Basics

A possibility in FDM 3D Printers, where a short, or a broken thermistor allows for a low or absent value for the heat probe to enter the controller
If Improperly Designed this will cause the heat to continually rise, with essentially no stopping point (Until the device breaks itself one way or another)
If not stopped this often causes fires
This can destroy the device, or the entire facility depending on the precautions taken

Solutions

Redundancy
Quality Soldering etc
Proper Code (Error Detection and Auto Shutoff)
Fire Extinguisher Systems (Either a Self Contained Fire Suppression System or a Automatic Fire Extinguisher Water Sprinkler System )