Using Flammable Hand Sanitizer. 1  1. Be extremely careful. 2  2. Buy a flammable variety of hand sanitizer. 3  3. Take the proper safety precautions.  4. Spread a thin layer of alcohol-based sanitizer on the concrete and ignite 1  it. 5. Run one finger quickly through the sanitizer.  6. Put the flame out by snapping your wrist forcefully.