Power Outage Food Safety Calculator (Fridge, Freezer, Ice & Dry Ice)

How it works

refrigerator ≈ 4 h unopened (USDA) × door factor × 0.97^(°C above 21) · freezer ≈ 48 h full / 24 h half / 12 h quarter, × 1.5 for a chest freezer, × the same factors · discard perishables held above 4 °C (40 °F) for more than 2 h · dry ice ≈ 25 lb per 10 ft³ per 2–3.5 days · block ice ≈ 10 lb per fridge per day

Food safety in a blackout is a race between the cold stored in the appliance and its contents and the heat leaking in: a refrigerator holds its safe temperature for only a few hours because it stores little cold, while a freezer full of frozen mass holds for a day or two — longer for a chest freezer whose cold air does not fall out when opened, shorter in a hot room or with the door swung often. The rule that decides the aftermath is time above four degrees, not appearance, and ice, dry ice or short generator cycles buy time by replacing the cold that leaks away.

Worked example

Thirty hours into an outage in a 24 °C room with the doors opened a few times, the refrigerator's window was about 2.9 hours, so the meat, dairy, eggs and leftovers must go while hard cheese, butter and condiments stay. A half-full upright freezer had about 17.5 hours, so each item needs checking for ice crystals; keeping an 8 ft³ freezer frozen would take about 10 lb of dry ice a day — 20 lb for the two days.

Frequently asked questions