When the grid goes down, will your home hold?

In a long outage, systems give out in a rough order. Timing varies by place and by how much backup a utility or carrier has. Each line names its source.

1. Hour 0

   Plug-in medical devices

   Oxygen concentrators, CPAPs and other devices that run on wall power stop unless they have a battery or backup supply. FDA advises planning for this before an outage.

   U.S. Food and Drug Administration, Tips About Medical Devices and Natural Disasters, accessed October 31, 2026

2. Hour 4

   Refrigerated food

   An unopened refrigerator keeps food cold for about 4 hours. FDA says to throw out perishable food that has been above 40°F for 4 hours or more.

   U.S. Food and Drug Administration, Food and Water Safety During Power Outages and Floods, current as of March 5, 2024

3. Hour 24 to 48

   The freezer

   A full freezer holds a safe temperature for about 48 hours, a half-full one for about 24, with the door kept shut.

   U.S. Food and Drug Administration, Food and Water Safety During Power Outages and Floods, current as of March 5, 2024

4. Hour 72

   Cell sites on backup power

   Cell sites keep running on batteries or generators until those run out. California requires carriers to keep at least 72 hours of backup power at sites in its high fire-threat districts.

   California Public Utilities Commission, CPUC Requires Wireless Companies to Better Serve Customers in Emergencies (press release, R.18-03-011), July 16, 2020

5. Days 2 to 3

   Water pressure, treatment and sewage

   Without power, pumps at a water utility can halt the production of treated water, and sewage can overflow. Backup power is not required under the Safe Drinking Water or Clean Water Acts. EPA's planning guide covers outages of 2 to 3 days and of several weeks.

   U.S. Environmental Protection Agency, Power Resilience: An Achievable Goal (EPA 810-F-24-018), June 2024

6. Day 4

   Fuel

   Four days after Hurricane Sandy made landfall, EIA estimated that 67% of gas stations in the New York metro area had no gasoline for sale.

   U.S. Department of Energy, Hurricane Sandy Situation Report #15, citing EIA's emergency survey, November 4, 2012

7. Day 28

   Insulin without a fridge

   Insulin vials and cartridges may be left unrefrigerated at 59 to 86°F for up to 28 days and still work, per FDA. Some products differ, so check the label.

   U.S. Food and Drug Administration, Insulin Storage and Switching Between Products in an Emergency, current as of September 28, 2026

8. Day 90+

   Replacement transformers

   In an extreme (G5) geomagnetic storm, NOAA says transformers may experience damage. Orders for new distribution transformers were taking about two years to fill in 2024, Congress's research service reports.

   Congressional Research Service, Electricity Distribution Transformers: Supply, Tariffs, and Policy Options (R48933), April 23, 2026