How to Avoid Heat Stroke When the Power Goes Out

The evacuation center was already at capacity by late afternoon on the second day — and it wasn’t the flood damage people were talking about. It was the heat. Air conditioning had gone out with the power, the building had no cross-ventilation, and families who had packed everything except a plan for staying cool were sitting on gymnasium floors, visibly wilting. The youngest children and the oldest adults went down first. The ones who had thought ahead — who had a battery-powered fan, a wet cloth, a plan for where the nearest cooling center was — were the only ones managing. Everyone else was improvising in the worst possible conditions.

Heat stroke during a disaster isn’t a freak outcome. It’s a predictable one. When a hurricane, flood, or major storm knocks out power in summer, the danger doesn’t pause while you deal with everything else. It compounds. And the window for preventing heat exhaustion from becoming heat stroke is shorter than most people expect — especially for children, elderly adults, and anyone on certain medications.

Your First Decision: The 90-Minute Rule When Power Goes Out in Heat

Here is the judgment call that matters most in the first hour after a summer power outage: if the indoor temperature reaches 90°F (32°C) and you have no working cooling, you have roughly 90 minutes before heat exhaustion becomes a serious risk for elderly adults and young children — less in high humidity. That’s not a comfortable buffer. It’s barely enough time to make a decision and act on it.

If any of these are true, leave for a cooling center now — do not wait:

• Anyone in the household is over 65 or under 5 years old
• Anyone takes medications that affect sweating or heat regulation (common with blood pressure and psychiatric medications)
• Indoor temperature has already hit 90°F and is still rising
• No battery-powered or manual cooling is available
• The outage is expected to last more than 2 hours

If none of those apply, you have a short window to shelter in place with active cooling measures — wet cloths on pulse points, battery fans, closed blinds on sun-facing windows, and hydration on a schedule (not just when thirsty). But re-evaluate every 30 minutes. Heat builds silently.

FEMA maintains a directory of cooling center locations that activates during heat emergencies — find your local options at fema.gov before you need them, not during.

What Heat Exhaustion Actually Looks Like — and the Line That Separates It from Heat Stroke

Most people misread the warning signs. They assume heat stroke looks dramatic from the start — someone collapsing, obviously in distress. In reality, the progression from heat exhaustion to heat stroke is quiet until it isn’t. The person most at risk is often the one saying “I’m fine, just a little tired.”

Heat exhaustion presents as heavy sweating, weakness, cold or pale or clammy skin, a fast but weak pulse, nausea, and possible fainting. The person is still sweating — that’s the body trying to compensate. Move them to a cool location, give water in small sips, and apply cool wet cloths. This is manageable without emergency services if caught early.

Heat stroke is a medical emergency. Key signals: body temperature above 103°F (39.4°C), hot and red skin that may be either dry or damp, rapid and strong pulse, and possible unconsciousness. If you see this combination, call 911 immediately and begin cooling the person — cool water immersion or ice packs to the neck, armpits, and groin — while waiting. Do not give water to someone who is not fully conscious.

NOAA’s heat safety resources provide the clearest public guidance on this distinction and are updated seasonally: noaa.gov.

Understanding WBGT — and Why Humidity Is Deadlier Than Temperature Alone

Most people track temperature during a heat emergency. Professionals track Wet Bulb Globe Temperature (WBGT) — a composite measure that factors in temperature, humidity, wind speed, and solar radiation. The reason WBGT matters in disaster contexts is that a power outage during high humidity is dramatically more dangerous than the same outage in dry heat.

When humidity is very high, sweat cannot evaporate efficiently from the skin. The body’s primary cooling mechanism fails. You can be in an 88°F room with 90% humidity and face greater heat stroke risk than someone in a 95°F room with 30% humidity. This is the core reason disasters during rainy or typhoon season — when humidity is already extreme — are so dangerous even at temperatures that feel manageable on a dry day.

The practical rule: if the outdoor humidity is above 70% and the temperature is above 85°F, treat any loss of air conditioning as an immediate heat risk, not a discomfort. The National Weather Service’s heat index chart — available through NOAA — translates temperature-humidity combinations into risk categories that are more reliable than either number alone.

During the 2003 European heat wave, which killed tens of thousands of people across France and neighboring countries, many of the deaths occurred in apartments that were hot but not extreme by temperature alone — it was the sustained humidity combined with no nighttime cooling that proved lethal. The lesson carried into North American preparedness planning: indoor air temperature at night matters as much as peak daytime heat.

What to Have Ready Before the Power Goes Out — Specific, Not Generic

The items that get forgotten in a heat emergency are rarely dramatic. Across disaster response settings, the recurring pattern is this: people grab the emergency bag and leave — but what they forget is the prescription medication that needs refrigeration, the reading glasses without which they can’t read any labels, and enough small bills to pay for water or a bus to the cooling center when payment systems are down. Those forgotten basics cause the most regret, every time.

For heat specifically, here is what actually matters at home before an emergency:

• Water stored specifically for heat emergencies: Plan for at least one gallon per person per day — more in extreme heat. In high-humidity conditions, thirst lags behind actual dehydration. Drink on a schedule, not on demand. See Smart Ways to Store Emergency Water and Food That Last for practical storage guidance.
• Battery-powered or USB-rechargeable fan: A compact personal fan with a built-in misting function can make a significant difference during the first hours of an outage. It’s a modest item that’s worth having charged and accessible year-round.
• Instant cold packs: The kind that activate by squeezing — no refrigeration needed. Applying them to the neck, wrists, and inner elbows drops perceived temperature quickly. Keep at least four per person in your kit.
• Electrolyte tablets or packets: Hydration without electrolytes can actually accelerate hyponatremia (sodium imbalance) in people who are sweating heavily. Oral rehydration salts are inexpensive and shelf-stable.
• Printed list of local cooling centers with hours and addresses: Phone batteries die. Apps require signal. A laminated card with two or three cooling center addresses costs nothing and works when nothing else does.
• Medications: Know which ones require refrigeration and have a plan — a small cooler with ice packs — for the first 24 hours. Know which ones reduce your body’s ability to handle heat (many blood pressure medications, antihistamines, and antipsychotics do).

One gear note worth making: a battery-powered evaporative cooling towel — the kind that stays cold when wet and waved briefly in air — is not a gimmick. In still air without a fan, it provides meaningful cooling for pulse-point application. Worth keeping in the bag alongside the cold packs.

The Mistake That Makes Everything Worse: Waiting for Official Guidance Before Acting

This is the pattern that repeats. People feel heat building, they’re uncomfortable, but they wait — for an official announcement, for neighbors to leave first, for the power to come back. The instinct to wait for confirmation before acting is human and understandable. In a heat emergency, it’s also dangerous.

Heat stroke is not preceded by a clear warning that distinguishes it from heat exhaustion in real time. By the time someone’s skin is hot and dry and their thinking is confused, the window for self-rescue is closing fast. The people who avoided the worst outcomes in evacuation centers I’ve seen were the ones who acted on the early signs, not the obvious ones.

The specific mistake: people open windows when the outdoor temperature is higher than the indoor temperature, believing they’re cooling the room. This actually accelerates indoor heating. During a daytime heat wave, keep windows and blinds on sun-facing sides closed until outdoor air temperature drops below indoor — typically after sundown. At night, open windows on opposite sides to create cross-ventilation. The directional logic matters.

A related misconception: fans cool the air. They don’t. Fans cool people by accelerating sweat evaporation. If no one is in the room, a running fan adds heat (from the motor) and does nothing useful. More critically — if indoor temperature is above 95°F and humidity is high, a fan alone no longer helps and may accelerate heat exhaustion in people who have stopped sweating. At that point, the only effective intervention is moving the person to a cooler environment.

If You’re Sheltering with Children or Elderly Adults: A Different Decision Timeline

The 90-minute buffer described earlier shrinks significantly for specific groups. Children have a higher surface-area-to-body-mass ratio and generate more heat relative to their size — they overheat faster than adults. Elderly adults often have impaired thirst perception, reduced sweating response, and may be on medications that further compromise heat regulation. For these groups, the decision to leave for a cooling center should happen earlier, with less tolerance for uncertainty.

The practical rule for these households: if outdoor temperature is forecast to exceed 95°F and power is out, relocate before conditions peak — not after. A cooling center is significantly easier to reach at 10 a.m. than at 2 p.m. when public transportation is crowded and the walk there is dangerous in itself.

There’s also the question of the bag. The most common kit failure in disaster response isn’t what’s inside — it’s that the bag is too heavy to carry while also managing a child or helping an elderly parent. If your emergency bag requires two free hands and full strength to move, it won’t make it out the door in an actual emergency. For heat-focused evacuations, a lighter, heat-specific day bag makes more sense than the full 72-hour kit: water, electrolytes, medication, ID, cash, phone charger, and a cooling item or two.

For households with elderly members who live alone, the decision framework shifts further — establishing a check-in protocol before the emergency, not during it, is the difference between a close call and a tragedy. The 【Explained by a Former Firefighter】Disaster Preparedness for Elderly Living Alone article covers this in depth.

The One Thing to Do Today — Before Any Emergency Arrives

Look up your nearest cooling center right now. Not in general terms — specifically: the name, address, hours of operation, and whether it accepts pets or people with mobility equipment. Write it down on paper. Put it somewhere you’ll find it when your phone is dead and you’re making decisions quickly.

That’s it. That’s the minimum viable action. Everything else builds from knowing where you’re going before you need to go there. Most cooling centers in North American cities are libraries, community centers, or schools — open during heat emergencies without any registration required. FEMA’s resources at FEMA.gov include local emergency management contacts who can direct you to the specific centers active in your area.

If you want to go one step further today: fill two water bottles, put them in the refrigerator, and locate whatever cooling items you already own — a wet cloth works — and put them where you’ll find them in the dark. That’s ten minutes and it covers the first critical hour of any summer power outage.

Heat stroke during a disaster is preventable almost every time it happens — which is what makes it the hardest kind of outcome to witness. The knowledge exists. The actions are simple. The window is just shorter than people expect, and the time to make decisions is before the heat builds, not after.

Primary reference: National Oceanic and Atmospheric Administration (NOAA) — Heat Safety Resources