The U.S. Department of Agriculture's Food Safety and Inspection Service said a refrigerator will keep food cold for about 4 hours if the door is kept closed, a full freezer will keep its temperature for about 48 hours -- 24 hours if half-full.
"If the power is out for an extended period of time, buy dry or block ice to keep the refrigerator as cold as possible," FSIS officials said in a statement. "Fifty pounds of dry ice should keep a fully-stocked 18-cubic-feet freezer cold for two days."
The FSIS also advises to:
-- Check refrigerator thermometer, it should be 40 degrees F or below to keep food safe.
-- Freezers should be at 0 degrees or lower, but if a freezer has no thermometer, check each package of food. If food still contains ice crystals or is at 40 degrees F or below when checked with a food thermometer, it may be safely refrozen.
-- Discard any perishable food -- meat, poultry, fish, soft cheeses, milk, eggs, leftovers and deli items -- kept in a refrigerator or freezer above 40 degrees F for 2 hours or more.