Cooling is electricity for a large share of the country. In a heat wave, a blackout moves people from discomfort to heat illness in a few hours, especially the old, the very young, and anyone on medications that impair cooling. Elevators trap the rest.

Heat illness does not announce itself like a fire. People get confused, stop sweating, or simply lie down. In a brick or concrete building that has soaked up the day, the indoor air can stay dangerous after the sun is down. The outage did not cause the heat wave. It removed the tool most apartments have for it.

The plan is location: the lowest floor you can reach, water, a way to wet skin and move air, and a cooling center you have actually visited. Battery fans are not frivolous. They are the summer version of the winter sleeping bag.

Lowest floor, because heat rises and because you may not have an elevator to come back up. Wet skin and moving air are the method, not a slogan. A battery fan moving air across damp cloth is a real intervention. A cooling center you have never visited is a rumor about an address.

Go look at the center before you need it. See how long it takes to get there on foot, whether it will take a person with a pet or a device, and what the building is on a normal day — a library, a school, a rec center. Write it down. The phone is part of the outage.

Check the same neighbors you would check in a freeze. Heat is quieter than a storm and just as lethal.

The knock is the same knock. Top floors, people who live alone, people who said they were fine at noon. Quiet is why the check has a clock. If you leave for a cooler place, leave a note on the door that says where you went, so the person who comes for you does not spend the hour on a door that will not answer.