Extreme Heat Preparedness: Staying Safe When It Is 100F and the Power Is Out

Almost every preparedness guide is written for cold. Blankets, heating, insulation, winter storms. Yet the National Weather Service consistently ranks extreme heat among the deadliest weather hazards in the United States, and the CDC attributes roughly 1,200 deaths a year to it — a figure most researchers consider a significant undercount, because heat usually appears on a death certificate as the cardiac or respiratory event it triggered. Heat kills quietly, indoors, mostly among people who did not think they were in danger. It also has an unusual property among hazards: the correct responses are cheap, and the wrong ones are widely believed.

Why Humidity Changes Everything

Your body sheds heat mainly by evaporating sweat, and evaporation slows as the air gets more humid. This is why the heat index — temperature combined with humidity — predicts danger far better than temperature alone: 90F at 70% humidity is harder on the body than 100F in dry desert air. The extreme version of this is the wet-bulb temperature, which measures what evaporation can actually achieve. At a wet-bulb temperature around 35C, sweating stops working entirely no matter how fit, hydrated or acclimatised you are, and healthy adults cannot survive extended exposure even at rest in shade. You will rarely meet that limit, but the principle matters for everyday decisions: check the heat index rather than the thermometer, and treat humid heat as considerably more dangerous than the number suggests.

The Two Emergencies, and Telling Them Apart

Learn this properly, because the two conditions look similar and the correct responses differ sharply. Heat exhaustion shows heavy sweating; cold, pale, clammy skin; a fast, weak pulse; nausea or vomiting; muscle cramps; tiredness and dizziness. Move the person somewhere cool, loosen their clothing, apply cool wet cloths or run a cool bath, and have them sip water. If they are vomiting, symptoms worsen, or symptoms last beyond an hour, get medical help. Heat stroke is a different category of event: body temperature of 103F or higher, skin that is hot and may be either dry or damp, a fast strong pulse, headache, confusion, slurred speech, and possible loss of consciousness. Call emergency services immediately. Move them somewhere cool and lower their temperature aggressively with cool cloths or a cool bath. Critically, do not give a person with heat stroke anything to drink — an altered mental state means they may not be able to swallow safely. Confusion is the signal that matters most: a person who has stopped sweating and started talking nonsense is in a medical emergency, not having a rough afternoon.

The Fan Myth

This is the most consequential correction in this guide. Almost everyone assumes a fan is a heat safety device. The CDC is explicit that when the temperature is in the high 90s F or above, electric fans will not prevent heat-related illness. The physics is unforgiving: a fan cools you by speeding evaporation from your skin, but once the air is hotter than your skin, blowing more of it over you transfers heat into you, much like a convection oven. Below the high 90s, fans genuinely help and are worth running. Above it, a fan can leave you feeling more comfortable while your core temperature climbs — which is precisely the dangerous combination. Once temperatures pass that threshold, the priority shifts from moving air to reaching a genuinely cooler place, and fans become useful mainly for exhausting hot air out of the building rather than blowing it over people.

Cooling a Home Without Air Conditioning

Work in this order, because it is the order of effectiveness. First, stop heat getting in: close curtains, blinds and shutters on any window the sun reaches, and do it in the morning before the room warms rather than after. Blocking sunlight at the glass is dramatically more effective than trying to cool air that has already absorbed it, and cheap blackout curtains or even cardboard and foil taped over a sun-facing window will noticeably change a room's afternoon temperature. Second, stop making heat indoors: no oven, no hob, no tumble dryer, minimal lighting, and unplug what you are not using. Cook outdoors or eat cold food. Third, flush the house at night, but only once outdoor air is actually cooler than indoor air — check before opening up, because opening windows during the hot part of the day makes things worse. Put a box fan in a window facing outwards to push hot air out, which draws cooler air in through windows elsewhere. Fourth, sleep low: heat stratifies upwards, so a ground floor or basement can be several degrees cooler than an upstairs bedroom on a bad night.

Cooling Your Body Directly

When you cannot cool the building, cool the person, which is cheaper and faster anyway. A cool shower or bath lowers core temperature more effectively than anything else available at home. Between showers, apply cool wet cloths to the pulse points where blood runs close to the surface — neck, wrists, inner elbows, groin, and the backs of the knees. A damp towel around the neck is remarkably effective for how little it costs. Wear loose, light-coloured, natural-fibre clothing. Freeze water bottles in advance: they chill a room slightly, they cool your skin directly, and they become drinking water as they thaw. Keep a spray bottle of water in the fridge for misting, which works well combined with a fan while temperatures remain below the fan threshold.

Hydration, Done Precisely

Thirst lags behind dehydration, so drinking when thirsty means drinking late. For anyone active in heat, OSHA guidance is about one cup of water every 15 to 20 minutes — roughly a quart an hour. There is an upper bound too: do not exceed around 48 ounces in a single hour, because rapidly drinking large volumes of plain water can dilute blood sodium to dangerous levels, a condition called hyponatremia that can be as serious as dehydration. If you are sweating heavily for several hours, you are losing salt as well as water, so include an electrolyte drink or eat something salty rather than relying on water alone. Skip alcohol, which both dehydrates and impairs your judgement about how hot you are getting, and go easy on very sugary drinks. Watch urine colour as a rough gauge: pale straw is fine, dark yellow means catch up. Extreme heat also drives up water consumption sharply, so if your household stores emergency water, a heat event will drain it faster than you planned for.

When Heat and a Power Cut Arrive Together

This is the scenario that turns uncomfortable into dangerous, and it is increasingly common, because the demand spike that extreme heat creates is exactly what overloads a grid. Plan for the combination specifically. Refrigerated medication is the first priority: unopened insulin needs refrigeration, and insulin held above about 86F begins losing potency, so know in advance whether a cool bag with ice packs or a small power station is your fallback. A modest portable power station will run a fan overnight, keep phones alive, and power a CPAP machine — worth checking your machine's draw against the station's capacity before you need to. Keep the fridge and freezer shut: a full freezer holds temperature for around 48 hours unopened, half that if half full. Freeze water bottles now so they buffer the freezer and provide cold water later. And know where your nearest cooling centre, library or air-conditioned shopping centre is, because the correct answer to a long heat-plus-outage event is often to leave the house rather than tough it out.

Who Is Actually at Risk

Heat deaths concentrate in predictable groups, and knowing them tells you who to check on. Adults over 65 regulate temperature less efficiently, sweat less, and often do not feel thirsty until well dehydrated. Infants and young children heat up faster relative to body mass and cannot remove their own clothing or fetch a drink. People with heart or lung conditions, diabetes, or kidney disease are at elevated risk. So is anyone taking diuretics, beta blockers, anticholinergics, antihistamines or certain antipsychotics, all of which can blunt temperature regulation or fluid balance — never stop a prescribed medication over this, but do ask a pharmacist how heat interacts with yours. Outdoor workers and anyone exercising in heat need acclimatisation over one to two weeks, not a single hard day. People living alone are at risk simply because nobody notices the early confusion. If you take one action from this section: agree with a neighbour to check on each other by phone or doorstep once a day during a heat warning. That arrangement costs nothing and catches the cases that actually kill.

Cars and Pets: The Non-Negotiable Rule

Never leave a person or an animal in a parked car, for any length of time, in any weather warm enough to matter. A car interior can rise around 20F in ten minutes and keep climbing, and cracking the windows makes almost no difference. Children have died in cars on days that felt merely pleasant outside. For pets, remember that dogs cool themselves by panting rather than sweating, which makes them far more vulnerable than people; walk them early morning or late evening, test pavement with the back of your hand before walking on it, and keep water available at all times. If you see a child or animal alone in a hot car and they appear distressed, call emergency services immediately.

Your Heat Kit and What It Costs

The genuinely useful heat kit is unusually cheap, because most of it is technique rather than gear. Blackout curtains or reflective window film for sun-facing windows, $20 to $40. A box fan, $20, useful below the fan threshold and for night flushing. Several reusable freezer packs and a few water bottles you keep frozen, under $15. A thermometer that reports humidity, so you can judge heat index and know when night air is actually cooler than indoor air, around $15. Electrolyte sachets, around $10. Beyond that, the meaningful purchases are ones that overlap with the rest of your preparedness: stored water, which a heat event consumes faster than you expect, and a power station if anyone in the household depends on refrigerated medication or a CPAP machine.

The Day-Before Checklist

When a heat warning is issued, do these the evening before. Fill and freeze bottles and freezer packs. Pre-cool the house overnight with windows open and a fan exhausting hot air. Charge every power bank and the power station. Confirm you have a cool-bag plan for refrigerated medication if the power goes. Check the heat index forecast rather than the temperature. Text the neighbours, elderly relatives and anyone living alone that you will check in daily. Plan meals that need no cooking. Identify the nearest air-conditioned public building and its opening hours. Move pet beds and water bowls to the coolest ground-floor room. None of that costs money, and it is most of what separates a difficult few days from a medical emergency.