It is advised that you wear heat protecting gloves and safety googles. Sodium hydroxide is caustic and can cause chemical burns; make sure that you do not get it in your eyes. Zinc powder is highly flammable. It is recommended that you have a Class D fire extinguisher available in case the metal power catches on fire. Make sure that you wash the treated pennies carefully so that traces of sodium hydroxide and zinc powder are not on the penny when you heat them in a flame or that they remain on the penny when you give it to the children. It is possible to also use a hot plate to heat the pennies to avoid an open flame.