There is no legal minimum working temperature in the United States. OSHA says outright that it has no standard covering work in cold environments, so nothing switches off at 20 degrees. What decides whether a shift is safe is wind chill, whether the crew is wet, how hard they are working, and who is out there - and the first injuries start warmer than most people think.
The quick answer
- No federal number exists. OSHA has no cold standard; cold stress falls under the General Duty Clause, Section 5(a)(1) of the OSH Act.
- Wet changes everything. Trench foot can occur at temperatures as high as 60 °F if feet stay wet, and hypothermia can occur above 40 °F in someone chilled by rain, sweat or immersion.
- Wind is the multiplier. At 0 °F with a 15 mph wind, the wind chill is -19 °F, and exposed skin can freeze in 30 minutes.
- The judgment is yours to document. Wind chill, exposure time, warm-up breaks, dry clothing and a buddy system are what an inspector will ask about after an incident.
What the law actually says
OSHA's cold stress guide puts it in one sentence: "Although OSHA does not have a specific standard that covers working in cold environments, under the Occupational Safety and Health Act (OSH Act) of 1970, employers have a duty to protect workers from recognized hazards, including cold stress hazards, that are causing or likely to cause death or serious physical harm in the workplace."
That is the same structure as heat: no rule, but a duty, and a duty is enforceable. A few ordinary standards also apply once cold is in the picture - the PPE hazard assessment of 29 CFR 1910.132(d) (OSHA has a 1998 letter of interpretation naming heat and cold stress as factors in it), first aid under 1926.50 and 1910.151, training under 1926.21, and recording and reporting under 29 CFR 1904.
Wind chill: the number to plan around
Wind chill is the temperature exposed skin feels when air temperature and wind speed are combined. The National Weather Service publishes the formula:
Two published anchors check the arithmetic: OSHA's example of 40 °F with a 35 mph wind giving a wind chill of 28 °F, and the NWS example of 0 °F with a 15 mph wind giving -19 °F. The table below is that formula applied, rounded to the nearest degree.
| Air temp | 5 mph | 15 mph | 25 mph | 35 mph |
|---|---|---|---|---|
| 40 °F | 36 | 32 | 29 | 28 |
| 30 °F | 25 | 19 | 16 | 14 |
| 20 °F | 13 | 6 | 3 | 0 |
| 10 °F | 1 | -7 | -11 | -14 |
| 0 °F | -11 | -19 | -24 | -27 |
| -10 °F | -22 | -32 | -37 | -41 |
Three limits of the index are worth knowing before you quote it on a pre-task plan. It is defined only for air temperatures at or below 50 °F and winds above 3 mph. Bright sunshine can raise the wind chill temperature by 10 to 18 °F, which is why a sheltered sunny wall and an exposed deck on the same building are not the same job. And wind chill applies to people and animals only: your equipment will cool to the air temperature, no further.
Why wet matters more than the thermometer
The published thresholds for cold injuries are all higher than "freezing," and every one of them involves moisture:
| Injury | Conditions | What it looks like |
|---|---|---|
| Trench foot (immersion foot) | Wet and cold, at temperatures as high as 60 °F; wet feet lose heat 25 times faster than dry feet | Redness, numbness, tingling, pain, swelling, leg cramps, blisters, bleeding under the skin, gangrene |
| Chilblains | Repeated exposure to temperatures just above freezing up to about 60 °F | Redness, itching, blistering, inflammation, ulceration in severe cases |
| Hypothermia | Core temperature below 95 °F; most likely in very cold conditions but possible above 40 °F when chilled by rain, sweat or immersion | Uncontrollable shivering first; then loss of coordination, confusion, slurred speech, shivering stops, slowed pulse and breathing, unconsciousness |
| Frostbite | Freezing of skin and tissue; air temperature below freezing | Reddened skin turning gray or white on fingers, toes, nose or earlobes; tingling, aching, loss of feeling, firm or hard tissue, blisters |
Two details from that list deserve to be read out loud at a toolbox talk. Shivering that stops is not improvement - it is the body giving up on rewarming itself, and it marks the move from mild to moderate hypothermia. And hypothermia impairs judgment early, so "he said he was fine" is exactly what a hypothermic worker says. That is why OSHA recommends the buddy system: the person next to you notices the fumbling and the slurred speech before you do.
What OSHA expects an employer to do
OSHA's cold stress guidance is a list of practices rather than triggers. It expects employers to:
- Know the wind chill temperature before the shift, so exposure risk can be gauged and the work planned around it.
- Train workers to recognize the conditions that lead to cold stress, the symptoms, the prevention measures and how to select clothing for cold, wet and windy conditions.
- Schedule frequent short breaks in warm dry areas, and schedule work during the warmest part of the day where the sequence allows.
- Use the buddy system and monitor workers' physical condition - "especially new workers who may not be used to working in the cold, or workers returning after spending some time away from work."
- Acclimatize new and returning workers by gradually increasing workload and allowing more frequent warm-up breaks as tolerance builds.
- Provide warm sweetened beverages, no alcohol, and encourage high-carbohydrate snacks - staying nourished is part of staying warm.
- Provide engineering controls such as radiant heaters, and shield work areas from drafts and wind where possible.
- Avoid bare skin on cold metal or wet surfaces, and keep dry spare clothing on site.
Clothing: three layers, and never cotton against the skin
OSHA's recommendation is at least three layers of loose-fitting clothing: an inner layer of wool, silk or synthetic to move moisture away from the body; a middle layer of wool, fleece or synthetic that insulates even when wet; and an outer wind and rain layer that still allows some ventilation so the worker does not overheat and soak the inner layers with sweat. Tight clothing is counterproductive because it cuts circulation to the extremities. Cotton loses its insulation value when wet; wool, silk and most synthetics do not. Add a hat or hood, insulated gloves, and insulated waterproof boots, and keep spare socks and gloves in the truck.
Cold PPE is a PPE decision like any other, which means it belongs in your written PPE hazard assessment rather than in an unwritten habit, and the day's wind chill and warm-up schedule belong on the pre-task plan.
The alerts changed names in 2024
If your winter weather plan names the alerts it responds to, it is probably out of date. Effective October 1, 2024, the National Weather Service renamed its cold products as part of hazard simplification:
| Old name | New name |
|---|---|
| Wind Chill Advisory | Cold Weather Advisory |
| Wind Chill Watch | Extreme Cold Watch |
| Wind Chill Warning | Extreme Cold Warning |
The reason for the change is worth passing on to the crew: cold is dangerous with or without wind, and the old names encouraged people to check the wind before taking the cold seriously. Thresholds for issuing these products are set locally by each NWS office, so the temperature that triggers an advisory in Minnesota is not the one that triggers it in Georgia. Note that OSHA's own winter weather pages, last reviewed in February 2023, still use the old product names.
First aid: what to do, and the two things never to do
Hypothermia. Call 911. Move the worker to a warm room or vehicle. Remove wet clothing and replace it with dry, then wrap the whole body including head and neck in layers of blankets plus a vapor barrier such as a tarp or garbage bag, leaving the face uncovered. If the worker is alert, give warm sweetened drinks - never alcohol, and never anything to an unconscious person. Place warm bottles or hot packs in the armpits, at the sides of the chest and at the groin. No pulse means CPR until the person responds or help arrives.
Frostbite. Get into a warm room. Do not walk on frostbitten feet or toes unless there is no choice. Wrap the area loosely in dry cloth and protect it from contact until medical help arrives.
Trench foot. Seek medical assistance. Remove wet boots and socks, dry the feet, keep them elevated, and avoid walking on them - walking on affected feet can cause tissue damage.
Bottom line
- No OSHA standard sets a minimum working temperature; cold stress is handled under the General Duty Clause.
- Cold injuries start well above freezing when the crew is wet: 60 °F for trench foot and chilblains, above 40 °F for hypothermia.
- Plan on wind chill, not air temperature - and remember sunshine can add 10 to 18 °F back.
- Warm-up breaks, dry spare clothing, warm sweet drinks, a buddy system and gradual acclimatization are the measures OSHA names.
- Never rub or field-rewarm frostbite, and treat shivering that has stopped as an emergency.
Put the day's wind chill and warm-up plan on paper with the pre-task plan generator, and write down the cold clothing decision where it belongs, in the PPE hazard assessment.