Fire In The Engine Bay

[Caduceus]

So I was driving home yesterday from my girlfriends' house when I noticed that "burning electronics" smell. Knowing that there's not too much on the car that could be going wrong it didn't surprise me that a few seconds later the tach needle started jumping around then just failed completely. Then I knew it was my car for sure and pulled over right away. I popped the hood an sure enough the tach amp was spewing white smoke out of the bottom of the unit. I burned my hand unscrewing the cap and then I found the silicone on top of the pcb was actually charred into a white powdery mess, and the black plastic housing was completely melted and mangled. So my questions are: Is this how the tach amps fail? Because if it is that's not friggin safe at all, if it wasn't me driving then someone probably wouldn't have noticed anything. Also why the hell would a fuse not blow?

Forgot to add, the car is an 82 300D T