That stuff is one of those things that truly legitimizes HAZMAT. Suppose your package got wet along the way, or the mailman simply sets it outside the recipient's door in the rain- don't laugh wet packages aren't uncommon in my life. And if carbide gets wet...
It wouldn't hurt a thing unless it was in an air tight container and got wet,or it was exposed to an open flame. It creates a gas when it gets wet that will ignite.It might explode if enough of it got wet enough inside an air tight container. If the gas expanded enough it might explode but it isn't like dynamite.
A miners light used Carbide inside an air tight container mixed with water.You would light the nozzle which is attached to a reflector for a light. Miners would wear them on their head. I never knew of any miners getting their heads blown off.