Weather Injuries: Hypothermia, Heat Stroke & Exposure

Hypothermia is a core temperature below 35°C (95°F). You will rarely have a reliable field thermometer. Stage it by what you see: shivering, speech, walking, and whether they still make sense. Wilderness Medical Society field care is built on those signs, not on a perfect number.

Infants often do not shiver. CDC warning signs: bright red, cold skin and very low energy. Older adults may go quiet and confused in a house that does not feel “that cold” to you.

Build a hypothermia wrap (the field burrito)

1. Insulate from the ground first. Pack, branches, dry bags, closed-cell foam, extra clothing. Conduction into dirt or snow steals heat as fast as wind.
2. Stop the wind. Tarp, vehicle, snow cave, lee of a wall. Then deal with wet clothes.
3. Cut wet clothes off once the person is out of the wind. Wrestling a soaked shirt over a confused head dumps more heat and can trigger a heart arrhythmia. WMS: remove wet clothes only when they are protected from the cold.
4. Dry layer against skin — any dry fabric. Then a vapor barrier (plastic sheet, bin bag, survival blanket) so sweat and remaining damp cannot keep evaporating. Then bulky insulation (sleeping bag, dry clothes, leaves stuffed in bags). Then a windproof / waterproof shell.
5. Cover the head and neck. Leave the face clear so you can watch breathing.
6. Warm the core, not the fingers first. CDC: chest, neck, and groin. Wrapped warm-water bottles or warm stones in cloth against the chest and armpits. Never scald. Never put a severe case against a stove, radiator, or open flame — numb skin burns, and a blast of heat on the limbs can dump cold blood back to the heart (afterdrop).

Afterdrop: core temperature can keep falling after rescue because cold blood from the limbs returns to the trunk. This is why WMS tells you not to stand or walk a mild case for about 30 minutes after you get them still, and why you warm the chest before the hands. They may look worse before they look better. Stay with the wrap.

If they look dead: CDC and Red Cross: a severe case may have no obvious pulse or breathing. Handle gently. Start CPR if you are trained and there are no signs of life. Keep insulating while you work. People have been revived after they looked finished. That is a hospital decision. Your job is airway, gentle CPR if indicated, and heat.

Heat exhaustion is the body losing water and salt faster than it can cope. Heat stroke is the thermostat failing: temperature climbs, the brain goes offline, organs cook. NIOSH: in heat stroke the temperature can rise to 41°C (106°F) or higher in 10–15 minutes. Do not wait for dry skin. Exertional heat stroke (work, hiking, running) often still sweats. Classic heat stroke (elderly in a hot room, parked car) is more often hot and dry. The diagnosis in the field is too hot plus a brain that is wrong.

Cooling order (fastest first)

Wilderness Medical Society: cold-water immersion is the gold-standard field cool-down for heat stroke after you have checked that they are breathing. NIOSH and CDC Yellow Book agree: soak the whole body, not a polite washcloth on the forehead.

1. Shade and strip. Move out of sun. Remove outer clothing, helmet, pack, shoes, socks. Someone stays and holds them.
2. Whole-body cold water if you can do it safely. Tub, livestock trough, cold stream, or a pond you can stand in. Ice water cools fastest. Tepid water still works. Hold the head. Do not drown a confused person. Stir the water.
3. Tarp “taco” if there is no tub. Person on a tarp or poncho. Dump the coldest water you have (ice if you have it). Fold the sides up and slosh the water over the skin. NIOSH names this tarp-assisted cooling. It is ugly and it works.
4. Soak and fan. Wet the skin, keep it wet, move air. Wet sheets rotated from a bucket beat a dry breeze. Ready.gov is right that a fan alone in a sealed hot room is not a treatment.
5. Ice or cold packs as a fallback, not the plan. Neck, armpits, groin, and as much skin as you can cover. Better than nothing. Worse than immersion.

Drinks — enough, not a flood

• Prevention while working in heat (NIOSH): about one cup (240 ml) of water every 15–20 minutes for moderate work under two hours. If sweating for many hours, include a salty snack or a sports-type drink. Do not try to force down more than about six cups (1.4 L) per hour.
• Drink to thirst on long days, plus salt in food. CDC Yellow Book: forcing huge volumes of plain water can cause exercise-associated hyponatremia — a swollen brain that looks like heat stroke but the person is not burning hot.
• Field salt drink if they are exhausted and can swallow: CDC Yellow Book method — ¼ to ½ teaspoon of table salt in 1 litre of water. A squeeze of citrus or a little sugar makes it drinkable. Plain water plus a salty snack is as good. No salt tablets swallowed dry — NIOSH: they irritate the gut and do not fix the problem.
• If they drank litres, are confused, and are not hot: stop free water. Salty snack or a strong broth if they can swallow. This is a medical emergency of a different kind. Cooling a hyponatremic brain does not fix it; more water makes it worse.

Rhabdomyolysis (dark cola urine after brutal heat work): stop work, drink water if they can, get to care. Muscle breakdown can wreck kidneys. You cannot treat that in a tarp.

Treat the whole-body cold first. A frostbitten hand on a dying core is a distraction. WMS frostbite guidelines: search for hypothermia and fix it before you run a thaw.

Frostbite — thaw or not

Trench foot — the quiet crippler

You do not need freezing air. CDC Yellow Book: hours of wet feet around 15°C (59°F) and below, plus tight boots, is enough. Soldiers lose miles to this, not to frostbite.

• Dry socks as a religion. Rotate. Sleep with feet dry even if that means bare feet in a bag and wet boots by the fire — not wet socks in the bag.
• Do not sleep in soaked boots “to keep them shaped.”
• On rewarming: dry, elevate, air. Skin may go red and agonising. That is the blood coming back. Do not plunge into hot water.
• Once trench foot is established, they may not walk well for days. Plan the group around that, or you will drag them into hypothermia next.

Air at 10°C (50°F) is uncomfortable. Water at 10°C can kill you. Water steals heat many times faster than air. Wind then strips the warm air film off wet skin and wet cloth. This is how people die on 8°C (46°F) spring days in a cotton shirt.

After a dunk: get horizontal out of the water. Strip wet layers in shelter. Wrap as in the hypothermia section. Even if they “feel fine,” afterdrop and delayed collapse are real. No hero walk in a dripping shirt.

Most weather deaths are clothing and timing failures, not mysterious physiology. Fix the boring things.

Cold — three layers, not one thick coat

• Mittens beat gloves. Fingers share heat. Wrist closure matters.
• Hat and neck. Cover them. A scarf or mask over the mouth also pre-warms air in deep cold (NWS / CDC clothing lists).
• Loose, not tight. Tight boots and gloves strangle blood flow and grow frostbite.
• Eat and drink in the cold. Shivering is a furnace that needs fuel. Dehydration thickens blood and worsens cold injury. Melt snow before you eat it — eating snow drops core temperature.

Heat — shade, pace, salt, acclimatise

• Light, loose, light-coloured clothing that covers skin. A wide hat. Sun on a dark shirt is a heater.
• Work the cool hours. CDC Yellow Book: most acclimatisation takes about 10 days of actual work in the heat, not sitting in it. First week in a new hot place: shorter tasks, more rest, watch the new person.
• Rest in real shade. Ground radiation cooks you next to a sun-baked wall. Lie on something off the dirt if you can.
• Wet the hat and shirt in dry heat and keep air moving. In high humidity, evaporation fails — slow down harder and hunt shade and water, not sweat.
• Never a closed car. Ready.gov / NHTSA: people and animals cook. Windows cracked is not enough on a warm day.

Weather injury is not fair. The people who look “fine” on a normal day are often the first to drop.

• Infants and small children. High surface area, poor shivering, cannot tell you. CDC: bright red cold skin and limp tiredness in babies. In heat they dehydrate fast and cook in cars and buggies. Check them more often than adults.
• Older adults. Weaker thirst signal, weaker sweat, weaker shiver, more heart and kidney disease. Ready.gov: extreme heat kills more people than most other weather hazards, and older adults take the hit. A cool-feeling house at 16°C (60°F) with wet clothes can still drop them.
• Injured, drunk, or exhausted people. Alcohol opens the skin vessels, lies about being warm, and wrecks judgment. Injury stops the movement that was keeping them warm. Exhaustion stops the shiver furnace.
• The unfit newcomer in a heat wave, and the hero who will not rest. Watch the person who “doesn’t need a break.”
• Anyone in a parked vehicle, tin shed, loft, or black tent at midday. Metal and glass are ovens. Get them out. Cool them as heat stroke until they prove they are not.

• “They’ll warm up if we keep walking.” Mild cold stress, yes. Once they stumble and mumble, walking pumps cold blood and burns the last fuel. Wrap first.
• “Rub the arms. Rub snow on frostbite.” You are grinding ice crystals through flesh. Never.
• “A tot of alcohol warms you.” It flushes heat to the skin and you lose it. CDC: no alcohol. Same in heat — it dehydrates and wrecks judgment.
• “Hot bath for everyone.” A shivering, alert, mild case who can get in and out may use a warm (not scalding) bath. A confused or unconscious hypothermic person can arrest when cold blood slams the heart. Wrap them.
• “Dry skin means it isn’t heat stroke.” Wrong for people who were working. Sweat does not rule it out. Brain signs do.
• “Just drink more water.” Exhaustion needs water and salt. Confusion without a high temperature after a water-chugging day may be hyponatremia. More water can kill.
• “Fever tablets will bring the temperature down.” Not this temperature. You waste time and may add organ stress.
• “A space blanket is a sleeping bag.” A thin reflective sheet is a vapor / radiant layer. Without insulation and a windbreak it is a shiny flag. Put it inside the wrap, not as the only layer in the wind.
• “They said they were fine.” Hypothermia and heat stroke both destroy insight. You decide from signs, not from their last stubborn sentence.

Moving feels like progress. With weather injuries it is often how the second death happens — the rescuer exhausts, or the patient afterdrops on the trail.