Arcing
Arcing is one cause of burn marks on the interior wall of your microwave. Some objects are not recommended for use in microwave ovens. Metal kitchen utensils, twist ties or aluminum foil can cause “arcing,” or sparks, in the appliance. The arcing produces burns and even holes on the wall of the microwave, and may lead to a fire if left unattended. Even the small staples in microwave popcorn bags have been known to burn the wall and spark a fire.
Metal Rack
Incorrect placement of the microwave’s metal rack can also cause a burn on the interior wall. Although the use of metal should generally be avoided, some microwave manufactures use metal racks, shelves or turntables in their appliances. These racks have been approved for use in the microwave. However, if the racks are placed in the microwave incorrectly -- for example, upside down or touching the sides of the appliance -- this will lead to burn marks and a possible fire. In addition, even if the microwave has a metal rack, it is still not safe to place other metals in the appliance, because they have not been approved for use.
Empty Appliance
Operating the appliance when it is empty can also cause burns on the microwave’s wall. Allowing an empty microwave to continue operating causes a number of problems. The microwave will begin to leak magnetic waves through the door and vent holes, and some of the microwave’s internal components will become damaged. In addition, arcing and burning will occur, and the life span of the microwave will be shortened.
Spilled Food
Failure to clean spattered food will result in burn marks on the microwave’s wall. All food placed in the microwave should be covered to avoid the possibility of spills. Food and liquid that have spattered and been allowed to remain in the microwave will absorb the microwave’s heat and cause burns on the walls and ceiling of the appliance. When spills are inevitable, use mild soapy water to remove them immediately.
Other Considerations
The U.S. Department of Agriculture warns that the composition of some foods, such as raw carrots and hot dogs, can also cause arcing and burning. In addition, there may be an internal malfunction in the microwave that is causing it to arc and burn. Discontinue use of the appliance until it can be examined and repaired by a professional.