The explosions are occurring due to the phones’ lithium ion batteries. Samsung have admitted that during the manufacturing process, the layer of plastic separating the positive and negative sides of the battery was punctured.
This led to the batteries short circuiting – posing a massive fire risk, as the positive and negative poles coming into contact triggered “excessive heat”.
These are just a few theories based on one battery expert's remote analysis of Samsung's initial findings. We don't have the whole truth yet, and the truth is what Samsung and government agencies around the world are looking for as we speak. Organizations like the US Consumer Product Safety Commission have officially stepped in to recall the Galaxy Note 7 and figure out what happened.
But that could take time. It took six months for the CPSC to complete its investigation into hoverboard battery fires, to give you some idea.