"We can't be certain exactly what happened at the port," Russell Datz, a Fisker spokesman, tells the New York Times Wheels blog. "But we think being submerged in 13 feet of saltwater had something to do with it."
Toyota spokeswoman Cindy Knight tells Wheels that the Prius likely went pyro because "saltwater got into the electrical system." Saltwater, as you probably know, is highly conductive and when it comes into contact with something like an electric car's battery, could cause a short circuit and a fire.
Daniel Abraham, chemical scientist at Argonne National Laboratory, gave the blog a more technical explanation. Salts in the water break into positive and negative ions that act as conductors and could have connected the batteries' positive and negative terminals. Next came a short circuit and then, possibly, a fire.
No one so far thinks the Karma batteries' lithium cores were to blame. Even though lithium will burn on contact with water, the metal used in hybrid batteries is pretty well protected and isn't likely the source of the fires.
So still no official cause of the fires, but an investigation is ongoing.