The real risk is if you get into a wreck and the car catches on fire. Some of the chemicals in all those batteries are very bad news when burnt. I know firefighters who won’t get near a burning hybrid without a full hazmat suit. Needless to say, if you are trapped in a burning hybrid, your life expectancy isn’t real good...
I'm glad that you brought this up. While I look forward to the emergence of ethanol, butanol technologies, I have heard that it is harder to put out an ethanol fire than a gasoline fire. If I remember correctly, some kind of foam that is not now readily available is needed to put out an ethanol fire, corrections welcome.