologically, a new worker. Build up exposure gradually over the first several days rather than sending the newest person to the hottest task on day one.

3 Recognizing heat illness

The reason to learn the progression is that the dangerous stage does not feel dangerous to the person in it. Confusion is a symptom, so the affected worker is the last one who will call for help. That is what the buddy system is for.

Two persistent myths to bury. Heat stroke does not require dry skin — a working person can be soaked in sweat and still be in heat stroke. And "walk it off in the truck with the AC on" wastes the minutes that decide whether someone survives with their brain intact. Cool first, transport second.

4 Cold stress: four injuries, one cause

Cold does not need to be extreme. OSHA's cold stress guidance is explicit that in regions unused to winter weather, near-freezing temperatures count, and that wetness — including from your own sweat — accelerates heat loss dramatically.

1. 1
   Trench foot — a non-freezing injury from prolonged wet and cold. It can occur at temperatures as high as 60 °F if the feet stay wet, because wet feet lose heat 25 times faster than dry feet. Redness, numbness, tingling, swelling, blisters. Dry the feet, keep them elevated, avoid walking on them, get medical help.
2. 2
   Chilblains — painful inflammation of small blood vessels from repeated exposure to temperatures from just above freezing up to about 60 °F. Redness, itching, blistering. Warm slowly, do not scratch.
3. 3
   Frostbite — freezing of skin and tissue, permanent damage and in severe cases amputation. Gray or white patches on fingers, toes, nose or ears; aching, then loss of feeling; firm or hard tissue. Do not rub and do not rewarm in the field if refreezing is possible — wrap loosely in dry cloth, protect it, and let medical professionals rewarm.
4. 4
   Hypothermia — normal body temperature of 98.6 °F dropping below 95 °F. It can happen above 40 °F when someone is chilled by rain, sweat or immersion. Uncontrollable shivering is the important early sign; loss of coordination, confusion, slurred speech and slowed breathing are moderate to severe. Call 911, move to warmth, remove wet clothing, wrap the whole body including head and neck with a vapor barrier over the blankets, warm sweet drinks only if fully alert, and warm packs to armpits, chest sides and groin.

Wind chill is the number to plan against, not the thermometer reading: OSHA's example is 40 °F air with a 35 mph wind producing a wind chill of 28 °F on exposed skin. The National Weather Service issues a Wind Chill Advisory when the values are potentially hazardous and a Wind Chill Warning when they are hazardous to life within minutes of exposure.

5 Controls that work in both directions

In both directions the same two rules apply. Wet is the multiplier — a soaked base layer in the cold, an impermeable suit in the heat — so managing moisture is half the job. And nobody assesses their own condition well: the buddy check is the control that catches what the individual cannot.

6 What a crew should have in place

Because there is no federal standard prescribing it, the plan is whatever your employer has built — but the elements that show up in every serious heat or cold program are the same, and they are easy to check for:

• Someone checks the forecast — heat index or wind chill — and says it out loud at the morning huddle.
• Water and shade, or a heated shelter, are on site before the work starts, not fetched at noon.
• New and returning workers get a lighter first few days.
• Everyone has been told the symptoms and knows that reporting them is expected.
• A buddy system, so nobody works alone in extreme conditions.
• The emergency response is decided in advance: who calls 911, what the site address is, who meets the ambulance.

Five minutes at the tailgate covers all six. Our heat stress toolbox talk is written for exactly that meeting.