They have fireworks on the roof that are lit with a single spark. If something went wrong with a string of lights near them anything can happen. Disney takes safety with Ptro seriously especially after the inferno barge almost blew up when a shell that was launched from it exploded in the lunch tube. Fortunately it didn't do any major damage but they did relocate the lunch tube from it too the dock in the middle of the lagoon that both the inferno barge and the earth barge dock at during the show.