Class D fires are a completely different animal, there are extinguishers for that, they work by melting and making a crust over the fire. I do know ABC extinguishers won't touch a D fire. (I've had the unmitigated joy of experiencing one, a small one, but it wouldn't go out...) We eventually had to cool it as much as possible with a fog nozzle and eject it over the side. I think foam has some success with D fires, but I don't remember for certain anymore. But unless you have lots of aluminum or magnesium finely divided (powder) you shouldn't have to worry too much about that.
