If it seems likely that your freezer will not be operating properly within one or two days, dry ice may help keep some frozen food from spoiling. However, dry ice is very expensive and is not easy to obtain in some areas. If a flood (or other emergency) is predicted, and you decide to use dry ice, locate a source in advance, and obtain it quickly.
Your power company may be able to direct you to a source of dry ice.
Wear gloves when handling dry ice. Do not touch it with your bare hands because it causes severe frostbite and tissue damage.
Allow 2.5 to 3 pounds of ice per cubit foot of freezer space. (More will be needed for an upright freezer because ice should be placed on each shelf.)
Place boards or heavy cardboard on top of packages. Place dry ice on top of boards. In an upright freezer, place ice on each shelf.
Cover the freezer with blankets, but do not lock it or cover air vent openings. Gas given off by the dry ice needs a place to escape. Open basement or room windows or doors to vent out the gas from dry ice.