How to Survive a Blackout in a Heat Wave

What keeps emergency management officials up at night? Terrorist attacks. The Big One. A direct hit from a Category 5 hurricane.

But when it comes to climate-related disasters, one fear often rises above the rest: a blackout during a heat wave.

According to new research published this spring, a two-day citywide blackout in Phoenix during a heat wave could lead to half the population — some 789,600 people — requiring emergency medical attention in a metropolitan area with just 3,000 available beds. As many as 12,800 people could die, the equivalent of more than nine Hurricane Katrinas.

Power outages can happen during a heat wave for a number of reasons. The most obvious is because of strain on the power grid, as everyone cranks up their air conditioning at the same time. By one estimate, “two-thirds of North America is at risk of energy shortfalls this summer during periods of extreme demand.” Blackouts can be both city- and state-wide, like when 11 million people were without power following a deadly grid failure in Texas in 2021; or rolling, to prevent a more catastrophic failure; or localized, like when a wildfire takes down transmission lines.

Storms can also knock out power, cutting off access to life-saving air conditioning. Excessive heat killed 12 nursing home residents in Florida in the aftermath of a 2017 hurricane, the same year that hundreds died in Puerto Rico after Hurricane Maria lead to a months-long blackout.

There’s another possibility that has been quietly discussed by emergency officials, too: a malicious cyberattack that takes down the grid during a time of extreme heat. “What happens when a cyberattack disables access to electricity for weeks, coordinated with record-breaking heatwaves, which are significant public health concerns in themselves?” a 2021 piece in The American Journal of Medicine mused, only to conclude that “the impact on the health-care system” — including hospitals, which can run on generators but would be quickly overwhelmed — “would be catastrophic.”

So if the power goes out during a heat wave, what do you do?

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What to do before the power goes out

No, you’re not psychic: You can’t predict when a power outage will leave you without your AC. But you are an informed person who’s aware that heat waves are becoming more common and intense and that extreme heat is the deadliest weather phenomenon in the United States. Virtually every American can benefit from having a plan in place for how to deal with extreme heat in the absence of AC, since nowhere is climate-proof.

At the most basic, the emergency agencies that informed this article — primarily American Red Cross, Centers for Disease Control and Prevention, and Ready.gov, all of which can be consulted for further resources — say you should have an emergency kit prepared and up to date in your home, and sign up for emergency alerts. (Also prepare a separate emergency kit for your pets if you have any.) This should include directions to your local cooling center in addition to a hospital.

Next, “Take an inventory of your essential electrical needs,” advises the American Red Cross. “Then consider how you would live without them when the power goes out.” That list might include backup batteries for phones, fans, CPAP machines, or any other medical devices.

Also consider buying misting spray bottles (we’ll get to those later) and a cooler where you can stash food if the refrigerator goes down. Battery-operated fans can additionally be useful to have on hand, particularly in humid areas, despite many public health organizations warning against them. Extra gallons of water are a part of every emergency kit, and important to have on hand as well.

Finally, make a habit of checking in on the vulnerable people in your life ahead of time — in particular, older people who live alone — and confirm they have air conditioning units that are working. Of the 72 people who died in Oregon's Multnomah County, which makes up the bulk of the city of Portland, during a heat wave in 2021, only three were found to have a functioning AC unit.

What to do as soon as the power goes out

The first thing you want to do if the power goes out during a heat wave, regardless of how severe you anticipate the situation being, is prevent the loss of whatever cool air there still is inside your house. At the most basic, this means covering your windows to keep out sunlight by drawing the blinds.

If you anticipate the power being out for more than a few hours — perhaps because one of the emergency alerts you signed up for warns you the blackout could last for days — take more dramatic measures, like using blackout curtains if you have them, or reflective, foil-covered pieces of cardboard in the windows to bounce heat off your home. The most important thing, though, is to get the windows covered with something; even a towel will do if you don’t have drapes or blinds. If you have a multi-story home and anticipate a long-lasting power outage, begin to shut upstairs doors (hot air rises!) with plans on keeping those rooms closed off for the duration of the blackout. Any particularly drafty doors or windows can be further sealed with a rolled-up towel. In a worst-case-scenario event, you’ll be staying downstairs until your air conditioning turns back on, so keep that in mind as you move through the rooms.

As you’re making your sweep, also snag any medications you have stored, since heat can alter their efficacy. Many meds will become less potent or altered when exposed to high temperatures; aspirin, for example, breaks down into acetic acid and salicylic acid, which can upset the stomach.

Preventatively turn off and disconnect appliances, too, in order to avoid damage from a surge when the power returns (this is generally good advice no matter what the blackout conditions are). Then establish yourself in your darkest, coolest room — it’s likely on the north side of your home or apartment. Generally avoid south-facing rooms, followed by east- and west-facing rooms, since they get the most sunlight. Hunkering down in the basement is also potentially a good option.

Keep your refrigerator closed until about four hours have passed, at which point you should move the contents and stash them in a cooler. A full freezer can stay at a safe temperature for up to 48 hours, but as FoodSafety.gov will remind you, “when in doubt, throw it out.”

What to do if it starts to get hot inside

We know dangerously little about how indoor heat works. But we know that it kills — studies have found that people are most likely to succumb to heat-related illnesses in their own homes.

As a rule of thumb, if your body is exposed to temperatures of 90 degrees or higher, you are potentially at risk of heat exhaustion, which can lead to heat stroke, the National Weather Service notes. Keep in mind, though, that it can “feel like” 90 degrees when the temperature on the thermometer is as low as 86 degrees, because of humidity. If your home starts to feel hot, pay close attention to both the indoor heat and humidity and consult the NWS’s heat index to understand your risk.

Prolonged exposure to high temperatures increases the strain on your body and the danger of heat illness. While 90 degrees might be technically survivable for a healthy adult, “the temperature needs to drop to at least 80 degrees for” the body to begin to recover from extreme heat, CNN reports — part of why overnight highs can actually be deadlier than daytime highs.

Keep in mind your own vulnerabilities to heat, too: The elderly and the prepubescent are most at risk, but people taking antidepressants, antipsychotics, anticholinergics, diuretics, and ACE inhibitors can all have severe heat intolerance, too, Yale Climate Connection observes. Additionally, the publication notes, certain diabetes medications, including insulin, can be less effective when exposed to high heat. People with heart disease, kidney issues, or diabetes should be especially cautious about their health during heat waves because of the intense strain on these systems.

If the temperature starts to climb inside your home during a power outage, it is imperative to act quickly to stay healthy. Drink lots of water, but do so consistently, not in guzzling bursts; we’re limited in how much water we can absorb by how fast our kidneys can function. In extreme conditions, the body can absorb up to a liter of water per hour, but it’s often much less. It’s more important, then, to sip continually throughout the day.

If you have the option to do so, spend as much time in air-conditioned spaces as possible, particularly in the afternoon — movie theaters, malls, public libraries, community lake or pool, and friends’ and family’s homes in an area with power are all potential options. Cooling centers are also a terrific option since they are free, can be equipped with backup generators, and may have other resources handy to help you beat the heat.

But let’s assume, for whatever reason, these options are unavailable. Many cooling centers, including most of those in Los Angeles, for example, do not have backup generators, and they can quickly become crowded — one study that looked at Atlanta, Detroit, and Phoenix found that at most, 2 percent of the city population could be accommodated by existing cooling facilities.

Water, then, becomes your best friend. The evaporation of water from our skin helps pull heat away, so begin a regime of keeping a sheen of water on your skin, whether that’s by using a handheld mister or by placing cool wet towels on your body (the head and neck, armpits, and groin are the warmest parts of our bodies, so focus your efforts there). This is an especially good technique if you have a battery-powered fan to sit in front of. Though fans get a bad rap for creating “a false sense of comfort,” in the words of Ready.gov, used properly they can absolutely help — just keep in mind they stop working very effectively once it’s above about 95 degrees.

Showers can help keep you cool too, just don’t be tempted to take an especially cold one; as Popular Science explains, you don’t want to reach the point of shivering, a response that counterproductively increases our internal temperature.

Switch into light, airy clothes and avoid physical activity as much as you can. At night, keep an eye on the temperature; if it’s cool enough outside, open all your windows to create a cross-flow of air, but be sure to close your windows up after temperatures begin to climb again in the morning.

Pay attention to how your body is responding and know the symptoms of heat exhaustion and heat stroke (we have a guide for that here). Typically the first signs are cramps, headaches, or dizziness.

What to do if you need to evacuate your home

If you begin to feel too hot or sick, it’s time to evacuate your home. Heat illness can go from “uncomfortable” to deadly within 90 minutes, so it’s better to act decisively and get to safety rather than wait and get sicker, when your decision-making abilities begin to erode.

Check what heat relief options exist in your area. Many cities now have programs designed to protect people during extreme heat events, such as the Heat Relief Network in Phoenix, which offers everything from hydration sites to air-conditioned respite centers. Urban areas frequently offer free air-conditioned bus rides to cooling centers, too. But because some of these sites might be unavailable during a major power outage, check local government websites for information.

Before leaving your home, collect any medications and important documents you might need. Also bring any animals you have at home — as the Red Cross emphasizes, “If it’s not safe for you to stay behind then it’s not safe to leave pets behind either.”

If you believe you have the symptoms of heat exhaustion, seek medical attention immediately. But keep in mind, hospitals will likely be overwhelmed during a major power outage — it’s better to have a plan for dealing with the heat long before you ever get sick, rather than try to deal with illness after it’s already set in.

Read more about heat waves:

This Is How You Die of Extreme Heat

Don’t Be Too Chill About Your Air Conditioning Dependency

The Mystery of Indoor Heat

The Heat Tracker: A Complete List of 2023 Heat Waves