Quote from : The Lightning Thief Book

If I had my way," Dionysus said, "I would cause your molecules to erupt in flames. We'd sweep up the ashes and be done with a lot of trouble. But Chiron seems to feel this would be against my mission at this cursed camp: to keep you little brats safe from harm." "Spontaneous combustion is a form of harm, Mr. D," Chiron put in. "Nonsense," Dionysus said. "Boy wouldn't feel a thing. Nevertheless, I've agreed to restrain myself. I'm thinking of turning you into a dolphin instead, sending you back to your father.