Dry ice is solid carbon dioxide ( CO2 ). Exposed to room temperature, it undergoes sublimination... that is it becomes a gas without "melting" into a liquid state first. Exposed to higher temperatures, such as that from a small flame, it's going to do the same thing, only perhaps slightly faster. Now, CO2 is not flamable and is reasonably safe to handle. It tends to sink in air, which is why it is commonly used in making a "fog" that likes to lay near the floor for concerts, movies, etc. It's also used in some fire extinguishers, because it's non-flamable and can be used to smother a flame. ... which is exactly what's going to happen here. The CO2 gas subliminating from your solid CO2 is going to smother the flame of your lighter.