About 10 years ago Disneyland decided to do something about the disadvantages of blackpowder as a lift charge for their shells. As said it generates a lot of ground smoke, gives extra noise what sometimes is not wanted, and tributes to the enviroment pollution due to the big amount of firework displays shot every summer.
Disneyland experienced with flammable gas, ignited by the shells's timefuse/electrical fuse, but finaly they found the best solution in using compressed air. This is more save, gives almost no noise when a shell is shot, gives no pollution, and saves money on longer terms.
Disneyland has his own pyrotechnical department were the firework is made and/or prepaired. In order to save the cost and the enviroment they also changed from karton shell parts to plastic shell parts.
The blown plastic shell parts could easally be re-collected in the surrounding area's. Karton shell parts break up in smaller parts and can be solved by water/rain, making them hard to re-collect and finaly causing more pollution in the park.
People even did tests with plastic shellparts which were not only re-collectable for recycling, but also re-usable. That kind of shell parts should only break open at their lid/seam, so that the half shell parts could be re-collected for re-use. But as far as I know, this was no succes.