For a normal capacitor, the electric charge will remain in the capacitor for a long time after the power is switched off. If this is touched you could get an electric shock. When using a safety capacitor this period is very short. By shunting the surge energy to ground it can protect people and devices from high voltage surges.
All safety capacitors are classified as either X and/or Y capacitors.
Class X capacitors are primarily used between L (Line) and N (Neutral) applications.
Class Y capacitos are primarily used between L (Line) and G (Ground) or between N (Neutral) and G (Ground) applications.
Typically, you can select ceramic safety capacitor and film safety capacitor for your application.