I understand that, but I guess the writers really like to break the laws of physics and not have a lot of things making sense. SpongeBob isn't the only show though when you think about it. It happened in FOP too. And as for SpongeBob:
In SpongeBob fire turned off when Patrick was saying "Hey If we're underwater how can there be a?" After patrick says that there isn'tany fire the flames go out on the firewood, but then they flames appear again after Patrick steps on the firewood and shouts "That's it!" After him and SpongeBob fought over candy bars. Strange isn't it? I'd like to know why this keeps happening in cartoons. You are right, Its mind-boggling seeing fire underwater, same thing with being able to drown in Goo Lagoon when they are already underwater.