E-cigarettes have ignited in hold luggage and caused fires several times already. For this reason, passengers are now only permitted to carry e-cigarettes in hand luggage.
The Canada-based International Civil Aviation Organization (ICAO) has banned these devices in hold luggage due to the risk of fire. The charging of e-cigarettes inside the aircraft is also banned as the heating elements in the devices erroneously switch on, causing fires in luggage. Intervention in such an eventuality is easier inside the aircraft cabin than in the cargo hold.
Although you have access to your e-cigarettes in your hand luggage, their use on board is banned on most airlines as with normal cigarettes.