The Allegheny County Health Department has issued the following tips on how to preserve perishable foods during a power outage and how to tell when foods are spoiled and should be discarded.

• Use appliance thermometers in refrigerators and freezers. Safe temperatures are a maximum of 40 degrees Fahrenheit for refrigerators and zero degrees for freezers. Most foodborne illnesses are caused by bacteria that multiply quickly above 40 degrees.

• Keep freezer doors shut. A full freezer should keep safe about two days, a half-full freezer a day. Add bags of ice or dry ice to the freezer if the power will be out an extended time. Thawed foods that still contain ice crystals or feel cold to the touch can be safely refrozen.

• Refrigerated items should be safe as long as the power is out no more than four to six hours, but keep the door closed as every time you open it cold air escapes. Discard any perishable food that has been above 40 degrees for two hours or more or that has an unusual odor, color or texture.

• Never taste food to determine its safety. Some foods may look and smell fine, but if they've been at room temperature longer than two hours, bacteria that cause foodborne illness can begin to multiple very quickly.

• For more advice on the handling of specific foods call the health department at 412-687-ACHD or visit www.achd.net.