Skill · The clock
Food safety in a blackout
Four hours for the fridge. About a day or two for the freezer. Then the food is not a debate.
Federal steps in this chapter do not change by state. Local orders for Arizona come from Arizona Department of Emergency Management.
5 min read · Updated October 2026
USDA’s clocks
The U.S. Department of Agriculture’s Food Safety and Inspection Service publishes the numbers households should memorize. A refrigerator will keep food at a safe temperature for about 4 hours if you do not open the door. A full freezer holds about 48 hours, a half-full freezer about 24 hours, again if the door stays closed. Put a thermometer in both so you are not guessing.
Perishable food held above 40°F for more than 2 hours should be discarded. If the room itself is hotter than 90°F, that window shrinks to 1 hour. That includes meat, poultry, fish, eggs, milk, leftovers, and opened baby formula. Food that still has ice crystals or is at 40°F or below can be refrozen or cooked, with the details on the USDA page. When in doubt, throw it out. Do not taste food to decide.
- Group what you will eat first, while it is still cold, and eat from the fridge before you open the deep freeze.
- A cooler with ice can extend the clock for a few high-value items. Keep the drain closed and the lid shut.
- Generators can run a fridge if they are outdoors and the cord is right. They cannot make unsafe food safe again.
- After a flood, discard anything not in a waterproof container, and discard wooden spoons and other porous items that touched floodwater. When in doubt, USDA and CDC both lean toward throwing it out.
How to
USDA’s Food Safety and Inspection Service publishes the clocks. A refrigerator keeps food safe for about 4 hours if the door stays shut. A full freezer holds about 48 hours, a half-full freezer about 24 hours, door shut.
Step 1. Keep doors shut
Step 2. Read the clocks
4 hours fridge. 48 or 24 hours freezer
Step 3. Check 40°F
Use a thermometer, not a guess
Step 4. Throw it out
Do not taste food to decide
Step 5. Use a cooler
Lid shut, for a few items
| Data point | Value | Source |
|---|---|---|
| Closed fridge | About 4 hours if the door stays shut | USDA FSIS |
| Full freezer | About 48 hours, door shut | USDA FSIS |
| Half-full freezer | About 24 hours, door shut | USDA FSIS |
| Above 40°F | Discard perishable food held above 40°F for more than 2 hours | USDA FSIS |
| Room above 90°F | That window shrinks to 1 hour | USDA FSIS |
Worked example
The fridge door stayed shut. After about 4 hours, perishable food above 40°F is discarded. If the room is above 90°F, the window is 1 hour, not 2. A full freezer, door shut, is about 48 hours. A half-full freezer is about 24 hours. When in doubt, throw it out. Do not taste it.
When in doubt, throw it out. Do not taste food to decide.
Checklist
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Sources
Public pages this chapter leans on. They win if anything here is out of date.
- USDA FSIS — Keep food safe during emergencies
A closed refrigerator keeps food safe for up to 4 hours.
- USDA FSIS — Food safety
Hub if the deep link moves
- Ready.gov — Power outages
What else fails with the grid