Heat illness is a progression, not a single event: cramps, then exhaustion, then stroke. The first two are reversible with shade, water, and cooling. Heat stroke is a medical emergency and the only correct action is aggressive cooling plus evacuation. The threshold that matters is a heat index of 103 °F — above that, stop strenuous activity.
The index thresholds
| Heat index | Risk | Action |
|---|---|---|
| Under 90 °F | Low | Normal activity, drink to thirst |
| 90–102 °F | Moderate | Limit midday effort, 1 L/hour |
| 103–115 °F | High | No strenuous activity 11 a.m.–4 p.m. |
| Above 115 °F | Extreme | Shade, water, evacuation if symptoms |
Heat index is temperature plus humidity. 95 °F at 60% humidity is 104 on the index — the humidity is what stops sweat from cooling you.
Hydration plan
| Condition | Per person per hour | Per day |
|---|---|---|
| Sitting in shade, 90 °F | 0.5 L | 3–4 L |
| Light activity | 0.7 L | 5–6 L |
| Hiking in heat | 1 L | 7–10 L |
| Children | 60–70% of adult | — |
Add electrolytes when sweating for more than two hours. Water alone replaces volume but not sodium, and hyponatremia is a real risk for people who drink litres without salt.
Cooling steps, in order
- Move to shade or a vehicle with AC.
- Remove excess clothing and loosen what stays.
- Wet the neck, wrists, armpits, and groin with cool water.
- Fan the person; evaporation does the cooling.
- Sip cool water with electrolytes, not ice-cold gulps.
- Lie down with legs slightly elevated.
Cold water immersion is the fastest cooling method for heat stroke, but at camp a wet cloth plus fan is usually what you have. Start it immediately.
Symptom progression
| Stage | Signs | Response |
|---|---|---|
| Heat cramps | Muscle cramps, heavy sweating | Stop, shade, electrolytes |
| Heat exhaustion | Headache, nausea, dizziness, clammy skin, weakness | Shade, lie down, cool, fluids over 30 min |
| Heat stroke | Confusion, no sweating, hot dry skin, collapse, seizure | Emergency: cool aggressively, call for help |
The dangerous transition is confusion. A person who stops making sense in heat is a heat stroke until proven otherwise.
Evacuation threshold
Evacuate immediately when any of these is true:
- confusion, slurred speech, or unusual behaviour,
- loss of consciousness or seizure,
- temperature above 104 °F,
- no improvement after 30 minutes of cooling and fluids,
- inability to drink.
Do not wait for morning. Heat stroke deteriorates fast and organ damage begins within an hour.
Prevention
- Schedule effort before 10 a.m. and after 4 p.m.
- Drink on a schedule, not on thirst.
- Wear loose, light-coloured long sleeves; they shade better than skin.
- Eat salty snacks in heat; sodium loss matters.
- Never leave a child or pet in a vehicle, even for five minutes.
- Check on the quiet person in the group — heat illness makes people withdraw.
Who is at risk first
Heat illness does not hit evenly. The people most likely to go down are the ones who will not say anything:
| Group | Why | Watch for |
|---|---|---|
| Children | Smaller body mass, slower acclimatisation | Quiet, flushed, stops playing |
| Over 60 | Reduced thirst response | Drinking less, confusion |
| On medication | Diuretics, beta-blockers, antihistamines | Dizziness on standing |
| New arrivals | Not acclimatised to heat | Effort in the first 48 hours |
| Heavy sweaters | Large sodium loss | Cramps, salt stains |
Assign one person to check on each of these every hour. Heat illness makes people withdraw, and withdrawal is easy to miss in a group.
Acclimatisation takes time
The body adapts to heat over 7–14 days, and the first two days are the riskiest. If you arrive from a cool climate, treat day one as a rest day: shade, short walks, and extra water. Sweat rate and plasma volume change measurably within a week, but not within an afternoon.
A note on alcohol and caffeine
Both increase urine output and impair the judgement that keeps you out of trouble. Save them for the evening, after the heat has passed, and drink water alongside.
The heat kit
| Item | Why |
|---|---|
| 2 L water per person minimum | Baseline |
| Electrolyte tablets | Sodium replacement |
| Wet cloth or bandana | Fast cooling |
| Thermometer | Confirms fever vs heat |
| Shade tarp | Removes direct sun |
Where to go next
For hot-weather camping generally, see the hot weather guide; for the broader response sequence, the safety guide; for water planning, the water guide.
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