Yes. The heating element is a resistive wire that becomes very hot when current passes through it.  You can tell that this has happened if the boot dryer does not work well and smoke appears. When a boot dryer gets a fire, you can usually smell smoke, but it may be hard to find the exact source of the fire. A work boot dryer will catch on fire if it gets very hot. If it is too hot to hold, it can ignite. Also, some people use them to heat their shoes, which can be dangerous if they get too hot!