A working dehumidifier will not cause a fire if it is working and connected properly. They are no more apt to cause a fire than any other electrical appliance. If the unit overheats it will shut off on the internal overload protection. If it draws to much electricity from the outlet, it will trip the circuit breaker. Those items will prevent a fire. A dehumidifier does use a fair amount of current, so the plug will get warm (not hot), to the touch. If the unit is working, stop worrying about it. It will be fine. Lightning causes many more home fires than dehumidifiers.