"Class C" is now technically an obsolete term, but I still use it. It was the US Department of Transportation classification for consumer fireworks. The new classification is 1.4, meaning "no significant hazard beyond the package in the event of ignition or initiation during transport". 1.3 is then one step up from that and fireworks such as display-class shells are in this category.

Fireworks Buyers Guide
General buying guide
Reviews of class C fireworks
Class C Prices
The Great Class C Conspiracy
Inside a cake
Inside different Class C shells
Inside Roman Candles
Inside the Warhead Launcher

Assorted Class C fireworks