Is potassium metal an explosion risk?
Yes, as an alkali metal, potassium is an explosion risk. It will react violently with water.
Peroxides have been known to develop on the exterior surface of potassium metal. These peroxides have been known to react explosively with the light oil (kerosene) in which the product is stored when the science instructor cuts the product into small pieces. Be sure you provide personal protection when dealing with this very reactive metal. If you have a choice as to which alkali metal you elect to buy and use, sodium metal might be your better choice since, upon aging, it does not develop peroxides.
A science teacher's best option is to purchase potassium already pre-cut. Flinn Scientific offers a bottle of five small pieces for demonstration purposes. ( Catalog # P0204)