The two main rules to follow are these: never place objects on top of the microwave that block its ventilation, and never place objects or products on top that could overheat and be damaged, or that are made of combustible materials (the appliance also generates heat externally). These categories include small appliances and heavy utensils, which would block the ventilation on top of the microwave; products such as books, cloths, medicines, paper, and anything else that could be easily flammable; particularly delicate objects such as those made of thin glass, which could crack from the heat; and any foods that could be affected by excessive heat, especially bread and baked goods, eggs, and fresh foods such as fruit and vegetables.
