But the 10 mg of material are contained inside a ceramic rod in oxide form which won't oxidize because its already oxidized (assuming the designers are smart) and is somewhat refractory in a fire anyway, inside a thick walled steel boiler which is inside some kind of containment thingy and its surrounded by inches (feet?) of metal inside the engine compartment.

On the other hand, 30 gallons of gasoline is in a cheap tank made out of cookie cutter metal so it tears open in a minor crash and there's a puddle of it underneath the seat you're strapped into. And it burns. Really well. So a giant pool of it is currently on fire, underneath your feet. Whoops. Unfortunately this happens fairly often.

The lithium battery is more complicated to model. They burn, really well, but if properly vented they can't explode. So its kind of like driving a truck with 1000 pounds of grilling charcoal in the back... if it ignites, and you just sit there, you'll eventually be grilled like a bratwurst, but its going to take a heck of a long time, so unless you're alone and unconscious in abandoned distant wilderness for 15 minutes you're OK.